Asterisks (*) indicate new or modified steps as compared to Christensen et al.1
1. Material Setup
<ol>
	<li>The cell culture procedure requires large quantities of eggs isolated from gravid adults. Grow C. elegans on 8P agar plates seeded with NA22 (available through the C. elegans Genetic Consortium - CGC) bacteria to isolate large quantities of eggs. In these plates the amount of peptone used is 8 times the amount that is normally used for NGM plates. The higher peptone concentration sustains the growth of NA22 bacteria more efficiently, which contrary to OP50-, grow in thick layers.</li>
</ol>
8P plates recipe:
Dissolve 3 g NaCl, 20 g Bacto-Peptone, 25 g agar in 1 L of sterile distilled water and autoclave for 30 min. Let the medium cool at 55 &deg;C and then add sterile-filtered 1 ml of cholesterol (5 mg/ml in EtOH), 1 ml of 1 MgCl2, 1 ml of MgSO4 and 25 ml of KP buffer (stock of 500 ml: 5 g K2HPO4, 30 g KH2PO4, pH 6.00). Pour liquid agar medium into 10 cm Petri dishes (25 ml/plate).
<ol start="2">
	<li>The next day spread the whole surface of each enriched peptone agar plate with 1 ml of NA22 E. coli cultured overnight in 2XYT media (16 g Tryptone, 10 g Yeast extract, 5 g NaCl in 1 L of sterile water, pH 7.0) at 37 &deg;C. These bacteria constitute an abundant food source that will form a thick layer supporting the growth of large quantities of gravid adults. Leave seeded plates overnight at room temperature to allow growth of the bacteria. The process can be accelerated by incubation at 37 &deg;C for 4-5 hr.</li>
	<li>Transfer starved animals to seeded 8P plates. Wash animals off a starved NGM plate using 5-6 ml of M9 buffer or water and add 1-2 ml of this suspension to each 8P plate.</li>
	<li>Allow growth and multiplication of the animals until the plates are populated at confluence by gravid adults.</li>
	<li>Isolate the eggs required for the preparation of C. elegans embryonic cells, from gravid adults using 5-6 ml of lysis solution.</li>
</ol>
Lysis solution recipe
5 ml of Fresh Bleach, 1.25 ml of 10 N NaOH and 18.5 ml of sterile H2O. This mixture must be prepared fresh prior to each use.
<ol start="6">
	<li>Wash the eggs isolated from gravid adults using egg buffer:</li>
</ol>
Egg buffer recipe
118 mM NaCl, 48 mM KCl, 2 mM CaCl2, 2 mM MgCl2, 25 mM Hepes, pH 7.3, osmolarity 340 mOsm.
<ol start="7">
	<li>Remove the eggshell that surrounds the eggs by treatment with chitinase. Chitinase is an enzyme with highest activity at acidic pH 25. Dissolve chitinase (Sigma, catalog no. C6137) in egg buffer pH 6.5 at a final concentration of 2 mg/ml. Store the chitinase stock solution at -20 &deg;C in 1 ml aliquots in sterile 15 ml conical tubes. Aliquots can be stored at -20 &deg;C up to a few months.</li>
	<li>Grow C. elegans cultured cells on autoclaved coverslips (12 mm diameter) covered with peanut lectin. Dissolve peanut lectin in sterile water (0.5 mg/ml). Peanut lectin solution should not be filtered or autoclaved. It also does not need to be treated with UV light. Store 2 ml aliquots at -20 &deg;C for up to 6 months.</li>
	<li>Complete cell culture medium (500 ml) contains 500 ml L-15 culture medium from Gibco, 50 ml Fetal Bovine Serum (heat inactivated), 7.7 g sucrose (45 mOsm), 5 ml of 100 U/ml Penicillin and of 100 &mu;g/ml Streptomycin (2%). The complete medium is then filtered using a 0.20 &mu;m pore filter.</li>
</ol>
Note that the egg buffer and the culture medium have osmolarity of 340 and 345 mOsm respectively. Indeed, contrary to mammalian cells, C. elegans cells have a relatively high osmolarity that needs to be taken into count when preparing solutions that will come in direct contact with the plasma membrane of the cells. The recipes of these reagents were adjusted to reach the desired osmolarity, which was measured using an osmometer 1. It is not necessary to use an osmometer if these recipes are followed exactly and care is used in preparing these reagents. However, one should use an osmoter if other solutions need to be prepared, whose recipes are not reported here or in any of the publications that use C. elegans cultured cells.
2. Egg Isolation
<ol>
	<li>It is recommended to begin with at least four 8P plates to collect enough eggs for 12 wells of cultured cells (in 24-well plates).</li>
	<li>Before starting with the procedure thaw one tube of peanut lectin stock solution. Place autoclaved coverslips at the bottom of the wells in a 24-well plate and add 200 &mu;l of peanut lectin to the coverslips. Incubate for 1 hr or until the cells are ready to be plated. Remove completely the peanut lectin and wash the wells once with 1 ml of sterile autoclaved water. Complete removal of the peanut lectin from the coverslips is essential for avoiding cell clumping.</li>
	<li>Wash the gravid adults off the agar plates using sterile autoclaved water. Collect the suspension into two sterile conical 50 ml tube. Leave the tubes on ice for up to 5 min to allow precipitation of the worms at the bottom of the tubes (*). Remove the water with a transfer plastic pipette and replace it with fresh sterile autoclaved water. Pellet worms by table-top centrifugation at 200 x g (~1,200 rpm) for 10 min (*). Repeat this last step at least 3.</li>
	<li>Transfer worms into a sterile 15 ml conical tube and pellet them at 200 x g (~1,200 rpm) for 10 min (*). Do not use higher centrifugation speed to avoid collecting the bacteria at the bottom of the tube as well. Sometimes after centrifugations the worms are not completely pelleted. After each wash and before removal the supernatant, place the tubes for 5 min on ice. In chilled water worms precipitate to the bottom of the tube.</li>
	<li>Remove the water and add 5-6 ml of lysis solution (see Material set up). Rock the suspension gently for 5-10 min and then begin monitoring worm lysis under the stereomicroscope every 2-3 min. A drop of suspension can be also placed on a coverslip for easier inspection. The incubation time varies depending on the freshness of the bleach; buy small bottles of bleach and open a new bottle every month.</li>
	<li>When ~70-80% of worms are lysed (10 min from the beginning of the incubation), stop the lysis reaction by adding 9 ml of egg buffer pH 7.3 (see Material set up). Centrifuge the suspension at 200 x g (~1,200 rpm)for 10 min. From this point on have a Bunsen burner on, on the bench to prevent re-contamination of the eggs (*).</li>
	<li>Carefully remove the supernatant using a sterile plastic transfer pipette and wash the pellet 3-4x with egg buffer until the solution is clear. Make sure to mix the pellet well in the egg buffer during each wash.</li>
	<li>Eggs are separated from the animal carcasses using 30% sucrose solution. Resuspend the pellet in 2 ml of sterile egg buffer and add 2 ml of 60% sucrose solution (stock in sterile egg buffer). Mix well and centrifuge for 20 min at 200 x g (~1,200 rpm) (*).</li>
	<li>Carefully remove the tubes from the centrifuge. The eggs are floating at the top of the solution. Using a P1000 pipettor and sterile tips, transfer all eggs into a fresh sterile 15 ml conical tube.</li>
	<li>Add 10 ml of sterile egg buffer to the tube and centrifuge at 200 x g (~1,200 rpm) for 10 min. Repeat the wash 3 x. Make sure the eggs are completely resuspended in the egg buffer during each wash.</li>
</ol>
3. Embryonic Cells Dissociation
Conduct the next steps of the procedure under sterile conditions using a laminar flow hood. While animals are gown on bacteria plates, the washes and the treatment with the lysis solution containing bleach should eliminate most if not all the bacteria. Thus using a laminar hood at this point of the procedure prevents new contamination of the egg suspension.
<ol>
	<li>Resuspend pelleted eggs in 1 ml of 2 mg/ml chitinase (stock in egg buffer pH 6.5 (*)) and transfer them to a new sterile 15 ml conical tube. Rock the tube for 10-30 min at room temperature. The exact incubation time changes according to the freshness of the enzyme and the temperature of the room and should therefore be determined for each preparation. It is recommended to start monitoring the eggs under an inverted cell-culture microscope after 10 min of incubation. Note: in our experience, low pH increases the chitinase enzymatic activity. For this reason we use egg buffer at pH 6.5 to dissolve chitinase (recipe reported above, where pH is adjusted to 6.5 using NaOH).</li>
	<li>When ~ 80% of the eggshells are digested by the chitinase treatment (Figures 1 A-B), pellet the eggs by centrifugation at 900 x g (~2,500 rpm) for 3 min (*). Using a P1000 pipettor and sterile tips, remove carefully the supernatant and add 3 ml of L-15 medium (*).</li>
	<li>Transfer the eggs into a 6 cm diameter plate and gently dissociate the cells using a 10 ml sterile syringe equipped with a 18 G needle. Monitor the degree of dissociation by placing a drop of suspension into a fresh plastic Petri dish and by viewing under the microscope. Do not aspirate air into the syringe during this procedure to avoid damaging cells. Continue the dissociation until ~ 80% of the cells are dissociated.</li>
	<li>Filter the suspension using a sterile 5 &mu;m Millipore filter. Cell suspensions must be filtered in order to remove cell clumps, undigested eggs and hatched larvae. Filter additional 4-5 ml of fresh L-15 media through the filter to recover all the cells. Do not use excessive force during the filtration step to avoid damaging the filter and/or the cells.</li>
</ol>
4. Culturing Cells
<ol>
	<li>Pellet the dissociated cells by centrifugation at 900 x g (~2,500 rpm) for 3 min (*). Using a P1000 pipettor and sterile tips carefully remove all the supernatant. Resuspend the pelleted cells in complete L-15 medium and plate 1 ml/well. The amount of the medium added depends on the number of 8P plates used, the confluence of the worms on the plates, and the type of experiments that will be performed on the cells. The cell density can be determined using a hemocytometer. For patch-clamp recordings plating density of ~ 230,000 cells/cm2 is optimal.</li>
	<li>Keep the 24 wells plate in a plastic Tupperware container containing wet paper towels to avoid evaporation of culture medium. Store the container in a humidified incubator at 20 &deg;C and ambient air.</li>
	<li>The cells are usually ready for the experiments within 24 hr when the morphological differentiation and expression of GFP markers are complete. Cells can be kept in culture for up to 2 weeks but they are usually most healthy up to 7-9 days after plating. The medium needs to be replaced once a day to maintain healthy cells.</li>
</ol>

C. elegans is a powerful model organism for deciphering the genetic pathways involved in development, behavior and ageing. Its convenience stems primarily from the ease with which it can be genetically manipulated and from its short life cycle. Despite its convenience, C. elegans has its limitations. C. elegans cells are tiny and confined within a pressurized cuticle that limits the application of methods that require direct access to the cells, such as electrophysiological and pharmacological ...

Caenorhabditis elegans (C. elegans) is a powerful model organism for investigating the molecular bases of cellular function, differentiation, and behavior. While its genome, metabolic and biosynthetic pathways are similar to vertebrates', its genetic and molecular tractability are far greater 2. Among its advantages are its size and simple anatomy, its rapid life cycle (3 days at 25 &deg;C), short life-span (2 weeks) and large number of offspring (&gt;200). Due to its hermaphroditic nature and short life cycle, molecular and genetic manipulations are straightforward in C. elegans, including the generation of transgenic animals 3,4 and the application of gene knock-down techniques such as RNA interference 5. C. elegans body and eggshell are transparent. Therefore cells can be easily visualized in both the adult and the embryo using standard microscopy. In the last 40 years, the C. elegans community has created invaluable resources for C. elegans research including a large collection of mutants, knockouts and transgenics, a detailed description of anatomy and development 6,7, including the full reconstruction of the nervous system 8, and a completely sequenced genome which is well annotated and available to the whole community (<a href="http://www.wormbase.com" target="_blank">www.wormbase.com</a>).
Despite the numerous advantages, some experimental approaches have been challenging in C. elegans. These include the ones that require accessibility to the plasma membrane of the cells and isolation of tissues or cell types. Indeed C . elegans tissues are confined within its pressurized hydrostatic skeleton, which is not easily digested by enzymatic treatment or detergents. At the end of 1990s Miriam Goodman and Janet Richmond pioneered methods for electrophysiological recordings of C. elegans neurons and muscle cells in situ 9,10. While these methods gave us important insights into neuronal and muscle function in vivo, they are challenging and low throughput. Alternative methods to study cell function in vivo had been developed, mostly notably in vivo calcium imaging using genetically encoded calcium sensors such as GCamP and cameleon 11-13. These methods though, do not allow the use of pharmacological tools because they are applied on intact living animals.
The first attempt at culturing C. elegans cells in vitro in large scale was made by Laird Bloom during the preparation of his PhD thesis 14. Unfortunately, difficulties encountered with poor adhesion of the cells to the substrate, poor cell differentiation and survival prevented the establishment of this early protocol as a robust cell culture method. In 1995 Edgar and colleagues published a procedure to investigate cell division and morphogenesis by isolation and culture of a single C . elegans embryos 15. Embryonic cells obtained by digestion of the eggshells with a combination of enzymatic treatment and manual dissociation, continued to proliferate, producing up to ~500 cells 15. Subsequently, Leung and coworkers cultured a small numbers of blastomeres to study intestinal morphogenesis. They showed that one in vitro isolated E blastomere produced polarized intestinal cells that created a structure analogous to the intestinal lumen by interacting with each other through apical adherens junctions 16. Buechner and colleagues also reported a similar method for culturing C . elegans embryonic cells in vitro 17.
Based on this early work, Christensen and colleagues developed a robust protocol for culturing embryonic C . elegans cells in vitro 1. They showed that isolated C . elegans cells can differentiate into various cell types and maintain the features that they possess in vivo, including the expression of cell-specific markers. Several techniques that are challenging in vivo, can be applied on isolated C. elegans embryonic cells. These include electrophysiological 1,18 19, imaging, and immunochemical techniques 20,21, as well as isolation of specific cell types by Fluorescent-Activated Cell Sorting (FACS) for the construction of cell-specific cDNA libraries 22,23. Gene knockdown techniques such as RNA interference (RNAi) can be applied on cultured C. elegans cells 1 and a novel metabolic labeling method using Azido-sugar as a tool for glycoprotein discovery has been recently developed for in vitro cultured C. elegans cells 24.
In conclusion, the cell culture method expands the array of techniques that can be applied to the C. elegans model in an effort to decipher gene function in the context of a living organism. We describe here the protocol for culturing C. elegans embryonic cells in vitro, which is largely based on the protocol first described by Christiansen and colleagues 1.

<table border="1">
	<tbody>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>REAGENTS</td>
		</tr>
		<tr>
			<td>Bacto Peptone</td>
			<td>VWR International Inc.</td>
			<td>90000-382</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Difco Agar Granulated</td>
			<td>VWR International Inc.</td>
			<td>90000-784</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Bacto Tryptone</td>
			<td>VWR International Inc.</td>
			<td>90000-284</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Bacto Yeast Extract</td>
			<td>VWR International Inc.</td>
			<td>90000-724</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Leibovitz's L-15 Medium (1x) Liquid</td>
			<td>Invitrogen</td>
			<td>11415-064</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Invitrogen</td>
			<td>16140-063</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Penicillin-streptomycin</td>
			<td>Sigma</td>
			<td>P4333-100ML</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Chitinase from Streptomyces Griseus</td>
			<td>Sigma</td>
			<td>C6137-25UN</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>NA22 Escherichia coli</td>
			<td>Caenorhabditis Genetics Center</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Peanut Lectin</td>
			<td>Sigma</td>
			<td>L0881-10MG</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Sigma</td>
			<td>57903-1KG</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>D-(+)Glucose</td>
			<td>Sigma</td>
			<td>67528-1KG</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Ethylene glycol-bis (2-aminoethylether), N,N,N',N'- tetraacidic acid (EGTA)</td>
			<td>Sigma</td>
			<td>E0396-25G</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Hepes</td>
			<td>Sigma</td>
			<td>H3375-500G</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Cholesterol</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma</td>
			<td>57653-1KG</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma</td>
			<td>P9333-500G</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>CaCl2</td>
			<td>Sigma</td>
			<td>C1016-500G</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>MgCl2</td>
			<td>Sigma</td>
			<td>M8266-100G</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>MgSO4</td>
			<td>Sigma</td>
			<td>M2643-500 g</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>K2HPO4</td>
			<td>Sigma</td>
			<td>P2222-500G</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Sigma</td>
			<td>P9791-500G</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>NaOH</td>
			<td>Sigma</td>
			<td>S8045-500G</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>KOH</td>
			<td>Sigma</td>
			<td>P1767-500G</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Autoclaved distilled H2O</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Bleach</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>EQUIPMENT</td>
		</tr>
		<tr>
			<td>101-1000 &mu;l Blue Graduated Pipet Tips</td>
			<td>USA Scentific</td>
			<td>1111-2821</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>10 ml Sterilized Pipet Individually Wrapped</td>
			<td>USA Scentific</td>
			<td>1071-0810</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Ergonomic Variable Volume (100-1000 &mu;l) Pipettor with tip ejector</td>
			<td>VWR International Inc.</td>
			<td>89079-974</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Portable Pipet Aid, Drummond</td>
			<td>VWR International Inc.</td>
			<td>53498-103</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Transfer Plastic Pipet Sterile</td>
			<td>VWR International Inc.</td>
			<td>14670-114</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>15 ml Conical Tube</td>
			<td>USA Scentific</td>
			<td>1475-1611</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>50 ml Conical Tube</td>
			<td>USA Scentific</td>
			<td>1500-1811</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Sterile 18 gauge Needles</td>
			<td>Becton, Dickinson and Co.</td>
			<td>305196</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Sterile 10 ml Syringes</td>
			<td>Becton, Dickinson and Co.</td>
			<td>305482</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Plastic Syringe Filters Corning 0,20 &mu;m pore size</td>
			<td>Corning</td>
			<td>431224</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Acrodic 25 mm Syringe filter w/5 &mu;m versapor Membrane</td>
			<td>VWR International Inc.</td>
			<td>28144-095</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>60x15 mm Petri Dish Sterile</td>
			<td>VWR International Inc.</td>
			<td>82050-548</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>100x15 mm Petri Dish Sterile</td>
			<td>VWR International Inc.</td>
			<td>82050-912</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>12 mm Diameter Glass Coverslips</td>
			<td>VWR International Inc.</td>
			<td>48300-560</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Clear Cell Culture Plates 24 Well Flat Bottom w/lid</td>
			<td>Thomas scientific</td>
			<td>6902A09</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Dumont #5- Fine Forceps</td>
			<td>Fine Science Tools</td>
			<td>11254-20</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Centrifuge 5702</td>
			<td>Eppendorf</td>
			<td>022629883</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Laminar Flow Hood</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Inverted Microscope with x10 objective</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Ambient air humidified Incubator</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
	</tbody>
</table>

a method for culturing embryonic c. elegans cells

C. elegans is a powerful model system, in which genetic and molecular techniques are easily applicable. Until recently though, techniques that require direct access to cells and isolation of specific cell types, could not be applied in C. elegans. This limitation was due to the fact that tissues are confined within a pressurized cuticle which is not easily digested by treatment with enzymes and/or detergents. Based on early pioneer work by Laird Bloom, Christensen and colleagues 1 developed a robust method for culturing C. elegans embryonic cells in large scale. Eggs are isolated from gravid adults by treatment with bleach/NaOH and subsequently treated with chitinase to remove the eggshells. Embryonic cells are then dissociated by manual pipetting and plated onto substrate-covered glass in serum-enriched media. Within 24 hr of isolation cells begin to differentiate by changing morphology and by expressing cell specific markers. C. elegans cells cultured using this method survive for up 2 weeks in vitro and have been used for electrophysiological, immunochemical, and imaging analyses as well as they have been sorted and used for microarray profiling.

C. elegans cultured cells differentiate and express cell specific markers
Christensen and colleagues using trypan blue staining demonstrated that &gt;99% of embryonic C. elegans cells survive the isolation procedure. At day 9 and 22 after plating, 85% and 65%, respectively are still alive 1. Isolated embryonic C. elegans cells must adhere to a substrate in order to differentiate. Cells that fail to adhere form clumps and it is not clear whether they survive. ...

Watch this Scientific Journal Video about A Method for Culturing Embryonic C. elegans Cells at JoVE.com

A Method for Culturing Embryonic C. elegans Cells

We describe here a revised protocol for large-scale culture of embryonic C. elegans cells. Embryonic C. elegans cells cultured in vitro using this method, appear to differentiate and recapitulate the expression of genes in a cell specific manner. Techniques that require direct access to the cells or isolation of specific cell types from the other tissues can be applied on C. elegans cultured cells.

A Method for Culturing Embryonic C. elegans Cells

C. elegans is a powerful model system, in which genetic and molecular techniques are easily applicable. Until recently though, techniques that require ...

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15.4K Views.  University of Miami. We describe here a revised protocol for large-scale culture of embryonic C. elegans cells. Embryonic C. elegans cells cultured in vitro using this method, appear to differentiate and recapitulate the expression of genes in a cell specific manner. Techniques that require direct access to the cells or isolation of specific cell types from the other tissues can be applied on C. elegans cultured cells.

Video: A Method for Culturing Embryonic C. elegans Cells

Generation of Stable Transgenic C. elegans Using Microinjection

Transgenic Caenorhabditis elegans can be readily created via microinjection of a DNA plasmid solution into the gonad 1. The plasmid DNA rearranges to form extrachromosomal concatamers that are stably inherited, though not with the same efficiency as actual chromosomes 2. A gene of interest is co-injected with an obvious phenotypic marker, such as rol-6 or GFP, to allow selection of transgenic animals under a dissecting microscope. The exogenous gene may be expressed from its native promoter for cellular localization studies. Alternatively, the transgene can be driven by a different tissue-specific promoter to assess the role of the gene product in that particular cell or tissue. This technique efficiently drives gene expression in all tissues of C. elegans except for the germline or early embryo 3. Creation of transgenic animals is widely utilized for a range of experimental paradigms. This video demonstrates the microinjection procedure to generate transgenic worms. Furthermore, selection and maintenance of stable transgenic C. elegans lines is described.

This video demonstrates the technique of microinjection into the gonad of C. elegans to create transgenic animals.

Transgenic Caenorhabditis elegans can be readily created via microinjection of a DNA plasmid solution into the gonad 1.  The plasmid DNA rearranges to ...

Application of a C. elegans Dopamine Neuron Degeneration Assay for the Validation of Potential Parkinson's Disease Genes

Improvements to the diagnosis and treatment of Parkinson's disease (PD) are dependent upon knowledge about susceptibility factors that render populations at risk. In the process of attempting to identify novel genetic factors associated with PD, scientists have generated many lists of candidate genes, polymorphisms, and proteins that represent important advances, but these leads remain mechanistically undefined. Our work is aimed toward significantly narrowing such lists by exploiting the advantages of a simple animal model system. While humans have billions of neurons, the microscopic roundworm Caenorhabditis elegans has precisely 302, of which only eight produce dopamine (DA) in hemaphrodites. Expression of a human gene encoding the PD-associated protein, alpha-synuclein, in C. elegans DA neurons results in dosage and age-dependent neurodegeneration.
Worms expressing human alpha-synuclein in DA neurons are isogenic and express both GFP and human alpha-synuclein under the DA transporter promoter (Pdat-1). The presence of GFP serves as a readily visualized marker for following DA neurodegeneration in these animals. We initially demonstrated that alpha-synuclein-induced DA neurodegeneration could be rescued in these animals by torsinA, a protein with molecular chaperone activity 1. Further, candidate PD-related genes identified in our lab via large-scale RNAi screening efforts using an alpha-synuclein misfolding assay were then over-expressed in C. elegans DA neurons. We determined that five of seven genes tested represented significant candidate modulators of PD as they rescued alpha-synuclein-induced DA neurodegeneration 2. Additionally, the Lindquist Lab (this issue of JoVE) has performed yeast screens whereby alpha-synuclein-dependent toxicity is used as a readout for genes that can enhance or suppress cytotoxicity. We subsequently examined the yeast candidate genes in our C. elegans alpha-synuclein-induced neurodegeneration assay and successfully validated many of these targets 3, 4.
Our methodology involves generation of a C. elegans DA neuron-specific expression vector using recombinational cloning of candidate gene cDNAs under control of the Pdat-1 promoter. These plasmids are then microinjected in wild-type (N2) worms, along with a selectable marker for successful transformation. Multiple stable transgenic lines producing the candidate protein in DA neurons are obtained and then independently crossed into the alpha-synuclein degenerative strain and assessed for neurodegeneration, at both the animal and individual neuron level, over the course of aging.

Application of a C. elegans Dopamine Neuron Degeneration Assay for the Validation of Potential Parkinson&#039;s Disease Genes

This video demonstrates how to use C. elegans to assess dopaminergic neuron neurodegeneration as a model for Parkinson's disease. Furthermore, genetic screens are used to identify factors that either enhance degeneration or are neuroprotective.

Improvements to the diagnosis and treatment of Parkinson's disease (PD) are dependent upon knowledge about susceptibility factors that render populations ...

Generation of Transgenic C. elegans by Biolistic Transformation

The number of laboratories using the free living nematode C. elegans is rapidly growing. The popularity of this biological model is attributed to a rapid generation time and short life span, easy and inexpensive maintenance, fully sequenced genome, and array of RNAi resources and mutant animals. Additionally, analysis of the C. elegans genome revealed a great similarity between worms and higher vertebrates, which suggests that research in worms could be an important adjunct to studies performed in whole mice or cultured cells. A powerful and important part of worm research is the ability to use transgenic animals to study gene localization and function. Transgenic animals can be created either via microinjection of the worm germline or through the use of biolistic bombardment. Bombardment is a newer technique and is less familiar to a number of labs. Here we describe a simple protocol to generate transgenic worms by biolistic bombardment with gold particles using the Bio-Rad PDS-1000 system. Compared with DNA microinjection into hermaphrodite germline, this protocol has the advantage of not requiring special skills from the operator with regards to identifying worm anatomy or performing microinjection. Further multiple transgenic lines are usually obtained from a single bombardment. Also in contrast to microinjection, biolistic bombardment produces transgenic animals with both extrachromosomal arrays and integrated transgenes. The ability to obtain integrated transgenic lines can avoid the use of mutagenic protocols to integrate foreign DNA. In conclusion, biolistic bombardment can be an attractive method for the generation of transgenic animals, especially for investigators not interested in investing the time and effort needed to become skilled at microinjection.

Generation of Transgenic C. elegans by Biolistic Transformation

Transgenic worms are commonly used in C. elegans research. Described is a simple, yet effective, protocol to introduce transgenes into worms using biolistic bombardment with DNA-coated gold particles. The effort involved and results of bombardment compare favorably with microinjection for the generation of transgenic animals.

The number of laboratories using the free living nematode C. elegans is rapidly growing. The popularity of this biological model is attributed to a rapid ...

The Production of C. elegans Transgenes via Recombineering with the galK Selectable Marker

The creation of transgenic animals is widely utilized in C. elegans research including the use of GFP fusion proteins to study the regulation and expression pattern of genes of interest or generation of tandem affinity purification (TAP) tagged versions of specific genes to facilitate their purification. Typically transgenes are generated by placing a promoter upstream of a GFP reporter gene or cDNA of interest, and this often produces a representative expression pattern. However, critical elements of gene regulation, such as control elements in the 3' untranslated region or alternative promoters, could be missed by this approach. Further only a single splice variant can be usually studied by this means. In contrast, the use of worm genomic DNA carried by fosmid DNA clones likely includes most if not all elements involved in gene regulation in vivo which permits the greater ability to capture the genuine expression pattern and timing. To facilitate the generation of transgenes using fosmid DNA, we describe an E. coli based recombineering procedure to insert GFP, a TAP-tag, or other sequences of interest into any location in the gene. The procedure uses the galK gene as the selection marker for both the positive and negative selection steps in recombineering which results in obtaining the desired modification with high efficiency. Further, plasmids containing the galK gene flanked by homology arms to commonly used GFP and TAP fusion genes are available which reduce the cost of oligos by 50% when generating a GFP or TAP fusion protein. These plasmids use the R6K replication origin which precludes the need for extensive PCR product purification. Finally, we also demonstrate a technique to integrate the unc-119 marker on to the fosmid backbone which allows the fosmid to be directly injected or bombarded into worms to generate transgenic animals. This video demonstrates the procedures involved in generating a transgene via recombineering using this method.

The Production of C. elegans Transgenes via Recombineering with the galK Selectable Marker

The ability to produce transgenes for Caenorhabditis elegans using genomic DNA carried by fosmids is particularly attractive as all of the native regulatory elements are retained. Described is a simple and robust procedure for the production of transgenes via recombineering with the galK selectable marker.

The creation of transgenic animals is widely utilized in C. elegans research including the use of GFP fusion proteins to study the regulation and ...

Robust Generation of Hepatocyte-like Cells from Human Embryonic Stem Cell Populations

Despite progress in modelling human drug toxicity, many compounds fail during clinical trials due to unpredicted side effects. The cost of clinical studies are substantial, therefore it is essential that more predictive toxicology screens are developed and deployed early on in drug development (Greenhough et al 2010). Human hepatocytes represent the current gold standard model for evaluating drug toxicity, but are a limited resource that exhibit variable function. Therefore, the use of immortalised cell lines and animal tissue models are routinely employed due to their abundance. While both sources are informative, they are limited by poor function, species variability and/or instability in culture (Dalgetty et al 2009). Pluripotent stem cells (PSCs) are an attractive alternative source of human hepatocyte like cells (HLCs) (Medine et al 2010). PSCs are capable of self renewal and differentiation to all somatic cell types found in the adult and thereby represent a potentially inexhaustible source of differentiated cells. We have developed a procedure that is simple, highly efficient, amenable to automation and yields functional human HLCs (Hay et al 2008 ; Fletcher et al 2008 ; Hannoun et al 2010 ; Payne et al 2011 and Hay et al 2011). We believe our technology will lead to the scalable production of HLCs for drug discovery, disease modeling, the construction of extra-corporeal devices and possibly cell based transplantation therapies.

This article will focus on the generation of human hepatic endoderm from human embryonic stem cell populations.

Despite progress in modelling human drug toxicity, many compounds fail during clinical trials due to unpredicted side effects. The cost of clinical ...

RNAi Screening to Identify Postembryonic Phenotypes in C. elegans

C. elegans has proven to be a valuable model system for the discovery and functional characterization of many genes and gene pathways1. More sophisticated tools and resources for studies in this system are facilitating continued discovery of genes with more subtle phenotypes or roles. 
Here we present a generalized protocol we adapted for identifying C. elegans genes with postembryonic phenotypes of interest using RNAi2. This procedure is easily modified to assay the phenotype of choice, whether by light or fluorescence optics on a dissecting or compound microscope. This screening protocol capitalizes on the physical assets of the organism and molecular tools the C. elegans research community has produced. As an example, we demonstrate the use of an integrated transgene that expresses a fluorescent product in an RNAi screen to identify genes required for the normal localization of this product in late stage larvae and adults. First, we used a commercially available genomic RNAi library with full-length cDNA inserts. This library facilitates the rapid identification of multiple candidates by RNAi reduction of the candidate gene product. Second, we generated an integrated transgene that expresses our fluorecently tagged protein of interest in an RNAi-sensitive background. Third, by exposing hatched animals to RNAi, this screen permits identification of gene products that have a vital embryonic role that would otherwise mask a post-embryonic role in regulating the protein of interest. Lastly, this screen uses a compound microscope equipped for single cell resolution.

RNAi Screening to Identify Postembryonic Phenotypes in C. elegans

We describe a sensitized method to identify postembryonic regulators of protein expression and localization in C. elegans using an RNAi-based genomic screen and an integrated transgene that expresses a functional, fluorescently tagged protein.

C. elegans has proven to be a valuable model system for the discovery and functional characterization of many genes and gene pathways1. More sophisticated ...

Preparation of Mouse Embryonic Fibroblast Cells Suitable for Culturing Human Embryonic and Induced Pluripotent Stem Cells

In general, human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs)1 can be cultured under variable conditions. However, it is not easy to establish an effective system for culturing these cells. Since the culture conditions can influence gene expression that confers pluripotency in hESCs and hiPSCs, the optimization and standardization of the culture method is crucial.
The establishment of hESC lines was first described by using MEFs as feeder cells and fetal bovine serum (FBS)-containing culture medium2. Next, FBS was replaced with knockout serum replacement (KSR) and FGF2, which enhances proliferation of hESCs3. Finally, feeder-free culture systems enable culturing cells on Matrigel-coated plates in KSR-containing conditioned medium (medium conditioned by MEFs)4. Subsequently, hESCs culture conditions have moved towards feeder-free culture in chemically defined conditions5-7. Moreover, to avoid the potential contamination by pathogens and animal proteins culture methods using xeno-free components have been established8.
To obtain improved conditions mouse feeder cells have been replaced with human cell lines (e.g. fetal muscle and skin cells9, adult skin cells10, foreskin fibroblasts11-12, amniotic mesenchymal cells13). However, the efficiency of maintaining undifferentiated hESCs using human foreskin fibroblast-derived feeder layers is not as high as that from mouse feeder cells due to the lower level of secretion of Activin A14. Obviously, there is an evident difference in growth factor production by mouse and human feeder cells.
Analyses of the transcriptomes of mouse and human feeder cells revealed significant differences between supportive and non-supportive cells. Exogenous FGF2 is crucial for maintaining self-renewal of hESCs and hiPSCs, and has been identified as a key factor regulating the expression of Tgf&beta;1, Activin A and Gremlin (a BMP antagonist) in feeder cells. Activin A has been shown to induce the expression of OCT4, SOX2, and NANOG in hESCs15-16.
For long-term culture, hESCs and hiPSCs can be grown on mitotically inactivated MEFs or under feeder-free conditions in MEF-CM (MEF-Conditioned Medium) on Matrigel-coated plates to maintain their undifferentiated state. Success of both culture conditions fully depends on the quality of the feeder cells, since they directly affect the growth of hESCs.
Here, we present an optimized method for the isolation and culture of mouse embryonic fibroblasts (MEFs), preparation of conditioned medium (CM) and enzyme-linked immunosorbent assay (ELISA) to assess the levels of Activin A within the media.

The quality of mouse embryonic fibroblasts (MEFs) is dictated by the right strain of mouse such as CF-1. Pluripotency-supportive MEFs and conditioned media (CM) obtained from these should contain optimal concentrations of Activin A, Gremlin and Tgf&beta;1 needed for the Activin/Nodal and FGF pathways to co-operatively maintain self-renewal and pluripotency.

In general, human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs)1 can be cultured under variable conditions. However, it ...

A System for ex vivo Culturing of Embryonic Pancreas

The pancreas controls vital functions of our body, including the production of digestive enzymes and regulation of blood sugar levels1. Although in the past decade many studies have contributed to a solid foundation for understanding pancreatic organogenesis, important gaps persist in our knowledge of early pancreas formation2. A complete understanding of these early events will provide insight into the development of this organ, but also into incurable diseases that target the pancreas, such as diabetes or pancreatic cancer. Finally, this information will generate a blueprint for developing cell-replacement therapies in the context of diabetes.
 During embryogenesis, the pancreas originates from distinct embryonic outgrowths of the dorsal and ventral foregut endoderm at embryonic day (E) 9.5 in the mouse embryo3,4. Both outgrowths evaginate into the surrounding mesenchyme as solid epithelial buds, which undergo proliferation, branching and differentiation to generate a fully mature organ2,5,6. Recent evidences have suggested that growth and differentiation of pancreatic cell lineages, including the insulin-producing &beta;-cells, depends on proper tissue-architecture, epithelial remodeling and cell positioning within the branching pancreatic epithelium7,8. However, how branching morphogenesis occurs and is coordinated with proliferation and differentiation in the pancreas is largely unknown. This is in part due to the fact that current knowledge about these developmental processes has relied almost exclusively on analysis of fixed specimens, while morphogenetic events are highly dynamic.
 Here, we report a method for dissecting and culturing mouse embryonic pancreatic buds ex vivo on glass bottom dishes, which allow direct visualization of the developing pancreas (Figure 1). This culture system is ideally devised for confocal laser scanning microscopy and, in particular, live-cell imaging. Pancreatic explants can be prepared not only from wild-type mouse embryos, but also from genetically engineered mouse strains (e.g. transgenic or knockout), allowing real-time studies of mutant phenotypes. Moreover, this ex vivo culture system is valuable to study the effects of chemical compounds on pancreatic development, enabling to obtain quantitative data about proliferation and growth, elongation, branching, tubulogenesis and differentiation. In conclusion, the development of an ex vivo pancreatic explant culture method combined with high-resolution imaging provides a strong platform for observing morphogenetic and differentiation events as they occur within the developing mouse embryo.

A System for ex vivo Culturing of Embryonic Pancreas

Here, we describe a method for isolation, culture and manipulation of mouse embryonic pancreas. This represents an excellent ex vivo system for studying various aspects of pancreatic development, including morphogenesis, differentiation and growth. Pancreatic bud explants can be cultured for several days and used in a range of different applications, including whole-mount immunofluorescence and live imaging.

The pancreas controls vital functions of our body,  including the production of digestive enzymes and regulation of blood sugar  levels1. Although in the ...

Basic Caenorhabditis elegans Methods: Synchronization and Observation

Research into the molecular and developmental biology of the nematode Caenorhabditis elegans was begun in the early seventies by Sydney Brenner and it has since been used extensively as a model organism 1. C. elegans possesses key attributes such as simplicity, transparency and short life cycle that have made it a suitable experimental system for fundamental biological studies for many years 2. Discoveries in this nematode have broad implications because many cellular and molecular processes that control animal development are evolutionary conserved 3.
C. elegans life cycle goes through an embryonic stage and four larval stages before animals reach adulthood. Development can take 2 to 4 days depending on the temperature. In each of the stages several characteristic traits can be observed. The knowledge of its complete cell lineage 4,5 together with the deep annotation of its genome turn this nematode into a great model in fields as diverse as the neurobiology 6, aging 7,8, stem cell biology 9 and germ line biology 10. 
An additional feature that makes C. elegans an attractive model to work with is the possibility of obtaining populations of worms synchronized at a specific stage through a relatively easy protocol. The ease of maintaining and propagating this nematode added to the possibility of synchronization provide a powerful tool to obtain large amounts of worms, which can be used for a wide variety of small or high-throughput experiments such as RNAi screens, microarrays, massive sequencing, immunoblot or in situ hybridization, among others. 
Because of its transparency, C. elegans structures can be distinguished under the microscope using Differential Interference Contrast microscopy, also known as Nomarski microscopy. The use of a fluorescent DNA binder, DAPI (4',6-diamidino-2-phenylindole), for instance, can lead to the specific identification and localization of individual cells, as well as subcellular structures/defects associated to them.

Basic Caenorhabditis elegans Methods: Synchronization and Observation

The easiness of maintaining and propagating the nematode C. elegans make it a nice model organism to work with. The possibility of synchronizing worms allows the work with a significant amount of subjects at the same developmental stage, what facilitates the study of one particular process in many animals.

Research into the molecular and developmental biology of the nematode Caenorhabditis elegans was begun in the early seventies by Sydney Brenner and it has ...

C. elegans Chemotaxis Assay

Many organisms use chemotaxis to seek out food sources, avoid noxious substances, and find mates. Caenorhabditis elegans has impressive chemotaxis behavior.
 The premise behind testing the response of the worms to an odorant is to place them in an area and observe the movement evoked in response to an odorant. Even with the many available assays, optimizing worm starting location relative to both the control and test areas, while minimizing the interaction of worms with each other, while maintaining a significant sample size remains a work in progress 1-10. The method described here aims to address these issues by modifying the assay developed by Bargmann et al.1. A Petri dish is divided into four quadrants, two opposite quadrants marked "Test" and two are designated "Control". Anesthetic is placed in all test and control sites. The worms are placed in the center of the plate with a circle marked around the origin to ensure that non-motile worms will be ignored. Utilizing a four-quadrant system rather than one 2 or two 1 eliminates bias in the movement of the worms, as they are equidistant from test and control samples, regardless of which side of the origin they began. This circumvents the problem of worms being forced to travel through a cluster of other worms to respond to an odorant, which can delay worms or force them to take a more circuitous route, yielding an incorrect interpretation of their intended path. This method also shows practical advantages by having a larger sample size and allowing the researcher to run the assay unattended and score the worms once the allotted time has expired.

C. elegans Chemotaxis Assay

A method of quantitatively evaluating the chemotactic response of Caenorhabditis elegans is described. A chemotactic index (CI) was employed as a way to precisely evaluate the response of worms to certain targets, and serve as a platform of comparison between strains and compounds of interest.

Many organisms use chemotaxis to seek out food sources, avoid noxious substances, and find mates.  Caenorhabditis elegans has impressive chemotaxis ...