Partial funding from the USDA multi-state research project W-2171 "Germ Cell and Embryo Development and Manipulation for the Improvement of Livestock" is gratefully acknowledged. The artistic talents of Ryan Callahan, who prepared the technical illustrations for the video portion of this article, are also gratefully acknowledged.

1. Evaluating Suitability of Embryos for Cryopreservation1
<ol>
<li>Specimens harvested from the reproductive tract of individual donor females should be placed into an isotonic embryo holding medium for 10 minutes prior to evaluation using a stereomicroscope. Be certain to keep embryos from each donor female separate from one another to enable identification of parentage of embryo transfer offspring.</li>
<li>Using low magnification (&le; 10X), specimens from an individual donor female should be segregated into separate groups consisting of unfertilized ova, degenerate embryos, or transferable quality embryos. Only quality grade 1 or 2 embryos at the compact morula through expanded blastocyst stages of development are suitable for cryopreservation, and all others should be discarded (unless synchronous recipient females are available for quality grade 3 embryos and a post-transfer pregnancy rate of approximately 25-30% is deemed acceptable).</li>
<li>Inspect quality grade 1 and 2 compact morula through expanded blastocyst stage embryos at a magnification &ge; 50X to ensure that the zona pellucida of the embryo is intact and that there is no material (e.g., cells, mucus) adhering to the zona pellucida. Any embryo with a cracked or missing zona pellucida or with a zona pellucida having adherent material should be segregated from other embryos and either be discarded or processed separately.</li>
</ol>
2. Washing Embryos to Reduce Likelihood of Disease Transmission2
<ol>
<li>Move zona pellucida-intact embryos in a minimal volume of isotonic embryo holding medium into the first well of embryo washing medium (e.g., phosphate buffered saline augmented with antibiotics and bovine serum albumin, newborn calf serum, or polyvinyl alcohol). Keep embryos from each donor female separate, and do not attempt to wash more than 10 embryos at one time. Move embryos in a minimal volume of medium into each successive wash to achieve a serial dilution &ge; 1:100, and be certain to use sterile embryo handling tips that are changed between each successive wash.</li>
<li>Move embryos through 4 more washes as described in 2.1.</li>
<li>If transmission of viral diseases is of concern, wash embryos two times in a 0.25% trypsin solution, for a total combined exposure time to trypsin of no more than 90 seconds.</li>
<li>After the two trypsin washes, wash embryos 5 times more in embryo washing medium as described in 2.1.</li>
<li>After the final embryo wash, place embryos into isotonic embryo holding medium.</li>
</ol>
3. Dehydrating Embryos Prior to Cryopreservation3
<ol>
<li>Embryos should be transferred in a minimal volume of isotonic embryo holding medium into a hypertonic solution (1.4-1.5 Molar concentration) of a cryoprotective agent (CPA) such as ethylene glycol or glycerol.</li> 
<li>Allow embryos to sit in freezing medium (hypertonic CPA solution) until they reach osmotic equilibrium. Because ethylene glycol permeates embryonic cells more rapidly than does glycerol, equilibration times are typically less for embryos in ethylene glycol (5 min) than in glycerol (10 min). Part of this equilibration time may be achieved during and after embryos are loaded into straws (described in next step).</li>
</ol>
4. Loading Embryos into a 0.25 ml Plastic Straw for Cryopreservation
<ol>
<li>Attach the cotton plug end of a 0.25 ml plastic straw (11.5 cm working length) to an embryo loading device, and aspirate approximately 1.3 cm of hypertonic CPA solution into a properly labeled straw. A variety of labeling procedures exists, including use of printed labels attached to either a straw sealing plug or to another straw connected with a straw adapter.</li>
<li>Remove the straw from the CPA solution, and aspirate approximately 0.15 cm of air to create a tiny air bubble within the straw.</li>
<li>Aspirate a single embryo in approximately 0.8 cm of hypertonic CPA solution into the straw.</li>
<li>Remove the straw from the CPA solution and aspirate approximately 0.15 cm of air to create a second tiny air bubble within the straw (air bubbles serve to physically isolate the embryo within the straw).</li>
<li>Aspirate approximately 9.1 cm of CPA solution to completely fill the straw, being certain to draw in a sufficient volume of CPA solution to moisten the polyvinylchloride (PVC) powder that exists within the cotton plug end of the straw. The CPA solution causes the PVC powder to gel and seal that end of the straw.</li>
<li>Seal the other end of the straw with PVC powder, plastic straw sealing plugs, or a heat sealer.</li>
</ol>
5. Placing Embryos into a Controlled Rate Embryo Freezing Machine
<ol>
<li>Either methanol bath or liquid nitrogen vapor freezing machines may be programmed for cryopreservation of preimplantation embryos.</li> 
<li>Load the straws containing the embryos into a freezing machine whose temperature has been cooled from ambient temperature to -6&deg;C. Load straws cotton plug end up (unless plastic straw sealing plugs or straw adapters are being used, in which case cotton plug end is placed down).</li>
<li>Allow embryos to sit at this temperature for at least 2 minutes before proceeding.</li>
</ol>
6. Seeding
<ol>
<li>Once embryos have cooled to -6&deg;C, use a pair of tongs supercooled in liquid nitrogen (or a cotton-tipped stick immersed in liquid nitrogen) to induce ice crystal formation in the CPA solution inside the straw by touching the tongs (or cotton tipped stick) to the column of solution either above or below the embryo.</li> 
<li>The water in the CPA solution will crystallize in the region exposed to liquid nitrogen, and ice crystals will spread to the column of CPA solution immediately surrounding the embryo.</li>
<li>Hold embryos at seeding temperature for 10 minutes before further cooling.</li>
</ol>
7. Continuing Dehydration of Embryos 
<ol>
<li>Cool embryos at a rate of 0.5&deg;C/min down to a temperature of -34&deg;C. This cooling rate is important to ensure continued dehydration of the embryo.</li>
<li>Hold embryos at -34&deg;C for 10 minutes before plunging embryos into liquid nitrogen (-196&deg;C).</li>
<li>Place cryopreserved embryos into an appropriately labeled goblet (filled with liquid nitrogen) attached to an appropriately labeled cane, and place the cane into a canister of a liquid nitrogen dewar for short- or long-term storage.</li>
</ol>
8. Thawing Cryopreserved Embryos
<ol>
<li>Pull the canister into the neck of the liquid nitrogen dewar, ensuring that the canister remains below the frost line in the dewar.</li>
<li>Locate the cane containing the embryo to be thawed, and quickly and carefully remove the straw from the goblet, being certain not to warm other straws in the goblet.</li>
<li>Hold the straw in air for 3-5 seconds (to reduce the incidence of a cracked zona pellucida4), and then submerge into a 37&deg;C water bath for an additional 25-30 seconds.</li>
<li>Remove the straw from the water bath, wipe the straw (being careful not to smudge the embryo identification on the straw), use a straw cutting device to snip off the non-cotton plug end of the straw (if sealed using heat or PVC powder), or carefully remove the plastic sealing plug, and either:
<ol type="a">
<li>load the straw into an embryo transfer device and transfer as quickly as possible to a synchronous embryo recipient (but ONLY if the embryo was cryopreserved using ethylene glycol as the CPA), or</li>
<li>hold the open end of the straw over a dish containing a 1.0 Molar concentration of sucrose (a non-permeating compound), and use a pair of scissors to cut off the cotton plug end of the straw. Contents of the straw should freely flow into the sucrose solution, but pushing a small column of air through the straw may be necessary if any residual medium exists inside the straw. Allow embryos to remain in sucrose solution for 10 minutes, and then transfer embryos into isotonic embryo holding medium for 10 minutes. Evaluate embryos post-thaw, load into a new straw, and transfer to suitable recipient females.</li>
</ol>
</li>
</ol>
9. Representative Results:
A variety of factors may influence the pregnancy and live birth rates resulting from the transfer of frozen-thawed preimplantation embryos to synchronous recipient females5. Embryos at developmental stages less advanced than compact morula or more advanced than expanded blastocyst often do not survive the cryopreservation process as well as embryos at the compact morula, early blastocyst, blastocyst, and expanded blastocyst stages of embryonic development. Embryos of quality grade 1 and 2 yield higher post-thaw pregnancy rates than do quality grade 3 embryos (which typically are not cryopreserved due to the low post-thaw pregnancy rates). Embryos mishandled during the embryo freezing or embryo thawing procedures are likely to exhibit reduced pregnancy rates. Embryos transferred to recipient females whose estrous cycles are not synchronized with that of the donor female typically produce lower pregnancy rates. Embryos produced in vitro or manipulated in some manner (e.g., biopsied or bisected) usually yield lower pregnancy rates. Under optimal conditions, pregnancy rates obtained after transfer of frozen-thawed in vivo derived embryos is typically 60-70% in cattle6,7, 65-75% in sheep8,9,10,11, and 60-70% in goats12,13,14,15. Similarly, pregnancy rates obtained after transfer of frozen-thawed in vitro produced embryos is typically 40-50% in cattle6,16, 25-35% in sheep17, and 30-40% in goats18.

<img src="/files/ftp_upload/2764/2764table1.jpg" alt="Table 1" /> 
Table 1. Expected pregnancy rates following transfer of frozen-thawed embryos from domestic ruminant livestock species to synchronous recipient females.

<ol>
	<li>Lindner, G. M., Wright, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bovine+embryo+morphology+and+evaluation.">Bovine embryo morphology and evaluation.</a> Theriogenology. 20, 407-416 (1983).</li><li>Stringfellow, D. A., Stringfellow, D. A., Givens, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recommendations+for+the+sanitary+handling+of+in+vivo+derived+embryos.">Recommendations for the sanitary handling of in vivo derived embryos.</a> Manual of the International Embryo Transfer Society. , 65-68 (2010).</li><li>Youngs, C. R., Leibo, S. P., Godke, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Embryo+cryopreservation+in+domestic+mammalian+livestock+species.">Embryo cryopreservation in domestic mammalian livestock species.</a> CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources. , (2010).</li><li>Rall, W. F., Meyer, T. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zona+fracture+damage+and+its+avoidance+during+the+cryopreservation+of+mammalian+embryos.">Zona fracture damage and its avoidance during the cryopreservation of mammalian embryos.</a> Theriogenology. 31, 683-692 (1989).</li><li>Spell, A. R., Beal, W. E., Corah, L. R., Lamb, G. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluating+recipient+and+embryo+factors+that+affect+pregnancy+rates+of+embryo+transfer+in+beef+cattle.">Evaluating recipient and embryo factors that affect pregnancy rates of embryo transfer in beef cattle.</a> Theriogenology. 56, 287-297 (2001).</li><li>Hasler, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+current+status+of+oocyte+recovery,+in+vitro+embryo+production,+and+embryo+transfer+in+domestic+animals,+with+an+emphasis+on+the+bovine.">The current status of oocyte recovery, in vitro embryo production, and embryo transfer in domestic animals, with an emphasis on the bovine.</a> J. Anim. Sci. 76, 52-74 (1998).</li><li>Hasler, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Factors+affecting+frozen+and+fresh+embryo+transfer+pregnancy+rates+in+cattle.">Factors affecting frozen and fresh embryo transfer pregnancy rates in cattle.</a> Theriogenology. 56, 1401-1415 (2001).</li><li>Heyman, Y., Vincent, C., Garnier, V., Cognie, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transfer+of+frozen-thawed+embryos+in+sheep.">Transfer of frozen-thawed embryos in sheep.</a> Veterinary Record. 120, 83-85 (1987).</li><li>McGinnis, L. K., Duplantis, S. C., Youngs, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cryopreservation+of+sheep+embryos+using+ethylene+glycol.">Cryopreservation of sheep embryos using ethylene glycol.</a> Anim. Reprod. Sci. 30, 273-280 (1993).</li><li>Shelton, J. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Factors+affecting+viability+of+fresh+and+frozen-thawed+sheep+demi-embryos.">Factors affecting viability of fresh and frozen-thawed sheep demi-embryos.</a> Theriogenology. 37, 713-721 (1992).</li><li>Bettencourt, E. M., Bettencourt, C. M., Silva, J. C. E., Ferreira, P., Matos, C. P., Ram&#227;o, R. J., Rocha, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fertility+rates+following+the+transfer+of+ovine+embryos+cryopreserved+using+three+protocols.">Fertility rates following the transfer of ovine embryos cryopreserved using three protocols.</a> Small Ruminant Research. 82, 112-116 (2009).</li><li>Chemineau, P., Procureur, R., Cogni&#233;, Y., Lef&#232;vre, P. C., Locatelli, A., Chupin, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Production,+freezing+and+transfer+of+embryos+from+a+bluetongue-infected+goat+herd+without+bluetongue+transmission.+Theriogenology.">Production, freezing and transfer of embryos from a bluetongue-infected goat herd without bluetongue transmission. Theriogenology.</a> 26, 279-290 (1986).</li><li>Baril, B., Casamitjana, P., Perrin, J., Vallet, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Embryo+production+freezing+and+transfer+in+Angora,+Alpine+and+Saanen+goats.">Embryo production freezing and transfer in Angora, Alpine and Saanen goats.</a> Zuchthyg. 24, 101-115 (1989).</li><li>Guignot, F., Bouttier, A., Baril, G., Salvetti, P., Pignon, P., Beckers, J. F., Touz&#233;, J. L., Cogni&#233;, J., Traldi, A. S., Cogni&#233;, Y., Mermillod, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+vitrification+method+allowing+direct+transfer+of+goat+embryos.">Improved vitrification method allowing direct transfer of goat embryos.</a> Theriogenology. 66, 1004-1011 (2006).</li><li>Nowshari, M. A., Holtz, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+culture+of+goat+morulae+to+blastocysts+before+freezing.">In vitro culture of goat morulae to blastocysts before freezing.</a> Theriogenology. 44, 983-988 (1995).</li><li>Machatkova, M., Hulinska, P., Reckova, Z., Hanzalova, K., Spanihelova, J., Pospisil, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+production+of+embryos+from+high+performance+cows+and+the+development+of+frozen-thawed+embryos+after+transfer:+a+field+study.">In vitro production of embryos from high performance cows and the development of frozen-thawed embryos after transfer: a field study.</a> Veterinarni Medicina. 53, 358-364 (2008).</li><li>Mart&#237;nez, A. G., Valc&#225;rcel, A., Furnus, C. C., de Matos, D. G., Iorio, G., de las Heras, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cryopreservation+of+in+vitro-produced+ovine+embryos.">Cryopreservation of in vitro-produced ovine embryos.</a> Small Ruminant Research. 63, 288-296 (2006).</li><li>Han, Y., Meintjes, M., Graff, K., Denniston, R., Zhang, L., Ziomek, C., Godke, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Caprine+offspring+born+from+fresh+and+frozen-thawed+in+vitro-produced+embryos.">Caprine offspring born from fresh and frozen-thawed in vitro-produced embryos.</a> Veterinary Record. 149, 714-716 (2001).</li><li>Leibo, S. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+one-step+method+for+direct+nonsurgical+transfer+of+frozen-thawed+bovine+embryos.">A one-step method for direct nonsurgical transfer of frozen-thawed bovine embryos.</a> Theriogenology. 21, 767-790 (1984).</li><li>Voelkel, S. A., Hu, Y. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+ethylene+glycol+as+a+cryoprotectant+for+bovine+embryos+allowing+direct+transfer+of+frozen-thawed+embryos+to+recipient+females.">Use of ethylene glycol as a cryoprotectant for bovine embryos allowing direct transfer of frozen-thawed embryos to recipient females.</a> Theriogenology. 37, 687-697 (1992).</li><li>Rall, W. F., Fahy, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ice-free+cryopreservation+of+mouse+embryos+at+-196&#176;C+by+vitrification.">Ice-free cryopreservation of mouse embryos at -196&#176;C by vitrification.</a> Nature. 313, 573-575 (1985).</li><li>Notter, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+importance+of+genetic+diversity+in+livestock+populations+of+the+future.">The importance of genetic diversity in livestock populations of the future.</a> J. Anim. Sci. 77, 61-69 (1999).</li><li>Thibier, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Data+retrieval+committee+statistics+of+embryo+transfer-+year+2008.+The+worldwide+statistics+of+embryo+transfers+in+farm+animals.">Data retrieval committee statistics of embryo transfer- year 2008. The worldwide statistics of embryo transfers in farm animals.</a> Embryo Transfer Newsletter. 27, 13-19 (2009).</li></ol>

No conflicts of interest declared.

Because embryos consist predominantly of water, it is crucial that preimplantation embryos be adequately dehydrated and slowly cooled in accordance with the protocol described herein to avoid intracellular ice crystal formation. Once the cooling process has begun, it is important to maintain unidirectional temperature change and to avoid temperature fluctuations. Initiation of ice crystal formation ("seeding") at an appropriate temperature for the specific CPA solution is critical. 
Modifications to this slow cooling/rapid thawing method for preimplantation embryo cryopreservation include the one-step method (where the last column of medium loaded into the straw is sucrose instead of CPA solution)19 and the direct transfer method (where embryos frozen in ethylene glycol are thawed and transferred directly to the uterus of a recipient female without first removing the ethylene glycol from the embryo)20. To reduce the volume of ethylene glycol deposited into the uterus of a direct transfer (DT) recipient female, it is advisable to fill the 0.25 ml straw with 6 cm holding medium before continuing as described previously. It should be noted that a voluntary standard exists within the commercial embryo transfer industry that preimplantation embryos cryopreserved for DT should be frozen in yellow-colored straws and stored in yellow-colored goblets in the liquid nitrogen dewar. The commercial industry also has specific labeling requirements for all cryopreserved embryos that should be followed.
One alternative to this method is vitrification21, a non-equilibrium method of cryopreservation where a more highly concentrated (6-8 M) CPA solution is cooled ultra-rapidly causing the CPA solution to change from liquid to a "glassy" state without ice crystal formation. Vitrification is likely better suited for cryopreservation of embryos that are less developmentally advanced than compact morula due to their increased temperature sensitivity.
This technique has application for preservation of unique germplasm resources22, as well as to the international commercial embryo transfer industry where more than 55% of approximately 500,000 bovine preimplantation embryos transferred in calendar year 2008 were cryopreserved.23

<table border="1">
	<tbody>
 	<tr>
 	<th>Name of the reagent</th>
 <th>Company</th>
 <th>Catalog number</th>
 <th>Comments (optional)</th>
 </tr>
 <tr>
 	<td>BioLife freeze medium</td>
 <td>Agtech, Inc.</td>
 <td>C18, C18A</td>
 <td>1.5 M ethylene glycol</td>
 </tr>
 <tr>
 	<td>Emcare ethylene glycol freeze solution</td>
 <td>ICPBio Reproduction</td>
 <td>IC8, IC10</td>
 <td>1.5 M ethylene glycol</td>
 </tr>

 <tr>
 	<td>ViGro ethylene glycol freeze plus</td>
 <td>Bioniche Animal Health</td>
 <td>EVM835</td>
 <td>1.5 M ethylene glycol</td>
 </tr>

 <tr>
 	<td>Emcare 10% glycerol freeze solution</td>
 <td>ICPBio Reproduction</td>
 <td>IC12</td>
 <td>1.34 M glycerol</td>
 </tr>

 <tr>
 	<td>Emcare 1 M sucrose thaw</td>
 <td>ICPBio Reproduction</td>
 <td>IC16</td>
 <td>1.0 M sucrose</td>
 </tr>

 <tr>
 	<td>ViGro one-step thaw</td>
 <td>Bioniche Animal Health</td>
 <td>EVM247, EVM847</td>
 <td>1.0 M sucrose</td>
 </tr>

 <tr>
 	<td>ViGro
thaw 1-2-3 plus
</td>
 <td>Bioniche Animal Health</td>
 <td>EVM248, EVM848</td>
 <td>5%, 2.5%, 0% glycerol with 0.5, 0.5, 0.6% sucrose</td>
 </tr>
 <tr>
 	<td>Emcare CSU thawing kit
</td>
 <td>ICPBio Reproduction</td>
 <td>IC20</td>
 <td>6%, 3%, 0% glycerol with 10.3% sucrose</td>
 </tr>
 <tr>
 	<td>BioLife holding and transfer medium</td>
 <td>Agtech, Inc.</td>
 <td>C15, C15A</td>
 <td>modified PBS with 0.4% BSA (bovine serum albumin)</td>
 </tr>
 <tr>
 	<td>Emcare holding solution</td>
 <td>ICPBio Reproduction</td>
 <td>IC2, IC4, IC6</td>
 <td>0.4% BSA (bovine serum albumin), MOPS buffer (inert zwitterions)</td>
 </tr>
 <tr>
 	<td>ViGro holding plus</td>
 <td>Bioniche Animal Health</td>
 <td>EVM024, EVM824</td>
 <td>&nbsp;</td>
 </tr>

 <tr>
 	<td>SYNGRO
Holding medium
</td>
 <td>Bioniche Animal Health</td>
 <td>ESM024, ESM224, ESM828</td>
 <td>contains hyaluronan; no products of animal origin</td>
 </tr>

 <tr>
 	<td>BioLife 
modified D- PBS
</td>
 <td>Agtech, Inc.</td>
 <td>C06</td>
 <td>modified Dulbecco&#x2019;s phosphate buffered saline</td>
 </tr>

 <tr>
 	<td>BioLife
BSA Fraction V
</td>
 <td>Agtech, Inc.</td>
 <td>B09</td>
 <td>lyophilized bovine serum albumin, fraction V</td>
 </tr>

 <tr>
 	<td>BioLife
antibiotic-antimycotic
</td>
 <td>Agtech, Inc.</td>
 <td>B01</td>
 <td>amphotericin-B, penicillin G, streptomycin sulfate</td>
 </tr>

 <tr>
 	<td>BioLife
trypsin kit
</td>
 <td>Agtech, Inc.</td>
 <td>C22A</td>
 <td>25 g lyophilized trypsin, sterile water, sterile D-PBS </td>
 </tr> 
 </tbody>
</table>
<table border="1">
	<tbody>
 	<tr>
 	<th>Name of the equipment</th>
 <th>Company</th>
 <th>Catalog number</th>
 <th>Comments (optional)</th>
 </tr> 
 <tr>
 	<td>Biol-Cool controlled rate freezer</td>
 <td>FTS Systems</td>
 <td>BC-IV -40</td>
 <td>Methanol bath freezer</td>
 </tr>
 <tr>
 	<td>Freeze Control controlled rate freezer</td>
 <td>Cryologic</td>
 <td>CL2200</td>
 <td>Liquid nitrogen freezer</td>
 </tr>
 </tbody>
</table>

cryopreservation of preimplantation embryos of cattle, sheep, and goats

Preimplantation embryos from cattle, sheep, and goats may be cryopreserved for short- or long-term storage. Preimplantation embryos consist predominantly of water, and the avoidance of intracellular ice crystal formation during the cryopreservation process is of paramount importance to maintain embryo viability. Embryos are placed into a hypertonic solution (1.4 &#x2013; 1.5 M) of a cryoprotective agent (CPA) such as ethylene glycol (EG) or glycerol (GLYC) to create an osmotic gradient that facilitates cellular dehydration. After embryos reach osmotic equilibrium in the CPA solution, they are individually loaded in the hypertonic CPA solution into 0.25 ml plastic straws for freezing. Embryos are placed into a controlled rate freezer at a temperature of -6&deg;C. Ice crystal formation is induced in the CPA solution surrounding the embryo, and crystallization causes an increase in the concentration of CPA outside of the embryo, causing further cellular dehydration. Embryos are cooled at a rate of 0.5&deg;C/min, enabling further dehydration, to a temperature of -34&deg;C before being plunged into liquid nitrogen (-196&deg;C). Cryopreserved embryos must be thawed prior to transfer to a recipient (surrogate) female. Straws containing the embryos are removed from the liquid nitrogen dewar, held in room temperature air for 3 to 5 sec, and placed into a 37&deg;C water bath for 25 to 30 sec. Embryos cryopreserved in GLYC are placed into a 1 M solution of sucrose for 10 min for removal of the CPA before transfer to a recipient (surrogate) female. Embryos cryopreserved in EG, however, may be directly transferred to the uterus of a recipient.

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Cryopreservation of Preimplantation Embryos of Cattle, Sheep, and Goats

Preimplantation embryos may be cryopreserved after placement into a hypertonic cryoprotective solution to cause cellular dehydration. After equilibration, ice crystal formation is induced in the solution surrounding the embryo. Further dehydration occurs as the embryo is slowly cooled to subzero temperatures before plunging into liquid nitrogen for storage.

Preimplantation embryos from cattle, sheep, and goats may be cryopreserved for short- or long-term storage.  Preimplantation embryos consist predominantly ...

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Research

JoVE Journal

Biology

30.5K Views.  Iowa State University. Preimplantation embryos may be cryopreserved after placement into a hypertonic cryoprotective solution to cause cellular dehydration. After equilibration, ice crystal formation is induced in the solution surrounding the embryo. Further dehydration occurs as the embryo is slowly cooled to subzero temperatures before plunging into liquid nitrogen for storage.

Video: Cryopreservation of Preimplantation Embryos of Cattle, Sheep, and Goats

Dissection of 6.5 dpc Mouse Embryos

Analysis of gene expression patterns during early stages of mammalian embryonic development can provide important clues about gene function, cell-cell interaction and signaling mechanisms that guide embryonic patterning. However, dissection of the mouse embryo from the decidua shortly after implantation can be a challenging procedure, and detailed step-by-step documentation of this process is lacking.

Here we demonstrate how post-implantation (6.5 dpc) embryos are isolated by first dissecting the uterus of a pregnant mouse (detection of the vaginal plug was designated day 0.5 poist coitum) and subsequently dissecting the embryo from maternal decidua. The dissection of Reichert's membrane is described as well as the removal of the ectoplacental cone.

Isolation of postimplantation-stage embryos allows one to study gene patterning and analyze cell-lineage decision making processes during embryonic development, but proper dissection of the early embryo can be challenging. This protocol describes a method for isolating early primitive-streak-stage embryos (~6.5 days post coitum [dpc]).

Analysis of gene expression patterns during early stages of mammalian embryonic development can provide important clues about gene function, cell-cell ...

Plastic Embedding and Sectioning of Xenopus laevis Embryos

Plastic sections maintain true tissue morphology in thin sections of tissue that can be immunostained with fluorescent secondary antibodies, making this method more useful than paraffin-embedded or frozen sections for many types of tissue. The method for staining, plastic embedding, and sectioning is demonstrated in this video.

Collection and Cryopreservation of Hamster Oocytes and Mouse Embryos

Embryos and oocytes were first successfully cryopreserved more than 30 years ago, when Whittingham et al. 1 and Wilmut 2 separately described that mouse embryos could be frozen and stored at -196 &deg;C and, a few years later, Parkening et al. 3 reported the birth of live offspring resulting from in vitro fertilization (IVF) of cryopreserved oocytes. Since then, the use of cryopreservation techniques has rapidly spread to become an essential component in the practice of human and animal assisted reproduction and in the conservation of animal genetic resources. Currently, there are two main methods used to cryopreserve oocytes and embryos: slow freezing and vitrification. A wide variety of approaches have been used to try to improve both techniques and millions of animals and thousands of children have been born from cryopreserved embryos. However, important shortcomings associated to cryopreservation still have to be overcome, since ice-crystal formation, solution effects and osmotic shock seem to cause several cryoinjuries in post-thawed oocytes and embryos. Slow freezing with programmable freezers has the advantage of using low concentrations of cryoprotectants, which are usually associated with chemical toxicity and osmotic shock, but their ability to avoid ice-crystal formation at low concentrations is limited. Slow freezing also induces supercooling effects that must be avoided using manual or automatic seeding 4. In the vitrification process, high concentrations of cryoprotectants inhibit the formation of ice-crystals and lead to the formation of a glasslike vitrified state in which water is solidified, but not expanded. However, due to the toxicity of cyroprotectants at the concentrations used, oocytes/embryos can only be exposed to the cryoprotectant solution for a very short period of time and in a minimum volume solution, before submerging the samples directly in liquid nitrogen 5. In the last decade, vitrification has become more popular because it is a very quick method in which no expensive equipment (programmable freezer) is required. However, slow freezing continues to be the most widely used method for oocyte/embryo cryopreservation. In this video-article we show, step-by-step, how to collect and slowly freeze hamster oocytes with high post-thaw survival rates. The same procedure can also be applied to successfully freeze and thaw mouse embryos at different stages of preimplantation development.

In this video-article we present a step-by-step demonstration on how to collect and cryopreserve hamster oocytes with high post-thaw survival rates. The same procedure can also be applied to successfully freeze and thaw mouse embryos at different stages of preimplantation development.

Embryos and oocytes were first successfully cryopreserved more than 30 years ago, when Whittingham et al. 1 and Wilmut 2 separately described that mouse ...

Upright Imaging of Drosophila Embryos

Several well-known morphogenetic gradients and cellular movements occur along the dorsal/ventral axis of the Drosophila embryo. However, the current techniques used to view such processes are somewhat limited. The following protocol describes a new technique for mounting fixed and labeled Drosophila embryos for coronal viewing with confocal imaging. This method consists of embedding embryos between two layers of glycerin jelly mounting media, and imaging jelly strips positioned upright. The first step for sandwiching the embryos is to make a thin bedding of glycerin jelly on a slide. Next, embryos are carefully aligned on this surface and covered with a second layer of jelly. After the second layer is solidified, strips of jelly are cut and flipped upright for imaging. Alternatives are described for visualizing the embryos depending upon the type of microscope stand to be used. Since all cells along the dorsal-ventral axis are imaged within a single confocal Z-plane, our method allows precise measurement and comparison of fluorescent signals without photobleaching or light scattering common to 3D reconstructions of longitudinally mounted embryos.

Upright Imaging of Drosophila Embryos

Here we present a mounting protocol for stained Drosophila embryos in an upright position that allows imaging of cross-sections using Confocal microscopy.

Several well-known morphogenetic gradients and cellular movements occur along the dorsal/ventral axis of the Drosophila embryo. However, the current ...

Cryopreservation of Mouse Embryos by Ethylene Glycol-Based Vitrification

Cryopreservation of mouse embryos is a technological basis that supports biomedical sciences, because many strains of mice have been produced by genetic modifications and the number is consistently increasing year by year. Its technical development started with slow freezing methods in the 1970s1, then followed by vitrification methods developed in the late 1980s2. Generally, the latter technique is advantageous in its quickness, simplicity, and high survivability of recovered embryos. However, the cryoprotectants contained are highly toxic and may affect subsequent embryo development. Therefore, the technique was not applicable to certain strains of mice, even when the solutions are cooled to 4&deg;C to mitigate the toxic effect during embryo handling. At the RIKEN BioResource Center, more than 5000 mouse strains with different genetic backgrounds and phenotypes are maintained3, and therefore we have optimized a vitrification technique with which we can cryopreserve embryos from many different strains of mice, with the benefits of high embryo survival after vitrifying and thawing (or liquefying, more precisely) at the ambient temperature4.
Here, we present a vitrification method for mouse embryos that has been successfully used at our center. The cryopreservation solution contains ethylene glycol instead of DMSO to minimize the toxicity to embryos5. It also contains Ficoll and sucrose for prevention of devitrification and osmotic adjustment, respectively. Embryos can be handled at room temperature and transferred into liquid nitrogen within 5 min. Because the original method was optimized for plastic straws as containers, we have slightly modified the protocol for cryotubes, which are more easily accessible in laboratories and more resistant to physical damages. We also describe the procedure of thawing vitrified embryos in detail because it is a critical step for efficient recovery of live mice. These methodologies would be helpful to researchers and technicians who need preservation of mouse strains for later use in a safe and cost-effective manner.

An ethylene glycol-based vitrification method for mouse embryos is described. It is advantageous to other methods in its simplicity and low embryonic toxicity, and therefore can be broadly applicable to many strains of mice, including inbred and gene-modified mice.

Cryopreservation of mouse embryos is a technological basis that supports biomedical sciences, because many strains of mice have been produced by genetic ...

Isolation and Purification of Kinesin from Drosophila Embryos

Motor proteins move cargos along microtubules, and transport them to specific sub-cellular locations. Because altered transport is suggested to underlie a variety of neurodegenerative diseases, understanding microtubule based motor transport and its regulation will likely ultimately lead to improved therapeutic approaches. Kinesin-1 is a eukaryotic motor protein which moves in an anterograde (plus-end) direction along microtubules (MTs), powered by ATP hydrolysis. Here we report a detailed purification protocol to isolate active full length kinesin from Drosophila embryos, thus allowing the combination of Drosophila genetics with single-molecule biophysical studies. Starting with approximately 50 laying cups, with approximately 1000 females per cup, we carried out overnight collections. This provided approximately 10 ml of packed embryos. The embryos were bleach dechorionated (yielding approximately 9 grams of embryos), and then homogenized. After disruption, the homogenate was clarified using a low speed spin followed by a high speed centrifugation. The clarified supernatant was treated with GTP and taxol to polymerize MTs. Kinesin was immobilized on polymerized MTs by adding the ATP analog, 5'-adenylyl imidodiphosphate at room temperature. After kinesin binding, microtubules were sedimented via high speed centrifugation through a sucrose cushion. The microtubule pellet was then re-suspended, and this process was repeated. Finally, ATP was added to release the kinesin from the MTs. High speed centrifugation then spun down the MTs, leaving the kinesin in the supernatant. This kinesin was subjected to a centrifugal filtration using a 100 KD cut off filter for further purification, aliquoted, snap frozen in liquid nitrogen, and stored at -80 &deg;C. SDS gel electrophoresis and western blotting was performed using the purified sample. The motor activity of purified samples before and after the final centrifugal filtration step was evaluated using an in vitro single molecule microtubule assay. The kinesin fractions before and after the centrifugal filtration showed processivity as previously reported in literature. Further experiments are underway to evaluate the interaction between kinesin and other transport related proteins.

Isolation and Purification of Kinesin from Drosophila Embryos

This is a protocol to isolate active full length Kinesin from Drosophila embryos for single-molecule biophysical studies. We show how to collect embryos, make the embryo lysate, and then polymerize microtubules (MTs). Kinesin is purified by immobilizing it on the MTs, spinning down the Kinesin-MT complexes, and then releasing the kinesin from the MTs via ATP addition.

Motor proteins move cargos along microtubules, and transport them to specific sub-cellular locations. Because altered transport is suggested to underlie a ...

Mouse Sperm Cryopreservation and Recovery using the I&middot;Cryo Kit

Thousands of new genetically modified (GM) strains of mice have been created since the advent of transgenesis and knockout technologies. Many of these valuable animals exist only as live animals, with no backup plan in case of emergency. Cryopreservation of embryos can provide this backup, but is costly, can be a lengthy procedure, and generally requires a large number of animals for success. Since the discovery that mouse sperm can be successfully cryopreserved with a basic cryoprotective agent (CPA) consisting of 18&#37; raffinose and 3&#37; skim milk, sperm cryopreservation has become an acceptable and cost-effective procedure for archiving, distributing and recovery of these valuable strains.
 Here we demonstrate a newly developed I&bull;Cryo kit for mouse sperm cryopreservation. Sperm from five commonly-used strains of inbred mice were frozen using this kit and then recovered. Higher protection ratios of sperm motility (&gt; 60&#37;) and rapid progressive motility (&gt; 45&#37;) compared to the control (basic CPA) were seen for sperm frozen with this kit in 5 inbred mouse strains. Two cell stage embryo development after IVF with the recovered sperm was improved consistently in all 5 mouse strains examined. Over a 1.5 year period, 49 GM mouse lines were archived by sperm cryopreservation with the I&bull;Cryo kit and later recovered by IVF.

Mouse Sperm Cryopreservation and Recovery using the I&amp;middot;Cryo Kit

Here we demonstrate the newly developed I&#x2022;Cryo kit for mouse sperm cryopreservation. Two-cell stage embryo development with frozen-thawed sperm was improved consistently in 5 mouse strains with the use of this kit. Over a 1.5 year period, 49 genetically modified mouse lines were archived by sperm cryopreservation with the I&#x2022;Cryo kit and later successfully recovered by IVF.

Thousands of new genetically modified (GM) strains of mice have been created since the advent of transgenesis and knockout technologies.  Many of these ...

Analysis of Oxidative Stress in Zebrafish Embryos

High levels of reactive oxygen species (ROS) may cause a change of cellular redox state towards oxidative stress condition. This situation causes oxidation of molecules (lipid, DNA, protein) and leads to cell death. Oxidative stress also impacts the progression of several pathological conditions such as diabetes, retinopathies, neurodegeneration, and cancer. Thus, it is important to define tools to investigate oxidative stress conditions not only at the level of single cells but also in the context of whole organisms. Here, we consider the zebrafish embryo as a useful in vivo system to perform such studies and present a protocol to measure in vivo oxidative stress. Taking advantage of fluorescent ROS probes and zebrafish transgenic fluorescent lines, we develop two different methods to measure oxidative stress in vivo: i) a &#8220;whole embryo ROS-detection method&#8221; for qualitative measurement of oxidative stress and ii) a &#8220;single-cell&#160;ROS detection method&#8221; for quantitative measurements of oxidative stress. Herein, we demonstrate the efficacy of these procedures by increasing oxidative stress in tissues by oxidant agents and physiological or genetic methods. This protocol is amenable for forward genetic screens and it will help address cause-effect relationships of ROS in animal models of oxidative stress-related pathologies such as neurological disorders and cancer.

Here we report a protocol to measure oxidative stress in living zebrafish embryos. This procedure allows reactive oxygen species (ROS) detection in both whole embryo tissues and single-cell populations. This protocol will accomplish both qualitative and quantitative analyses.

High levels of reactive oxygen species (ROS) may cause a change of cellular redox state towards oxidative stress condition. This situation causes ...

Isolation of microRNAs from Tick Ex Vivo Salivary Gland Cultures and Extracellular Vesicles

Ticks are important ectoparasites that can vector multiple pathogens. The salivary glands of ticks are essential for feeding as their saliva contains many effectors with pharmaceutical properties that can diminish host immune responses and enhance pathogen transmission. One group of such effectors are microRNAs (miRNAs). miRNAs are short non-coding sequences that regulate host gene expression at the tick-host interface and within the organs of the tick. These small RNAs are transported in the tick saliva via extracellular vesicles (EVs), which serve inter-and intracellular communication. Vesicles containing miRNAs have been identified in the saliva of ticks. However, little is known about the roles and profiles of the miRNAs in tick salivary vesicles and glands. Furthermore, the study of vesicles and miRNAs in tick saliva requires tedious procedures to collect tick saliva. This protocol aims to develop and validate a method for isolating miRNAs from purified extracellular vesicles produced by ex vivo organ cultures. The materials and methodology needed to extract miRNAs from extracellular vesicles and tick salivary glands are described herein.

Isolation of microRNAs from Tick Ex Vivo Salivary Gland Cultures and Extracellular Vesicles

The present protocol describes the isolation of microRNAs from tick salivary glands and purified extracellular vesicles. This is a universal procedure that combines commonly used reagents and supplies. The method also allows the use of a small number of ticks, resulting in quality microRNAs that can be readily sequenced.

Ticks are important ectoparasites that can vector multiple pathogens. The salivary glands of ticks are essential for feeding as their saliva contains many ...

Optimizing Coral Sperm Cryopreservation from Threatened Coral Species

A Semi-Automated Workflow for the Cryopreservation of Coral Sperm to Support Biobanking and Aquaculture

Coral reefs are facing a crisis as the frequency of bleaching events caused by ocean warming increases, resulting in the death of corals on reefs around the world. The subsequent loss of genetic diversity and biodiversity can diminish the ability of coral to adapt to the changing climate, so efforts to preserve existing diversity are essential to maximize the resources available for reef restoration now and in the future. The most effective approach to secure genetics long-term is cryopreservation and biobanking, which permits the frozen storage of living samples at cryogenic temperatures in liquid nitrogen indefinitely. Cryopreservation of coral sperm has been possible since 2012, but the seasonal nature of coral reproduction means that biobanking activities are restricted to just a few nights per year when spawning occurs. Improving the efficiency of coral sperm processing and cryopreservation workflows is therefore essential to maximizing these limited biobanking opportunities. To this end, we set out to optimize cryopreservation processing pathways for coral sperm by building on existing technologies and creating a semi-automated approach to streamline the assessment, handling, and cryopreservation of coral sperm. The process, which combines computer-assisted sperm analysis, barcoded cryovials, and a series of linked auto-datasheets for simultaneous editing by multiple users, improves the efficiency of both sample processing and metadata management in the field. Through integration with cross-cutting research programs such as the Reef Restoration and Adaptation Program in Australia, cryopreservation can play a crucial role in large-scale reef restoration programs by facilitating the genetic management of aquaculture populations, supporting research to enhance thermal tolerance, and preventing the extinction of coral species. The described procedures will be utilized for coral cryopreservation and biobanking practitioners on reefs worldwide and will provide a model for the transition of cryopreservation technologies from research laboratories to large-scale applications.

Author Spotlight: Developing Efficient Cryopreservation and Biobanking Technologies for Global Reef Restoration

This protocol describes a semi-automated pathway to improve the efficiency and capacity of processing and cryopreservation of sperm from threatened coral species, aiming to secure genetic diversity and support reef restoration efforts.

Coral reefs are facing a crisis as the frequency of bleaching events caused by ocean warming increases, resulting in the death of corals on reefs around ...