Name: an optimized o9-1/hydrogel system for studying mechanical signals in neural crest cells
Uploaded: 2021-08-13T13:00:00
Description: Watch this Scientific Journal Video about An Optimized O9-1/Hydrogel System for Studying Mechanical Signals in Neural Crest Cells at JoVE.com

We thank Dr. Ana-Maria Zaske, operator of Atomic Force Microscope-UT Core facility at the University of Texas Health Sciences Center, for the contributed expertise in AFM in this project. We also thank the funding sources from the National Institutes of Health (K01DE026561, R03DE025873, R01DE029014, R56HL142704, and R01HL142704 to J. Wang).

1. Hydrogel preparation
NOTE: All steps must be performed in a cell culture hood that has been disinfected with ethanol and ultraviolet (UV)-sterilized before use to maintain sterility. Tools, such as tweezers and pipettes, must be sprayed with ethanol. Buffer solutions must also be sterile-filtered.
<ol>
	<li>Preparation of aminosilane-coated glass coverslips
	<ol>
		<li>Place the desired number of glass coverslips onto a piece of laboratory wipe. 
		NOTE: Prepare an additional 3-4 cov...

The goal of the current study is&#160;to provide an effective and efficient in vitro system to better understand the impact of mechanical signals in NCCs. In addition to following the step-by-step protocol mentioned above, researchers need to keep in mind that the cell culture of O9-1 NCCs is affected by the type of glass coverslips used to prepare hydrogels. For instance, it was noted that cells seeded on a specific type of glass coverslip (see the Table of Materials) survived and proliferated ...

Neural crest cells (NCCs) are a group of stem cells during vertebrate embryogenesis with a remarkable ability to migrate and contribute to the development of various organs and tissues. NCCs can differentiate into different cell types, including sensory neurons, cartilage, bone, melanocytes, and smooth muscle cells, depending on the location of axial origin and the local environmental guidance of the NCC1,2. With the ability to differentiate into a wide array of cell types, genetic abnormalities that cause dysregulation at any stage of neural crest (NC) development can lead to numerous congenital diseases2. For instance, perturbations during the formation, migration, and development of NCCs lead to developmental disorders known collectively as neurocristopathies1,3. These diseases range from craniofacial defects due to failure in NCC formation, such as Treacher Collins syndrome, to the development of various cancers due to NCC metastatic migratory ability, as seen in melanoma3,4,5,6. Over the last few decades, researchers have made remarkable discoveries about the roles and mechanisms of NCCs in development and diseases, with the majority of findings being focused on chemical signals7,8. More recently, mechanical signals have been indicated to play a critical but poorly understood role in NCC development9,10.
The environmental cues of NCCs play a critical role during their development, including the regulation of NCC differentiation into various cell types. Environmental cues, e.g., physical cues, influence pivotal behaviors and cellular responses, such as functional diversification. Mechanotransduction allows cells to sense and respond to those cues to maintain various biological processes2. NCCs are surrounded by neighboring cells and different substrates, such as the extracellular matrix (ECM), which can give rise to mechanical stimuli to maintain homeostasis and adapt to the changes through fate determination, proliferation, and apoptosis11. Mechanotransduction begins at the plasma membrane where the sensory component of mechanical extracellular stimuli occurs, resulting in the intracellular regulation of the cell12. Integrins, focal adhesions, and junctions of the plasma membrane relay mechanical signals, such as shearing forces, stress, and the stiffness of surrounding substrates, into chemical signals to produce cellular responses12. The relaying of chemical signals from the plasma membrane to the final cellular regulation is carried out via different signaling pathways to finalize vital processes for the organism, such as differentiation.
Several studies have suggested that mechanical signaling from substrate stiffness plays a role in cell differentiation13,14. For instance, previous studies have shown that mesenchymal stem cells (MSCs) grown on soft substrates with a stiffness similar to that of brain tissue (in the range of 0.1-1.0 kPa) resulted in neuronal cell differentiation15,16. However, more MSCs differentiate into myocyte-like cells when grown on 8-17 kPa substrates mimicking the stiffness of muscle, while osteoblast-like differentiation was observed when MSCs were cultured on stiff substrates (25-40 kPa)15,16. The significance of mechanotransduction is highlighted by the irregularities and abnormalities in the mechanical signaling pathway that potentially lead to severe developmental defects and diseases, including cancer, cardiovascular diseases, and osteoporosis17,18,19. In cancers, normal breast tissue is soft, and the risk of breast cancer increases in stiff and dense breast tissue, an environment that is more akin to breast tumors15. With this knowledge, the effects of mechanical signaling on NCC development can be studied through simple manipulation of substrate stiffness through an in vitro system, providing further advantages and possibilities in understanding the fundamentals of NC-related disease progression and etiology.
To study the impact of mechanical signals in NCCs, we established an efficient in vitro system for NCCs based on the optimization of previously published methods and evaluation of the responses of NCCs to different mechanical signals20,21. A detailed protocol was provided for varying hydrogel stiffness preparation and evaluation of the impact of mechanical signaling in NCCs. To achieve this, O9-1 NCCs are utilized as the NC&#160;model to study the effects and changes in response to stiff versus soft hydrogels. O9-1 NCCs are a stable NC cell line isolated from mouse embryo (E) at day 8.5. O9-1 NCCs mimic NCCs in vivo because they can differentiate into various NC-derived cell types in defined differentiation media22. To study the mechanical signaling of NCCs, a matrix substrate was fabricated with tunable elasticity from varying concentrations of acrylamide and bis-acrylamide solutions to achieve the desired stiffness, correlating to the biological substrate stiffness20,21,23. To optimize the conditions of matrix substrate for NCCs, specifically O9-1 cells, modifications were made from the previously published protocol20. One change made in this protocol was to incubate hydrogels in collagen I, diluted in 0.2% acetic acid instead of 50 mM HEPES, at 37 &#176;C overnight. The low pH of acetic acid leads to a homogeneous distribution and higher collagen I incorporation, thus allowing for a more uniform attachment of the ECM protein24. In addition, a combination of horse serum and fetal bovine serum (FBS) was used at the concentrations of 10% and 5% in phosphate buffer saline (PBS), respectively, before storing the hydrogels in the incubator. Horse serum was used as an additional supplement to FBS due to its ability to promote cell proliferation and differentiation at the concentration of 10%25.
With this method, a biological environment was mimicked by the ECM protein coating (e.g., Collagen I) to create an accurate in vitro environment for NCCs to grow and survive20,21. The stiffness of the prepared hydrogels was quantitatively analyzed via atomic force microscopy (AFM), a well-known technique to depict the elastic modulus26. To study the effect of different stiffness levels on NCCs, wild-type O9-1 cells were cultured and prepared on hydrogels for immunofluorescence (IF) staining against filamentous actin (F-actin) to show the differences in cell adhesion and morphologies in response to changes in substrate stiffness. Utilizing this in vitro system, researchers will be able to study the roles of mechanical signaling in NCCs and its interaction with other chemical signals to gain a deeper understanding of the relationship between NCCs and mechanical signaling.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>12 mm #1 Corning 0211 Glass Coverslip</td>
			<td>Chemglass Life Sciences</td>
			<td>CLS-1763-012</td>
			<td></td>
		</tr>
		<tr>
			<td>2% Bis-Acrylamide</td>
			<td>Sigma Aldrich</td>
			<td>M1533</td>
			<td></td>
		</tr>
		<tr>
			<td>24-well plate</td>
			<td>Greiner Bio-one</td>
			<td>662165</td>
			<td></td>
		</tr>
		<tr>
			<td>25 mm #1 Corning 0211 Glass Coverslip</td>
			<td>Chemglass Life Sciences</td>
			<td>CLS-1763-025</td>
			<td></td>
		</tr>
		<tr>
			<td>3-aminopropyl triethoxysilane (APTS)</td>
			<td>Sigma Aldrich</td>
			<td>A3648</td>
			<td></td>
		</tr>
		<tr>
			<td>4-well cell culture plate</td>
			<td>Thermo Scientific</td>
			<td>179830</td>
			<td></td>
		</tr>
		<tr>
			<td>4% Paraformaldehyde</td>
			<td>Sigma Aldrich</td>
			<td>J61899-AP</td>
			<td></td>
		</tr>
		<tr>
			<td>40% Acrylamide</td>
			<td>Sigma Aldrich</td>
			<td>A4058</td>
			<td></td>
		</tr>
		<tr>
			<td>50% glutaraldehyde</td>
			<td>Sigma Aldrich</td>
			<td>G7651</td>
			<td></td>
		</tr>
		<tr>
			<td>6-well cell culture plate</td>
			<td>Greiner Bio-one</td>
			<td>657160</td>
			<td></td>
		</tr>
		<tr>
			<td>AFM cantilever (spherical bead)</td>
			<td>Novascan</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>AFM software</td>
			<td>Catalyst NanoScope</td>
			<td></td>
			<td>Model: 8.15 SR3R1</td>
		</tr>
		<tr>
			<td>Alexa Fluor 488 Phalloidin</td>
			<td>Thermo Fisher</td>
			<td>A12379</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium Persulfate (APS)</td>
			<td>Sigma Aldrich</td>
			<td>248614</td>
			<td>Powder</td>
		</tr>
		<tr>
			<td>anti-AP-2&#945; Antibody</td>
			<td>Santa Cruz</td>
			<td>sc-12726</td>
			<td></td>
		</tr>
		<tr>
			<td>anti-Vinculin antibody</td>
			<td>Abcam</td>
			<td>ab129002</td>
			<td></td>
		</tr>
		<tr>
			<td>Atomic Force Microscopy (AFM) Bioscope Catalyst</td>
			<td>Bruker Corporation</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Collagen type I (100mg)</td>
			<td>Corning</td>
			<td>354236</td>
			<td></td>
		</tr>
		<tr>
			<td>DAPI (4&#39;,6-Diamidino-2-Phenylindole, Dihydrochloride)</td>
			<td>Thermo Fisher</td>
			<td>D1306</td>
			<td></td>
		</tr>
		<tr>
			<td>Dichloromethylsilane (DCMS)</td>
			<td>Sigma Aldrich</td>
			<td>440272</td>
			<td></td>
		</tr>
		<tr>
			<td>Donkey serum</td>
			<td>Sigma Aldrich</td>
			<td>D9663</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Modified Eagle Medium (DMEM)</td>
			<td>Corning</td>
			<td>10-017-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum (FBS)</td>
			<td>Corning</td>
			<td>35-010-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescence microscope</td>
			<td>Leica</td>
			<td></td>
			<td>Model DMi8</td>
		</tr>
		<tr>
			<td>Fluoromount-G mounting medium</td>
			<td>SouthernBiotech</td>
			<td>0100-35</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Sigma Aldrich</td>
			<td>H3375</td>
			<td>Powder</td>
		</tr>
		<tr>
			<td>Horse serum</td>
			<td>Corning</td>
			<td>35-030-CI</td>
			<td></td>
		</tr>
		<tr>
			<td>iScript Reverse Transcription Supermix</td>
			<td>Bio-Rad</td>
			<td>1708841</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin antibiotic</td>
			<td>Thermo Fisher</td>
			<td>15140148</td>
			<td></td>
		</tr>
		<tr>
			<td>RNeasy micro kit</td>
			<td>Qiagen</td>
			<td>74004</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterile 1x PBS</td>
			<td>Hyclone</td>
			<td>SH30256.02</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterile deionized water</td>
			<td>Hardy Diagnostics</td>
			<td>U284</td>
			<td></td>
		</tr>
		<tr>
			<td>sulfo-SANPAH</td>
			<td>Thermo Fisher</td>
			<td>22589</td>
			<td></td>
		</tr>
		<tr>
			<td>SYBR green</td>
			<td>Applied Biosystems</td>
			<td>4472908</td>
			<td></td>
		</tr>
		<tr>
			<td>TEMED</td>
			<td>Sigma Aldrich</td>
			<td>T9281</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma Aldrich</td>
			<td>X100</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween 20</td>
			<td>Sigma Aldrich</td>
			<td>P9416</td>
			<td></td>
		</tr>
	</tbody>
</table>

an optimized o9-1/hydrogel system for studying mechanical signals in neural crest cells

Neural crest cells (NCCs) are vertebrate embryonic multipotent cells that can migrate and differentiate into a wide array of cell types that give rise to various organs and tissues. Tissue stiffness produces mechanical force, a physical cue that plays a critical role in NCC differentiation; however, the mechanism remains unclear. The method described here provides detailed information for the optimized generation of polyacrylamide hydrogels of varying stiffness, the accurate measurement of such stiffness, and the evaluation of the impact of mechanical signals in O9-1 cells, a NCC line that mimics in vivo NCCs.
Hydrogel stiffness was measured using atomic force microscopy (AFM) and indicated different stiffness levels accordingly. O9-1 NCCs cultured on hydrogels of varying stiffness showed different cell morphology and gene expression of stress fibers, which indicated varying biological effects caused by mechanical signal changes. Moreover, this established that varying the hydrogel stiffness resulted in an efficient in vitro system to manipulate mechanical signaling by altering gel stiffness and analyzing the molecular and genetic regulation in NCCs. O9-1 NCCs can differentiate into a wide range of cell types under the influence of the corresponding differentiation media, and it is convenient to manipulate chemical signals in vitro. Therefore, this in vitro system is a powerful tool to study the role of mechanical signaling in NCCs and its interaction with chemical signals, which will help researchers better understand the molecular and genetic mechanisms of neural crest development and diseases.

Hydrogel preparation and stiffness assessment through AFM and the Hertz model 
Here, a detailed protocol is provided to generate polyacrylamide hydrogels of varying stiffness by regulating the ratio of acrylamide and bis-acrylamide. However, the polyacrylamide hydrogels are not ready for the adhesion of cells due to the lack of ECM proteins. Thus, sulfo-SANPAH, acting as a linker, covalently binds to the hydrogels and reacts with the primary amines of ECM proteins to allow the adhesion of ECM protei...

Watch this Scientific Journal Video about An Optimized O9-1/Hydrogel System for Studying Mechanical Signals in Neural Crest Cells at JoVE.com

An Optimized O9-1/Hydrogel System for Studying Mechanical Signals in Neural Crest Cells

Detailed step-by-step protocols are described here for studying mechanical signals in vitro using multipotent O9-1 neural crest cells and polyacrylamide hydrogels of varying stiffness.

Neural crest cells (NCCs) are vertebrate embryonic multipotent cells that can migrate and differentiate into a wide array of cell types that give rise to ...

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