Analysis of Trunk Neural Crest Cell Migration using a Modified Zigmond Chamber Assay

Summary

An approach to analyze the migration of explanted cells (trunk neural crest cells) is described. This method is inexpensive, gentle, and capable of distinguishing chemotaxis from both chemokinesis and other influences on migratory polarity such as those derived from cell-cell interactions within the primary trunk neural crest cell culture.

Abstract

Neural crest cells (NCCs) are a transient population of cells present in vertebrate development that emigrate from the dorsal neural tube (NT) after undergoing an epithelial-mesenchymal transition ^1,2. Following EMT, NCCs migrate large distances along stereotypic pathways until they reach their targets. NCCs differentiate into a vast array of cell types including neurons, glia, melanocytes, and chromaffin cells ^1-3. The ability of NCCs to reach and recognize their proper target locations is foundational for the appropriate formation of all structures containing trunk NCC-derived components ³. Elucidating the mechanisms of guidance for trunk NCC migration has therefore been a matter of great significance. Numerous molecules have been demonstrated to guide NCC migration ⁴. For instance, trunk NCCs are known to be repelled by negative guidance cues such as Semaphorin, Ephrin, and Slit ligands ^5-8. However, not until recently have any chemoattractants of trunk NCCs been identified ⁹.

Conventional in vitro approaches to studying the chemotactic behavior of adherent cells work best with immortalized, homogenously distributed cells, but are more challenging to apply to certain primary stem cell cultures that initially lack a homogenous distribution and rapidly differentiate (such as NCCs). One approach to homogenize the distribution of trunk NCCs for chemotaxis studies is to isolate trunk NCCs from primary NT explant cultures, then lift and replate them to be almost 100% confluent. However, this plating approach requires substantial amounts of time and effort to explant enough cells, is harsh, and distributes trunk NCCs in a dissimilar manner to that found in in vivo conditions.

Here, we report an in vitro approach that is able to evaluate chemotaxis and other migratory responses of trunk NCCs without requiring a homogenous cell distribution. This technique utilizes time-lapse imaging of primary, unperturbed trunk NCCs inside a modified Zigmond chamber (a standard Zigmond chamber is described elsewhere¹⁰). By exposing trunk NCCs at the periphery of the culture to a chemotactant gradient that is perpendicular to their predicted natural directionality, alterations in migratory polarity induced by the applied chemotactant gradient can be detected. This technique is inexpensive, requires the culturing of only two NT explants per replicate treatment, avoids harsh cell lifting (such as trypsinization), leaves trunk NCCs in a more similar distribution to in vivo conditions, cuts down the amount of time between explantation and experimentation (which likely reduces the risk of differentiation), and allows time-lapse evaluation of numerous migratory characteristics.

Protocol

1. Day 1: Isolation of trunk neural tubes for overnight culture on coverslips

1. Incubate chick eggs for 56 h at 38° C. Remove the eggs from incubation, mildly spray them with 70% Ethanol, and then allow them to dry. Break the eggs open into a UV-sterilized glass tray.
2. Extract each embryo from its yolk and place it in chick Ringer's. Do this by first cutting around its blood islands with curved scissors; then, with blunt forceps, pick the embryo up by its extraembryonic membrane and place it in a sterile plastic Petri dish containing chick Ringer′s solution.
3. Isolate the trunk of each embryo by trimming off excess extraembryonic membranes a....

Discussion

Conducting chemotaxis research on trunk NCCs has proven challenging for a series of reasons. Trunk NCCs constitute a heterogeneous stem cell population that will differentiate if cultured long-term; therefore, trunk NCCs must be obtained from primary explantation of the trunk-level NT. Conventional methods to study the chemotactic response of homogenously distributed cell populations in vitro are difficult to test on trunk NCCs since they first require that cells are isolated and homogenously replated in .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
DMEM	Omega Scientific	DM-22
Penicillin Streptomycin Solution	Omega Scientific	PS-20	100X Stock Concentration
L-Glutamine	Omega Scientific	GS-60	100X Stock Concentration
Fetal Bovine Serum	Omega Scientific	FB-11	Lot# 105247 (or another that is comparable)
Modified Zigmond chamber	Home made	N/A	Reservoir volume: ~ 160 μl ea; for additional specifications, see Fig. 4 and the supplemental fabrication protocol
Cell culture dish	Denville	T6040	40 x 10 mm
Fibronectin	BD	354008	10X Stock prepped by diluting 1 mg FN in 1 ml H2O and 9 ml DMEM
Coverslips	Fisher	12-548-B	Precleaned; 22 x 22 mm
L15 medium	Thermo Scientific	SH30525.02
Petroleum Jelly	Comforts	011110794642	100%
Centrifuge tube	Biologix	10-9152	15 ml
Dispase	Cell Systems	4Z0-850	10X Stock Concentration
Syringe	BD	309602	1 ml
Needle	BD	305127	25 G x 1.5 in.
Alexa Fluor 488-IgM	Invitrogen	A21042	Stock is 2 mg/ml; 7 moles dye/mole IgM
Dissecting Forceps	FST	Misc.	Dumont #5 or 55; straight tipped; stainless steel or titanium
Tungsten Needle	N/A	N/A	Home made; placed in a pin holder
Blunt Forceps	Tiemann	160-18	Used for transferring embryos to Ringer's from egg yolk
Supplemental Protocol: Fabrication of a Modified Zigmond Chamber
Please refer to Figure 4 as a reference for the protocol below:
Purchase a sheet of 3/16" thick polished acrylic (4.45 mm actual thickness). Using a table saw, cut chamber blanks oversized to the rough dimensions of 33.25 mm x 64.57 mm. This allows 3.175 mm extra material for machining. Set the chamber blank on a vise. With a milling machine and a 6.35 mm (1/4") end mill bit, finish machining the sides of the chamber to their exact dimensions: 30.07 mm x 61.39 mm. Position the chamber blank on the milling machine and locate the center of the blank along both the x and y axes with an edge finder; then zero the center location. Acquire the chamber height (z-axis) by touching the end mill bit to the top surface and zero the height. Using a 3.91 mm (0.154") end mill bit, offset the bit 3.03 mm along the x-axis (positive direction) for the first reservoir. Begin machining into the chamber to a depth of 2.84 mm while moving along the y-axis (positive direction) to 7.62 mm (0.300") and then traverse to 7.62 mm (0.300") in the opposite (negative) direction to a complete reservoir length of 15.24 mm (0.600"). Offset the bit to 3.03 mm (0.119") along the x-axis (negative direction) and repeat the same process for the second reservoir. Position the chamber on its edge and drill a hole using a 1.09 mm (0.043 in.) drill bit on the end of each reservoir (4 total) that connects the end of the reservoir to the side of the chamber for loading medium during experimentation. Soak the chamber well in warm soapy water to help remove any chemical contaminants. Soak and rinse the chamber well in double-distilled water to remove any soap. The chambers are now ready to use as described above.