Effect of hyaluronic acid on the emergence of neural crest cells from the neural tube of the quail, Coturnix coturnix japonica.

Hyaluronic acid (HA) added to the medium of quail neural tubes explanted in vitro influences the number of migratory neural crest cells that emerge, compared with controls. Neural crest cells were counted with an ocular grid after 20 h of migration into 0.1 mm wide areas or 'bins' lying parallel to the neural tube, and the results were analyzed by linear regression. A low concentration of HA (5 micrograms/ml) significantly decreased the total number of neural crest cells in all bins adjacent to the neural tube, whereas several high concentrations of HA (250, 500, and 1000 micrograms/ml) significantly increased the number of neural crest cells. Intermediate concentrations of HA (50 and 100 micrograms/ml) did not differ from that of controls. Linear regressions of number of cells versus distance from the tube showed no significant differences among the slopes of control, low HA, and high HA treatments, providing evidence that HA does not influence the rate of cell migration. Scanning electron microscopy showed that cells in neuroepithelia exposed to low HA (5 micrograms/ml) appeared in tighter contact, while cells of neuroepithelia in high HA (500 micrograms/ml) appeared more loosely organized, compared with controls. Cells in tight contact could be restrained from leaving the neuroepithelium, whereas cells in loose contact could more readily move out of the neural tube, thus explaining the differences in cell numbers in low HA and high HA, respectively. We conclude that HA can be a factor in the differential adhesivity among neuroepithelial cells and may be important in the initial separation of the neural crest from the neural tube.