Effects of formamide on neuroepithelial cells and on interkinetic nuclear migration in the chick embryo.

Young chicken embryos were incubated on media containing formamide at concentrations of 0-1, 0-25, 0-31, 0-37, 0-43 and 0-5 M. In the neuroepithelium of these embryos we found that (1) the 0-1 M concentration had no detectable effect, (2) the 0-25 M concentration only affected mitosis which was blocked in metaphase so that mitotic figures accumulated near the neurocoele, (3) 0-31 M formamide totally inhibited interkinetic nuclear migration and affected only slightly the cell asymmetry, (4) the 0-37 M concentration considerably reduced the amount of cytoplasmic microtubules and that the cells became round, (5) at 0-43 M formamide, all microtubules had disappeared and all cells were spherical, (6) 0-5 M formamide all cells were spherical, detached from one another and the epithelium had lost its usual characteristics. Our results on exposure of the cells to low temperature (2 degrees C) suggest that formamide directly affects microtubules. All the effects observed at concentrations up to 0-43 M formamide are reversible.