Early development of the brain and spinal cord in dysraphic mice.

Abstract

The development and closure of the neural folds was studied in C57BL/6J and loop-tail (Lp) mutant mice by means of scanning electron microscopy on a series of embryos ranging in age from 7.5 to 9.0 days of gestation. The normal embryos (C57BL/6J; +/+; Lp/+) showed a transitional zone of flattened cells lying between the surface ectoderm and neuroepithelial cells at the apices of the neural folds in the presumptive hindbrain and spinal cord, and ruffles occurred at the boundary between the flattened cells and surface ectoderm in regions of the folds which were about to fuse. In the abnormal loop-tail homozygotes (Lp/Lp) which exhibit dysraphism, the ruffles were arranged erratically along the zone of flattened cells. Moreover, at the stage when the folds became apposed and fused in the normal embryos, the abnormals showed ruffles extending the entire length of the unfused folds, thereby distinguishing the abnormals from retarded n normal embryos. Within the neural groove of the hindbrain region, the lateral neuroepithelial cells of the abnormal dysraphic embryos exhibited more flattened surfaces and fewer villous projections than in the normal embryos. The abnormal embryos also lagged behind their normal littermates in converting the body axis from the initial V-shape to the C-shaped configuration.