Evidence for repair in trypan blue-treated mouse egg cylinders: an electron microscopic study

The question of whether mammalian fetuses can correct damage induced by teratogens during early stages of embryogenesis was reinvestigated. Toward this purpose female mice were injected on day 6 of gestation with the teratogenic dye trypan blue. Within 6, 24, and 48 hr of exposure to the teratogen, egg cylinders were removed, sectioned, and prepared for electron microscopic analysis. The following organelles were examined: 1) mitochondria, 2) Golgi apparatus, 3) endoplasmic reticulum, and 4) free polysomes. On the ultrastructural level, exposure to trypan blue lead within 6 hr to fragmentation of the endoplasmic reticulum and a depletion of free polysomes in the endoderm of the egg cylinders. In ectodermal cells only the distribution of polysomes was disturbed following exposure to trypan blue. Egg cylinders harvested 24 hr after injection of trypan blue had partially recovered. Their endoplasmic reticulum and polysomes appeared closer to controls. The cells of both germ layers of most egg cylinders obtained 48 hr after injection were indistinguishable from controls when viewed with the electron microscope. No consistent changes were found in mitochondria or Golgi apparatus following trypan blue treatment. It is concluded that mouse embryos appear to be able to correct damage sustained during the egg cylinder stage, and that in spite of earlier injury affecting both germ layers such egg cylinders can develop normally as revealed by microscopic examination.