Studies of developmental abnormalities at the molecular level of mouse embryos homozygous for the t12 lethal mutation.

Embryos obtained by crossing heterozygous t12 mutant mice were labeled metabolically with 14C-amino acids at the mid-morula stage, and the protein pattern of single embryos was examined by two-dimensional polyacrylamide gel electrophoresis. After labeling, the morphology was still normal. The genotypes of the embryos could be identified by the allelic forms of Tcp-1 (p63/6.9) protein on the gel. In t12/t12 embryos, the bulk of syntheses of macromolecules such as proteins and RNAs [poly(A)+, as well as poly(A)-RNA] was normal, however, syntheses of several proteins were markedly reduced. Some of these proteins present in reduced amounts appeared to be components of cytokeratin-type intermediate filaments (endo A and endo B), judging from their insolubility in non-ionic detergent, their appearance in the mid-morula stage, their location in trophectodermal cells, and their electrophoretic mobilities. These observations suggest that mechanisms for the induction of the intermediate filament proteins are defective in embryos homozygous for the t12 mutation. Possible relationships between the morphological abnormalities of the embryos and their defective synthesis of intermediate filaments are discussed.