MICE HOMOZYGOUS FOR A NULL MUTATION OF ACTIVIN BETA(B) ARE VIABLE ANDFERTILE

We have made a null mutation in the mouse activin beta(B) gene by dele ting the portion of the gene encoding the proteolytic cleavage site an d the majority of the coding region for the mature processed protein. Mice homozygous for this mutation complete embryogenesis and are compl etely viable. Approximately 40% of the homozygous mutant animals are b orn with open eyes. Aside from the incompletely penetrant eye defects, histopathological analysis has not revealed any other abnormalities i n homozygous mutant animals. Breeding tests have shown that both male and female homozygous mutant animals are fertile.