Transgenes encoding both type I and type IV c-abl proteins rescue the lethality of c-abl mutant mice

Mice carrying homozygous mutations in the c-abl gene (abl-(m1) or abl2) exhibit severe, though variable phenotypes, including a high rate of postnatal mortality, runting, morphological abnormalities, a susceptibility to infections, and selected immune system defects. To further determine the role of the c-Abl protein in vivo, we have generated three lines of mice expressing c-abl transgenes. These minigenes encode the two major forms of the c-abl gene product (c-Abl types I and IV) and a kinase defective type IV c-Abl. The transgenic lines, in Abl-positive genetic backgrounds, were phenotypically almost indistinguishable from their non-transgene littermates and expressed the c-abl transgene in a variety of tissues at levels comparable to that of the endogenous c-abl gene. When the transgenes were introduced into a mutant c-abl strain by mating, the mutant c-abl phenotype was almost completely rescued by either of the c-abl type I or type IV transgenes, but not by the kinase-defective transgene. These findings suggest that either of the two alternatively spliced c-abl gene products can provide the in vivo functions of c-Abl, and that these functions are dependent on kinase activity.