Genes coding for mouse activin beta C and beta E are closely linked and exhibit a liver-specific expression pattern in adult tissues.

Five activin beta subunits have been isolated to date, and a comparative analysis of amino acid identity has suggested that the activin beta C, beta D and beta E subunits represent a distinct subset. Based on genomic cloning studies, we now report that the mouse activin beta C and beta E genetic loci are closely linked-i.e, the coding sequences are separated by 5.5-kbp. These genes also show similarities in structural organization as well as a unique liver-restricted pattern of expression in adult mice. Our results suggest that tandem duplication of an ancestral gene generated the mouse activin beta C and beta E genetic loci, and they provide further evidence for the postulate that the beta C-beta E subunits form a distinct subset of related activins. To our knowledge, this report is the first to demonstrate close chromosomal linkage between members of the TGF-beta superfamily as well as a liver-restricted expression pattern for a TGF-beta-like gene.