Genes Coding for Mouse Activin βCand βEAre Closely Linked and Exhibit a Liver-Specific Expression Pattern in Adult Tissues

Five activin β subunits have been isolated to date, and a comparative analysis of amino acid identity has suggested that the activin βC, βDand βEsubunits represent a distinct subset. Based on genomic cloning studies, we now report that the mouse activin βCand βEgenetic 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 βCand βEgenetic loci, and they provide further evidence for the postulate that the βC-βEsubunits 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-β superfamily as well as a liver-restricted expression pattern for a TGF-β-like gene.