Darmin is a novel secreted protein expressed during endoderm development in Xenopus

Endoderm development is an area of intense interest in developmental biology, but progress has been hampered by the lack of specific markers for differentiated endodermal cells. In an unbiased secretion cloning screen of Xenopus gastrula embryos we isolated a novel gene, designated Darmin. Darmin encodes a secreted protein of 56 kDa containing a peptidase M20 domain characteristic of the glutamate carboxypeptidase group of zinc metalloproteases. We also identified homologous Darmin genes in other eukaryotes and in prokaryotes suggesting that Darmin is the founding member of a family of evolutionarily conserved proteins. Xenopus Darmin showed zygotic expression in the early endoderm and later became restricted to the midgut. By secretion cloning of Xenopus cleavage-stage embryos we isolated another novel protein, designated Darmin-related (Darmin-r) due to its sequence similarity with Darmin. Darmin-r was maternally expressed and showed at later stages expression in the lens and pronephric glomus. The endoderm-specific expression of Darmin makes this gene a useful marker for the study of endoderm development.