Meeting Abstract

P3.50  Wednesday, Jan. 6  Dorsoventral patterning by BMP-gremlin interactions in segmental ectoderm of the leech Helobdella KUO, D.-H.*; WEISBLAT, D.A.; Univ. of California, Berkeley; Univ. of California, Berkeley dhkuo@berkeley.edu

BMPs are evolutionarily conserved players in dorsoventral (DV) patterning of bilaterian embryos. They are best known acting as a morphogen in DV patterning of Drosophila and vertebrates, but it is less clear whether BMP acts in a similar way in other species, particularly in those with cell lineage-dependent embryogenesis. To see how BMPs act in lineage-driven DV patterning, we characterized the roles of BMPs in DV patterning of segmental ectoderm in the leech Helobdella. Segmental ectoderm of the leech arises from four bilateral pairs of teloblasts (N, O/P, O/P and Q). The N and Q lineages give rise to the ventralmost and dorsalmost portions of the segmental ectoderm respectively; their fates are specified as soon as the teloblasts are born. The ipsilateral O/P lineages are positionally specified to adopt either the ventrolateral (O) fate or the dorsolateral (P) fate. We identified Hau-BMP5-8, expressed specifically in the dorsalmost Q lineage, as a short-range signal that induces the P fate. Moreover, BMP signal upregulates Hau-gremlin, a secreted BMP antagonist. We showed that Hau-gremlin selectively antagonizes Hau-BMP2/4 and Hau-DVR, both of which are broadly expressed in normal development. In contrast, Hau-BMP5-8 is not sensitive to Hau-gremlin-mediated antagonism. Hence, we propose that the dorsally localized Hau-BMP5-8 specifies the dorsolateral P lineage and upregulates Hau-gremlin, which in turn prevents the ventrolateral O lineage from adopting P fate by inhibiting the globally distributed Hau-BMP2/4 and Hau-DVR. The mechanism by which BMPs patterns leech ectoderm has apparently deviated significantly from the paradigmatic morphogen gradient models.