Meeting Abstract
60.2 Sunday, Jan. 5 13:45 Wnt signaling in the leech posterior growth zone FLORES, V.R.*; WEISBLAT, D.A.; Univ. of California, Berkeley; Univ. of California, Berkeley vrf2@berkeley.edu
Segmented groups (vertebrates, arthropods, annelids) are very successful taxa within the three bilaterian super-phyla (Deuterostomia, Ecdysozoa, Lophotrochozoa, respectively). Each of these also contains unsegmented taxa, raising the question of whether segmentation evolved once or multiple times. We study segmentation in a leech (Helobdella austinensis) because it represents the understudied super-phylum Lophotrochozoa, and because its lineage-driven segmentation is not seen in model systems. In leech, segments arise from a posterior growth zone (PGZ) comprising five pairs of lineage-restricted stem cells (teloblasts) and their progeny (segmental founder cells called blast cells). Wnt signaling is a conserved pathway that affects transcription, cell polarity, stem cell maintenance and/or cell adhesion. Wnt signaling is involved in segmentation of vertebrates and arthropods; and Wnt components are expressed in the Helobdella PGZ. Thus, we hypothesized that Wnt signaling also operates in leech segmentation. To test this, we microinject select blastomeres with a translation-blocking antisense morpholino oligomer (ASMO) to knock down Disheveled (Dsh), a key scaffolding protein that transduces divergent Wnt signals. Injecting Dsh-ASMO into a left or right precursor of the ipsilateral ectodermal teloblasts yields morphant embryos with teloblasts that vary in number, size and position relative to controls. Often, teloblasts arising from injected cells form an adherent cluster, in contrast to their normal disposition as discrete spheres wrapped by macromere processes. Time-lapse video and confocal microscopy will be used to further characterize these defects. We will also identify localization of other Wnt pathway proteins. Together, these results can give insight into how Wnt signaling regulates the formation of lineage-restricted stem cells.
