Meeting Abstract
TGF-beta superfamily signaling regulates a variety of developmental processes and has a conserved role in patterning the dorsal-ventral body axis. Within this signaling family, there are two distinct branches: the Activin/Nodal pathway and the BMP pathway. The spiralians are a large bilaterian clade that exhibit enormous body plan diversity. Members of this superclade share a highly stereotypic early development program called spiral cleavage, and signals emanating from single cells during early cleavages are critical for patterning the dorsal-ventral body axis. Studies in the mollusks Crassostrea gigas and Tritia obsolete, as well as the annelid Helobdella robusta have suggested the BMP pathway plays a crucial role in dorsal-ventral axis patterning. However, previous pharmacological inhibition studies in the annelid Capitella teleta suggests that signaling via the ALK4/5/7 receptor, an Activin/Nodal pathway receptor, patterns the dorsal-ventral axis. In this study, we further determine the role of the Activin/Nodal pathway as it functions in C. teleta axis patterning. Antisense morpholino oligonucleotides were designed to target Ct-Smad2/3 and Ct-Smad1/5/8, receptor signal transducers specific to the Activin/Nodal and BMP pathways, respectively. Morphants were raised to larval stages and scored for phenotypic anomalies in body axes formation. Our findings confirm that axial patterning in C. teleta occurs at the 16 cell stage, 1-2 cleavage divisions before their spiralian counter parts, the mollusks, and utilizes the Activin/Nodal branch of the TGF-beta superfamily, but not the BMP pathway. Furthermore, these findings highlight an important molecular difference in the induction of axes between annelids and mollusks.
