Meeting Abstract

70.6  Sunday, Jan. 6  Borrowing from the past: Remodeling adult tissue by larval cell recruitment during Ciona heart development DAVIDSON, Brad*; NUNAN, Linda; University of Arizona; University of Arizona bjd18@email.arizona.edu

During chordate evolution, there have been dramatic life-history shifts between direct and indirect modes of development. These shifts may facilitate the emergence of new traits. During transitions between developmental modes, larval cell lineages could be recruited to enlarge or restructure adult tissues. We have experimentally demonstrated the potential for such a recruitment event in the embryos of the invertebrate chordate, Ciona intestinalis. In Ciona, pre-cardiac lineage cells undergo an asymmetric division; the larger daughters differentiate into larval tail muscle cells while the smaller daughters form heart precursor cells that do not differentiate until post-larval stages. We have determined that this asymmetric fate specification and associated shift in developmental timing is mediated by fibroblast growth factor (FGF) signaling. We have also demonstrated that FGF mediates heart specification through activation of the transcription factor Ets1/2. Expression of a dominant negative FGF receptor or a repressor form of Ets1/2 in the pre-cardiac lineage converts all daughter cells into tail muscle precursors. Conversely, targeted expression of constitutively active Ets1/2 converts all daughter cells into heart precursors; transforming a larval lineage (tail muscle precursors) into a post-larval lineage (heart precursors). Furthermore, our data suggests that these newly recruited cells form beating heart tissue and can generate a novel heart compartment. We have employed comparative micro-array expression analysis on sorted heart cells to identify the transcriptional targets of Ets1/2. We are currently investigating how these target genes promote cardiac specification and repress tail muscle differentiation.