ARENAS-MENA , Cesar *; UVEGES, Tracy ; DASARI, Srividya ; ALVARENGA-MAGANA, Jose; FISCHLER, Andrew ; CLEMENTE, Alfonso; DEAS , Joseph ; San Diego State University; San Diego State University; San Diego State University; San Diego State University; San Diego State University; San Diego State University; San Diego State University; : Gene expression studies in the indirectly developing serpulid annelid Hydroides elegans

The blastomere territories in which an indirectly developing serpulid embryo is progressively subdivided are being characterized at once by the embryonic mRNA expression pattern of randomly selected genes enriched for differentiation representatives. The identification of these early gene expression patterns defines a minimal spatial and temporal limit for the specification processes that establish these embryonic territories. In addition, the mRNA expression patterns of GATA and SOX transcription factors, as well as signaling molecules known to play evolutionarily conserved cell-type specification roles among bilaterians are also being studied. These characterizations, in combination with an improved anatomical description, are the initial steps towards a deep understanding of this relatively simple embryo. Eventually, the elucidation of the regulatory processes controlling these gene expression patterns will reveal the evolutionarily conserved and derived steps leading to the developmental mode of this polychaete. The nature of the ancestral specification machinery used to establish the ectoderm, endoderm and mesoderm cell precursors is also illuminated by these characterizations. Furthermore, despite a broad phylogenetic distribution, very few indirectly developing animals have been characterized with modern developmental biology tools. In the context of an annelid with a well-developed free-feeding trochophore larva these studies modestly contribute to solve the extremely complex question of indirect development evolution in bilaterians.