DEGNAN, BM; LEYS, SP; LARROUX, C; LIUBICICH, ; HINMAN, VF; Univ. of Queensland; Univ. of Alberta; Univ. of Queensland; Univ. of Queensland; Univ. of Queensland: Developmental genes in sponges and the antiquity of animal development

The last common ancestor of all animals possessed features shared between the most basal metazoan lineage – Porifera – and the rest of animal kingdom. To identify ancient and conserved developmental processes we investigated the development of the demosponge Reniera sp. and a number of genes that are expressed during its embryogenesis and metamorphosis. The sponge body plan consists of multiple cell types that are bound by collagen-based ECM and apparently interact through an ancient suite of conserved protein families whose origin extends beyond the Metazoa. During embryogenesis and formation the sponge larva there is clear evidence of extensive cellular rearrangements akin to eumetazoan gastrulation that results in a larva with differentiated cells patterned along anteroposterior and centrolateral axes. At metamorphosis the cells of this highly ordered larva dissociate, transdifferentiate, migrate and reorganise into an adult body plan with less overt cell patterning. In a survey of developmentally-expressed genes in Reniera sp. we identified (i) a diversity transcription factor genes, most of which belong to metazoan-specific families and include members of POU, LIM-HD, Pax, Bar, Prox2, Fox, Sox, Ets and nuclear hormone receptor families, and (ii) 63 different protein-coding cDNAs that include components of conserved signalling pathways. Analysis of transcript abundance and localisation suggests most genes are differentially expressed and functional throughout development. These data suggest that many of the fundamental components of the highly conserved regulatory program used in bilaterian development were present in the ancestor that gave rise to all metazoan lineages, including sponges.