Invited Speaker Annual Conference of the Genetics Society of Australasia with the NZ Society for Biochemistry & Molecular Biology

Developmental genomics of sponges (621)

Maja Adamska 1
  1. Australian National University, Acton, ACT, Australia

Sponges are likely to be the oldest of the extant animal lineages. In contrast to the eumetazoans (complex animals such as corals, insects and vertebrates), sponges have no nerves, muscles or gut. A decade ago, analysis of the first sequenced sponge genome (of the demosponge Amphimedon) demonstrated that development of the simple sponge body plan is governed by a limited number regulatory genes, suggesting a gradual assembly of the complex eumetazoan developmental toolkit.

However, sponges are a diverse phylum, composed of four distinct lineages: demosponges, hexactinellids, calcisponges and homoscleromorphs. We have sequenced genomes and transcriptomes of several calcisponges, including calcaroneans (Sycon and Leucosolenia) and calcineans (Clathrina and Pericharax), and a demosponge distantly related to Amphimedon (Halisarca). For some, we have also generated transcriptome datasets representing embryonic and postembryonic development and regeneration.

We have uncovered unexpected complexity and diversity of developmental toolkits among sponges, with calcisponge developmental regulatory gene families generally more complex than those in demosponges. Significant gene losses must have occurred independently in the calcisponge and demosponge lineages, followed by gene family expansions occurring independently in the calcaronean and calcinean lineages, and leading to spectacular developmental toolkit diversity among sponge species.

Gene expression analysis suggests deep conservation of body plan patterning and regeneration mechanisms between sponges and the eumetazoans. Strikingly, in the “expanded” gene families, sequence conservation correlates with similarity of gene expression profiles across the sponge species.

Overall, while sponges are clearly not “living fossils”, they provide a wonderful window into the evolutionary history of animal genomes.