Meeting Abstract

20.1  Thursday, Jan. 3  Genesis and expansion of metazoan transcription factor gene classes: insights from choanoflagellate, sponge, and cnidarian genomes LARROUX, C*; LUKE, GN; KOOPMAN, PK; SHIMELD, SM; DEGNAN, BM; University of Queensland; University of Reading; University of Queensland; University of Oxford; University of Queensland clarroux@sib.uq.edu.au

The invention of a basic developmental program may have been a key step accompanying the transition to multicellularity in animals. Novel transcription factors were likely to have been crucial to the increase in regulatory complexity that must have accompanied this step. Using whole genome information from the demosponge Amphimedon queenslandica, a representative of what may be the most ancient living animal lineage, the cnidarian Nematostella vectensis, belonging to the sister group of the bilaterians, and the choanoflagellate Monosiga brevicollis, one of the closest protist relatives of Metazoa, we provide a detailed picture of the early evolution of a variety of transcription factor genes (such as homeobox, Sox, T-box, and Fox genes) in metazoans. Comparative genomic analysis reveals that novel domains of transcription factors arose very early in metazoan evolution after the choanoflagellate-metazoan divergence. Phylogenetic analyses of classes indicate that they then gradually diversified at the base of Metazoa before bilaterian radiation, following different evolutionary trajectories. While the cnidarian-bilaterian ancestor probably had a set of transcription factors resembling that of the protostome-deuterostome ancestor, the genome of the demosponge-eumetazoan ancestor seems to have included fewer gene members in each class. Sponges thus appear to represent an intermediate stage in the evolution of the metazoan genome. Transcription factor orthologues present in sponge, cnidarian, and bilaterian genomes may indicate some of the core regulatory components underlying the origin of animal development and multicellularity.