Meeting Abstract

P3.59  Thursday, Jan. 6  Patterning of the larval apical territory by a conserved cassette of transcription factors MARLOW, H*; ARENDT, D; EMBL Heidelberg; EMBL Heidelberg heather.marlow@embl.de

While many studies have addressed the evolution of centralized nervous systems, few studies have focused on the molecular architecture governing the specification and differentiation of the apical tuft, often referred to as the larval brain. Animal phyla throughout the Bilateria, which are united by bilateral symmetry, a through gut and three embryonic tissue layers, possess both a pelagic larval dispersal stage and a morphologically distinct adult form. Broad phylogenetic distribution of these groups indicates that the ancestral eubilaterian had a ciliated larva and lends support to the idea that larval brains evolved early in the animal tree. This is further supported by the presence of a biphasic outgroup with a planula larva, the Cnidaria. Investigation of the apical ectoderm by in situ hybridization implicates a core cassette of transcription factors as key neural regional patterners. We find that these transcription factors are localized in nested patterns surrounding the larval apical tuft during the specification and differentiation of the neurons found there in animals as diverse as Cnidarians and Polychaetes. We find that distinct types of neurons develop from each of these regions, further supporting the idea that each of these territories specifies a unique cellular fate. Furthermore, functional analysis by morpholino knockdown reveals that these transcription factors influence the expression of other members of the larval apical patterning network resulting in neural defects. We propose that this apical patterning network is conserved across the Eumetazoa, making it one of the oldest identified transcription factor networks.