Meeting Abstract

13.2  Tuesday, Jan. 4  Competing Signals Drive Telencephalon Diversity SYLVESTER, JB*; RICH, CA; YI, C; STREELMAN, JT; Georgia Institute of Technology; Georgia Institute of Technology; Georgia Institute of Technology; Georgia Institute of Technology jsylvester@gatech.edu

The brain is the best-studied vertebrate organ and it has played an important role in the evolution of our own species. The rapid expansion of the cerebral cortex, or telencephalon (tel), is a defining aspect of hominid evolution. The processes that control growth in the tel have been well described in the ‘late equals large’ model, but little is known about the evolution of functional domains within the tel. We investigate comparative tel development in ecologically distinct cichlid fishes lineages from Lake Malawi (East Africa) to study diversity. The two dorso-ventral developmental domains of the tel, the pallium and subpallium, are correlated with adult cichlid ecotypes; species that are visually specialized have a larger pallium, whereas smell/taste oriented fish have a larger subpallium. As a consequence, visual vs. smell/taste cichlids differ in the initial position of the pallial-subpallial boundary (PSB) and early allocation of cells to the pallium and subpallium. These two domains are patterned by wnt and shh pathways respectively, along the dorsal/ventral axis. Expansion of shh relative to wnt leads to a larger allocation of cells to the subpallium in smell/taste embryos, whereas visual embryos are characterized by increased wnt influence and a larger pallium. These results suggest that diversity within the telencephalon is determined by a ‘tug-of-war’ between dorsal wnt and ventral shh.