Meeting Abstract
35.3 Monday, Jan. 5 Brain diversity develops at the boundaries SYLVESTER, JB*; RICH, CA; LOH, YE; FRASER, GJ; STREELMAN, JT; Georgia Institute of Technology; Georgia Institute of Technology; Georgia Institute of Technology; Georgia Institute of Technology; Georgia Institute of Technology gth644s@mail.gatech.edu
The brain is the best-studied vertebrate organ. Modifications of brain structure are largely responsible for novel behaviors that galvanized evolutionary radiation of fishes, birds and primates. Following decades of research in model organisms, we know a great deal about how the process of development makes a brain. However, we know less about the developmental mechanisms employed during the evolution of brain diversity. The literature suggests that brain diversity evolves via neurogenesis, as the cells of previously patterned brain regions proliferate, differentiate and/or undergo apoptosis. Here, we use Lake Malawi cichlid fishes to explore an underappreciated mechanism of brain diversification. We ask if brains vary among recently evolved evolutionary lineages because of developmental patterning; that is, do initial neural compartments differ in size and organization, prior to subsequent neurogenesis? First, we show divergence among major Malawi lineages (rock- vs. sand-dwellers) in the proportion of the embryonic brain allocated to telencephalic vs. thalamic prosomeres, prior to neurogenesis. Next, we demonstrate variation among lineages in a gene regulatory circuit (otx2, shh, irx1, wnt1) known to position the embryonic boundary (the zona limitans intrathalamica, ZLI) between the thalamus and the anterior forebrain. Notably, we have previously identified a single nucleotide polymorphism in irx1, alternately fixed in rock- versus sand-dwelling Malawi lineages. We propose that changes in the deployment of irx1 affects the relative orientation of the ZLI and hence the size and structure of initial forebrain compartments in rock- vs. sand-dwelling Malawi cichlids. Thus, differences in early patterning might lay prosomeric foundations on which neurogenesis builds as brains develop diversity.
