CARRUTH, L.L.; ARNOLD, A.P.; Georgia State Univeristy; University of California, Los Angeles: Sex differences in the songbird brain: using molecular tools to investigate brain sexual differentiation in a comparative model

Early in development, male and female brains diverge in their patterns of growth and differentiation, especially in brain regions involved in the control of behavior. The classical model of brain sexual differentiation states that testosterone is aromatized in the brain into estrogen which then acts to either initiate male neural development or inhibit female neural development. One vertebrate model that is ideal for studying sexual differentiation is the Australian zebra finch (Taeniopygia guttata). Male zebra finches sing a courtship song while females do not. This distinct behavioral dimorphism is paralleled by large morphological sex differences in the neural circuit for song learning and production. The differentiation of these morphological sex differences has previously been thought to be under hormonal control, but despite extensive research, sexual differentiation of the avian song system does not appear to completely follow this model. We are now examining different factors or mechanisms that may influence early song system development. We identified early markers of sexual differentiation (genes that might or might not respond to hormone treatment) using suppression subtractive hybridization on mRNA from hatchling male or female zebra finch telencephalon in order to isolate cDNAs representing genes that are expressed at a higher level in one sex or the other. Plasmid libraries were constructed of cDNAs that are enriched in male or female brain. We are characterizing these cDNAs and confirming their differential expression using mRNA dot blots, northern analysis, and in situ hybridization. Some of the cDNAs correspond to recognized avian genes, some are linked to the sex chromosomes, and several clones are novel.