DIFFERENTIAL GENE EXPRESSION BETWEEN NEOCORTICAL AREAS IN THE DEVELOPING MOUSE C.A. Leamey1,2*; K.H. Wang1,3; S. Tonegawa1,3; M. Sur1,2 1. Center for Learning and Memory, 2. Dept Brain and Cognitive Science, 3. Biology, MIT, Cambridge, MA, USA Neocortical areas are characterised by their unique patterns of afferent, efferent and intrinsic connections. We are interested in understanding the mechanisms which underlie the development of these patterns of connectivity. To do this we have made use of a commercially available high density DNA microarray to identify genes which are differentially expressed between sensory neocortical areas in early postnatal mice. Tissue from the presumptive somatosensory and visual cortices of postnatal day (P)0-1 Black 6 mice was removed and total RNA was extracted. cDNA synthesis and in vitro transciption reactions were then performed to produce biotinylated cRNA. Three separately prepared pairs of samples were then hybridised to the microarray which contains multiple oligos corresponding to over 12,000 known genes and expressed sequence tags (ESTs). Results were analysed according to specific criteria which required that the genes pass an absence/presence call, a difference call and have a fold change of at least 2 for all 3 of the pairs of samples used. Using these criteria we have found 8 genes and ESTs which are expressed at higher levels in the visual cortex than in the somatosensory cortex, and 7 genes and ESTs which are more highly expressed in the somatosensory cortex than visual cortex. The differentially expressed genes include a protein tyrosine phosphatase receptor, a growth factor and a transcription factor. We are currently confirming the differential expression of these genes by hybridising additional samples to the microarray and by in situ hybridisation. Supported by: NIH grant EY11512 and NS39022 to MS and MH58880 and NS32925 to ST