Institute of Zoology, University of Basel, CH-4051 Basel, Switzerland, , ~ Department of Neuroscience, University of Pennsylvania, PA-19104 Philadelphia, USA, § IIGB, CNR,I-80125 Naples, Italy, # Institut fuer Genetik, University of Hohenheim, D-70593 Stuttgart, Germany, % Biocenter, University of Basel, CH-4055 Basel, Switzerland, @ University of Tsukuba, Tsukuba, Japan,
We have studied the functional role of a set of developmental control genes in constructing the embryonic brain of Drosophila. Among these are a subset of the HOM-C genes, head gap genes, as well as other regulatory genes involved in anterior head patterning. For all of these genes, we have carried out high- resolution neuroanatomical expression studies using laser confocal microscopy together with molecular markers for neuromeric borders. In addition, we have analysed the null mutant phenotypes that result in the developing brain when the genes are deleted. Our results indicate that a surprisingly large number of these developmental regulatory genes are involved in brain regionalization and differentiation, and that elimination of any one of these genes causes marked structural defects in defined brain regions. To analyse their functional role further, we are using genetic methods to overexpress the genes, as well as their mammalian homologs, with the goal of transforming ganglia and creating ectopic brain anlagen. Considering the expression, loss-of-function, and gain-of-function phenotypes of these genes in Drosophila, and of their homologs in vertebrate brains, we postulate that an evolutionarily conserved program underlies brain development in all higher animals. - Supported by the Swiss NSF.