Transcriptional control of dendritic patterning in Drosophila neurons

Many neurons receive most of their input through thin processes, called dendrites, that form synapses with the axons of other neurons. Dendrites can be highly branched and have complex architecture. The shape and size of the dendrites of a single neuron determine the number and specificity of the axonal contacts it receives. Therefore, the development of the correct pattern of dendritic branching, or arborization, on different neurons is essential for the proper functioning of the nervous system. Neuronal subtypes in mammals and insects can have specific patterns of dendrite branching [1,2], and several unbiased genome-wide 'forward' genetic screens in Drosophila have identified factors that regulate dendritic morphogenesis in both the peripheral and central nervous systems [3-5]. But although these studies uncovered dozens of genes that might have essential roles in dendritic morphogenesis, most of the genes have yet to be cloned and characterized, and the information on genetic pathways has been sparse. Except for a few identified transcription factors that have been implicated in dendritic morphogenesis in flies and mammals [6-14], little is known about the overall transcriptional programs that specify the characteristic patterns of dendritic arborization in different neurons.Over the past few years, however, large-scale 'reverse' genetic approaches such as RNA interference (RNAi) have emerged to help characterize molecular pathways. Screens based on RNAi have been used to analyze cellular processes in cultured insect cells [15,16] and in intact Drosophila embryos [17,18]. In a recent paper in Genes and Development, Parrish et al. [19] report the results of an in vivo RNAi-based screen set up to examine transcription factor networks that control several aspects of dendritic morphogenesis in Drosophila.Parrish and colleagues [19] took advantage of the simple and stereotyped dendrite branching patterns of type I dendritic arborization (DA) neurons in the Drosophila