The Novel Zinc-BED transcription factor, bedwarfed, is essential for dendritic growth and scaling. Eswar P R Iyer, Srividya C Iyer, Luis Sullivan, Yukting Lau, Shaurya Prakash, Vihitha Thota, Farheen Shaikh, Daniel N Cox. School of Systems Biology, Krasnow Institute for Advanced Study, George Mason Univ, Fairfax, VA.

   Dendrites are the primary points of sensory and synaptic inputs to a neuron, and play an important role in synaptic integration and neural function. Despite the functional importance of dendrites, relatively less is known regarding the underlying molecular mechanisms regulating cell-type specific dendritic patterning. From a large-scale screen for dendritic regulators, we identified a previously uncharacterized and evolutionarily conserved zinc-finger BED-type transcription factor, which we have named bedwarfed (bdwf), that contains a DNA-binding domain found in chromatin boundary element binding proteins and transposases. Here we report our systematic characterization of bdwf function in regulating cell-type specific dendrite development. Both loss-of-function and gain-of-function studies reveal bdwf regulates dendritic outgrowth, branching and scaling in Drosophila dendritic arborization (da) sensory neurons. Expression analyses indicate Bdwf protein is localized to both the nucleus and punctate granules in the cytoplasm of da neurons. Furthermore, we demonstrate that bdwf genetically interacts with the homeodomain transcription factor, cut, in morphologically complex da neurons where Bdwf and Cut are co-expressed and mutually regulate each others expression. We also show that Bdwf co-localizes and interacts with ribosomal proteins suggesting this molecule may function in a ribonucleoprotein complex to direct dendrite arborization. Finally, we demonstrate that Bdwf and its ribosomal interactors are essential for regulating cytoskeletal protein expression by promoting actin-rich dendritic processes, while restricting tubulin expression in da neuron subclasses. Taken together, these results provide novel mechanistic insight into complex combinatorial and multi-functional roles of transcription factors in determining class-specific dendrite development.