Cross-talk between cellular identity specification and axon growth cone guidance in the developing Drosophila embryonic nerve cord. Mary Ann Manavalan, Gaziova Ivana, Bhat Krishna M. Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, TX.

   Guiding axon growth cones towards their synaptic targets is one of the fundamental processes in a developing nervous system. Several major signaling systems have been known to guide axons along the way to their synaptic targets. Mutational disruptions in these signaling systems cause axon guidance defects. However the role of cellular identity specification within the nerve cord in influencing growth cone guidance has never been examined in detail apart from the specification of neurons that send out pioneering axons. Our analysis of axon guidance defects in mutations that alter cellular identity specifications and division patterns indicates that mis-specification of neuroblasts (NBs) that lie in the path of pioneering axons can stall or misroute axons across the midline or even send axons out into the periphery/peripheral system in the Drosophila embryonic CNS. This occurs without altering the expression of some of the major guidance molecules such as Slit or Roundabout. In this work, we will define type of changes in cellular identity that causes such misrouting using mutational tools. We will also show that while expression of certain transcription factors in ectopic sites can induce expression of such axon guidance molecules as roundabout or slit, it plays little, if any, role in regulating the expression of these genes in cells where they are normally expressed.