Interplay between axonal Wnt5-Vang and dendritic Wnt5-Drl/Ryk signaling controls glomerular patterning in the Drosophila antennal lobe [preprint]

Despite the importance of dendritic targeting in neural circuit assembly, the mechanisms by which it is controlled still remain incompletely understood. We previously showed that in the developing Drosophila antennal lobe, the Wnt5 protein forms a gradient that directs the ~45° rotation of a cluster of projection neuron (PN) dendrites, including the adjacent DA1 and VA1d dendrites. We report here that the Van Gogh (Vang) transmembrane planar cell polarity (PCP) protein is required for the rotation of the DA1/VA1d dendritic pair. Cell type-specific rescue and mosaic analyses showed that Vang functions in the olfactory receptor neurons (ORNs), suggesting a codependence of ORN axonal and PN dendritic targeting. Loss of Vang suppressed the repulsion of the VA1d dendrites by Wnt5, indicating that Wnt5 signals through Vang to direct the rotation of the DA1 and VA1d glomeruli. We observed that the Derailed (Drl)/Ryk atypical receptor tyrosine kinase is also required for the rotation of the DA1/VA1d dendritic pair. Antibody staining showed that Drl/Ryk is much more highly expressed by the DA1 dendrites than the adjacent VA1d dendrites. Mosaic and epistatic analyses showed that Drl/Ryk specifically functions in the DA1 dendrites in which it antagonizes the Wnt5-Vang repulsion and mediates the migration of the DA1 glomerulus towards Wnt5. Thus, the nascent DA1 and VA1d glomeruli appear to exhibit Drl/Ryk-dependent biphasic responses to Wnt5. Our work shows that the final patterning of the fly olfactory map is the result of an interplay between ORN axons and PN dendrites, wherein converging pre- and postsynaptic processes contribute key Wnt5 signaling components, allowing Wnt5 to orient the rotation of nascent synapses through a PCP mechanism

Survey of Candidate Genes Functioning in the Drosophila Wnt5 Signaling Pathway

The Wnt5 signaling pathway plays a fundamental role in establishing proper glomerular organization in drosophila melanogaster. The Wnt5 protein generates a gradient that allows for the precise termination of projection neuron dendrites. The signaling mechanisms that transduce the Wnt5 signal in the dendrites are unknown. There are several families of genes that may act as receptors to the Wnt5 protein including Derailed-2, Frizzled and Ror. In addition, the Src64B kinase has been proposed to act as a downstream signaling protein. The aim of the project is to determine if these candidate molecules function in the Wnt5 signaling pathway using the technique of genetic interactions. By co-expressing wnt5 and the candidate genes the hope is to induce morphological changes in the Drosophila antennal lobes. Phosphatidylinositide 3-kinase (PI3K) also plays a role in neural development and it was also tested. No morphological changes in the antennal lobes were found when the wnt5 gene was co-expressed with the Frizzled and Frizzled-2, suggesting that these genes are not involved in Wnt5 signaling. Over-expression of PI3K and Src64B constitutively active (Src64BCA) genes appeared to be lethal in flies precluding their analyses. Interestingly, a mutant construct, Derailed; Derailed-2, showed strong morphological changes in the antennal lobes suggesting that Derailed-2 may act in Wnt5 signaling. Analysis continues on the Derailed-2 and Ror genes