Search for genes involved in neuronal morphogenesis in the adult Drosophila melanogaster

The search for genes involved in synaptogenesis, dendritogenesis and axon pathfinding during the development of Drosophila melanogaster have allowed the identification of a variety of phylogenetically conserved genes. During larval stage, Drosophila, has a second wave of neurogenesis that together with an important phase of embryonic neuronal circuit remodeling, which include dendrite pruning, axon retraction and neuronal programmed death, will determine the neuronal network of the adult brain. This new network has notorious differences from the networks formed during the embryonic stage, been the most important the complexity of the circuits on their morphology and connectivity. These circuits are the substrate of behaviors such as courtship, circadian locomotor activity and sleep among others as well as social behaviors such as aggression and adaptive processes like learning and memory. Most of these behaviors can be evaluated and for some of them the neuronal circuit responsible is known. We are conducting a genetic screen with the goal to find genes that alter the connectivity and/or neuronal morphogenesis of neurons of the adult brain. For these we are conducting two types of screens using a gain of function approach and a loss of function approach. The gain of function approach has the advantage of overcome the problem of finding genes that may be necessary for neuronal morphogenesis but have pleiotropic functions during development.

Figure 1. HNT overexpression in retina cells associates to axon overshooting. (A) Schematic representation of 3rd instar larval (L3) optic lobe and (D) adult optic lobe.  (B, C, E-H) Whole-mount larval (B and C) and adult brains (E-H) expressing CD8-GFP under the control of GMR-Gal4 driver immunostained for CD8 (green) and DLGPDZ (red in E-H). (B) A clear limit between lamina and medulla axons (lamina plexus) is observed in WT larvae. (C) HNT-overexpressing larva shows axons that stop in different positions (arrow) disturbing the lamina plexus together with an overgrowth of the Bolwig`s organ (arrowhead in C). (E) In the adult wild type medulla, inner photoreceptor axons stop in M3 (R8) or M6 (R7) layer (labeled in E) not entering into the Lobula (labeled Lo in E). (F) In HNT-overexpressing flies, we found axons that stop in different layers in the medulla (med) or even further into the lobula. (G) Superficial view of an optic lobe, showing the axons that come out of the lamina in WT or (H) HNT-overexpressing adult brain; thicker projections compared to WT are observed in the HNT-overexpressing brain. (I, J) Whole mount larval brains of control and HNT overexpressing flies immunostained with N-Cadherin (Magenta) and Repo (Green). (I) In control larva three rows of glial cells, the epithelial glia (eg), marginal glia (mg) and medulla glia (meg) surround the lamina plexus. (J) When HNT is overexpressed the three rows of glial cells remains similar to the control. Quantification of lamina plexus defects in optic lobes (K) or Bolwig´s organ (L) of third instar larvae. (M) Quantification of the defects in adult optics lobes. Scale bar: (C, H, J) 20 μm, numbers on the right of the bars correspond to the number of optic lobes scored.