title: Patched regulation of axon guidance is by specifying neural identity in the Drosophila nerve cord.
abstract: Within an axon bundle, one or two are pioneering axons and the rest are follower axons. Pioneering axons are projected first and the follower axons are projected later but follow a pioneering axon(s) pathway. It is not clear whether the pioneering axons have a guidance role for follower axons. In this paper, we have investigated the role of Patched (Ptc) in regulating the guidance of medial tract, one of the longitudinal tracts in the nerve cord. In patched mutants the medial longitudinal tract fails to fasciculate on its own side along the nerve cord, instead it abnormally crosses the midline and fasciculates with the contralateral tract. Interestingly, the medial tracts cross the midline ignoring the axon-repellant Slit on the midline and Roundabout on growth cones. The medial tract is pioneered by neurons pCC and vMP2. Our results show that guidance defects of this tract are due to loss and mis-specification of vMP2, which results in the projection from pCC to either stall or project outward near the location of vMP2. Thus, both pioneering neurons are necessary for the proper guidance of pioneering and follower axons. We also show that the loss of Ptc activity in the neuroectoderm prior to the formation of S1 and S2 neuroblasts causes the majority of axon guidance defects. These results provide insight into how mis-specification and loss of neurons can non-autonomously contribute to defects in axon pathfinding.
authors.affiliation: Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: Tanuja T
authors.initials: TT
authors.lastname: Merianda
authors.forename: Vandana
authors.initials: V
authors.lastname: Botta
authors.forename: Krishna Moorthi
authors.initials: KM
authors.lastname: Bhat
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D019521:Body Patterning; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster / Q000196:embryology* / Q000235:genetics; D004625:Embryo, Nonmammalian / Q000166:cytology; D047108:Embryonic Development; D018507:Gene Expression Regulation, Developmental; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics; D009687:Nuclear Proteins / Q000378:metabolism; D038081:Organogenesis; D000072079:Patched Receptors; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D000072086:Smoothened Receptor; D019076:Transgenes
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D029721:Drosophila Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D000072079:Patched Receptors; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D000072086:Smoothened Receptor; C089449:sim protein, Drosophila; C066819:sli protein, Drosophila; C100664:smo protein, Drosophila