Commissureless is required both in commissural neurones and midline cells for axon guidance across the midline.
In the absence of Commissureless (Comm) function, axons are unable to extend across the central nervous system midline. Comm downregulates levels of Roundabout (Robo), a receptor for the midline repellent Slit, in order to allow axons to cross the midline. comm transcript is expressed at high levels in the midline glia and Comm protein accumulates on axons at the midline. This has led to the hypothesis that Comm moves from the midline glia to the axons, where it can reduce Robo levels. We have found that expression of Comm in the midline cells is unable to rescue the comm phenotype and that tagged versions of Comm are not transferred to axons. A re-examination of Comm protein expression and the use of targeted RNA interference reveal that correct midline crossing requires that Comm is expressed in the commissural axons and midline glia. We suggest that accumulation of Comm protein at the midline spatially limits Comm activity and prevents it from being active on the contralateral side of the central nervous system.
Georgiou
Marios
M
Molecular Neurobiology Group, MRC Centre for Developmental Neurobiology, Guy's Hospital Campus, King's College, London SE1 1UL, UK.
Tear
Guy
G
D000818:Animals; D001369:Axons; D002470:Cell Survival / Q000235:genetics; D002490:Central Nervous System / Q000196:embryology*; D004330:Drosophila / Q000196:embryology* / Q000235:genetics; D029721:Drosophila Proteins; D004625:Embryo, Nonmammalian; D004627:Embryonic Induction; D018507:Gene Expression Regulation, Developmental; D005821:Genetic Techniques; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D012313:RNA / Q000235:genetics; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism; D000097905:Roundabout Proteins
D029721:Drosophila Proteins; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D012313:RNA; D011971:Receptors, Immunologic; D000097905:Roundabout Proteins; C110665:comm protein, Drosophila