title: Distribution of GAP-43, beta-III tubulin and F-actin in developing and regenerating axons and their growth cones in vitro, following neurotrophin treatment.
abstract: Brain derived neurotrophic factor (BDNF) when added to explant cultures of both embryonic and adult retinal ganglion cell (RGC) axons exerted a marked effect on their growth cone size and complexity and also on the intensity of GAP-43, beta-III tubulin and F-actin immunoreaction product in their axons. GAP-43 was distributed in axons, lamellipodia, and filopodia whereas beta-III tubulin was distributed along the length of developing and adult regenerating axons and also in the C-domain of their growth cones. BDNF-treated developing RGC growth cones were larger and displayed increased numbers of GAP-43 and microtubule-containing branches. Although filopodia and lamellipodia were lost from both developing and adult RGC growth cones following trkB-IgG treatment, the intensity of the immunoreaction product of all these molecules was reduced and trkB-IgGs had no effect on the axonal distribution of betas-III tubulin and GAP-43. BDNF-treated growth cones also displayed increased numbers of F-actin containing filopodia and axonal protrusions. This study demonstrates, for the first time, that trkB-IgG treatment causes the loss of F-actin in the P-domain of growth cone tips in developing and regenerating RGC axons. Although microtubules and F-actin domains normally remained distinct in cultured growth cones, beta-III tubulin and F-actin overlapped within the growth cone C-domain, and within axonal protrusions of adult RGC axons, under higher concentrations of BDNF. The collapse of RGC growth cones appeared to correlate with the loss of F-actin. In vitro, trkB signalling may therefore be involved in the maintenance and stabilisation of RGC axons, by influencing F-actin polymerisation, stabilisation and distribution.
authors.affiliation: Department of Anatomy and Developmental Biology, University College London, WC1E 6BT.
authors.forename: Ovokeloye
authors.initials: O
authors.lastname: Avwenagha
authors.forename: Gregor
authors.initials: G
authors.lastname: Campbell
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Bird
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D000199:Actins / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism / Q000494:pharmacology; D005333:Fetus; D019922:GAP-43 Protein / Q000187:drug effects / Q000378:metabolism*; D020439:Growth Cones / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D007074:Immunoglobulin G / Q000378:metabolism / Q000494:pharmacology; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D009414:Nerve Growth Factors / Q000494:pharmacology*; D009416:Nerve Regeneration / Q000187:drug effects / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000187:drug effects / Q000378:metabolism; D009924:Organ Culture Techniques; D011554:Pseudopodia / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D020813:Receptor, trkB / Q000187:drug effects / Q000378:metabolism; D012160:Retina / Q000166:cytology / Q000196:embryology / Q000254:growth & development; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D014404:Tubulin / Q000187:drug effects / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
chemical_list: D000199:Actins; D019208:Brain-Derived Neurotrophic Factor; D019922:GAP-43 Protein; D007074:Immunoglobulin G; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; C488416:Tubb3 protein, rat; D014404:Tubulin; C462941:beta3 tubulin, mouse; D020813:Receptor, trkB