INCREASED EXPRESSION OF SPECIFIC RECOGNITION MOLECULES BY RETINAL GANGLION-CELLS AND BY OPTIC PATHWAY GLIA ACCOMPANIES THE SUCCESSFUL REGENERATION OF RETINAL AXONS IN ADULT ZEBRAFISH

Retinal ganglion cells (RGCs) in adult zebrafish can regenerate their axons. We show that successful axonal regeneration is accompanied by t he re-expression by RGCs of mRNAs encoding specific recognition molecu les that are expressed at high levels in the larval retina but are dow n-regulated in the adult. Message levels for l1.1 and l1.2 (two homolo gs of mammalian L1), n-cam (homologous to mammalian N-CAM), beta3 (rel ated to the beta3 and beta2 subunits of mammalian Na,K-ATPase), and tn -c (homologous to mammalian tenascin-C) were high in larval RGCs under going axonogenesis and low in adult RGCs. After an optic nerve crush, axotomized adult RGCs showed increased levels of l1.1, l1.2, and n-cam mRNA expression, whereas the levels of beta3 and tn-cmRNA remained un changed. The optic nerve crush also induced the expression of some of these mRNAs in the optic nerve and tract where they are not normally d etectable. This lesion induced up-regulation by presumptive glia was o bserved for l1.1, l1.2, n-cam and beta3 but not for tn-c. The combinat ion of a neuronal (intrinsic) response to axotomy with an environmenta l (extrinsic) response may be an important determinant allowing for th e successful axonal regeneration. (C) 1996 Wiley-Liss, Inc.