TENASCIN DEMARCATES THE BOUNDARY BETWEEN THE MYELINATED AND NONMYELINATED PART OF RETINAL GANGLION-CELL AXONE IN THE DEVELOPING AND ADULT-MOUSE

The molecular determinants controlling the topographically restricted distribution of neural cells in the mammalian CNS are largely unknown. In the mouse, myelin-forming oligodendrocytes are differentially dist ributed along retinal ganglion cell axons. These axons are myelin free intraretinally and in the most proximal (i.e., retinal) part of the o ptic nerve, but become myelinated in the distal (i.e., chiasmal) part of the optic nerve. Tenascin protein and mRNA are detectable in increa sed amounts at the retinal end of the developing optic nerve before th e arrival of oligodendrocyte progenitor cells and are restricted to th is region in the adult optic nerve. Tenascin is a nonadhesive substrat e for oligodendrocytes and their progenitor cells in vitro when offere d as a substrate in choice with polyornithine. These observations sugg est that tenascin is critical for the establishment and maintenance of the restricted distribution of myelin-forming oligodendrocytes along retinal ganglion cell axons of the mouse.