Activation of epidermal growth factor receptors directs astrocytes to organize in a network surrounding axons in the developing rat optic nerve.

In postnatal developing optic nerves, astrocytes organize their processes in a cribriform network to group axons into bundles. In neonatal rat optic nerves in vivo, the active form of EGFR tyrosine kinase is abundantly present when the organization of astrocytes and axons is most actively occurring. Blocking activity of EGFR tyrosine kinase during the development of rat optic nerves in vivo inhibits astrocytes from extending fine processes to surround axons. In vitro, postnatal optic nerve astrocytes, stimulated by EGF, organize into cribriform structures which look remarkably like the in vivo structure of astrocytes in the optic nerve. In addition, when astrocytes are co-cultured with neonatal rat retinal explants in the presence of EGF, astrocytes that are adjacent to the retinal explants, re-organize to an astrocyte-free zone into which neurites grow out from the retinal tissue. We hypothesize that in the developing optic nerve, EGFR activity directs the formation of a histo-architectural structure of astrocytes which surrounds axons and provides a permissive environment for axon development.