Widespread expression of β1 integrins in the developing chick retina: Evidence for a role in migration of retinal ganglion cells

Abstract

During extension of axons, critical neuronal interactions with extracellular matrix (ECM) and other cells are thought to be mediated in part by heterodimeric β1 integrin receptors. In this report, we examine the expression and function of β1 integrins in the developing chick retina. Expression of the β1 subunit, assayed by in situ hybridization and antibody staining of dissociated cells, was widespread in undifferentiated neuroepithelial cells, before the initiation of axons. Expression persisted in most retinal cell layers throughout embryonic development, during and after axon extension. The repertoire of β1-associated α subunits was examined using reverse transcription-polymerase chain reaction. In addition to the α6 and α8 subunits previously reported, chick homologues of the α2 and α4 subunits were detected. Developmental Northern blots revealed varying patterns of integrin subunit expression and showed that expression of β1 and the mRNAs of its associated α subunits are not always coregulated during retinal development. The timing and distribution of expression suggested that β1 integrins may be involved in other developmental events in addition to axon extension. To address functions carried out by β1 integrins in the early retina, explanted eye cups were incubated in the presence of function blocking anti-β1 antibody and migration of newly born retinal ganglion cells (RGCs) was assessed. RGC migration from the ventricular zone to the vitreal border was significantly inhibited, suggesting that β1 integrins play a role in neuroblast migration in the retina.