Molecular Basis for the Developmental Loss of Axon Growth Ability in RGCs

Abstract

Abstract: : Purpose: To understand why RGCs lose the ability to regenerate their axons in the mature CNS. We recently found that amacrine cells signal neonatal rat retinal ganglion cells (RGCs) to undergo a profound and apparently irreversible loss of intrinsic axon growth ability. Concurrently, retinal maturation triggers RGCs to greatly increase their dendritic growth ability. These results suggest that adult CNS neurons fail to regenerate not only because of CNS glial inhibition but also because of a loss of competence to rapidly extend their axons. In order to understand the molecular basis of this loss, we are presently investigating whether it is mediated by stable changes in gene expression. Methods: In order to identify the gene changes responsible, we are presently comparing RGC genes expressed along a developmental timecourse from E17 to P21 by microarray analysis (Affymetrix), as well as genes regulated by exposure to amacrine cell membranes. Results: We found that transcription inhibition completely prevented the ability of amacrine membranes to induce loss of axon growth ability, indicating that changes in gene expression are required. Cluster analysis confirms that purified RGCs provide highly reproducible microarray data. Here we demonstrate that 122 genes are coordinately regulated both during development and in response to amacrine cell membranes. These genes fall into a spectrum of biological function. Conclusions: We have identified a limited number of candidate genes that may underlie the developmental loss of axon growth ability by RGCs. Altering levels of expression of the final set of candidate genes may revert P8 RGCs to an embryonic axon growth phenotype, and could lead to improved axon regeneration in vivo.

Keywords: regeneration • ganglion cells • gene microarray