Abstract
Retinal vascular development is mediated by astrocytes, which induce the developing vascular endothelium to migrate across the retina in response to the astrocyte-secreted, hypoxia-induced, VEGF. Normally, neither astrocytes nor blood vessels enter the oveal region during development, and the fovea forms only after the foveal avascular zone (FAZ) has been defined. OCT shows that if the foveal region is vascularized, the foveal depression is absent. We aimed to identify genes differentially expressed in the acular region of human fetal retinas, which might have a role in guidance of retinal vessels and specification of the FAZ.
RNA of high purity was extracted from 5 mm biopsies of the foveal region (‘fovea’), corresponding nasal retina (‘nasal’), and the remaining ‘surround’ of 4 19–20 week gestation fetuses. Samples (12 in total) were hybridized to Affymetrix GeneChips® (HG-U133 Plus 2). Cluster analysis showed that biopsy location (‘fovea’ vs. ‘nasal’ vs. ‘surround’) was the most significant determinant of gene expression profile; thus, gene expression data from each of the biopsies was pooled by location for further analysis. Over 4000 genes are differentially expressed between the fovea and non-foveal arrays (p [[lt]] 0.01). Of these, about half are linked with processes that distinguish the more mature foveal region with the poorly differentiated peripheral retina and have been discounted. Genes associated with axon guidance comprise about 16% of the remaining pool (fovea vs. surround). Using quantitative PCR we confirmed differential expression of Eph A6 and its ligands; in situ hybridisation for EphA6 reveals a high-to-low, centre-to-periphery distribution of EphA6 mRNA, consistent with a role in defining the foveal avascular area. Further PCR and in situ hybridization analyses are in progress to confirm differential expression of other genes of interest.
Supported by the Ophthalmic Research Institute of Australia and the Australian Research Council ARC Centres of Excellence program.