Abstract
Purpose: :
To examine the gene expression of fetal retinal sheet transplants, and retinal progenitor cell (RPC) transplants placed within the sub-retinal space of rhodopsin-mutant retinal degenerate rats.
Methods: :
This study was designed to compare the differential expression of genes amongst four experimental conditions: (1) retinal sheet transplants, (2) cell cultured RPCs prior to transplantation, (3) RPC transplants, and (4) the wild-type photoreceptor layer of normal human placental alkaline phosphatase / green fluorescent protein (hPAP/GFP) double-labeled rats. Using a laser capture microdissection system the photoreceptor layer of a wild-type rat and the transplanted layer from sheet and RPC transplants from transplanted degenerate rats were harvested. Gene expression profiles were generated with an Affymetrix rat genome microarray. Differentially expressed genes from the biological process "light stimulus" were used in a two-way cluster analysis of pair-wise comparisons across the various experimental conditions.
Results: :
Genome-wide expression profiling revealed differential expression in genes integral to visual perception. In silico analysis revealed that gene processes involved with visual perception were most significantly enriched amongst the pair-wise experimental conditions. Subsequent two-way cluster analysis of genes involved in visual perception revealed a specific pattern of gene expression across a limited number of genes. Specifically, sheet transplants were found to express rhodopsin, which was downregulated in RPC transplants and RPCs prior to transplantation. Notably, all of the transplants were found to have enhanced expression of glutamate receptor mGluR6, which is exclusively found in bipolar cells. Arrestin / retinal S-antigen, which is specific for photoreceptors, was found to be upregulated in all of the transplants when compared against RPCs.
Conclusions: :
Differences in gene expression between fetal retinal sheet transplants, cell cultured RPCs, RPC transplants, and wild-type photoreceptors were profiled using an oligonucleotide microarray system. An understanding of these patterns of differential gene expression provides some insight into the behavior of retinal transplants. Specifically, these patterns suggest that fetal retinal sheet transplants may be further differentiated towards the photoreceptor phenotype than RPC transplants. Thus, we have devised a system to specifically evaluate retinal transplants in order to more fully understand their biology, and direct their differentiation towards photoreceptors.
Keywords: transplantation • gene/expression • retina