Abstract
Purpose: :
In the vertebrate retina, specific cell types are generated in two distinct stages of histogenesis, which are evolutionarily conserved. These two stages of histogenesis are sustained by populations of retinal stem cells/progenitors, which are distinguishable by differential gene expression and preferences to give rise to specific cell types (James et al, 2004, J Neurobiol, 61, 359). Knowledge about their molecular signature as it changes during retinal development is essential to understand the mechanism underlying the generation of different cell types and address issues related to degenerative changes leading to vision loss using the stem cell approach. We have begun the molecular characterization of retinal stem cells in different stages of retinal development.
Methods: :
We have previously demonstrated that retinal stem cells/progenitors can be enriched prospectively as the side population (SP) cells, using the Hoechst dye efflux assay (Bhattacharya et al, 2003, IOVS, 44, 2764). Retinal stem cells/progenitors and differentiated cells were prospectively enriched as SP and non-SP (NSP) cells from different stages of retinal development (E12, E14, E16, E18, PN1 and PN3) and compared with each other for differential expression of genes using micro array analysis and expression of progenitor specific markers using immunocytochemical analysis.
Results: :
We were able to enrich SP cells successfully from each stage of retinal development. The proportion of SP cells decreased successfully as development progressed. For example, the proportion of SP cells was higher during early than late histogenesis. These cells preferentially expressed immunoreactivities corresponding to neural (e.g., Nestin, Sox2, Musashi1, cKit, Notch1, SSEA, ABCG2) and retinal (e.g., Rx, Pax6, Chx10) progenitor markers. They can generate clonal neurospheres and cells therein can differentiate along neuronal and glial lineage, albeit with different proclivity. A comparison of transcription profile of E12 SP and NSP cells reveal an increase in transcripts corresponding to genes involved in stem, cell maintenance (e.g., Rx, FGFRs, Hes class, CyclinA, CyclinD, Notch1, Fzds, Gli).
Conclusions: :
Retinal stem cells/progenitors can be prospectively isolated from different stages of retinal development and their proportion decreases with development. They express neural and retinal progenitor properties and potential. A comparison of their molecular signature will be presented.
Keywords: retina • gene screening • flow cytometry