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F. Ahmed, S. Bhattacharya, G. Hegde, I. Ahmad; Nrl-Dependent Diffusible Factors Regulate Retinal Stem Cell/Progenitor Differentiation Into Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1279.
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We have demonstrated that neonatal rodent retinal cells elaborate potent photoreceptor promoting factors capable of inducing photoreceptor differentiation in progenitors obtained from heterologous ES cells (Zhao et al., 2002, BBRC 297:177-184; Zhao et al., 2008, Stem Cells 26:939-949). Evidence has emerged that the neural retina leucine-zipper (Nrl) protein plays a critical role in the regulation of both rod and cone differentiation; ectopic expression of Nrl completely suppresses cone differentiation while concurrently directing precursors towards rod sub lineage (Cheng et al., 2006, Human Mol. Genet. 15: 2588 - 2602; Oh et al, 2007, PNAS 104:1679-84). Here, to characterize the elusive photoreceptor-promoting activities we tested the hypothesis that Nrl-dependent diffusible factors(s) regulate the differentiation of rods and cones.
Retina from E14 embryos and PN1 pups of wild type (wt) mice were dissociated and cultured in the presence of EGF and FGF2 to generate neurospheres. Neurospheres were cultured in conditioned medium (CM) obtained from PN1 Nrl-/- or wt retina for 5-7 days, followed by RT-PCR and immunocytochemical analyses of regulators and markers of rod and cone photoreceptors.
We observed a decrease in the expression of markers corresponding to rods in wt E18 neurospheres, exposed to Nrl-/- retinal CM, compared to those cultured in wt retinal CM. In contrast, expression of S cone and cone-specific markers increased in neurospheres cultured in Nrl-/- retinal CM, compared to those in wt retinal CM. The positive effects of Nrl-/- retinal CM on the expression cone-specific genes were relatively greater in E14 neurospheres than in PN1 neurospheres.
Our preliminary data suggest that Nrl-dependent diffusible factor(s) influence the differentiation processes of both rod and cone precursors and may play important role in determining the relative numbers of photoreceptors.
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