Retinoid X receptor ? gene transcripts are expressed by a subset of early generated retinal cells and eventually restricted to photoreceptors

Abstract

We have examined the distribution of the retinoid X receptor gamma (RXRgamma) in the developing chicken retina by using in situ hybridization and RNase protection assays. We detected RXRgamma transcripts as early as 4 days of embryonic development (d4) in central regions of the retina, spreading to more peripheral regions by d8. The first few RXRgamma-positive cells were scattered within the depth of the retinal neuroepithelium, but as they increased in number they became localized predominantly to the apical (outer, ventricular) layer. The identity of the RXRgamma-positive cells at these stages is unknown, due to the lack of cell type-specific markers. By d10, when photoreceptors and ganglion cells have been generated and begun to establish their definitive layers, RXRgamma-positive cells were virtually restricted to the photoreceptor layer, and maintained this distribution to posthatch stages. RNase protection assays were performed on whole retinae to verify the temporal pattern of in situ hybridization results and showed that between d5 and d16 there was a significant increase in the mRNA levels of the RXRgamma2 isoform. Between d16 and early posthatch stages the level of RXRgamma2 mRNA did not change significantly. Consistent with previous studies, mRNA levels of the RXRgamma1 isoform were substantially lower than mRNA levels of the RXRgamma2 isoform at all time points examined. These results demonstrate that RXRgamma mRNA is expressed in photoreceptors in the developing chicken retina and implicate RXRgamma as the earliest marker of photoreceptor differentiation documented to date.

Retinoic acid receptors and retinoid X receptors in the mature retina: Subtype determination and cellular distribution

“…15 The observation that the RXRγ transcript is also present in the neural retinal cells is more surprising, since previous reports have shown that RXRγ has a very limited postnatal tissue distribution compared to other nuclear retinoid receptors. 35 RXRγ expression by cone photoreceptor cells was previously also reported by Hoover et al 36 They show the presence of RXRγ mRNA by in situ hybridization in the chick retina at two weeks post-hatching. Unfortunately, their results do not allow them to exclude rod photoreceptors from also expressing RXRγ.…”

Notch 1 inhibits photoreceptor production in the developing mammalian retina

“…As predicted by the microarray results, a significant increase in photoreceptor markers concomitant with a decrease in retinal ganglion cell markers were observed. Thyroid hormone receptor ␤ 2 and retinoid x receptor gene ␥ are two additional genes involved in early photoreceptor development (Forrest et al, 2002;Hoover et al, 1998). Both of these genes were also observed to be upregulated in Notch1 CKO 917 RESEARCH ARTICLE Notch signaling in mouse retinal development Fig.…”

The chickenRaxLgene plays a role in the initiation of photoreceptor differentiation

“…However, there were fewer cells expressing visinin transcript within the EnRaxL∆C virusinfected domains. To further investigate whether EnRaxL∆C interfered with the proper development of photoreceptor cells, or just visinin marker gene expression, we examined the expression of another photoreceptor-specific gene, RXRγ (Rxrg) (Hoover et al, 1998). Rxrg exhibited a uniform pattern C.-M. A. Chen and C. L. Cepko of expression in the control, uninfected E7.5 retina (data not shown).…”