Rax Homeoprotein Regulates Photoreceptor Cell Maturation and Survival in Association with Crx in the Postnatal Mouse Retina

Abstract

A number of homeodomain transcription factors, which play significant roles in retinal development, have been identified in vertebrates (1-4). Rax is a homeodomain transcription factor that is essential for various processes in vertebrate retinal development (5). The Rax gene was first identified as a paired-type homeobox gene expressed in the optic vesicle and the presumptive diencephalon area in the early mouse embryo (6, 7). Rax is evolutionarily well conserved from Drosophila melanogaster to humans. Rax is highly expressed in retinal progenitor cells (RPCs), and its expression in the retina gradually decreases as RPCs become postmitotic and begin to differentiate. Rax-null mutant mice exhibit a reduction of brain size and an absence of the optic vesicle (5, 7). Mutations in human RAX are associated with anophthalmia and microphthalmia (8, 9). Rax overexpression promotes the proliferation of RPCs in frogs and zebra fish (7,(10)(11)(12)(13). In addition to the function in RPCs, Rax plays significant roles in the development of photoreceptor cells and Müller glial cells (14)(15)(16)(17)(18)(19).Rax paralog genes have been identified in various vertebrate species (20)(21)(22). In Xenopus laevis, two Rax genes (xRx and xRx-L/xRx2) have been identified (7, 21), and in zebra fish, three Rax genes (zRx1 to zRx3) have been isolated (7). Interestingly, the expression pattern of zebra fish Rx3 showed more similarity to that of frog and mouse Rax genes than to that of the zebra fish Rx1 and Rx2 genes (23). In chicks, two Rax genes (cRax and cRaxL/ cRax2) have been identified (20). The chick Rax2 gene is expressed in both retinal progenitor cells and early-developing photoreceptors, while chick Rax is predominantly expressed in retinal progenitor cells. It was also reported that chick Rax2 is implicated in cone photoreceptor differentiation and that the expression of a putative dominant negative allele of a chick Rax2 gene caused a significant reduction in the level of expression of cone photoreceptor genes (20). Human RAX2/QRX, which is expressed in the outer nuclear layer (ONL) and inner nuclear layer (INL) of the adult human retina, was identified to be a PCE-1-binding protein by acting synergistically with CRX and NRL to modulate the expression of photoreceptor genes. Monkey, cow, and dog genomes also contain two Rax genes. On the other hand, the Rax2 gene is absent from mouse and rat genomes (22). This raises the question of whether mouse Rax plays an essential role in photoreceptor development during postnatal stages like human Rax2 does.In the current study, we investigated a functional role for Rax in postnatal mouse retinas, which contain a single Rax gene. We report that mouse Rax modulates the expression of photoreceptor genes in the postnatal retina by interacting with Crx. Conditional ablation of Rax in postnatal photoreceptors led to a significant decrease in the level of expression of rod and cone genes and to cone photoreceptor cell death, suggesting that Rax is essential for the maturation of rods and co...

Multiple intrinsic factors act in concert with Lhx2 to direct retinal gliogenesis

“…That Rax electroporation affects photoreceptor development is consistent with a previously demonstrated role of Rax in later stages of photoreceptor differentiation43. The complete lack of gliogenic effects resulting from Rax electroporation may also be due to high levels of Rax expression induced by electroporation of CAG-based expression plasmids in this study4445, compared to the relatively weak retroviral promoters used to drive Rax expression in previous reports16.…”

A modulatory role of the Rax homeobox gene in mature pineal gland function: Investigating the photoneuroendocrine circadian system of a Rax conditional knockout mouse

“…; Irie et al . ), and although CRX is capable of driving gene expression independently, RAX itself does not appear to stimulate gene expression in the absence of CRX (Irie et al . ).…”

“…; Irie et al . ), but the role of Rax in context of the pineal gland is unclear. Rax controls development of the eye and forebrain (Furukawa et al .…”

“…Cone-rod homeobox (CRX) has been shown to act in concert with the retinal and anterior neural fold homeobox gene (Rax) encoded transcription factor RAX to control gene expression in retinal photoreceptors (Kimura et al 2000;Irie et al 2015), but the role of Rax in context of the pineal gland is unclear. Rax controls development of the eye and forebrain (Furukawa et al 1997a;Mathers et al 1997), but expression in the pineal gland is restricted to peri-and postnatal stages (Asbreuk et al 2002;Rohde et al 2011;Muranishi et al 2012).…”

Cul3‐Klhl18 ubiquitin ligase modulates rod transducin translocation during light‐dark adaptation

“…A full‐length cDNA fragment of mouse Klhl18 was amplified by PCR using mouse retinal cDNA as a template and subcloned into the pCAGGSII‐3xFLAG, pCAGGSII‐2xHA (Irie et al , ), and pCAGGSII (Omori et al , ) vectors. The cDNA fragments encoding the Klhl18‐N and Klhl18‐C were amplified by PCR using the plasmid encoding full‐length Klhl18.…”