Disease relevance of Crx

• These studies implicate Crx as a potentially important regulator of photoreceptor cell development and gene expression and also identify it as a candidate gene for CORDII and other retinal diseases [1].
• The results suggest that one mechanism of SCA7 disease pathogenesis is transcription dysregulation, and that Crx transcription interference is a predominant factor in SCA7 cone-rod dystrophy retinal degeneration [2].
• A 215-bp proximal promoter fragment containing a TATA box, an Sp1 site and four cone-rod homeobox-binding sites is sufficient to direct expression in cultured retinoblastoma cells and in cone photoreceptors and the pineal gland in transgenic Xenopus laevis [3].

High impact information on Crx

• In the mouse, targeted inactivation of Crx causes a reduction in pineal gene expression and attenuated entrainment to light/dark cycles [4].
• It acts synergistically with Crx to regulate rhodopsin transcription [5].
• Crx-/- mice do not elaborate photoreceptor outer segments and lacked rod and cone activity as assayed by electroretinogram (ERG) [6].
• Crx has been proposed to have a role in the regulation of photoreceptor-specific genes in the eye and of pineal-specific genes in the pineal gland [6].
• Overexpression of Crx using a retroviral vector increased the frequency of clones containing exclusively rod photoreceptors and reduced the frequency of clones containing amacrine interneurons and Müller glial cells [7].

Biological context of Crx

• In transient transfection studies, Crx transactivates rhodopsin promoter-reporter constructs [1].
• Human Crx maps to chromosome 19q13.3, the site of a cone rod dystrophy (CORDII) [1].
• Chromatin immunoprecipitation assays on mouse retina demonstrated that Nr2e3 and Crx co-occupy the promoter/enhancer region of several rod and cone genes in the rod photoreceptor cells [8].
• DNase I footprinting assays identified three potential Crx binding sites within a 55-bp segment beginning 29 bp upstream of the transcription start point [9].
• Coexpression of a dominant negative inhibitor of Nrl abolished Nrl transactivation but had no effect on Crx [9].

Anatomical context of Crx

• Crx, a novel Otx-like paired-homeodomain protein, binds to and transactivates photoreceptor cell-specific genes [1].
• Altogether, our findings suggest that Nr2e3 is a dual-function transcriptional regulator that acts in concert with Crx to promote and maintain the function of rod photoreceptors [8].
• The paired-type homeobox transcription factor, Crx, has a pivotal role in the terminal differentiation of vertebrate photoreceptors [10].
• In HeLa cells transfected with these promoters, co-transfection of a Crx expression vector with wild-type, but not with CRXE mutant promoter, activates CAT activity 20-fold over the background activity [11].

Associations of Crx with chemical compounds

• Crx also binds to and transactivates the genes for several other photoreceptor cell-specific proteins (interphotoreceptor retinoid-binding protein, beta-phosphodiesterase, and arrestin) [1].
• In an SCA7 transgenic mouse model that we developed, it was found that the cone-rod dystrophy involves altered photoreceptor gene expression due to interference with Crx, a homeodomain transcription factor containing a glutamine-rich region [2].
• Developmentally regulated expression of GABA receptor rho1 and rho2 subunits, L7 and cone-rod homeobox (CRX) genes in mouse retina [12].

Physical interactions of Crx

• Several mutant forms of human Nr2e3 identified from ESCS patients showed defects in interacting with Crx and/or in transcriptional regulatory function [8].
• Recombinant Crx binds in vitro not only to the Ret 4 site but also to the Ret 1 and BAT-1 sites [1].

Regulatory relationships of Crx

• It was also established that ataxin-7 must localize to the nucleus to repress Crx transactivation, and the likely nuclear localization signals were mapped to ataxin-7's carboxy-terminal region [2].
• Leukemia inhibitory factor blocks expression of Crx and Nrl transcription factors to inhibit photoreceptor differentiation [13].
• CNTF stimulation induces low levels of STAT3 phosphorylation in progenitors and differentiated neurons but a robust STAT3 activation among postmitotic photoreceptor precursors expressing the cone-rod homeobox gene Crx and newly differentiated rod photoreceptors [14].

Other interactions of Crx

• We also found that Otx2 transactivates the cone-rod homeobox gene Crx, which is required for terminal differentiation and maintenance of photoreceptor cells [15].
• Development of several new SSLP markers allowed us to refine the hyh candidate interval to a region defined by the cone-rod homeobox ( Crx) gene proximally and D7Mit56 distally [16].
• The most active segment contained a 177-bp upstream sequence including apparent Crx and Nrl transcription factor binding sites [9].
• In addition, we overexpressed another NAT, CrxOS, in mouse adult retina using adeno-associated viral vectors and we observed a significant decrease in the expression levels of the corresponding sense gene, Crx [17].
• Functional analysis of the rod photoreceptor cGMP phosphodiesterase alpha-subunit gene promoter: Nrl and Crx are required for full transcriptional activity [9].

Analytical, diagnostic and therapeutic context of Crx

• Immunoprecipitation assays confirmed this Nr2e3-Crx interaction and identified the DNA-binding domain of each protein as the interaction motif [8].
• Immunohistochemistry demonstrated that Crx and Nr2e3 are co-expressed by rod photoreceptors and their precursors [8].
• RT-PCR analysis was used to compare expression of these genes and putative targets of Crx regulation [18].
• RESULTS: We have characterized the transcriptional network controlled by Crx by microarray analysis of gene expression in developing retinal tissue from Crx(+/+) and Crx(-/-) mice [10].
• An animal model of LCA was recently created in which the cone-rod homeobox (crx) gene was disrupted using homologous recombination [19].

References