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Control of patterns of corneal innervation by Pax6.

ABSTRACT: Corneal nerves play essential roles in maintaining the ocular surface through provision of neurotrophic support, but genetic control of corneal innervation is poorly understood. The possibility of a neurotrophic failure in ocular surface disease associated with heterozygosity at the Pax6 locus (aniridia-related keratopathy [ARK]) was investigated.Patterns of corneal innervation were studied during development and aging in mice with different Pax6 dosages and in chimeras. Immunohistochemistry and ELISA-based assays were used to determine the molecular basis of defects seen in Pax6 mutants, and wound healing assays were performed.In adults, the Pax6(+/-) epithelium was less densely innervated than the wild-type epithelium, and radial projection of epithelial nerves was disrupted. Neurotrophic support of the corneal epithelium appeared normal. Directed nerve projection correlated with patterns of epithelial cell migration in adult wild-types, but innervation defects observed in Pax6(+/-) mice were not fully corrected in wound healing or chimeric models where directed epithelial migration was restored.Pax6 dosage nonautonomously controls robust directed radial projection of corneal neurons, and the guidance cues for growth cone guidance are not solely dependent on directed epithelial migration. There is little evidence that ARK represents neurotrophic keratitis.

SUBMITTER: Leiper LJ

PROVIDER: S-EPMC2654056 | biostudies-literature | 2009 Mar

REPOSITORIES: biostudies-literature

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Control of patterns of corneal innervation by Pax6.

Leiper Lucy J LJ Ou Jingxing J Walczysko Petr P Kucerova Romana R Lavery Derek N DN West John D JD Collinson J Martin JM

Investigative ophthalmology & visual science 20081121 3

<h4>Purpose</h4>Corneal nerves play essential roles in maintaining the ocular surface through provision of neurotrophic support, but genetic control of corneal innervation is poorly understood. The possibility of a neurotrophic failure in ocular surface disease associated with heterozygosity at the Pax6 locus (aniridia-related keratopathy [ARK]) was investigated.<h4>Methods</h4>Patterns of corneal innervation were studied during development and aging in mice with different Pax6 dosages and in ch ...[more]

PMID: 19029029

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Project description:Altered dosage of the transcription factor PAX6 causes multiple human eye pathophysiologies. PAX6?/? heterozygotes suffer from aniridia and aniridia-related keratopathy (ARK), a corneal deterioration that probably involves a limbal epithelial stem cell (LESC) deficiency. Heterozygous Pax6(+/Sey-Neu) (Pax6?/?) mice recapitulate the human disease and are a good model of ARK. Corneal pathologies also occur in other mouse Pax6 mutants and in PAX77(Tg/-) transgenics, which over-express Pax6 and model human PAX6 duplication.We used electron microscopy to investigate ocular defects in Pax6?/? heterozygotes (low Pax6 levels) and PAX77(Tg/-) transgenics (high Pax6 levels). As well as the well-documented epithelial defects, aberrant Pax6 dosage had profound effects on the corneal stroma and endothelium in both genotypes, including cellular vacuolation, similar to that reported for human macular corneal dystrophy. We used mosaic expression of an X-linked LacZ transgene in X-inactivation mosaic female (XLacZ(Tg/-)) mice to investigate corneal epithelial maintenance by LESC clones in Pax6?/? and PAX77(Tg/-) mosaic mice. PAX77(Tg/-) mosaics, over-expressing Pax6, produced normal corneal epithelial radial striped patterns (despite other corneal defects), suggesting that centripetal cell movement was unaffected. Moderately disrupted patterns in Pax6?/? mosaics were corrected by introducing the PAX77 transgene (in Pax6?/?, PAX77(Tg/-) mosaics). Pax6(Leca4/+), XLacZ(Tg/-) mosaic mice (heterozygous for the Pax6(Leca4) missense mutation) showed more severely disrupted mosaic patterns. Corrected corneal epithelial stripe numbers (an indirect estimate of active LESC clone numbers) declined with age (between 15 and 30 weeks) in wild-type XLacZ(Tg/-) mosaics. In contrast, corrected stripe numbers were already low at 15 weeks in Pax6?/? and PAX77(Tg/-) mosaic corneas, suggesting Pax6 under- and over-expression both affect LESC clones.Pax6?/? and PAX77(Tg/-) genotypes have only relatively minor effects on LESC clone numbers but cause more severe corneal endothelial and stromal defects. This should prompt further investigations of the pathophysiology underlying human aniridia and ARK.

Project description:BackgroundThe purpose of the study is to elicit the epigenetic mechanism involving CCCTC binding factor (CTCF)-mediated chromatin remodeling that regulates PAX6 gene interaction with differentiation-associated genes to control corneal epithelial differentiation.MethodsCell cycle progression and specific keratin expressions were measured to monitor changes of differentiation-induced primary human limbal stem/progenitor (HLS/P), human corneal epithelial (HCE) and human telomerase-immortalized corneal epithelial (HTCE) cells. PAX6-interactive and differentiation-associated genes in chromatin remodeling mediated by the epigenetic factor CTCF were detected by circular chromosome conformation capture (4C) and ChIP (Chromatin immunoprecipitation)-on-chip approaches, and verified by FISH (Fluorescent in situ hybridization). Furthermore, CTCF activities were altered by CTCF-shRNA to study the effect of CTCF on mediating interaction of Pax6 and differentiation-associated genes in corneal epithelial cell fate.ResultsOur results demonstrated that differentiation-induced human corneal epithelial cells expressed typical corneal epithelial characteristics including morphological changes, increased keratin12 expression and G0/G1 accumulations. Expressions of CTCF and PAX6 were suppressed and elevated following the process of differentiation, respectively. During corneal epithelial cell differentiation, differentiation-induced RCN1 and ADAM17 were found interacting with PAX6 in the process of CTCF-mediated chromatin remodeling detected by 4C and verified by ChIP-on-chip and FISH. Diminished CTCF mRNA with CTCF-shRNA in HTCE cells weakened the interaction of PAX6 gene in controlling RCN1/ADAM17 and enhanced early onset of the genes in cell differentiation.ConclusionOur results explain how epigenetic factor CTCF-mediated chromatin remodeling regulates interactions between eye-specific PAX6 and those genes that are induced/associated with cell differentiation to modulate corneal epithelial cell-specific differentiation.

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Control of patterns of corneal innervation by Pax6.

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Control of patterns of corneal innervation by Pax6.

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