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Alur RP, Vijayasarathy C, Brown JD, Mehtani M, Onojafe IF, Sergeev YV, Boobalan E, Jones M, Tang K, Liu H, Xia CH, Gong X, Brooks BP. Papillorenal syndrome-causing missense mutations in PAX2/Pax2 result in hypomorphic alleles in mouse and human. PLoS Genet 2010; 6:e1000870. [PMID: 20221250 PMCID: PMC2832668 DOI: 10.1371/journal.pgen.1000870] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2009] [Accepted: 02/02/2010] [Indexed: 11/21/2022] Open
Abstract
Papillorenal syndrome (PRS, also known as renal-coloboma syndrome) is an autosomal dominant disease characterized by potentially-blinding congenital optic nerve excavation and congenital kidney abnormalities. Many patients with PRS have mutations in the paired box transcription factor gene, PAX2. Although most mutations in PAX2 are predicted to result in complete loss of one allele's function, three missense mutations have been reported, raising the possibility that more subtle alterations in PAX2 function may be disease-causing. To date, the molecular behaviors of these mutations have not been explored. We describe a novel mouse model of PRS due to a missense mutation in a highly-conserved threonine residue in the paired domain of Pax2 (p.T74A) that recapitulates the ocular and kidney findings of patients. This mutation is in the Pax2 paired domain at the same location as two human missense mutations. We show that all three missense mutations disrupt potentially critical hydrogen bonds in atomic models and result in reduced Pax2 transactivation, but do not affect nuclear localization, steady state mRNA levels, or the ability of Pax2 to bind its DNA consensus sequence. Moreover, these mutations show reduced steady-state levels of Pax2 protein in vitro and (for p.T74A) in vivo, likely by reducing protein stability. These results suggest that hypomorphic alleles of PAX2/Pax2 can lead to significant disease in humans and mice. Congenital ocular malformations affecting the optic nerve are an important cause of childhood blindness. The papillorenal syndrome (PRS) is an autosomal dominant disorder that causes congenital optic nerve and kidney abnormalities, which may result in legal blindness and renal failure, respectively. Many cases of PRS are caused by mutations in the paired-box transcription factor PAX2. In this paper, we describe a novel mouse model of this human disease caused by a missense mutation in the Pax2 gene at the same position of one of the few disease-causing missense mutations in humans. We characterize the ocular and non-ocular phenotypes of this mouse and model the effect that murine and human Pax2/PAX2 mutations have on protein structure. We also experimentally test the effect these missense mutations have on protein localization, transactivation, and DNA binding, concluding that all three reduce steady-state levels of protein in vitro and (in p.T74A) in vivo by reducing protein stability. This work will help us better understand the pathophysiology of PRS and to dissect the molecular interactions important in normal PAX2 function.
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Affiliation(s)
- Ramakrishna P. Alur
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, United States of America
| | - Camasamudram Vijayasarathy
- Section for Translational Research in Retinal and Macular Degeneration, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, United States of America
| | - Jacob D. Brown
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, United States of America
- Department of Biochemistry, Molecular and Cellular Biology, Georgetown University School of Medicine, Washington, D.C., United States of America
| | - Mohit Mehtani
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, United States of America
| | - Ighovie F. Onojafe
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, United States of America
| | - Yuri V. Sergeev
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, United States of America
| | - Elangovan Boobalan
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, United States of America
| | - MaryPat Jones
- National Human Genome Research Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, United States of America
| | - Ke Tang
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Haiquan Liu
- School of Optometry and Vision Science Program, University of California Berkeley, Berkeley, California, United States of America
| | - Chun-hong Xia
- School of Optometry and Vision Science Program, University of California Berkeley, Berkeley, California, United States of America
| | - Xiaohua Gong
- School of Optometry and Vision Science Program, University of California Berkeley, Berkeley, California, United States of America
| | - Brian P. Brooks
- Section for Translational Research in Retinal and Macular Degeneration, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, United States of America
- Department of Biochemistry, Molecular and Cellular Biology, Georgetown University School of Medicine, Washington, D.C., United States of America
- * E-mail:
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Abstract
PURPOSE OF REVIEW To integrate knowledge on the embryologic and molecular basis of optic fissure closure with clinical observations in patients with uveal coloboma. RECENT FINDINGS Closure of the optic fissure has been well characterized and many genetic alterations have been associated with coloboma; however, molecular mechanisms leading to coloboma remain largely unknown. In the past decade, we have gained better understanding of genes critical to eye development; however, mutations in these genes have been found in few individuals with coloboma. CHD7 mutations have been identified in patients with CHARGE syndrome (coloboma, heart defects, choanal atresia, retarded growth, genital anomalies, and ear anomalies or deafness). Animal models are bringing us closer to a molecular understanding of optic fissure closure. SUMMARY Optic fissure closure requires precise orchestration in timing and apposition of two poles of the optic cup. The relative roles of genetics and environment on this process remain elusive. While most cases of coloboma are sporadic, autosomal dominant, autosomal recessive, and X-linked inheritance patterns have been described. Genetically, colobomata demonstrate pleiotropy, heterogeneity, variable expressivity, and reduced penetrance. Coloboma is a complex disorder with a variable prognosis and requires regular examination to optimize visual acuity and to monitor for potential complications.
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Affiliation(s)
- Lan Chang
- National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
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