This proposal investigates the underlying causes of human ocular diseases using mouse models, focusing on the Notch signaling pathway, which is broadly required during development. Notch signaling regulates proliferation, cell shape changes, differentiation, apoptosis and stem cell maintenance in specific cellular contexts. Dominant human mutations in the ligand Jagged1 or Notch2 receptor cause Alagille syndrome, in which some patients exhibit eye deformities. In the last funding period we discovered a Jag1- Notch1/2-Rbpj-Hes1 core signal is required for prenatal mouse lens formation. Mice lacking each of these genes exhibited progressive postnatal lens aphakia, loss of the pupillary opening and microphthalmia. Using germline or conditional mutant alleles, and deletion of two or more genes in complex mutants, we propose to investigate how Presenilin (Psen) proteases regulate Notch receptor activation to release a c-terminal polypeptide (NICD) that complexes in the nucleus to regulate downstream genes. Additional Notch-independent roles for Psen genes will also be explored. Moreover, the Notch ligands Dll1, Jag1 and Jag2 are posttranslationally regulated by ubiquitination. The addition of one or more ubiquitin molecules targets the ligands for degradation, or endocytic recycling within signal sending cells. We propose to explore the role of two families of E3 ubiquitin ligases, Neurl and Mib genes in the developing lens, for which nothing is currently known. Finally we will determine the independent, and combined, roles of the Hes1 and Hes5 downstream effector genes, during Notch regulation of growth versus differentiation. The studies described in this application will extend our understanding of how Notch promotes lens progenitor cell proliferation, promotes fiber cell differentiation and prevents inappropriate fiber cell mitoses or excess apoptosis. All experiments will employ complex conditional (cre-lox) mouse strains, including double and triple mutants, histology, immunohistochemistry, confocal microscopy, in situ hybridization, mouse embryology, Western blotting, qPCR and PCR genotyping. We hope to contribute new information to the processes of growth, morphogenesis and differentiation, which are fundamental to all cells and tissues.

Public Health Relevance

The goal of this study is to understand the underlying molecular mechanisms of mammalian lens formation, and the causes of lens dysgenesis, using mouse models. We propose to do this by investigating which aspects of lens formation require the Notch cell-cell signaling pathway. In other parts of the body, Notch signaling controls cell shape changes, growth, differentiation and death. For these reasons, mutations in the Notch pathway can cause cancer. The mechanisms by which the Notch pathway is regulated and functions in the lens are poorly understood. These studies will provide better understanding of lens development and contribute to the better design of disease therapies for lens dysgenesis syndromes, microphthalmia, Peters Anomaly, and Alagille syndrome.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Special Emphasis Panel (BVS)
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Araj, Houmam H
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University of California Davis
Anatomy/Cell Biology
Schools of Medicine
United States
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Le, Tien T; Conley, Kevin W; Mead, Timothy J et al. (2012) Requirements for Jag1-Rbpj mediated Notch signaling during early mouse lens development. Dev Dyn 241:493-504
Saravanamuthu, Senthil S; Le, Tien T; Gao, Chun Y et al. (2012) Conditional ablation of the Notch2 receptor in the ocular lens. Dev Biol 362:219-29
Charlton-Perkins, Mark; Brown, Nadean L; Cook, Tiffany A (2011) The lens in focus: a comparison of lens development in Drosophila and vertebrates. Mol Genet Genomics 286:189-213
Hufnagel, Robert B; Le, Tien T; Riesenberg, Ashley L et al. (2010) Neurog2 controls the leading edge of neurogenesis in the mammalian retina. Dev Biol 340:490-503
Le, Tien T; Conley, Kevin W; Brown, Nadean L (2009) Jagged 1 is necessary for normal mouse lens formation. Dev Biol 328:118-26
Riesenberg, Amy N; Liu, Zhenyi; Kopan, Raphael et al. (2009) Rbpj cell autonomous regulation of retinal ganglion cell and cone photoreceptor fates in the mouse retina. J Neurosci 29:12865-77
Rowan, Sheldon; Conley, Kevin W; Le, Tien T et al. (2008) Notch signaling regulates growth and differentiation in the mammalian lens. Dev Biol 321:111-22