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S. S. Saravanamuthu, C. Y. Gao, P. S. Zelenka; Lateral Induction of Jagged1 Through Jagged1-Notch2 Signaling During FGF-Induced Differentiation of Lens Epithelial Explants. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4344.
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© ARVO (1962-2015); The Authors (2016-present)
Notch signaling is an evolutionarily conserved pathway involved in cell fate decisions. Notch signaling is activated by direct interaction of Notch receptors (1-4) with ligands (Delta1,3,4 and Jagged1,2) on adjacent cells, resulting in proteolytic cleavage of the Notch intracellular domain (NICD), nuclear translocation, and transcription of target genes, including Hes and Hey transcription factors. Disruption of Notch signaling in the lens leads to aberrant expression of cell cycle inhibitory genes, inhibition of epithelial cell proliferation, premature differentiation, and a dysgenic lens. Here we investigate how Notch signaling and Notch ligand expression are regulated during differentiation.
Whole neonatal rat lens epithelia and FGF-treated central epithelial explants were used to examine Notch signaling during differentiation. Immunofluorescence microscopy and immunoblotting with specific antibodies were used to determine the subcellular localization and relative expression of Notch2 NICD (N2ICD), Jagged1(Jag1), N-cadherin (Ncad), E-cadherin (Ecad), and p57Kip2. RT-PCR was used to detect mRNA expression. Notch-Jag1 signaling was blocked using anti-Jag1 antibody. MAPK/ERK signaling was blocked with U0126.
Levels of Jag1, N2ICD, and Ncad were elevated and Ecad was diminished in early differentiating cells at the periphery of the epithelium. Central epithelial explants cultured in FGF showed induction of Jag1 mRNA and protein after 24hr, with a concomitant increase in Ncad and N2ICD. Jag1 induction was suppressed by U0126, indicating a requirement for MAPK/ERK signaling. Other growth factors (IGF1, EGF, PDGF) did not induce Jag1. Blockade of Jag1 function using anti-Jag1 antibody suppressed Jag1 induction and reduced levels of N2ICD, Ncad, and p57Kip2 in the FGF-treated explants.
FGF induces Jag1 and Jag1-Notch2 signaling during differentiation of lens epithelial explants via MAPK/ERK signaling. Jag1-Notch2 signaling is required for proper expression of not only Ncad and p57Kip2, but also Jag1 itself. This indicates a novel lateral induction of Jag1 expression through Jag1-Notch2 mediated feedback.
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