RBPJ-dependent and -independent Notch2 Signaling Regulates Ciliary Body Development in the Mouse Eye

Abstract

The ciliary body (CB) is a two-layered structure in the anterior eye, which is composed of the pigmented outer ciliary epithelium (OCE) and the non-pigmented inner ciliary epithelium (ICE). It is responsible for aqueous humor secretion and lens accommodation. Despite the important roles in maintaining normal eye functions, its development still remains poorly understood. The Notch signaling pathway is an evolutionarily conserved pathway that has diverse functions during tissue development and homeostasis. Canonical Notch signaling is mediated through the recombination signal binding protein for immunoglobulin kappa J region (RBPJ)-dependent transcription activation and repression. In this study, I have demonstrated that Notch2 and RBPJ are important regulators of CB development by conditionally deleting them in the developing CB. Conditional knockout of either Notch2 or RBPJ causes severe dysgenesis of the CB, although both of them are dispensable for cell fate determination of the ciliary margin zone (CMZ). RBPJ-dependent Notch2 signaling regulates CB morphogenesis partially through the promotion of cell proliferation and the maintenance of active bone morphogenetic protein (BMP) signaling in the OCE of the CB. Surprisingly, RBPJ-independent Notch2 modulates BMP signaling in the ciliary stroma cells via repressing the expression of two secreted BMP inhibitors, chordin-like 1 (Chrdl1) and neuroblastoma suppression of tumorigenicity 1 (Nbl1). In addition, Notch2-independent RBPJ also controls cell adhesion mediated by neural cadherin (N-cadherin) in the OCE to hold together two CB layers. Finally, I have shown that RBPJ in the ICE regulates Opticin (Optc) expression and secretion. Therefore, this study has revealed important roles of RBPJ-dependent canonical Notch2 signaling in regulating CB morphogenesis and development, and has also uncovered RBPJ-dependent and -independent regulation of BMP signaling by Notch2 in the developing CB.