👤 Murali R Kuracha

Sproutys (Sprys) are downstream targets and negative feedback regulators of the FGF-Ras-ERK signaling pathway. Our previous studies have shown that Spry1 and Spry2, through negative modulation of FGF-ERK signaling, allow lens vesicle separation from the overlying ectoderm and regulate corneal epithelial proliferation. Here we show that Spry1 and Spry2 are necessary for eyelid closure. Murine palpebral conjunctival epithelial cells that differentiate as inner eyelids and adjacent mesenchymal cells express Spry1 and Spry2 prior to eyelid closure. Conditional deletion of both Spry1 and Spry2, but not either one alone, in the ocular surface epithelial cells result in the "EOB" (eyes open at birth) phenotype suggesting redundant roles for these proteins during eyelid closure. Spry mutant eyelids show increased proliferation of conjunctival epithelial cells with concomitant induction of FGF targets, Erm, Pea3 and Dusp6 and elevated ERK phosphorylation. Peridermal cells at the leading edge of Spry-mutant eyelids showed reduced c-Jun, but not ERK, phosphorylation, reduced F-actin polymerization and reduced motility in vitro. Spry mutant eyelids also showed disruptions in epithelial mesenchymal interactions reflected in the enhanced mesenchymal Spry1 and Spry4 expression, disaggregation of BMP4-positive mesenchymal cells and loss of Shh in the eyelid epithelium. Spry mutant eyelids also showed increased Wnt signaling and reduced expression of Foxc1 and Foxc2, two transcription factors previously shown to be necessary for eyelid closure. Collectively, our results show that conjunctival epithelial Spry1 and Spry2 redundantly promote eyelid closure by (a) stimulating ERK-independent, c-Jun-mediated peridermal migration, (b) suppressing conjunctival epithelial proliferation through FGF-ERK signaling, (c) mediating conjunctival epithelial-mesenchymal interactions and (d) maintaining expression of Foxc1 and Foxc2. Show less

The studies reported here were performed to analyze the roles of Sproutys (Sprys), downstream targets and negative feedback regulators of the fibroblast growth factor (FGF) signaling pathway, in lens and corneal differentiation. Spry1 and -2 were conditionally deleted in the lens and corneal epithelial precursors using the Le-Cre transgene and floxed alleles of Spry1 and -2. Alterations in lens and corneal development were assessed by hematoxylin and eosin staining, in situ hybridization, and immunohistochemistry. Spry1 and -2 were upregulated in the lens fibers at the onset of fiber differentiation. FGF signaling was both necessary and sufficient for induction of Spry1 and -2 in the lens fiber cells. Spry1 and -2 single- or double-null lenses failed to separate from the overlying ectoderm and showed persistent keratolenticular stalks. Apoptosis of stalk cells, normally seen during lens vesicle detachment from the ectoderm, was inhibited in Spry mutant lenses, with concomitant ERK activation. Prox1 and p57(KIP2), normally upregulated at the onset of fiber differentiation were prematurely induced in the Spry mutant lens epithelial cells. However, terminal differentiation markers such as β- or γ-crystallin were not induced. Corneal epithelial precursors in Spry1 and -2 double mutants showed increased proliferation with elevated expression of Erm and DUSP6 and decreased expression of the corneal differentiation marker K12. Collectively, the results indicate that Spry1 and -2 (1) through negative modulation of ERKs allow lens vesicle separation, (2) are targets of FGF signaling in the lens during initiation of fiber differentiation and (3) function redundantly in the corneal epithelial cells to suppress proliferation. Show less