Xhairy2 functions in Xenopus lens development by regulating p27(xic1) expression.

Lens of vertebrate eyes is derived from competent pre-placodal ectoderm in response to signal(s) from retinal lineage. We herein report that the Xenopus Hes gene Xhairy2, which is expressed in pre-placodal ectoderm, is required for lens development from the initial stage. We show that Xhairy2 knockdown reduced the expression of lens marker genes at every step of lens determination, eventually resulting in ocular lens malformation. Interestingly, retina marker gene expression and retinal anlage morphology remained normal upon Xhairy2 knockdown. Furthermore, loss of lens field caused by Xhairy2 depletion was partially rescued by simultaneous knockdown of the cell cycle inhibitor gene p27(xic1). These results suggest that Xhairy2 is required for lens development through the regulation of p27(xic1) expression, independent of the known cascade of transcription factors. Based on these findings, we propose that Xhairy2 may maintain an intracellular environment in which inducing signal(s) can be accepted.