Pax6 organizes the anterior eye segment by guiding two distinct neural crest waves.

Cranial neural crest (NC) contributes to the developing vertebrate eye. By multidimensional, quantitative imaging, we traced the origin of the ocular NC cells to two distinct NC populations that differ in the maintenance of sox10 expression, Wnt signalling, origin, route, mode and destination of migration. The first NC population migrates to the proximal and the second NC cell group populates the distal (anterior) part of the eye. By analysing zebrafish pax6a/b compound mutants presenting anterior segment dysgenesis, we demonstrate that Pax6a/b guide the two NC populations to distinct proximodistal locations. We further provide evidence that the lens whose formation is pax6a/b-dependent and lens-derived TGF beta signals contribute to the building of the anterior segment. Taken together, our results reveal multiple roles of Pax6a/b in the control of NC cells during development of the anterior segment. Author summary Neural crest (NC) cells are pluripotent embryonic stem cells that originate from neural tissue during early embryogenesis. The origin and fate of NC cells have been studied intensively in various animal species showing that the eye receives input from NC cells. There are several inherited diseases like aniridia, Peters anomaly, Axenfeld-Rieger syndrome and congenital glaucoma affecting structures of the eye derived from NC cells. As of yet, it has remained unclear how the congenital abnormalities of the eye develop in these patients. We have applied genetic tools and multidimensional live imaging to study the dynamics of NC cell behaviour during eye formation. We found that two waves of NC cell populations with different properties contribute to distinct parts of the eye. By using zebrafish mutants as disease models for human anterior segment dysgenesis, we demonstrate that proper guidance of the two NC populations is crucial for a normal development of the anterior segment of the eye.