Lwigale, P. | Search bioRxiv

bioRxiv2021

Nephronectin-Integrin α8 signaling is required for proper migration of periocular neural crest cells during chick corneal development

During development, cells aggregate at tissue boundaries to form normal tissue architecture of organs. However, how cells are segregated into tissue precursors remains largely unknown. Cornea development is a perfect example of this process whereby neural crest cells aggregate in the periocular region prior to their migration and differentiation into corneal cells. Our recent RNA-Seq analysis identified upregulation of Nephronectin (Npnt) transcripts during early stages of corneal development where its function has not been investigated. We found that Npnt mRNA and protein are expressed by various ocular tissues including the migratory periocular neural crest (pNC), which also express the integrin alpha 8 (Itg8) receptor. Knockdown of either Npnt or Itg8 attenuated cornea development, whereas overexpression of Npnt resulted in cornea thickening. Moreover, overexpression of Npnt variants lacking RGD binding sites did not affect corneal thickness. Neither the knockdown or augmentation of Npnt caused significant changes in cell proliferation, suggesting that Npnt directs pNC migration into the cornea. In vitro analyses showed that Npnt promotes pNC migration from explanted periocular mesenchyme, which requires Itg8. Combined, these findings show that Npnt specifies and tunes cell migration into the presumptive cornea ECM by providing a substrate for Itg8-positive pNC cells.

developmental biology↗

bioRxiv2019

Primary cilia deficiency in neural crest cells causes Anterior Segment Dysgenesis

During eye embryogenesis, neural crest cells (NCC) of the periocular mesenchyme (POM) migrate to the anterior segment (AS) of the eye and then differentiate into the corneal stroma and endothelium, ciliary body, iris stroma, and the trabecular meshwork. Defective development of these structures leads to anterior segment dysgenesis (ASD) that in 50% of the cases leads to glaucoma, a leading cause of blindness. Here, we show that the primary cilium is indispensable for normal AS development and that its ablation in NCC induces ASD phenotypes including; small and thin cornea, impaired stromal keratocyte organization, abnormal iridocorneal angle with reduced anterior chamber and corneal neovascularization. These defects are similar to those described in patients with AS conditions such as Axenfeld-Rieger syndrome and Peters anomaly. Mechanistically, disruption of the primary cilium in the NCC resulted in reduced hedgehog (Hh) signaling in the POM, canonically activated by the Indian Hedgehog ligand expressed by endothelial cells of the choroid. This caused decreased cell proliferation in a subpopulation of POM cells surrounding the retinal pigmented epithelium. Moreover, primary cilium ablation in NCC also led to a decreased expression of Foxc1 and Pitx2, two transcription factors identified as major ASD causative genes. These findings suggest that primary cilia are indispensable for NCC to form normal AS structures via Hh signaling. Defects in primary cilia could, therefore, contribute to the pathogenesis of ASD, and to their complications such as congenital glaucoma.

developmental biology↗