Congenital eye and craniofacial anomalies are associated with the dysregulation of retinoic acid (RA) levels during embryogenesis. In the present study, we observed that RA and pitx2a cooperatively regulate early cranial neural crest migration from the rhombencephalon to the pharyngeal arches and from the mesencephalon and prosencephalon to the periocular mesenchyme and frontonasal processes. The cranial neural crest tracked toward areas of high RA activity (i.e., developing eye) and circumvented areas of low RA activity (i.e., mesencephalon). Although previous studies have shown that RA increased pitx2a expression at later stages of cranial neural crest development, in these studies we found that RA inhibited pitx2a expression in the early migrating ventral cranial neural crest. Increased RA or decreased Pitx2a expression decreased cell survival and inhibited ventral neural crest migration. Decreased RA or increased pitx2a expression markedly disrupted both dorsal and ventral neural crest migration. The tight control of RA and subsequent regulation of pitx2 were required for precise cranial neural crest survival and migration. These alterations in the neural crest in the periocular mesenchyme and frontonasal processes may reflect the craniofacial dysmorphism and microphthalmia observed in cases of increased (i.e., as resulting from isoretinoin exposure) or decreased (i.e., as may occur in fetal alcohol syndrome) RA signaling during pregnancy

PurposeMutations in the CYP1B1 gene are the most commonly identified genetic causes of primary infantile-onset glaucoma. Despite this disease association, the role of CYP1B1 in eye development and its in vivo substrate remain unknown. In the present study, we used zebrafish to elucidate the mechanism by which cyp1b1 regulates eye development.MethodsZebrafish eye and neural crest development were analyzed using live imaging of transgenic zebrafish embryos, in situ hybridization, immunostaining, TUNEL assay, and methylacrylate sections. Cyp1b1 and retinoic acid (RA) levels were genetically (morpholino oligonucleotide antisense and mRNA) and pharmacologically manipulated to examine gene function.ResultsUsing zebrafish, we observed that cyp1b1 was expressed in a specific spatiotemporal pattern in the ocular fissures of the developing zebrafish retina and regulated fissure patency. Decreased Cyp1b1 resulted in the premature breakdown of laminin in the ventral fissure and altered subsequent neural crest migration into the anterior segment. In contrast, cyp1b1 overexpression inhibited cell survival in the ventral ocular fissure and prevented fissure closure via an RA-independent pathway. Cyp1b1 overexpression also inhibited the ocular expression of vsx2, pax6a, and pax6b and increased the extraocular expression of shha. Importantly, embryos injected with human wild-type but not mutant CYP1B1 mRNA also showed colobomas, demonstrating the evolutionary and functional conservation of gene function between species.ConclusionsCyp1b1 regulation of ocular fissure closure indirectly affects neural crest migration and development through an RA-independent pathway. These studies provide insight into the role of Cyp1b1 in eye development and further elucidate the pathogenesis of primary infantile-onset glaucoma.