Department of Biology, University of Kentucky, USA.
Department of Biology, University of Kentucky, USA.
Dev Biol. 2019 Aug 1;452(1):43-54. doi: 10.1016/j.ydbio.2019.04.012. Epub 2019 Apr 26.
Fusion of the optic fissure is necessary to complete retinal morphogenesis and ensure proper function of the optic stalk. Failure of this event leads to congenital coloboma, one of the leading causes of pediatric blindness. Mechanistically it is widely accepted that the basement membrane (BM) surrounding the maturing retina needs to be remodeled within the fissure in order to facilitate subsequent epithelial sheet fusion. However, the mechanism driving BM remodeling has yet to be elucidated. As a first step to understanding this critical molecular event we comprehensively characterized the core composition of optic fissure BMs in the zebrafish embryos. Zebrafish optic fissure BMs were found to express laminin a1, a4, b1a, c1 and c3, nidogen 1a, 1b and 2a, collagen IV a1 and a2 as well as perlecan. Furthermore, we observed that laminin, perlecan and collagen IV expression persists in the fissure during fusion, up to 56 hpf, while nidogen expression is downregulated upon initiation of fusion, at 36 hpf. Using immunohistochemistry we also show that nidogen is removed from the BM prior to that of laminin, indicating that remodeling of the BM is an ordered event. Lastly, we characterized retinal morphogenesis in the absence of nidogen function and documented retinal malformation similar to what is observed in laminin mutants. Taken together, we propose a model of BM remodeling where nidogen acts as a linchpin during initiation of optic fissure fusion.
视裂融合对于完成视网膜形态发生和确保视柄的正常功能是必要的。如果这一事件失败，就会导致先天性视网膜裂孔，这是儿童失明的主要原因之一。从机制上讲，人们普遍认为，成熟视网膜周围的基膜（BM）需要在裂孔内重塑，以促进随后的上皮片融合。然而，驱动 BM 重塑的机制尚未阐明。作为理解这一关键分子事件的第一步，我们全面描述了斑马鱼胚胎中视裂 BM 的核心组成。斑马鱼视裂 BM 被发现表达层粘连蛋白 a1、a4、b1a、c1 和 c3、巢蛋白 1a、1b 和 2a、IV 型胶原 a1 和 a2 以及硫酸乙酰肝素蛋白聚糖。此外，我们观察到，在融合过程中，包括 56 hpf 时，层粘连蛋白、硫酸乙酰肝素蛋白聚糖和 IV 型胶原的表达在裂孔中持续存在，而巢蛋白的表达在融合开始时（36 hpf）下调。通过免疫组织化学，我们还表明，在层粘连蛋白之前，巢蛋白从 BM 中被去除，这表明 BM 的重塑是一个有序的事件。最后，我们在缺乏巢蛋白功能的情况下对视网膜形态发生进行了特征描述，并记录到类似于层粘连蛋白突变体中观察到的视网膜畸形。综上所述，我们提出了一个 BM 重塑模型，其中巢蛋白在视裂融合开始时起关键作用。
