Hammerschmidt Matthias, Kramer Carina, Nowak Matthias, Herzog Wiebke, Wittbrodt Joachim
Max-Planck Institute for Immunobiology, Freiburg, Germany.
Dev Dyn. 2003 May;227(1):128-33. doi: 10.1002/dvdy.10281.
The mechanisms of patterning and morphogenesis of vertebrate eye primordia are heavily debated. Taking advantage of the maternal effect of a zebrafish smad5 null mutation (Mm169), we investigate the effect of early signaling by members of the bone morphogenetic proteins (Bmps) on eye field patterning and optic vesicle morphogenesis. In contrast to previous Xenopus and chick studies demonstrating a late dorsalizing effect of Bmp4 expressed in the dorsal neural retina itself, we show that patterning of the eye primordia already starts during blastula and early gastrula stages. At these stages, bmps expressed on the ventrolateral side of the embryo promote dorso-distal fates in the entire neuroectoderm, including the eye primordia. Despite a normal split of the eye field in the midline, the eye primordia of Mm169 embryos fail to evaginate laterally. They display a concentric pattern with retinal cells in the center and optic stalk cells in the periphery, representing a flattened version of the topologic relationships present in the mature wild-type eye. Different interpretations of these latter findings are presented. They can be best explained with a model according to which zebrafish eye morphogenesis occurs as a telescopic extension of disc-like, concentric primordia, similar to the development of appendages from imaginal discs in Drosophila.
脊椎动物眼原基的模式形成和形态发生机制一直存在激烈争论。利用斑马鱼smad5无效突变(Mm169)的母体效应,我们研究了骨形态发生蛋白(Bmp)成员早期信号对眼场模式形成和视泡形态发生的影响。与之前在非洲爪蟾和鸡上的研究不同,那些研究表明在背侧神经视网膜本身表达的Bmp4具有晚期背化效应,我们发现眼原基的模式形成在囊胚期和原肠胚早期就已经开始。在这些阶段,胚胎腹外侧表达的bmp促进整个神经外胚层包括眼原基的背-远侧命运。尽管眼场在中线正常分裂,但Mm169胚胎的眼原基未能向外侧外翻。它们呈现出一种同心模式,中心是视网膜细胞,外周是视神经柄细胞,代表了成熟野生型眼中存在的拓扑关系的扁平版本。本文对这些后期发现给出了不同解释。用一个模型可以最好地解释这些发现,根据该模型,斑马鱼眼形态发生是作为盘状同心原基的伸缩性延伸而发生的,类似于果蝇成虫盘中附肢的发育。