Kitamoto Junko, Hyer Jeanette
Department of Ophthalmology and Neurosurgery, University of California, San Francisco, CA 94143, USA.
Mol Vis. 2010 Dec 14;16:2701-17.
Wnt2b is normally expressed at the optic cup lip and is implicated in ciliary body induction. The lens has often been considered an organizer for the anterior eye, but recent studies demonstrate that the anterior cell fates are correctly specified in the absence of the lens. This study uses Wnt2b as a marker to reveal the mechanism behind the specification of the anterior domain of the optic cup.
Developing chick embryos were used as a model system. Eyes were microsurgically manipulated to assess the role of the lens in the development of the anterior optic cup. Eyes were molecularly manipulated, using fibroblast growth factor expressing replication-incompetent retrovirus, introduced into the retinal pigmented epithelium (RPE) domain. Ectopic fibroblast growth factor transformed the RPE into nonpigmented epithelium (NPE; ciliary body). As the virus does not spread, discrete borders between RPE and NPE were experimentally created. Wnt2b expression was assessed after surgical and molecular manipulation.
Contrary to expectations, we found that the lens is not able to induce Wnt2b expression in optic cup tissue: When the optic cup lip is experimentally misspecified such that it no longer contains the juxtaposition of pigmented and nonpigmented tissue, Wnt2b is not expressed. In addition, if the prelens ectoderm is removed from the optic vesicle before morphogenesis, the resulting lensless optic cup expresses Wnt2b even though it was not in contact with lens tissue. We also show that ectopic lenses do not induce Wnt2b in optic cup tissue. The ciliary body/anterior eye domain is specified at the border of RPE and the NPE of the ciliary body. During development, this border is normally found at the optic cup lip. We can manipulate tissue specification using retroviral-mediated gene transfer, and create ectopic borders between nonpigmented and pigmented tissue. At such borders, Wnt2b is ectopically expressed in the absence of lens contact. Finally, we describe a role for the lens in maintenance of Wnt2b expression and demonstrate support for this in two ways: First, we show that if the lens is removed from the formed optic cup, endogenous Wnt2b expression is specifically lost from the optic cup lip; and second, we show that while ectopic Wnt2b expression is initially found in the majority of ectopic borders, as eye development proceeds ectopic expression is maintained only in those borders that are close to the lens.
Taken together, the results provide support for a model in which the anterior optic cup domain, as described in part by Wnt2b expression, is specified through the elaboration of a border within the optic neuroepithelium rather than through interactions with the surrounding environment.
Wnt2b通常在视杯边缘表达，并与睫状体诱导有关。晶状体常被认为是眼前部的组织者，但最近的研究表明，在没有晶状体的情况下，前部细胞命运也能正确指定。本研究使用Wnt2b作为标记物，以揭示视杯前部区域指定背后的机制。
以发育中的鸡胚作为模型系统。通过显微手术对视进行操作，以评估晶状体在眼前部视杯发育中的作用。利用表达成纤维细胞生长因子的复制缺陷型逆转录病毒对视进行分子操作，并将其引入视网膜色素上皮（RPE）区域。异位的成纤维细胞生长因子将RPE转化为无色素上皮（NPE；睫状体）。由于病毒不会扩散，因此通过实验创建了RPE和NPE之间的离散边界。在手术和分子操作后评估Wnt2b的表达。
与预期相反，我们发现晶状体无法诱导视杯组织中Wnt2b的表达：当通过实验错误指定视杯边缘，使其不再包含色素组织和无色素组织的并置时，Wnt2b不表达。此外，如果在形态发生之前从视泡中移除晶状体前外胚层，即使所得的无晶状体视杯未与晶状体组织接触，它也会表达Wnt2b。我们还表明，异位晶状体不会在视杯组织中诱导Wnt2b表达。睫状体/眼前部区域在睫状体的RPE和NPE的边界处指定。在发育过程中，这个边界通常位于视杯边缘。我们可以使用逆转录病毒介导的基因转移来操纵组织指定，并在无色素和色素组织之间创建异位边界。在这样的边界处，在没有晶状体接触的情况下，Wnt2b会异位表达。最后，我们描述了晶状体在维持Wnt2b表达中的作用，并通过两种方式证明了这一点：第一，我们表明，如果从形成的视杯中移除晶状体，视杯边缘会特异性地丧失内源性Wnt2b表达；第二，我们表明，虽然异位Wnt2b表达最初在大多数异位边界中发现，但随着眼睛发育的进行，异位表达仅在那些靠近晶状体的边界中维持。
综上所述，这些结果支持了一个模型，即如部分由Wnt2b表达所描述的眼前部视杯区域，是通过视神经上皮内边界的形成来指定的，而不是通过与周围环境的相互作用。
