Seville Rachel A, Nijjar Sarbjit, Barnett Mark W, Massé Karine, Jones Elizabeth A
Cell and Molecular Development Group, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
Development. 2002 Apr;129(7):1693-704. doi: 10.1242/dev.129.7.1693.
Vertebrate kidney organogenesis is characterised by the successive formation of the pronephros, the mesonephros and the metanephros. The pronephros is the first to form and is the functional embryonic kidney of lower vertebrates; although it is vestigial in higher vertebrates, it is a necessary precursor for the other kidney types. The Xenopus pronephros is a simple paired organ; each nephron consists of a single large glomus, one set of tubules and a single duct. The simple organisation of the pronephros and the amenability of Xenopus laevis embryos to manipulation make the Xenopus pronephros an attractive system in which to study organogenesis. It has been shown that pronephric tubules can be induced to form in presumptive ectodermal tissue by treatment with RA and activin. We have used this system in a subtractive hybridisation screen that resulted in the cloning of Xenopus laevis annexin IV (Xanx-4). Xanx-4 transcripts are specifically located to the developing pronephric tubules, and the protein to the luminal surface of these tubules. Temporal expression shows zygotic transcription is upregulated at the time of pronephric tubule specification and persists throughout pronephric development. The temporal and spatial expression pattern of Xanx-4 suggests it may have a role in pronephric tubule development. Overexpression of Xanx-4 yields no apparent phenotype, but Xanx-4 depletion, using morpholinos, produces a shortened, enlarged tubule phenotype. The phenotype observed can be rescued by co-injection of Xanx-4 mRNA. Although the function of annexins is not yet clear, studies have suggested a role for annexins in a number of cellular processes. Annexin IV has been shown to have an inhibitory role in the regulation of epithelial calcium-activated chloride ion conductance. The enlarged pronephric tubule phenotype observed may be attributed to incorrect modulation of exocytosis, membrane plasticity or ion channels and/or water homeostasis. In this study, we demonstrate an in vivo role for annexin IV in the development of the pronephric tubules in Xenopus laevis.
脊椎动物肾脏器官发生的特点是依次形成前肾、中肾和后肾。前肾是最早形成的，是低等脊椎动物的功能性胚胎肾脏；尽管它在高等脊椎动物中是退化的，但它是其他肾脏类型的必要前体。非洲爪蟾的前肾是一个简单的成对器官；每个肾单位由一个大的肾小球、一组肾小管和一条单一的导管组成。前肾的简单组织结构以及非洲爪蟾胚胎易于操作的特性，使得非洲爪蟾的前肾成为研究器官发生的一个有吸引力的系统。已经表明，通过用视黄酸（RA）和激活素处理，可诱导前肾小管在假定的外胚层组织中形成。我们在一个消减杂交筛选中使用了这个系统，结果克隆出了非洲爪蟾膜联蛋白IV（Xanx -4）。Xanx -4转录本特异性地定位于发育中的前肾小管，而该蛋白定位于这些肾小管的管腔表面。时间表达显示，合子转录在肾小管特化时上调，并在前肾发育过程中持续存在。Xanx -4的时间和空间表达模式表明它可能在前肾小管发育中起作用。Xanx -4的过表达没有产生明显的表型，但使用吗啉代寡核苷酸耗尽Xanx -4会产生肾小管缩短、增大的表型。通过共注射Xanx -4 mRNA可以挽救观察到的表型。尽管膜联蛋白的功能尚不清楚，但研究表明膜联蛋白在许多细胞过程中起作用。膜联蛋白IV已被证明在调节上皮钙激活氯离子电导中具有抑制作用。观察到的增大的前肾小管表型可能归因于胞吐作用、膜可塑性或离子通道和/或水稳态的调节不正确。在本研究中，我们证明了膜联蛋白IV在非洲爪蟾前肾小管发育中的体内作用。
