They are expressed by all living organisms with the exception of certain unicellular organisms. Functional Implicationsĭirectory of Open Access Journals (Sweden)įull Text Available Annexins constitute an evolutionary conserved multigene protein superfamily characterized by their ability to interact with biological membranes in a calcium dependent manner. In this study, weĪnnexin-Phospholipid Interactions. The enlarged pronephric tubule phenotype observed may be attributed to incorrect modulation of exocytosis, membrane plasticity or ion channels and/or water homeostasis. Annexin IV has been shown to have an inhibitory role in the regulation of epithelial calcium-activated chloride ion conductance. Although the function of annexins is not yet clear, studies have suggested a role for annexins in a number of cellular processes. The phenotype observed can be rescued by co-injection of Xanx-4 mRNA. Overexpression of Xanx-4 yields no apparent phenotype, but Xanx-4 depletion, using morpholinos, produces a shortened, enlarged tubule phenotype. The temporal and spatial expression pattern of Xanx-4 suggests it may have a role in pronephric tubule development. Temporal expression shows zygotic transcription is upregulated at the time of pronephric tubule specification and persists throughout pronephric development. Xanx-4 transcripts are specifically located to the developing pronephric tubules, and the protein to the luminal surface of these tubules. We have used this system in a subtractive hybridisation screen that resulted in the cloning of Xenopus laevis annexin IV (Xanx-4). It has been shown that pronephric tubules can be induced to form in presumptive ectodermal tissue by treatment with RA and activin. 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. 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 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. Vertebrate kidney organogenesis is characterised by the successive formation of the pronephros, the mesonephros and the metanephros. Seville, Rachel A Nijjar, Sarbjit Barnett, Mark W Massé, Karine Jones, Elizabeth A Annexin IV (Xanx-4) has a functional role in the formation of pronephric tubules.
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