vasa gene

Vasa is an RNA binding protein with an ATP-dependent RNA helicase that is a member of the DEAD box family of proteins. The vasa gene, is essential for germ cell development and was first identified in Drosophila melanogaster, but has since been found to be conserved in a variety of vertebrates and invertebrates including humans. The Vasa protein is found primarily in germ cells in embryos and adults, where it is involved in germ cell determination and function, as well as in multipotent stem cells, where its exact function is unknown. Vasa is an RNA binding protein with an ATP-dependent RNA helicase that is a member of the DEAD box family of proteins. The vasa gene, is essential for germ cell development and was first identified in Drosophila melanogaster, but has since been found to be conserved in a variety of vertebrates and invertebrates including humans. The Vasa protein is found primarily in germ cells in embryos and adults, where it is involved in germ cell determination and function, as well as in multipotent stem cells, where its exact function is unknown. The Vasa gene is a member of the DEAD box family of RNA helicases in Drosophila melanogaster. Its human ortholog, Ddx4, is located on human chromosome 5q. It is syntenic to mouse chromosome 13, where the mouse vasa gene, is located. The gene is conserved in many invertebrates and vertebrate species such as C. elegans, Xenopus, Zebrafish, flatworms, echinderms, molluscs, nematodes, mice and rats as an important part of germ line maintenance and function. All vertebrate species, including Drosophila, have only one vasa ortholog but C. elegans has four Vasa genes, but only one (GLH-1) is essential. All DEAD box genes, including Vasa, have 9 conserved sequence motifs. The Vasa gene family evolved from a duplication event followed by acquiring certain domains. Early in the evolution of multicellular animals, the duplication of PL10 related DEAD-box gene occurred. This resulted in animals having both Vasa and PL10 genes, but plants and fungi only have PL10 genes and no Vasa. After the duplication event, the N-terminal region acquired Zn-knuckle domains which are now conserved in invertebrates. Vertebrates and insects both have lost the Zn-knuckle domains. The number of these domains vary between different species Vasa genes. An important property of Zn-knuckles, which can be categorized as classical zinc fingers, is that they are able to bind to single and double stranded DNA or RNA. The presence of Zn-knuckles in invertebrates and absence in vertebrates may be an indication of differences in target binding sites. Their presence may be important to functions outside germ line development. An exception to this theory is the presence of Zn-knuckles in all four C. elegans Vasa genes, which are restricted to functions in the germ line.  The protein product in humans has 724 amino acids, a molecular mass of 79 kDa and 8 conserved domains in all DEAD-box proteins that is involved in RNA helicase activity. Domain V contains the DEAD motif. As with other Vasa related proteins, human Vasa has a N terminus rich in glycine and RGG motif repeats that function in RNA binding. Vasa is regulated at the transcript and protein level. Developing embryos and adults regulate Vasa expression to cell and tissue specific locations. In Drosophila, zygotic transcription of Vasa occurs at pole cells, and stays germ-line specific throughout the life of the organism. The Vasa promoter is regulated through methylation. In cells were Vasa is transcribed successfully, the promoter is hypomethylated and in all other cells it is methylated. When Vasa is hypermethylated in testes, spermatogenesis defects may occur. Post-transcriptionally Vasa has several splice forms in different animals. In P. hawaiensis, Vasa transcript is uniformly distributed in the embryo and is localized depending on the stabilization of the 3’UTR (Untranslated Region to the germ line cells. Translation can be inhibited by cis regulatory elements in the transcript's 5' and 3' UTRs. They may inhibit translation by forming secondary RNA structures or binding trans-acting factors. Vasa expression localization is directed by repressing these translation inhibitory pathways.