Probable ATP-dependent RNA helicase required during spermatogenesis (PubMed:14706067, PubMed:9338598). Required to repress transposable elements and preventing their mobilization, which is essential for the germline integrity. Acts via the piRNA metabolic process, which mediates the repression of transposable elements during meiosis by forming complexes composed of piRNAs and Piwi proteins and governs the methylation and subsequent repression of transposons. Involved in the secondary piRNAs metabolic process, the production of piRNAs in fetal male germ cells through a ping-pong amplification cycle (By similarity). ATP + H2O = ADP + H(+) + phosphate Localizes to the cytoplasm of somatic cells, primordial germ cells (PGCs) and most adult germline cells, except spermatogonia where it is located in the nucleus (PubMed:8150200). Component of the meiotic nuage, also named P granule, a germ-cell-specific organelle required to repress transposon activity during meiosis (By similarity). An mRNA and protein component of germ plasm and primordial germ cells (PGCs). Doesn't appear to localize to the mitochondrial cloud of early oocytes. In contrast to its germ plasm localization, shows weak expression in the animal hemispheres of stage 1-5 embryos. Expressed in spermatogonia, spermatocytes and, to a lower extent, spermatids of the adult testis but not adult sperm. Expressed in oogonia and oocytes of the adult ovary. Somatically expressed in animal cells at the cleavage stages and in ecto- and mesodermal cells from the gastrula stage onwards. Prominent in cells of the entochord and somites from the neurula to the tail-bud stage, and in cells of somites and spinal cord at subsequent stages until stage 46. Expressed both maternally and zygotically. Expressed from stage I to stage III oocytes, with levels decreasing throughout oocyte growth. Expression levels then increase from unfertilized eggs through oocyte maturation. Belongs to the DEAD box helicase family. DDX4/VASA subfamily.