 Recent evidence suggests that the functional role of piwi proteins in germ-line determination is due to their capacity to interact with miRNAs.Components of the miRNA pathway appear to be present in pole plasm and to play a key role in early development and morphogenesis of "Drosophila melanogaster" embryos, in which germ-line maintenance has been extensively studied.Recently, a novel class of longer-than-average miRNAs known as Piwi-interacting RNAs (piRNAs) has been defined in mammalian cells, about 26-31 nucleotides long as compared to the more typical miRNA or siRNA of about 21 nucleotides.