Zebrafish germline small RNAs

Piwi proteins specify an animal-specific subclass of the Argonaute family, that in vertebrates are specifically expressed in germ cells. We demonstrate that zebrafish Piwi (Ziwi) is expressed in both the male and the female gonad, and is a component of a germline specifying structure, called nuage. Loss of Ziwi function results in a progressive loss of germ cells due to apoptosis during larval development. In animals that have only reduced Ziwi function, germ cells are maintained, but display abnormal levels of apoptosis in adults. In mammals, Piwi proteins have been found to associate with approximately 29-nucleotide long, testis specific RNA molecules, called piRNAs. Here we show that zebrafish piRNAs are present in both ovaries and testes. Furthermore, we show that piRNAs are modified at their 3’ end and that they are produced by a Dicer independent mechanism. Many ovarian piRNAs are derived from transposons, implicating a role for these molecules in the silencing of these repetitive elements in vertebrates. Keywords: high-throughput 454 sequencing sequencing of ~30 nt small RNAs from zebrafish ovaries and testes using 454 technology