Piwi proteins and piRNAs in mammalian oocytes and early embryos: From sample to sequence.

The role of the Piwi/piRNA pathway during mammalian oogenesis has remained enigmatic thus far, especially since experiments with Piwi knockout mice did not reveal any phenotypic defects in female individuals. This is in striking contrast with results obtained from other species including flies and zebrafish. In mouse oocytes, however, only low levels of piRNAs are found and they are not required for their function. We recently demonstrated dynamic expression of PIWIL1, PIWIL2, and PIWIL3 during mammalian oogenesis and early embryogenesis. In addition, small RNA analysis of human, crab-eating macaque and cattle revealed that piRNAs are also expressed in the female germline and closely resemble piRNAs from testis. Here, we thoroughly describe the experimental and computational methods that we applied for the generation, processing and analyses of next generation sequencing (NGS) data associated with our study on Piwi proteins and piRNAs in mammalian oocytes and embryos (Roovers et al., 2015). The complete sequence data is available at NCBI's Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo/) under the accession GSE64942.