Roles of MIWI, MILI and PLD6 in small RNA regulation in mouse growing oocytes. Kabayama Y et al. (2017) The mouse PIWI-interacting RNA (piRNA) pathway produces a class of 26-30-nucleotide (nt) small RNAs and is essential for spermatogenesis and retrotransposon repression. In oocytes, however, its regulation and function are poorly understood. In the present study, we investigated the consequences of loss of piRNA-pathway components in growing oocytes. When MILI (or PIWIL2), a PIWI family member, was depleted by gene knockout, almost all piRNAs disappeared. This severe loss of piRNA was accompanied by an increase in transcripts derived from specific retrotransposons, especially IAPs. MIWI (or PIWIL1) depletion had a smaller effect. In oocytes lacking PLD6 (or ZUCCHINI or MITOPLD), a mitochondrial nuclease/phospholipase involved in piRNA biogenesis in male germ cells, the piRNA level was decreased to 50% compared to wild-type, a phenotype much milder than that in males. Since PLD6 is essential for the creation of the 5' ends of primary piRNAs in males, the presence of mature piRNA in PLD6-depleted oocytes suggests the presence of compensating enzymes. Furthermore, we identified novel 21-23-nt small RNAs, termed spiRNAs, possessing a 10-nt complementarity with piRNAs, which were produced dependent on MILI and independent of DICER. Our study revealed the differences in the biogenesis and function of the piRNA pathway between sexes.//////////////////
NCBI Summary:
PIWIL2 belongs to the Argonaute family of proteins, which function in development and maintenance of germline stem cells (Sasaki et al., 2003 [PubMed 12906857]).[supplied by OMIM, Mar 2008]
General function
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Cellular localization
Nuclear
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Ovarian function
Germ cell development, Early embryo development
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Piwi Proteins and piRNAs in Mammalian Oocytes and Early Embryos. Roovers EF et al. (2015) Germ cells of most animals critically depend on piRNAs and Piwi proteins. Surprisingly, piRNAs in mouse oocytes are relatively rare and dispensable. We present compelling evidence for strong Piwi and piRNA expression in oocytes of other mammals. Human fetal oocytes express PIWIL2 and transposon-enriched piRNAs. Oocytes in adult human ovary express PIWIL1 and PIWIL2, whereas those in bovine ovary only express PIWIL1. In human, macaque, and bovine ovaries, we find piRNAs that resemble testis-borne pachytene piRNAs. Isolated bovine follicular oocytes were shown to contain abundant, relatively short piRNAs that preferentially target transposable elements. Using label-free quantitative proteome analysis, we show that these maturing oocytes strongly and specifically express the PIWIL3 protein, alongside other, known piRNA-pathway components. A piRNA pool is still present in early bovine embryos, revealing a potential impact of piRNAs on mammalian embryogenesis. Our results reveal that there are highly dynamic piRNA pathways in mammalian oocytes and early embryos.//////////////////
Expression regulated by
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Ovarian localization
Primordial Germ Cell, Oocyte
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Piwi Proteins and piRNAs in Mammalian Oocytes and Early Embryos. Roovers EF et al. (2015) Germ cells of most animals critically depend on piRNAs and Piwi proteins. Surprisingly, piRNAs in mouse oocytes are relatively rare and dispensable. We present compelling evidence for strong Piwi and piRNA expression in oocytes of other mammals. Human fetal oocytes express PIWIL2 and transposon-enriched piRNAs. Oocytes in adult human ovary express PIWIL1 and PIWIL2, whereas those in bovine ovary only express PIWIL1. In human, macaque, and bovine ovaries, we find piRNAs that resemble testis-borne pachytene piRNAs. Isolated bovine follicular oocytes were shown to contain abundant, relatively short piRNAs that preferentially target transposable elements. Using label-free quantitative proteome analysis, we show that these maturing oocytes strongly and specifically express the PIWIL3 protein, alongside other, known piRNA-pathway components. A piRNA pool is still present in early bovine embryos, revealing a potential impact of piRNAs on mammalian embryogenesis. Our results reveal that there are highly dynamic piRNA pathways in mammalian oocytes and early embryos.//////////////////
Global gene expression analysis in fetal mouse ovaries with and without meiosis and comparison of selected genes with meiosis in the testis. Olesen C et al. In order to identify novel genes involved in early meiosis and early ovarian development in the mouse, we used microarray technology to compare transcriptional activity in ovaries without meiotic germ cells at embryonic age 11.5 (E11.5) and E13.5 ovaries with meiosis. Overall, 182 genes were differentially expressed; 134 were known genes and 48 were functionally uncharacterized. A comparison of our data with the literature associated, for the first time, at least eight of the known genes with female meiosis/germ cell differentiation (Aldh1a1, C2pa, Tex12, Stk31, Lig3, Id4, Recql, Piwil2). These genes had previously only been described in spermatogenesis. The microarray also detected an abundance of vesicle-related genes of which four were upregulated (Syngr2, Stxbp1, Ric-8, SytIX) and one (Myo1c) was downregulated in E13.5 ovaries. Detailed analysis showed that the temporal expression of SytIX also coincided with the first meiotic wave in the pubertal testis. This is the first time that SytIX has been reported in non-neuronal tissue. Finally, we examined the expression of one of the uncharacterized genes and found it to be gonad-specific in adulthood. We named this novel transcript 'Gonad-expressed transcript 1' (Get-1). In situ hybridization showed that Get-1 was expressed in meiotic germ cells in both fetal ovaries and mature testis. Get-1 is therefore a novel gene in both male and female meiosis.
Follicle stages
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Altered Expression of Porcine Piwi Genes and piRNA during Development. Kowalczykiewicz D et al. Three Sus scrofa Piwi genes (Piwil1, Piwil2 and Piwil4) encoding proteins of 861, 985 and 853 aminoacids, respectively, were cloned and sequenced. Alignment of the Piwi proteins showed the high identity between Sus scrofa and Homo sapiens. Relative transcript abundance of porcine Piwil1, Piwil2 and Piwil4 genes in testes, ovaries and oocytes derived from sexually immature and mature animals was examined using Real-Time PCR. Expression of the three Piwi mRNAs was proved to be tissue specific and restricted exclusively to the gonads. In testes of adult pigs the highest relative transcript abundance was observed for the Sus scrofa Piwil1 gene. On the other hand, in testes of neonatal pigs the Piwil1 transcript level was over 2-fold reduced while the level of Piwil2 transcript was higher. As regards the expression of the Piwil4 transcript, its level was 34-fold elevated in testes of neonatal piglet when compared to adult male. In ovaries of prepubertal and pubertal female pigs transcript abundance of the three Piwi genes was significantly reduced in comparison with testes. However, similarly to testes, in ovaries of neonatal pigs the Piwil2 gene was characterized by the highest relative transcript abundance among the three Piwi genes analysed. In prepubertal and pubertal oocytes Piwil1 transcript was the most abundant whereas the expression of Piwil4 was undetectable. We also demonstrated that expression of piRNA occurs preferentially in the gonads of adult male and female pigs. Moreover, a piRNA subset isolated from ovaries was 2-3 nucleotides longer than the piRNA from testes.