MIWI2 Is Essential for Spermatogenesis and Repression of Transposons in the Mouse Male Germline

Cold Spring Harbor Laboratory, Howard Hughes Medical Institute, Watson School of Biological Sciences, 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA.
Developmental Cell (Impact Factor: 9.71). 04/2007; 12(4):503-14. DOI: 10.1016/j.devcel.2007.03.001
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Small RNAs associate with Argonaute proteins and serve as sequence-specific guides for regulation of mRNA stability, productive translation, chromatin organization, and genome structure. In animals, the Argonaute superfamily segregates into two clades. The Argonaute clade acts in RNAi and in microRNA-mediated gene regulation in partnership with 21-22 nt RNAs. The Piwi clade, and their 26-30 nt piRNA partners, have yet to be assigned definitive functions. In mice, two Piwi-family members have been demonstrated to have essential roles in spermatogenesis. Here, we examine the effects of disrupting the gene encoding the third family member, MIWI2. Miwi2-deficient mice display a meiotic-progression defect in early prophase of meiosis I and a marked and progressive loss of germ cells with age. These phenotypes may be linked to an inappropriate activation of transposable elements detected in Miwi2 mutants. Our observations suggest a conserved function for Piwi-clade proteins in the control of transposons in the germline.

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Available from: Henk van de Kant, Aug 14, 2014
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    • "The piRNAs are associated with members of the PIWI subfamily of Argonaute proteins; in the mouse there are three PIWI-like proteins: MIWI/ PIWIL1, MILI/PIWIL2 and MIWI2/PIWIL4. MIWI2 and MILI are involved in male meiotic progression and deletion of their genes leads to male sterility (Carmell et al., 2007; Kuramochi-Miyagawa et al., 2004). In addition, piRNAs are also involved in TE silencing at the transcriptional level by the DNA methylation in mammalian germ cells (Bourc'his and Bestor, 2004 and ref in: Castel and Martienssen (2013)). "
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    DESCRIPTION: Topaz1 (Testis and Ovary-specific PAZ domain gene 1) is a germ cell specific gene highly conserved in vertebrates. The putative protein TOPAZ1 contains a PAZ domain, specifically found in PIWI, Argonaute and Zwille proteins. Consequently, Topaz1 is supposed to have a role during gametogenesis and may be involved in the piRNA pathway and contribute to silencing of transposable elements and maintenance of genome integrity. Here we report Topaz1 inactivation in mouse. Female fertility was not affected, but male sterility appeared exclusively in homozygous mutants in accordance with the high expression of Topaz1 in male germ cells. Pachytene Topaz1 – deficient spermatocytes progress through meiosis without either derepression of retrotransposons or MSCI dysfunction, but become arrested before the post-meiotic round spermatid stage with extensive apoptosis. Consequently, an absence of spermatids and spermatozoa was observed in Topaz1−/− testis. Histological analysis also revealed that disturbances of spermatogenesis take place between post natal days 15 and 20, during the first wave of male meiosis and before the generation of haploid germ cells. Transcriptomic analysis at these two stages showed that TOPAZ1 influences the expression of one hundred transcripts, most of which are up-regulated in mutant testis at post natal day 20. Our results also showed that 10% of these transcripts are long non-coding RNA. This suggests that a highly regulated balance of lncRNAs seems to be essential during spermatogenesis for induction of appropriate male gamete production.
    • "The first type helps to maintain genome integrity, whereas the role of the second type is being debated (Weick & Miska, 2014). Three different mouse PIWI proteins participate in piRNA biogenesis and function in developing sperm; all three are essential for normal spermatogenesis but nonessential for oogenesis (Carmell et al., 2007; 16 Petr Svoboda et al. "
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    ABSTRACT: In mouse, the oocyte-to-embryo transition entails converting a highly differentiated oocyte to totipotent blastomeres. This transition is driven by degradation of maternal mRNAs, which results in loss of oocyte identity, and reprogramming of gene expression during the course of zygotic gene activation, which occurs primarily during the two-cell stage and confers blastomere totipotency. Full-grown oocytes are transcriptionally quiescent and mRNAs are remarkably stable in oocytes due to the RNA-binding protein MSY2, which stabilizes mRNAs, and low activity of the 5' and 3' RNA degradation machinery. Oocyte maturation initiates a transition from mRNA stability to instability due to phosphorylation of MSY2, which makes mRNAs more susceptible to the RNA degradation machinery, and recruitment of dormant maternal mRNAs that encode for critical components of the 5' and 3' RNA degradation machinery. Small RNAs (miRNA, siRNA, and piRNA) play little, if any, role in mRNA degradation that occurs during maturation. Many mRNAs are totally degraded but a substantial fraction is only partially degraded, their degradation completed by the end of the two-cell stage. Genome activation initiates during the one-cell stage, is promiscuous, low level, and genome wide (and includes both inter- and intragenic regions) and produces transcripts that are inefficiently spliced and polyadenylated. The major wave of genome activation in two-cell embryos involves expression of thousands of new genes. This unique pattern of gene expression is the product of maternal mRNAs recruited during maturation that encode for transcription factors and chromatin remodelers, as well as dramatic changes in chromatin structure due to incorporation of histone variants and modified histones.
    Current Topics in Developmental Biology 09/2015; 113:305-49. DOI:10.1016/bs.ctdb.2015.06.004 · 4.68 Impact Factor
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    • "It was long thought that in animals a deep and permament distinction was established early on in embryogenesis between germ line and somatic cell populations (Weismann, 1893). This view was initially supported by findings from model organisms such as fruit flies, C. elegans, zebrafish and mouse in which the germ line is segregated during early embryogenesis and in which deletion of germ line (or its precursors) leads to sterility (Carmell et al., 2007; Cox et al., 2000, 1998; Houwing et al., 2007; Sulston et al., 1983). However, as a wider diversity of organisms have been investigated, it has become clear that germ line development is much more variable than work on these models initially suggested (Extavour and Akam, 2003; Juliano et al., 2010). "
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    ABSTRACT: Animals that can reproduce by both asexual agametic reproduction and sexual reproduction must transmit or re-establish their germ line post-embryonically. Although such a dual reproductive mode has evolved repeatedly among animals, how asexually produced individuals establish their germ line remains poorly understood in most groups. We investigated germ line development in the annelid Pristina leidyi, a species that typically reproduces asexually by paratomic fission, intercalating a new tail and head in the middle of the body followed by splitting. We found that in fissioning individuals, gonads occur in anterior segments in the anterior-most individual as well as in new heads forming within fission zones. Homologs of the germ line/multipotency genes piwi, vasa, and nanos are expressed in the gonads, as well as in proliferative tissues including the posterior growth zone, fission zone, and regeneration blastema. In fissioning animals, certain cells on the ventral nerve cord express a homolog of piwi, are abundant near fission zones, and sometimes make contact with gonads. Such cells are typically undetectable near the blastema and posterior growth zone. Time-lapse imaging provides direct evidence that cells on the ventral nerve cord migrate preferentially towards fission zones. Our findings indicate that gonads form routinely in fissioning individuals, that a population of piwi-positive cells on the ventral nerve cord is associated with fission and gonads, and that cells resembling these piwi-positive cells migrate along the ventral nerve cord. We suggest that the piwi-positive ventral cells are germ cells that transmit the germ line across asexually produced individuals via migration along the ventral nerve cord. Copyright © 2015. Published by Elsevier Inc.
    Developmental Biology 06/2015; 405(1). DOI:10.1016/j.ydbio.2015.06.001 · 3.55 Impact Factor
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