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Zfrp8/PDCD2 is required in ovarian stem cells and interacts with the piRNA pathway machinery.

ABSTRACT: The maintenance of stem cells is central to generating diverse cell populations in many tissues throughout the life of an animal. Elucidating the mechanisms involved in how stem cells are formed and maintained is crucial to understanding both normal developmental processes and the growth of many cancers. Previously, we showed that Zfrp8/PDCD2 is essential for the maintenance of Drosophila hematopoietic stem cells. Here, we show that Zfrp8/PDCD2 is also required in both germline and follicle stem cells in the Drosophila ovary. Expression of human PDCD2 fully rescues the Zfrp8 phenotype, underlining the functional conservation of Zfrp8/PDCD2. The piRNA pathway is essential in early oogenesis, and we find that nuclear localization of Zfrp8 in germline stem cells and their offspring is regulated by some piRNA pathway genes. We also show that Zfrp8 forms a complex with the piRNA pathway protein Maelstrom and controls the accumulation of Maelstrom in the nuage. Furthermore, Zfrp8 regulates the activity of specific transposable elements also controlled by Maelstrom and Piwi. Our results suggest that Zfrp8/PDCD2 is not an integral member of the piRNA pathway, but has an overlapping function, possibly competing with Maelstrom and Piwi.

SUBMITTER: Minakhina S

PROVIDER: S-EPMC3879809 | biostudies-other | 2014 Jan

REPOSITORIES: biostudies-other

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Zfrp8/PDCD2 is required in ovarian stem cells and interacts with the piRNA pathway machinery.

Minakhina Svetlana S Changela Neha N Steward Ruth R

Development (Cambridge, England) 20140101 2

The maintenance of stem cells is central to generating diverse cell populations in many tissues throughout the life of an animal. Elucidating the mechanisms involved in how stem cells are formed and maintained is crucial to understanding both normal developmental processes and the growth of many cancers. Previously, we showed that Zfrp8/PDCD2 is essential for the maintenance of Drosophila hematopoietic stem cells. Here, we show that Zfrp8/PDCD2 is also required in both germline and follicle stem ...[more]

PMID: 24381196

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Project description:The importance of the Piwi-interacting RNA (piRNA) pathway for germ cell maintenance, genome integrity, DNA methylation and retrotransposon control raises possible roles of this pathway in cancer. Indeed aberrant expression of human PIWI orthologs and Maelstrom has been observed in various cancers. In this study we explored the expression and function of piRNA pathway genes in human ovarian cancer, based on our recent work, which showed widespread expression of piRNA pathway genes in the mammalian. Our work shows that PIWIL1 and MAEL expression is significantly increased in malignant EOC (n = 25) compared to benign tumor tissues (n = 19) and normal ovarian tissue (n = 8). The expression of PIWIL3 is lower in malignant and benign tissues when compared to normal ovary. Sequencing of PIWIL1 transcript revealed that in many tumors deletion of exon 17 leads to the introduction of a premature stop codon in the PIWI domain, likely due to a splicing error. In situ hybridization on tumor sections revealed that L1, PIWIL1, 2 and MAEL are specifically expressed in epithelial cells (cancerous cells) of EOC. Furthermore, PIWIL2 and MAEL are co-expressed in the stromal cells adjacent to tumor cells. Since PIWIL1 and MAEL are up regulated in malignant EOC and expressed in the epithelial cells, we investigated if these two genes affect invasiveness of ovarian cancer cell lines that do not normally express these genes. PIWIL1 and MAEL were transiently over expressed in the ovarian cancer cell line SKOV3, followed by real-time measurements of cell invasiveness. Surprisingly both PIWIL1 and MAEL over expression decreased the invasiveness of SKOV3 cells. Our findings support a growing body of evidence that shows that genes in this pathway are upregulated in cancer. In ovarian cancer we show for the first time that Piwil1 transcript may often be abnormal result in non functional product. In contrast to what has been observed in other cell types, we found that PIWIL1 and MAEL have a repressive effect on cell invasiveness.

Project description:Piwi proteins and their associated piRNAs are essential in the germline where they repress transposition, regulate translation, and guide epigenetic programming. Little is known, however, about the molecular mechanisms through which Piwi proteins and piRNAs mediate these processes. Here, we show that an evolutionarily conserved Tudor and KH-domain containing protein, Tdrkh (a.k.a. Tdrd2), partners with Miwi and Miwi2 in mice via symmetrically dimethylated arginine residues in Miwi and Miwi2. Tdrkh is localized to pi-bodies and piP-bodies and is required for nuclear localization of Miwi2. Genetic deletion of Tdrkh arrests meiosis at the zygotene stage, demethylates Line1 DNA, and up-regulates Line1 transposition, but does not promote apoptosis. Furthermore, Tdrkh mutants have severely reduced levels of mature piRNAs. Specifically, in Tdrkh mutants, piRNAs accumulate as a distinct population of 5’U-containing 31-37nt RNA that largely complements the missing mature piRNAs. These results demonstrate that the primary piRNA biogenesis pathway involves 3à5’ processing of the 31-37nt intermediates and that Tdrkh is required for this final step of piRNA biogenesis. However, Tdrkh is not required for the secondary piRNA biogenesis pathway (i.e., the ping pong cycle). These results shed light on mechanisms underlying primary piRNA biogenesis, an area in which information is conspicuously absent. Tdrkh-floxed mice were generated by the University of Connecticut Gene Targeting and Transgenic Facility. The targeting vector utilized C57Bl6 Tdrkh genome sequences from BAC clone RP23-263K17 (Chori BACPAC) and floxed exons 2-4 (the start codon is in exon 2) and was electroporated into D2 ES cells, a male hybrid C57Bl6/129SEV line. Clones that survived positive selection with G418 and negative selection with gancyclovir were expanded and screened by PCR with primers recognizing endogenous and exogenous (vector-derived) sequences. Positive clones were fused to CD-1 embryos, and germline transmission from resulting pups was confirmed by test crosses to CD-1 mice (which also confirmed that all gametes were derived from the targeted clones). Positive animals were bred to FLP mice to delete the neomycin-targeting cassette, resulting in Tdrkh cKO mice on a C57Bl6/129 background. cKO mice were bred with EIIa-Cre transgenic mice to excise the floxed exons 2-4 and generate Tdrkh +/- animals. Heterozygous animas were intercrossed to remove the EIIA transgene. Two independent knockout lines were generated from independent cKO founder lines and showed identical phenotypes in all experiments performed.

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Zfrp8/PDCD2 is required in ovarian stem cells and interacts with the piRNA pathway machinery.

Publications

Zfrp8/PDCD2 is required in ovarian stem cells and interacts with the piRNA pathway machinery.

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