Regulation of meiosis, piRNA biogenesis, DNA recombination, chromosome segregation, DNA double-strand break repair, chromosome synapsis, male infertility in humans.
Key words: meiosis, piRNA, homologous recombination, synaptonemal complex, synapsis, spermiogenesis, and male infertility
Description of Research
Our group focuses on the study of meiosis in mice and humans. Meiosis, a cell division unique to germ cells, allows the reciprocal exchange of genetic material between paternal and maternal genomes. Meiosis generates the genetic diversity necessary for evolution of species. Abnormality in meiosis is a leading cause of birth defects and infertility. Our research interests include molecular genetics of chromosomal synapsis, DNA double-strand break repair, homologous recombination, genetic causes of male infertility in humans, and piRNA biogenesis. Functional characterization of a number of new genes in our laboratory has uncovered novel regulatory mechanisms underlying key biological processes unique to germ cells. On one hand, our studies provide molecular insights into the development of germ cells in mice. On the other hand, these mouse studies have important implications for understanding the genetic causes of male infertility in humans and developing novel male contraceptives.
Biogenesis and function of piRNAs
Piwi-interacting RNAs are a diverse class of small non-coding RNAs implicated in the silencing of transposable elements and the safeguarding of genome integrity. In mammals, male germ cells express two genetically and developmentally distinct populations of piRNAs at the pre-pachytene and pachytene stages of meiosis, respectively. Pre-pachytene piRNAs are mostly derived from retrotransposons and required for their silencing. In contrast, pachytene piRNAs originate from ~3,000 genomic clusters and their biogenesis and function remain enigmatic. We previously reported that MOV10L1 is required for biogenesis of pre-pachytene piRNAs. Recently we have demonstrated that conditional inactivation of the putative RNA helicase MOV10L1 in mouse spermatocytes produces a specific loss of pachytene piRNAs, significant accumulation of pachytene piRNA precursor transcripts, and unusual polar conglomeration of Piwi proteins with mitochondria. Pachytene piRNA-deficient spermatocytes progress through meiosis without derepression of LINE1 retrotransposons, but become arrested at the post-meiotic round spermatid stage with massive DNA damage. Our results demonstrate that MOV10L1 acts upstream of Piwi proteins in the primary processing of pachytene piRNAs and suggest that, distinct from pre-pachytene piRNAs, pachytene piRNAs fulfill a unique function in maintaining post-meiotic genome integrity. Our studies have demonstrated that MOV10L1 is, to date, the only master regulator of the piRNA pathway in mammals.
The X chromosome and Male Infertility
We have identified TEX11 as the first X chromosome-encoded meiosis-specific factor in mammals. In principle, meiosis-specific genes could be located anywhere in the genome. However, no mouse sex chromosome-linked mutants with meiosis-specific defects had been reported, leading to the perception that meiosis-specific factors are rarely if ever encoded by the sex chromosomes. We were the first to clone Tex11, an X-linked germ cell-specific gene. In a recent study, by ablating the function of Tex11 in mice, we have demonstrated that Tex11 is essential for meiosis and fertility in males. Our findings have important implications for male infertility in humans, which accounts for about half of the cases of infertility among couples. An estimated 15% of couples are affected by infertility worldwide. Given that disruption of Tex11 causes azoospermia in mice, we surmise that mutations in the human TEX11 gene could be found in infertile men.
Regulation of Homologous Recombination
During meiosis, homologous chromosomes undergo synapsis and recombination. The arrangement of homologous chromosomes is tightly regulated by the synaptonemal complex (SC). SYCP2 is an integral component of SCs in mammals. Our genetic and cell biological studies demonstrate that SYCP2 is required for the formation of SCs and chromosomal synapsis. We also find that TEX11 interacts with SYCP2 and is a novel constituent of meiotic nodules involved in recombination. TEX11 promotes both synapsis and recombination, and thus may provide a physical link between these two fundamental meiotic processes. Additionally, we identify TEX15 as a novel meiosis-specific factor that functions earlier than TEX11 during meiotic recombination. In parallel with BRCA1 and BRCA2, TEX15 plays an essential role in the DNA repair pathway that regulates the loading of DNA repair proteins (RAD51/DMC1) onto sites of double strand breaks. We plan to further elucidate the role of these meiosis-specific factors in the regulation of homologous recombination.
Qi Fu, graduate student
Seth Kasowitz, postdoctoral fellow
Adrian Leu, research specialist
Mengcheng Luo, postdoctoral fellow
Fang Yang, research specialist
Jian Zhou, postdoctoral fellow
Luo M, Yang F, Leu NA, Landaiche J, Handel MA, Benavente R, La Salle S, Wang PJ. MEIOB exhibits single-stranded DNA-binding and exonuclease activities and is essential for meiotic recombination. Nature Communications 18: 2788, 2013.Zhou J, McCarrey JR, Wang PJ. A 1.1-Mb segmental deletion on the X chromosome causes meiotic failure in male mice Biol Reprod 88: 159, 2013.Zheng K & Wang PJ Blockade of pachytene piRNA biogenesis reveals a novel requirement for maintaining post-meiotic germline genome integrity PLoS Genetics 8: e1003038, 2012.Yang F, Wei Q, Adelstein RS, Wang PJ. Non-muscle myosin IIB is essential for cytokinesis during male meiotic cell divisions Dev Biol 369: 356-361, 2012.Jian Zhou, Fang Yang, N. Adrian Leu, P. Jeremy Wang MNS1 is essential for spermiogenesis and motile ciliary functions in mice PLoS Genetics 8: e1002516, 2012.Yang F, Cheng Y, An JY, Kwon YT, Eckardt S, Leu NA, McLaughlin KJ, Wang PJ. The ubiquitin ligase Ubr2, a recognition E3 component of the N-End rule pathway, stabilizes Tex19.1 during spermatogenesis. PLoS One 5: e14017, 2010.Zheng K, Xiol J, Reuter M, Eckardt S, Leu NA, McLaughlin KJ, Stark A, Sachidanandam R, Pillai RS, and Wang PJ. Mouse MOV10L1 associates with Piwi proteins and is an essential component of the Piwi-interacting RNA (piRNA) pathway. PNAS 107: 11841-11846, 2010.Pan J, Eckardt S, Leu NA, Buffone MG, Zhou J, Gerton GL, McLaughlin KJ, Wang PJ. Inactivation of Nxf2 causes defects in male meiosis and age-dependent depletion of spermatogonia. Dev Biol 330: 167-174, 2009.Yang F., Gell K., van der Heijden G.W., Eckardt S., Leu N.A., Page D.C., Benavente R., Her C., Höög C., McLaughlin K.J., Wang P.J. Meiotic failure in male mice lacking an X-linked factor Genes & Development 22: 682-691, 2008.Yang F, Eckardt S, Leu NA, McLaughlin KJ, Wang PJ. Mouse TEX15 is essential for DNA double-strand break repair and chromosomal synapsis during male meiosis. J. Cell Biol. 180: 673-679, 2008.