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Discovery of tMAC: a Drosophila testis-specific meiotic arrest complex paralogous to Myb-Muv B.

ABSTRACT: The Drosophila Myb-Muv B (MMB)/dREAM complex regulates gene expression and DNA replication site-specifically, but its activities in vivo have not been thoroughly explored. In ovarian amplification-stage follicle cell nuclei, the largest subunit, Mip130, is a negative regulator of replication, whereas another subunit, Myb, is a positive regulator. Here, we identified a mutation in mip40 and generated a mutation in mip120, two additional MMB subunits. Both mutants were viable, but mip120 mutants had many complex phenotypes including shortened longevity and severe eye defects. mip40 mutant females had severely reduced fertility, whereas mip120 mutant females were sterile, substantiating ovarian regulatory role(s) for MMB. Myb accumulation and binding to polytene chromosomes was dependent on the core factors of the MMB complex. In contrast to the documented mip130 mutant phenotypes, both mip40 and mip120 mutant males were sterile. We purified Mip40-containing complexes from testis nuclear extracts and identified tMAC, a new testis-specific meiotic arrest complex that contained Mip40, Caf1/p55, the Mip130 family member, Always early (Aly), and a Mip120 family member, Tombola (Tomb). Together, these data demonstrate that MMB serves diverse roles in different developmental pathways, and members of MMB can be found in alternative, noninteracting complexes in different cell types.

SUBMITTER: Beall EL

PROVIDER: S-EPMC1847709 | biostudies-literature | 2007 Apr

REPOSITORIES: biostudies-literature

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Discovery of tMAC: a Drosophila testis-specific meiotic arrest complex paralogous to Myb-Muv B.

Beall Eileen L EL Lewis Peter W PW Bell Maren M Rocha Michael M Jones D Leanne DL Botchan Michael R MR

Genes & development 20070402 8

The Drosophila Myb-Muv B (MMB)/dREAM complex regulates gene expression and DNA replication site-specifically, but its activities in vivo have not been thoroughly explored. In ovarian amplification-stage follicle cell nuclei, the largest subunit, Mip130, is a negative regulator of replication, whereas another subunit, Myb, is a positive regulator. Here, we identified a mutation in mip40 and generated a mutation in mip120, two additional MMB subunits. Both mutants were viable, but mip120 mutants h ...[more]

PMID: 17403774

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Project description:In the mammalian testis, the pool of spermatogonia is amplified by mitosis before these progenitor germ cells undergo meiosis to generate the haploid cells that give rise to sperm. Extensive changes in the transcriptome accompany the onset of the pachytene stage of meiosis, including the transcriptional activation of meiotic genes, the pachytene piRNA pathway, as well as mRNAs required later during spermiogenesis. How transcription is regulated to ensure the precise timing of this major reprogramming of gene expression remains largely uncharacterized. Here, we report that the testis-specific transcription factor TCFL5 is initially activated by the transcription factor A-MYB during meiosis. Subsequently, A-MYB and TCFL5 mutually reinforce their own transcription establishing a central regulatory circuit that regulates meiosis and spermiogenesis, as well as mediates pachytene piRNA production. TCFL5 drives the transcription of 476 genes required for meiosis including genes encoding pachytene piRNA biogenesis proteins, and 796 genes required for spermiogenesis. Tcfl5−/− mutant mice are sterile and spermatogenesis arrests at the mid- or late-pachytene stage of meiosis. Intriguingly, Tcfl5 haploinsufficiency leads to reduced male fertility suggesting germ cells are sensitive to Tcfl5 dosage to develop. Compromised TCFL5 expression underlies the reduced fertility phenotype directly or indirectly through regulating other transcription factors in Tcfl5+/− mutant mice. TCFL5 drives the transcription of evolutionarily younger pachytene piRNAs, while A-MYB regulates older pachytene piRNAs. Older and younger piRNAs mutually initiate their own processing providing evidence how these selfish genetic elements hijack meiotic transcriptional network to amplify themselves. We also demonstrate that TCFL5-mediated regulation of male meiosis and piRNA production is conserved in macaque. Our data establish a direct role of TCFL5 in ensuring the simultaneous activation of genes required for meiosis and spermiogenesis in mammals.

Project description:BACKGROUND:Meiotic sex chromosome inactivation (MSCI) during spermatogenesis has been proposed as one of the evolutionary driving forces behind both the under-representation of male-biased genes on, and the gene movement out of, the X chromosome in Drosophila. However, the relevance of MSCI in shaping sex chromosome evolution is controversial. Here we examine two aspects of a recent study on testis gene expression (Mikhaylova and Nurminsky, BMC Biol 2011, 9:29) that failed to support the MSCI in Drosophila. First, Mikhaylova and Nurminsky found no differences between X-linked and autosomal genes based on the transcriptional profiling of the early testis development, and thus concluded that MSCI does not occur in D. melanogaster. Second, they also analyzed expression data from several D. melanogaster tissues and concluded that under-representation on the X chromosome is not an exclusive property of testis-biased genes, but instead, a general property of tissue-specific genes. RESULTS:By re-analyzing the Mikhaylova and Nurminsky's testis data and the expression data on several D. melanogaster tissues, we made two major findings that refuted their original claims. First, the developmental testis data has generally greater experimental error than conventional analyses, which reduced significantly the power to detect chromosomal differences in expression. Nevertheless, our re-analysis observed significantly lower expression of the X chromosome in the genomic transcriptomes of later development stages of the testis, which is consistent with the MSCI hypothesis. Second, tissue-specific genes are also in general enriched with genes more expressed in testes than in ovaries, that is testis-biased genes. By completely excluding from the analyses the testis-biased genes, which are known to be under-represented in the X, we found that all the other tissue-specific genes are randomly distributed between the X chromosome and the autosomes. CONCLUSIONS:Our findings negate the original study of Mikhaylova and Nurminsky, which concluded a lack of MSCI and generalized the pattern of paucity in the X chromosome for tissue-specific genes in Drosophila. Therefore, MSCI and other selection-based models such as sexual antagonism, dosage compensation, and meiotic-drive continue to be viable models as driving forces shaping the genomic distribution of male-related genes in Drosophila.

Project description:Generally, knowledge of the mechanism regulating gene expression in primary spermatocytes is incomplete. We have used the lactate dehydrogenase gene (Ldhc) as a model to explore these mechanisms during spermatogenesis. Its 100-bp core promoter contained two essential elements common to many genes, a GC box and a CRE site. Here we report results that support a model in which transcription factor MYBL1 acts as a coactivator directing tissue-specific expression via the CRE cis element. We hypothesize that this is a common mechanism involving activation of multiple genes in the primary spermatocyte. MYBL1 is expressed predominantly as a tissue-specific transcription factor in spermatocytes and breast epithelial cells. Our finding that LDHC expression is lost in 21-day testes of MYBL1 mutant mice supports our hypothesis. In the GC1-spg germ cell line exogenous MYBL1 induces activity 4- to 8-fold, although extracts from these cells do not show MYBL1 binding activity for the Myb consensus sequences in the Ldhc promoter by EMSA. Rather, MYBL1 stimulates expression from a synthetic promoter containing only CRE elements, suggesting MYBL1 activates the promoter by interacting with protein that binds to a CRE element. Mutation of three Myb sites does not affect Ldhc promoter activity significantly (P > 0.05). CREB-binding protein (CBP) is a coactivator that interacts with CRE-binding protein CREB. We show that the transactivation domain (TAD) in MYBL1 interacts with the KIX domain in CBP, and the TAD domain and DNA binding domain in MYBL1 each interact with the CREB N-terminal domain. MYBL1 also stimulated expression from testis-specific genes Pgk2 (phosphoglycerate kinase 2) and Pdha2 (pyruvate dehydrogenase alpha 2) promoters, each of which contains CRE promoter elements and is expressed in primary spermatocytes. We propose that MYBL1 directs germ cell-specific activation via the CRE site of certain genes that are activated specifically in the primary spermatocyte, although other, more indirect effects of MYBL1 remain a possible explanation for our results.

Dataset Information

Discovery of tMAC: a Drosophila testis-specific meiotic arrest complex paralogous to Myb-Muv B.

Publications

Discovery of tMAC: a Drosophila testis-specific meiotic arrest complex paralogous to Myb-Muv B.

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