Periodic Reporting for period 4 - Meiotic telomere (Study of telomere function in germ cells, relevant to the regulations of homologous recombination and telomere length maintenance across generations)
Reporting period: 2023-07-01 to 2023-12-31
In order to faithfully transmit their genetic information to their progeny, eukaryotic species possess a specialized form of cell division called meiosis. During meiosis, the chromosome number is accurately halved through a single round of DNA replication followed by two successive rounds of cell division, and the result is haploid germ cells. The characteristic events during meiosis are the pairing and recombination of homologous chromosomes in prophase I, which ensure the correct segregation of homologous chromosomes in the following cell divisions. For proper pairing and recombination of homologs, meiotic chromosomes must move within the nucleus and this chromosome movement is driven by telomeres.
In this project, I seek to reveal the molecular regulation of telomeres and homologous recombination in murine germ cells by screening for novel regulatory proteins. The misregulation of meiotic recombination is related to human infertility and azoospermia, thus understanding the molecular mechanisms of meiotic recombination is important from both a scientific and clinical perspective.
After conducting research throughout the entire grant period, we have elucidated the fundamental principle of telomere-driven chromosome movements, including the regulation of telomere structure and rigidity during the movements regulated by the TERB1 MYB domain and the regulation of nuclear membrane fluidity modified by the synthesis of very-long-chain polyunsaturated fatty acids (VLC-PUFAs) by the AdipoR2 and ELOVL2 functional axis. Our work highlights that not only changes in telomere-binding proteins but also alterations in lipid species within the nuclear envelope are pivotal for faithful meiotic pairing/recombination and male fertility. Following pairing ensured by telomere-driven chromosome movements, homologous chromosomes are physically linked by homologous recombination. We found that the well-known cancer suppressor protein BRCA2 forms a meiosis-specific ternary complex with MEILB2 (Meiotic localizer of BRCA2) and BRME1 (BRCA2 and MEILB2 associating protein 1). This ternary complex is indispensable for recruiting DNA break repair proteins, such as RAD51 and DMC1, to accomplish homologous recombination. Finally, we made an unexpected finding regarding spindle formation in male meiosis I, which requires the cytoplasmic dynein complex containing a testis-upregulated light chain paralog, DYNLRB2. We showed that DYNLRB2 ensures spindle bipolarity in meiosis I through two distinct pathways: 1) maintaining centriole engagement in metaphase I and 2) recruiting NuMA to the spindle pole.
Overall, our research has shed light on the fundamental molecular mechanisms underlying mammalian meiosis, from homolog pairing and recombination to spindle formation. We are confident that the basic knowledge acquired in this project will be useful for understanding the etiology of human infertility and will be utilized for clinical diagnosis or even treatment in the future.
In this project, I seek to reveal the molecular regulation of telomeres and homologous recombination in murine germ cells by screening for novel regulatory proteins. The misregulation of meiotic recombination is related to human infertility and azoospermia, thus understanding the molecular mechanisms of meiotic recombination is important from both a scientific and clinical perspective.
After conducting research throughout the entire grant period, we have elucidated the fundamental principle of telomere-driven chromosome movements, including the regulation of telomere structure and rigidity during the movements regulated by the TERB1 MYB domain and the regulation of nuclear membrane fluidity modified by the synthesis of very-long-chain polyunsaturated fatty acids (VLC-PUFAs) by the AdipoR2 and ELOVL2 functional axis. Our work highlights that not only changes in telomere-binding proteins but also alterations in lipid species within the nuclear envelope are pivotal for faithful meiotic pairing/recombination and male fertility. Following pairing ensured by telomere-driven chromosome movements, homologous chromosomes are physically linked by homologous recombination. We found that the well-known cancer suppressor protein BRCA2 forms a meiosis-specific ternary complex with MEILB2 (Meiotic localizer of BRCA2) and BRME1 (BRCA2 and MEILB2 associating protein 1). This ternary complex is indispensable for recruiting DNA break repair proteins, such as RAD51 and DMC1, to accomplish homologous recombination. Finally, we made an unexpected finding regarding spindle formation in male meiosis I, which requires the cytoplasmic dynein complex containing a testis-upregulated light chain paralog, DYNLRB2. We showed that DYNLRB2 ensures spindle bipolarity in meiosis I through two distinct pathways: 1) maintaining centriole engagement in metaphase I and 2) recruiting NuMA to the spindle pole.
Overall, our research has shed light on the fundamental molecular mechanisms underlying mammalian meiosis, from homolog pairing and recombination to spindle formation. We are confident that the basic knowledge acquired in this project will be useful for understanding the etiology of human infertility and will be utilized for clinical diagnosis or even treatment in the future.
1, We have identified novel recombination regulators MEILB2 and BRME1 in mice. We found that BRME1-MEILB2 forms complex with the cancer suppressor BRCA2 and functions as a localizer of BRCA2 to meiotic DNA-break sites. Further by making knockout mice, we have established the essential role of the BRME1-MEILB2-BRCA2 ternary complex in the regulation of meiotic recombination. These works were published in Nature Communications (2020) and Nature Structural Molecular Biology (2021).
2, We have found that the MYB-like DNA-binding (MYB) domain of meiotic telomere protein TERB1 has a role in the suppression of telomere erosion during meiotic telomere movements. Without the TERB1 MYB domain, meiotic telomeres are fused, bridged, or ultimately eroded during meiotic prophase I. Our findings suggest that the TERB1 MYB domain might be required for the maintenance of telomeric DNA and, thus, genomic integrity in the long evolutionary period. This work is published in Cell Reports (2022)
3, We have identified that spindle formation in male meiosis I requires the cytoplasmic dynein complex containing a testis-upregulated light chain paralog, DYNLRB2. We showed that DYNLRB2 ensures spindle bipolarity in meiosis I through two distinct pathways: 1) maintaining centriole engagement in metaphase I and 2) recruiting NuMA to the spindle pole. This work is published in Nature Communications (2023)
4, We have discovered that the nuclear envelope in male meiosis I undergoes modification through the synthesis and incorporation of very-long-chain polyunsaturated fatty acids (VLC-PUFAs) by the AdipoR2 and ELOVL2 functional axis. This ensures a highly fluid membrane environment necessary for the peripheral distribution of meiotic telomeres and thus for faithful homolog synapsis/recombination and ultimately male fertility.
Overall, there were several unexpected discoveries that surpassed the initial research proposal. For instance, the control of spindle formation by DYNLRB2 was not originally included in the research plan. DYNLRB2 was identified by the KASH5 immunoprecipitation in this project and we reveiled their unexpect roles after making and analyzing the knockout mice. Additionally, the regulation of nuclear membrane fluidity by AdipoR2-ELOVL2 originated from an unexpected idea born out of collaboration with Marc Pilon's lab at the University of Gothenburg. Therefore, we conclude that the research progressed very productively and efficiently as a whole. Furthermore, the outcomes of this study are poised to provide foundational knowledge useful for understanding the causes of human infertility in the future and consequently for treatment. Indeed, concerning proteins like TERB1 and MEILB2 that we analyzed in this project, mutations have been consistently reported by several clinical research groups in infertility patients recently.
2, We have found that the MYB-like DNA-binding (MYB) domain of meiotic telomere protein TERB1 has a role in the suppression of telomere erosion during meiotic telomere movements. Without the TERB1 MYB domain, meiotic telomeres are fused, bridged, or ultimately eroded during meiotic prophase I. Our findings suggest that the TERB1 MYB domain might be required for the maintenance of telomeric DNA and, thus, genomic integrity in the long evolutionary period. This work is published in Cell Reports (2022)
3, We have identified that spindle formation in male meiosis I requires the cytoplasmic dynein complex containing a testis-upregulated light chain paralog, DYNLRB2. We showed that DYNLRB2 ensures spindle bipolarity in meiosis I through two distinct pathways: 1) maintaining centriole engagement in metaphase I and 2) recruiting NuMA to the spindle pole. This work is published in Nature Communications (2023)
4, We have discovered that the nuclear envelope in male meiosis I undergoes modification through the synthesis and incorporation of very-long-chain polyunsaturated fatty acids (VLC-PUFAs) by the AdipoR2 and ELOVL2 functional axis. This ensures a highly fluid membrane environment necessary for the peripheral distribution of meiotic telomeres and thus for faithful homolog synapsis/recombination and ultimately male fertility.
Overall, there were several unexpected discoveries that surpassed the initial research proposal. For instance, the control of spindle formation by DYNLRB2 was not originally included in the research plan. DYNLRB2 was identified by the KASH5 immunoprecipitation in this project and we reveiled their unexpect roles after making and analyzing the knockout mice. Additionally, the regulation of nuclear membrane fluidity by AdipoR2-ELOVL2 originated from an unexpected idea born out of collaboration with Marc Pilon's lab at the University of Gothenburg. Therefore, we conclude that the research progressed very productively and efficiently as a whole. Furthermore, the outcomes of this study are poised to provide foundational knowledge useful for understanding the causes of human infertility in the future and consequently for treatment. Indeed, concerning proteins like TERB1 and MEILB2 that we analyzed in this project, mutations have been consistently reported by several clinical research groups in infertility patients recently.
Until now, research on telomeres has mostly utilized somatic cells. This project represents a novel approach by focusing on telomere regulations during meiosis. Not only did we elucidate the regulation of telomere rigidity and movement by TERB1, but we also uncovered modifications for nuclear membrane components that bind telomeres. This introduces the groundbreaking notion that modulation of the testis lipidome serves as the foundation for meiotic chromosome dynamics. Furthermore, numerous new discoveries were made, such as the specialized meiotic functions of the well-known cancer suppressor protein BRCA2 and the unique regulations of the meiotic spindle. In summary, our interdisciplinary research has provided foundational molecular mechanisms for the molecular control of meiosis beyond existing research frameworks.