A dynamic population of prophase CENP-C is required for meiotic chromosome segregation

The functional organisation of the centromere and kinetochore during meiosis

Meiosis generates gametes through a specialised cell cycle that reduces the genome by half. Homologous chromosomes are segregated in meiosis I and sister chromatids are segregated in meiosis II. Centromeres and kinetochores play central roles in instructing this specialised chromosome segregation pattern. Accordingly, kinetochores acquire meiosis-specific modifications. Here we contextualise recent highlights in our understanding of how centromeres and kinetochores direct the sorting of chromosomes into gametes via meiosis.

A scATAC-seq atlas of stasis zone in rat skin burn injury wound process

Burn injuries often leave behind a "stasis zone", a region of tissue critically important for determining both the severity of the injury and the potential for recovery. To understand the intricate cellular and epigenetic changes occurring within this critical zone, we utilized single-cell assay for transposase-accessible chromatin sequencing (scATAC-seq) to profile over 31,500 cells from both healthy rat skin and the stasis zone at nine different time points after a burn injury. This comprehensive approach revealed 26 distinct cell types and the dynamic shifts in the proportions of these cell types over time. We observed distinct gene activation patterns in different cell types at various stages post-burn, highlighting key players in immune activation, tissue regeneration, and blood vessel repair. Importantly, our analysis uncovered the regulatory networks governing these genes, offering valuable insights into the intricate mechanisms orchestrating burn wound healing. This comprehensive cellular and molecular atlas of the stasis zone provides a powerful resource for developing targeted therapies aimed at improving burn injury recovery and minimizing long-term consequences.

Distinct checkpoint and homolog biorientation pathways regulate meiosis I in Drosophila oocytes

Mitosis and meiosis have two mechanisms for regulating the accuracy of chromosome segregation: error correction and the spindle assembly checkpoint (SAC). We have investigated the function of several checkpoint proteins in meiosis I of Drosophila oocytes. Increased localization of several SAC proteins was found upon depolymerization of microtubules by colchicine. However, unattached kinetochores or errors in biorientation of homologous chromosomes do not induce increased SAC protein localization. Furthermore, the metaphase I arrest does not depend on SAC genes, suggesting the APC is inhibited even if the SAC is not functional. Two SAC proteins, ROD of the ROD-ZW10-Zwilch (RZZ) complex and MPS1, are also required for the biorientation of homologous chromosomes during meiosis I, suggesting an error correction function. Both proteins aid in preventing or correcting erroneous attachments and depend on SPC105R for localization to the kinetochore. We have defined a region of SPC105R, amino acids 123-473, that is required for ROD localization and biorientation of homologous chromosomes at meiosis I. Surprisingly, ROD removal from kinetochores and movement towards spindle poles, termed "streaming," is independent of the dynein adaptor Spindly and is not linked to the stabilization of end-on attachments. Instead, meiotic RZZ streaming appears to depend on cell cycle stage and may be regulated independently of kinetochore attachment or biorientation status. We also show that Spindly is required for biorientation at meiosis I, and surprisingly, the direction of RZZ streaming.

Distinct checkpoint and homolog biorientation pathways regulate meiosis I in Drosophila oocytes

Mitosis and meiosis have two mechanisms for regulating the accuracy of chromosome segregation: error correction and the spindle assembly checkpoint (SAC). We have investigated the function of several checkpoint proteins in meiosis I of Drosophila oocytes. Evidence of a SAC response by several of these proteins is found upon depolymerization of microtubules by colchicine. However, unattached kinetochores or errors in biorientation of homologous chromosomes does not induce a SAC response. Furthermore, the metaphase I arrest does not depend on SAC genes, suggesting the APC is inhibited even if the SAC is silenced. Two SAC proteins, ROD of the ROD-ZW10-Zwilch (RZZ) complex and MPS1, are also required for the biorientation of homologous chromosomes during meiosis I, suggesting an error correction function. Both proteins aid in preventing or correcting erroneous attachments and depend on SPC105R for localization to the kinetochore. We have defined a region of SPC105R, amino acids 123-473, that is required for ROD localization and biorientation of homologous chromosomes at meiosis I. Surprisingly, ROD removal, or "streaming", is independent of the dynein adaptor Spindly and is not linked to the stabilization of end-on attachments. Instead, meiotic RZZ streaming appears to depend on cell cycle stage and may be regulated independently of kinetochore attachment or biorientation status. We also show that dynein adaptor Spindly is also required for biorientation at meiosis I, and surprisingly, the direction of RZZ streaming.

Meiosis-specific functions of kinetochore protein SPC105R required for chromosome segregation in Drosophila oocytes

The reductional division of meiosis I requires the separation of chromosome pairs towards opposite poles. We have previously implicated the outer kinetochore protein SPC105R/KNL1 in driving meiosis I chromosome segregation through lateral attachments to microtubules and coorientation of sister centromeres. To identify the domains of SPC105R that are critical for meiotic chromosome segregation, an RNAi-resistant gene expression system was developed. We found that the SPC105R C-terminal domain (aa 1284-1960) is necessary and sufficient for recruiting NDC80 to the kinetochore and building the outer kinetochore. Furthermore, the C-terminal domain recruits BUBR1, which in turn recruits the cohesion protection proteins MEI-S332 and PP2A. Of the remaining 1283 amino acids, we found the first 473 are most important for meiosis. The first 123 amino acids of the N-terminal half of SPC105R contain the conserved SLRK and RISF motifs that are targets of PP1 and Aurora B kinase and are most important for regulating the stability of microtubule attachments and maintaining metaphase I arrest. The region between amino acids 124 and 473 are required for lateral microtubule attachments and biorientation of homologues, which are critical for accurate chromosome segregation in meiosis I.

Meiosis-specific functions of kinetochore protein SPC105R required for chromosome segregation in Drosophila oocytes

The reductional division of meiosis I requires the separation of chromosome pairs towards opposite poles. We have previously implicated the outer kinetochore protein SPC105R/KNL1 in driving meiosis I chromosome segregation through lateral attachments to microtubules and co-orientation of sister centromeres. To identify the domains of SPC105R that are critical for meiotic chromosome segregation, an RNAi-resistant gene expression system was developed. We found that SPC105R's C-terminal domain (aa 1284-1960) is necessary and sufficient for recruiting NDC80 to the kinetochore and building the outer kinetochore. Furthermore, the C-terminal domain recruits BUBR1, which in turn recruits the cohesion protection proteins MEI-S332 and PP2A. Of the remaining 1283 amino acids, we found the first 473 are most important for meiosis. The first 123 amino acids of the N-terminal half of SPC105R contain the conserved SLRK and RISF motifs that are targets of PP1 and Aurora B kinase and are most important for regulating the stability of microtubule attachments and maintaining metaphase I arrest. The region between amino acids 124 and 473 are required for two activities that are critical for accurate chromosome segregation in meiosis I, lateral microtubule attachments and bi-orientation of homologs.