Survivin is a critical regulator of spindle organization and chromosome segregation during rat oocyte meiotic maturation

Exploring Plant Meiosis: Insights from the Kinetochore Perspective

The central player for chromosome segregation in both mitosis and meiosis is the macromolecular kinetochore structure, which is assembled by >100 structural and regulatory proteins on centromere DNA. Kinetochores play a crucial role in cell division by connecting chromosomal DNA and microtubule polymers. This connection helps in the proper segregation and alignment of chromosomes. Additionally, kinetochores can act as a signaling hub, regulating the start of anaphase through the spindle assembly checkpoint, and controlling the movement of chromosomes during anaphase. However, the role of various kinetochore proteins in plant meiosis has only been recently elucidated, and these proteins differ in their functionality from those found in animals. In this review, our current knowledge of the functioning of plant kinetochore proteins in meiosis will be summarized. In addition, the functional similarities and differences of core kinetochore proteins in meiosis between plants and other species are discussed, and the potential applications of manipulating certain kinetochore genes in meiosis for breeding purposes are explored.

Inhibition of survivin induces spindle disorganization, chromosome misalignment, and DNA damage during mouse embryo development

The early embryonic development is important for the subsequent embryo implantation, and any defects in this process can lead to embryonic aneuploidy, which causes miscarriage and birth defects. Survivin is the member of inhibitor of apoptosis protein (IAP) family, and it is also an essential subunit of chromosomal passenger complex (CPC), which regulates both apoptosis and cell cycle control in many models. However, the roles of survivin in mouse early embryos remain unclear. In the present study, we showed that survivin activity was essential for mouse early embryo development. Our results showed that survivin mainly accumulated at chromosomes at metaphase stage and located at the spindle midzone at anaphase and telophase stages during the first cleavage. Loss of survivin activity led to the failure of cleavage in early mouse embryos. Further analysis indicated that survivin involved into spindle organization and chromosome alignment. Moreover, inhibition of survivin induced oxidative stress and DNA damage, showing with the increase of ROS level, the positive γH2A signal, and the increase of Rad51 level. We also observed the occurrence of autophagy and apoptosis in the survivin-inhibited embryos. In summary, our study suggested that survivin was a critical regulator for early embryo development through its regulation on spindle organization, chromosome alignment, and DNA damage.

DNA topoisomerase II is dispensable for oocyte meiotic resumption but is essential for meiotic chromosome condensation and separation in mice

During mitosis, DNA topoisomerase II (TOP2) is required for sister chromatid separation. When TOP2 activity is inhibited, a decatenation checkpoint is activated by entangled chromatin. However, the functions of TOP2 in oocyte meiosis, particularly for homologous chromosome segregation during meiosis I, have not been investigated. In addition, it remains unknown if TOP2 inhibition activates a decatenation checkpoint at the G2/M transition in oocytes. In this study, we used mouse oocytes and specific inhibitors of TOP2 (ICRF-193 and etoposide) to investigate the role of TOP2 in meiosis. Our results indicated that an effective decatenation checkpoint did not exist in fully grown oocytes, as oocytes underwent the G2/M transition and reinitiated meiosis even when TOP2 activity was inhibited. However, oocytes treated with ICRF-193 had severe defects in chromosome condensation and homologous chromosome separation. Furthermore, condensed chromosomes failed to maintain their normal configurations in matured oocytes that were treated with ICRF-193. However, sister chromatid separation and subsequent chromosome decondensation during the exit from meiosis were not blocked by TOP2 inhibitors. These results indicated that TOP2 had a specific, crucial function in meiosis I. Thus, we identified important functions of TOP2 during oocyte maturation and provided novel insights into the decatenation checkpoint during meiosis.

The chromosomal passenger protein birc5b organizes microfilaments and germ plasm in the zebrafish embryo

Microtubule-microfilament interactions are important for cytokinesis and subcellular localization of proteins and mRNAs. In the early zebrafish embryo, astral microtubule-microfilament interactions also facilitate a stereotypic segregation pattern of germ plasm ribonucleoparticles (GP RNPs), which is critical for their eventual selective inheritance by germ cells. The precise mechanisms and molecular mediators for both cytoskeletal interactions and GP RNPs segregation are the focus of intense research. Here, we report the molecular identification of a zebrafish maternal-effect mutation motley as Birc5b, a homolog of the mammalian Chromosomal Passenger Complex (CPC) component Survivin. The meiosis and mitosis defects in motley/birc5b mutant embryos are consistent with failed CPC function, and additional defects in astral microtubule remodeling contribute to failures in the initiation of cytokinesis furrow ingression. Unexpectedly, the motley/birc5b mutation also disrupts cortical microfilaments and GP RNP aggregation during early cell divisions. Birc5b localizes to the tips of astral microtubules along with polymerizing cortical F-actin and the GP RNPs. Mutant Birc5b co-localizes with cortical F-actin and GP RNPs, but fails to associate with astral microtubule tips, leading to disorganized microfilaments and GP RNP aggregation defects. Thus, maternal Birc5b localizes to astral microtubule tips and associates with cortical F-actin and GP RNPs, potentially linking the two cytoskeletons to mediate microtubule-microfilament reorganization and GP RNP aggregation during early embryonic cell cycles in zebrafish. In addition to the known mitotic function of CPC components, our analyses reveal a non-canonical role for an evolutionarily conserved CPC protein in microfilament reorganization and germ plasm aggregation.

We address mechanisms by which germ cell precursors, a cell type that generates sperm and eggs for future generations, are specified in the zebrafish. Germ cell-specific genes are highly conserved across species, and in many animals germ cells are specified by the inheritance of germ plasm, a specialized cytoplasm containing specific proteins and RNAs corresponding to such conserved genes. Germ plasm is inherited as ribonucleoparticles, which are often present in the egg as singletons and which aggregate to generate larger masses that, when inherited by germ cell precursors, will initiate a germ cell-specific gene expression program. Here, we present the functional and molecular analysis of the zebrafish maternal gene, motley, which we show encodes a homologue of the Chromosomal Passenger Complex protein Survivin, or Birc5b. We found that, in addition to the expected role of this protein in cell division, characteristic of factors in this complex, Birc5b mediates germ plasm aggregation in the early zebrafish embryo through the coordination of dynamic changes in the cytoskeleton. Our studies provide a mechanistic basis to explain how germ cell determinants are transmitted from one generation to the next and reveal a non-conventional role for a Chromosomal Passenger Complex factor in this process.

XIAP: a potential determinant of ovarian follicular fate

X-linked inhibitor of apoptosis protein (XIAP), a member of the inhibitor of apoptosis protein family, is involved in regulating a number of functions including receptor-mediated intracellular signalling and early development. Its role as an endogenous caspase inhibitor, however, is the most highly characterised. Consequently, this protein has been implicated as an anti-apoptotic factor in the ovary.In vitroandin vivostudies have begun dissecting the stimuli and signalling networks that lead to XIAP upregulation in granulosa cells. The objective of this review is to briefly summarise the current knowledge concerning XIAP and its interactions with different caspases. Furthermore, XIAP's emerging role in the mammalian ovary will be explored and comparison is made with its functions in the mammary gland. Finally, the idea that XIAP may act as a molecular signalling switch in granulosa cells following detachment from underlying layers to promote follicular atresia will be introduced.