Biology subjects

Kitajima, T.

Publications and source records attributed to Kitajima, T..

4 recordsLinked to original sources

bioRxiv2024

Kinetochores promote timely spindle bipolarization to prevent microtubule attachment errors in oocytes

Incorrect kinetochore-microtubule attachment leads to chromosome segregation errors. The risk of incorrect attachments is particularly high in acentrosomal oocytes, where kinetochores are surrounded by randomly oriented microtubules until spindle bipolarization. How the timing of acentrosomal spindle bipolarization is coordinated with kinetochore-microtubule attachment is unknown. Here, we show that in mouse oocytes, kinetochores promote spindle bipolarization when microtubule attachment is unstable in early prometaphase. The kinetochore kinase MPS1 allows this function by regulating multiple pathways, including those mediated by the kinetochore proteins NDC80-NUF2 at their C-terminal domains and the antiparallel microtubule crosslinker PRC1. Inhibition of MPS1 delays spindle bipolarization to late prometaphase, thereby increasing incorrect kinetochore-microtubule attachments. Artificially accelerating spindle bipolarization by overexpressing KIFC1 prevents incorrect kinetochore-microtubule attachment in MPS1-inhibited oocytes. Thus, kinetochores autonomously promote timely acentrosomal spindle bipolarization prior to stabilizing microtubule attachment, thereby reducing the risk of egg aneuploidy.

cell biology↗

bioRxiv2024

Downstream metabolites of (+)-cis-12-oxo-phytodienoic acid function as noncanonical bioactive jasmonates in Arabidopsis thaliana.

(+)-cis-12-oxo-phytodienoic acid (cis-OPDA) is a biosynthetic precursor of the plant hormone (+)-7-iso-jasmonoyl-L-isoleucine (JA-Ile). It functions as an endogenous chemical signal independent of the JA-Ile receptor COI1-JAZ in Arabidopsis thaliana. The bioactive form of cis-OPDA that induces COI1-JAZ-independent gene expression remains unknown. In this study, we hypothesized that the genuine bioactive forms of cis-OPDA are the downstream metabolites, which upregulate the expression of the OPDA marker genes such as ZAT10/ERF5 in a JA-Ile-independent manner. These downstream metabolites function independently of the JA-Ile-COI1-JAZ-MYCs canonical jasmonate signaling module, and its electrophilic nature is essential for its bioactivity.

plant biology↗

bioRxiv2024

Tethering NDC80-NUF2 to microparticles is sufficient to enable their biorientation in the spindle

Faithful chromosome segregation requires biorientation, where the pair of kinetochores on the chromosome establish bipolar microtubule attachment. The integrity of the kinetochore, a macromolecular complex built on centromeric DNA, is required for biorientation, but components sufficient for biorientation remain unknown. In this study, we show that tethering the outer kinetochore heterodimer NDC80-NUF2 to the surface of microbeads with no bipolar cue is sufficient for them to establish a biorientation-like state in mouse oocytes. NDC80-NUF2 microbeads efficiently and stably align at the spindle equator, forming bipolar microtubule attachments. Furthermore, they can self-correct alignment errors. They align independently of the outer kinetochore proteins SPC24-SPC25, KNL1, the MIS12 complex, or inner kinetochore proteins. Aurora-mediated NDC80 phosphoregulation promoted microbead alignment under challenging conditions. Interestingly, larger microbeads align more rapidly, suggesting that large platform size enhances NDC80-NUF2-mediated biorientation. This study shows a biohybrid kinetochore design for synthetic biorientation of microscale particles in cells.

cell biology↗

bioRxiv2021

Production of offspring from azoospermic mice with meiotic failure: Precise biparental meiosis within halved oocytes

While the large volume of mammalian oocytes is necessary for embryo development, it can lead to error-prone chromosomal segregation during meiosis. Conversely, we hypothesized that smaller oocytes would have a great unidentified potential to stabilize unstable meiosis and improve the development of the resultant embryos. Here, we show that reducing ooplasmic volume can rescue highly error-prone fertilization using primary spermatocytes by preventing segregation errors of chromosomes during biparental meiosis. High-resolution live-imaging analysis revealed that erroneous chromosome segregation occurred in most (90%) spermatocyte-injected oocytes of normal size, but could be ameliorated to 40% in halved oocytes. The birth rate improved remarkably from 1% to 19% (P < 0.0001). Importantly, this technique enabled the production of offspring from azoospermic mice with spermatocyte arrest caused by STX2 deficiency, an azoospermia factor also found in humans. Thus, contrary to popular opinion, oocytes inherently have a strong potential for precise meiotic divisions, which can be evoked by reduction of the ooplasmic volume. Their potential might help rescue cases of untreatable human azoospermia with spermatocyte arrest.

developmental biology↗