Biology subjects

Pieper, G. H.

Publications and source records attributed to Pieper, G. H..

4 recordsLinked to original sources

bioRxiv2026

Meiotic kinetochore reconstitution identifies chromosome segregation factors

Kinetochores are complex protein assemblies at centromeres that direct and regulate chromosome segregation1. During gamete formation by meiosis, kinetochore specialisations drive two sequential and distinct segregation events to partition half the genome to the offspring2,3. Age-dependent segregation errors in human oocytes are a major cause of reproductive failure and are linked to kinetochore dysfunction4-6, however the molecular composition and function of mammalian meiotic centromeric chromatin and kinetochores remains poorly defined. Here, we reconstitute vertebrate meiosis I and II centromeric chromatin using meiosis I and II endogenous proteins to uncover conserved regulators of chromosome segregation in mammalian meiosis. We find that, in addition to canonical kinetochore proteins, a specific subset of chromatin regulators is enriched on meiotic centromeric chromatin. We discover previously unrecognized kinetochore proteins conserved from frogs to mouse and humans and demonstrate their localisation at mammalian oocyte centromeres. Among these, we show that the newly identified centromeric protein HSPBAP1, is required to maintain chromosome integrity and ensure faithful segregation in both mouse and human oocytes. These findings define the composition of vertebrate meiotic kinetochores and uncover conserved factors that safeguard mammalian meiotic chromosome segregation, a highly error-prone process and major cause of aneuploidy and reproductive failure in humans7.

cell biology↗

bioRxiv2025

Multi-nucleation in two-cell human embryos stems from spindle and metaphase plate incoherence in the first mitosis

The first embryonic division in humans is highly error-prone and a source of aneuploidies. Multi-nucleation is prevalent in two-cell human embryos, with unknown cause. Here, we live-image human zygotes to elucidate the features of the first mitosis that predispose embryos to multinucleation. We show that failure to collect chromosomes into a single mass and establish a bipolar spindle during zygotic metaphase leads to severe multi-nucleation. We find that KIF10/CENP-E kinesin activity is essential to prevent the formation of multiple spindle poles and to congress chromosomes onto a metaphase plate. Furthermore, although the spindle assembly checkpoint mediates a delay in response to a highly disorganised spindle, KIF10/CENP-E-inhibited embryos ultimately undergo the first mitosis with a chaotic anaphase. Therefore, defective chromosome congression in the zygote combined with a failure to sense this error cause multi-nucleation. Remarkably, multi-nucleation can be corrected during the second mitotic division in a KIF10/CENP-E-dependent manner. We suggest that multi-nucleation may be a safeguarding mechanism to prevent chromosome loss during the highly error-prone first embryonic mitosis.

cell biology↗

bioRxiv2023

Age-dependent loss of cohesion protection in human oocytes

Aneuploid human eggs (oocytes) are a major cause of infertility, miscarriage and chromosomal disorders. Such aneuploidies increase greatly as women age, originating from defective linkages between sister-chromatids (cohesion) in meiosis. We found evidence that loss of a specific pool of the cohesin protector protein, shugoshin 2 (Sgo2) contributes to this phenomenon. Our data indicate that Sgo2 preserves sister chromatid cohesion in meiosis by protecting a cohesin bridge between sister chromatids. In human oocytes, Sgo2 localizes to both sub-centromere cups and the pericentromeric bridge which spans the sister chromatid junction. Sgo2 normally colocalizes with cohesin, however, in oocytes from older women, Sgo2 is frequently lost specifically from the pericentromeric bridge and sister chromatid cohesion is weakened. Mps1 and Bub1 kinase activities maintain Sgo2 at sub-centromeres and the pericentromeric bridge. Removal of Sgo2 throughout meiosis I by Mps1 inhibition reduces cohesion protection, increasing the incidence of single chromatids at meiosis II. Therefore, Sgo2 deficiency in human oocytes can exacerbate the effects of maternal age by rendering residual cohesin at pericentromeres vulnerable to loss in anaphase I. Our data show that maternal age-dependent loss of Sgo2 at the pericentromere bridge in human oocytes impairs cohesion integrity and contributes to the increased incidence of aneuploidy observed in human oocytes with advanced maternal age.

cell biology↗

bioRxiv2019

ESCRT-III/Vps4 controls heterochromatin-nuclear envelope attachments

In eukaryotes chromosomes are compartmentalized within the nucleus delimited by the double membrane of the nuclear envelope (NE). Defects in the function and structure of the NE are linked to disease1,2. During interphase, the NE organizes the genome and regulates its expression3. As cells enter mitosis, chromosomes are released from the NE, which is then remodelled to form the daughter nuclei at mitotic exit4. Interactions between the NE and chromatin underpinning both interphase and post-mitotic NE functions are executed by inner nuclear membrane (INM) proteins such as members of the evolutionarily conserved chromatin-binding LEM-domain family5-8. How chromatin tethering by these transmembrane proteins is controlled in interphase and if such a regulation contributes to subsequent NE dynamics in mitosis remains unclear. Here we probe these fundamental questions using an emerging model organism, the fission yeast Schizosaccharomyces japonicus, which breaks and reforms the NE during mitosis9,10. We show that attachments between heterochromatin and the transmembrane Lem2-Nur1 complex are continuously remodelled in interphase by the ESCRT-III/AAA-ATPase Vps4 machinery. ESCRT-III/Vps4 mediates the release of Lem2-Nur1 from heterochromatin as a prerequisite for the timely progression through mitosis. Failure in this process leads to persistent association of chromosomes with the INM, which prevents Lem2-Nur1 from re-localizing to the sites of NE sealing around the mitotic spindle and severely delays re-establishment of nucleocytoplasmic compartmentalization. Our work establishes the INM transmembrane Lem2-Nur1 complex as a substrate for ESCRT-III/Vps4 to couple dynamic tethering of chromosomes to the INM with the establishment of nuclear compartmentalization.

cell biology↗