Centromere protein b-null mice display decreasing reproductive performance through successive generations of breeding due to diminishing endometrial glands

FBXO38 Ubiquitin Ligase Controls Centromere Integrity via ZXDA/B Stability

Alterations in the gene encoding the E3 ubiquitin ligase substrate receptor FBXO38 have been associated with several diseases, including early-onset motor neuronopathy. However, the cellular processes affected by the enzymatic action of FBXO38 are not yet known. Here, we identify the zinc finger proteins ZXDA/B as its interaction partners. FBXO38 controls the stability of ZXDA/B proteins via ubiquitination and proteasome-dependent degradation. We show that ZXDA/B proteins associate with the centromeric protein CENP-B and that the interaction between ZXDA/B and FBXO38 or CENP-B is mutually exclusive. Functionally, ZXDA/B factors control the protein level of chromatin-associated CENP-B. Furthermore, their inappropriate stabilization leads to upregulation of CENP-A and CENP-B positive centromeric chromatin. Thus we demonstrate a previously unknown role of cullin-dependent protein degradation in the control of centromeric chromatin integrity.

CENP-A: A Histone H3 Variant with Key Roles in Centromere Architecture in Healthy and Diseased States

Centromeres are key architectural components of chromosomes. Here, we examine their construction, maintenance, and functionality. Focusing on the mammalian centromere- specific histone H3 variant, CENP-A, we highlight its coevolution with both centromeric DNA and its chaperone, HJURP. We then consider CENP-A de novo deposition and the importance of centromeric DNA recently uncovered with the added value from new ultra-long-read sequencing. We next review how to ensure the maintenance of CENP-A at the centromere throughout the cell cycle. Finally, we discuss the impact of disrupting CENP-A regulation on cancer and cell fate.

DNA Sequences in Centromere Formation and Function

Faithful chromosome segregation during cell division depends on the centromere, a complex DNA/protein structure that links chromosomes to spindle microtubules. This chromosomal domain has to be marked throughout cell division and its chromosomal localization preserved across cell generations. From fission yeast to human, centromeres are established on a series of repetitive DNA sequences and on specialized centromeric chromatin. This chromatin is enriched with the histone H3 variant, named CENP-A, that was demonstrated to be the epigenetic mark that maintains centromere identity and function indefinitely. Although centromere identity is thought to be exclusively epigenetic, the presence of specific DNA sequences in the majority of eukaryotes and of the centromeric protein CENP-B that binds to these sequences, suggests the existence of a genetic component as well. In this review, we will highlight the importance of centromeric sequences for centromere formation and function, and discuss the centromere DNA sequence/CENP-B paradox.

DNA Sequence-Specific Binding of CENP-B Enhances the Fidelity of Human Centromere Function

Human centromeres are specified by a stably inherited epigenetic mark that maintains centromere position and function through a two-step mechanism relying on self-templating centromeric chromatin assembled with the histone H3 variant CENP-A, followed by CENP-A-dependent nucleation of kinetochore assembly. Nevertheless, natural human centromeres are positioned within specific megabase chromosomal regions containing α-satellite DNA repeats, which contain binding sites for the DNA sequence-specific binding protein CENP-B. We now demonstrate that CENP-B directly binds both CENP-A's amino-terminal tail and CENP-C, a key nucleator of kinetochore assembly. DNA sequence-dependent binding of CENP-B within α-satellite repeats is required to stabilize optimal centromeric levels of CENP-C. Chromosomes bearing centromeres without bound CENP-B, including the human Y chromosome, are shown to mis-segregate in cells at rates several-fold higher than chromosomes with CENP-B-containing centromeres. These data demonstrate a DNA sequence-specific enhancement by CENP-B of the fidelity of epigenetically defined human centromere function.

Centromeres of filamentous fungi

How centromeres are assembled and maintained remains one of the fundamental questions in cell biology. Over the past 20 years, the idea of centromeres as precise genetic loci has been replaced by the realization that it is predominantly the protein complement that defines centromere localization and function. Thus, placement and maintenance of centromeres are excellent examples of epigenetic phenomena in the strict sense. In contrast, the highly derived "point centromeres" of the budding yeast Saccharomyces cerevisiae and its close relatives are counter-examples for this general principle of centromere maintenance. While we have learned much in the past decade, it remains unclear if mechanisms for epigenetic centromere placement and maintenance are shared among various groups of organisms. For that reason, it seems prudent to examine species from many different phylogenetic groups with the aim to extract comparative information that will yield a more complete picture of cell division in all eukaryotes. This review addresses what has been learned by studying the centromeres of filamentous fungi, a large, heterogeneous group of organisms that includes important plant, animal and human pathogens, saprobes, and symbionts that fulfill essential roles in the biosphere, as well as a growing number of taxa that have become indispensable for industrial use.

Differential impact of prostaglandin H synthase 1 knockdown on platelets and parturition

Platelet activation is a hallmark of severe preeclampsia, and platelet PGH synthase 1-derived (PGHS1-derived) thromboxane A(2) (TxA(2)) has been implicated in its pathogenesis. However, genetic disruption of PGHS1 delays parturition. We created hypomorphic PGHS1 (PGHS1(Neo/Neo)) mice, in which the substantial but tissue-dependent variability in the inhibition of PGHS1-derived eicosanoids achieved by low-dose aspirin treatment is mimicked, to assess the relative impact of this strategy on hemostatic and reproductive function. Depression of platelet TxA(2) by 98% in PGHS1(Neo/Neo) mice decreased platelet aggregation and prevented thrombosis. Similarly, depression of macrophage PGE(2) by 75% was associated with selectively impaired inflammatory responses. PGF(2alpha) at 8% WT levels was sufficient to induce coordinated temporal oxytocin receptor (OTR) expression in uterus and normal ovarian luteolysis in PGHS1(Neo/Neo) mice at late gestation, while absence of PGHS1 expression in null mice delayed OTR induction and the programmed decrease of serum progesterone during parturition. Thus, extensive but tissue-dependent variability in PG suppression, as occurs with low-dose aspirin treatment, prevents thrombosis and impairs the inflammatory response but sustains parturition. PGHS1(Neo/Neo) mice provide a model of low-dose aspirin therapy that elucidates how prevention or delay of preeclampsia might be achieved without compromising reproductive function.