Michael A. Lampson

Centromeres ensure faithful chromosome segregation, yet the satellite arrays typically underlying these loci exhibit remarkable variation in sequence, organization, and size across individuals and species. Recent advances in long-read genome assemblies and experimental model systems have begun to reveal that this diversity is not simply tolerated but can directly influence centromere function during female meiosis. Asymmetry between centromeric satellite arrays of homologous chromosomes can lead to asymmetries in kinetochore proteins and spindle interactions, biased chromosome orientation on the spindle, and ultimately non-Mendelian inheritance by centromere drive. Emerging evidence further suggests that centromeric satellite asymmetry can increase meiotic chromosome segregation errors and aneuploidy, particularly in the context of small arrays. In this review, we discuss recent progress linking centromeric satellite variation with meiotic chromosome behavior, centromere drive, and segregation fidelity.

Tandemly repeated, non-coding satellite DNAs are among the most rapidly evolving genetic elements in eukaryotic genomes, changing in identity, copy number, and genomic distribution. A growing list of empirical studies suggests that this rapid evolution has profound consequences on core biological processes. Here, we review recent studies that investigate the satellite DNA-mediated biology revealed by generating either inter-species hybrids or genotypes expressing divergent, satellite DNA-interacting proteins from a closely related species. The genetic incompatibilities that arise implicate chromosome segregation, DNA repair, the establishment of silent heterochromatin, and the spatial organization of chromosomes as essential processes vulnerable to the rapid evolution of satellite DNA. We discuss emergent themes from this relatively young body of literature and future challenges for the field.

Pericentromeres are heterochromatic regions adjacent to centromeres that ensure accurate chromosome segregation. Despite their conserved function, they are composed of rapidly evolving A/T-rich satellite DNA. To test the functional consequences of this rapid sequence evolution, we establish hybrid mouse embryos as a model system to compare divergent satellite arrays from distinct species in a common cytoplasm. We show that variation in satellite sequence impacts heterochromatin formation, recruitment of the Chromosome Passenger Complex (CPC), and interactions with the mitotic spindle. Differences in satellite DNA sequence alter pericentromere packaging by Polycomb Repressive Complex 1 (PRC1), as satellite arrays that recruit PRC1 are enriched for specific A/T sequences that the PRC1 AT-hook preferentially binds. Furthermore, PRC1 heterochromatin modifies pericentromere function by inhibiting recruitment of the CPC, increasing microtubule forces on kinetochores during mitosis. Our results provide a direct link between satellite DNA composition and mitotic chromosome behavior and highlight early embryogenesis as a critical point in development that is sensitive to satellite DNA evolution.

Centromeres are epigenetically specified chromosomal sites that support kinetochore assembly and often embedded within large satellite DNA arrays. Recent telomere to telomere genome assemblies have revealed extensive variation in centromeric satellite arrays between chromosomes and between individuals, but the functional significance of this variation remains unclear. To determine how satellite array size influences centromere function, we generated hybrid mouse models in which homologous chromosomes with different array sizes are paired in meiosis I, creating array size asymmetry across each meiotic bivalent. When an extremely small array is paired with a moderate size array, we find that array size asymmetry leads to functional asymmetry in both centromere chromatin and interactions with spindle microtubules, lagging chromosomes in anaphase I, and increased aneuploidy in MII eggs. In contrast, pairing an extremely large array with a moderate array does not lead to functional centromere asymmetry. Together, these results suggest a threshold model in which centromere array size is tolerated across a broad range, but minimal arrays become functionally limiting when paired with larger arrays in meiosis.

Summary: Long-read sequencing has enabled precise measurements of highly repetitive centromeric satellites and their rapid divergence between species ^1–7 . Large satellite arrays emerge from libraries of shorter arrays via stochastic expansions ^8,9 , but understanding the selective pressures constraining such expansions remains a major challenge. Here, using the mouse “major” satellite as a model, we reveal reciprocal functional constraints between increasing satellite copy number and abundance of a conserved architectural protein in female meiosis. We show that HMGA2 (high mobility group AT-hook 2) is enriched at major satellite, and its expression correlates with major satellite copy number: both are high in Mus musculus compared to the closely related Mus spretus . To test functional constraints, we modulated HMGA2 abundance by depletion or overexpression and used a musculus / spretus hybrid to generate oocytes with intermediate HMGA2 expression and major satellite copy number. We find that HMGA2 depletion disrupts major satellite packaging in major satellite-rich musculus but not hybrid oocytes, indicating that increasing copy number requires high HMGA2 expression. Conversely, HMGA2 overexpression disrupts chromosome segregation in major satellite-poor spretus but not hybrid oocytes, indicating that high HMGA2 expression requires expanded major satellite arrays. Based on these results, we propose a co-evolution model in which satellite expansion is constrained by architectural protein abundance, whereas protein abundance is constrained reciprocally by satellite array size.

Traditional pharmacology has limited control of drug activity and localization in space and time. Herein, we describe an approach for kinase regulation using conditional localization pharmacology (CLP), where an inactive caged inhibitor is localized to a site of interest in a dormant state using intracellular protein tethering. The activity of the inhibitor can be regulated with spatial and temporal precision in a live cellular environment using light. As a proof of concept, a photocaged MPS1 kinase inhibitor (reversine) bearing a HaloTag ligand tether was designed to manipulate the cell cycle. We demonstrate that this new caged reversine halo probe (CRH) strategy is capable of efficient localization and exceptional spatiotemporal control over spindle assembly checkpoint (SAC) silencing and mitotic exit.

Anaphase chromosome segregation depends on forces exerted by spindle microtubules. Current models propose two force-generating mechanisms: kinetochore–microtubule (kMT) depolymerization pulls chromosomes toward spindle poles (anaphase A), while antiparallel microtubule sliding in the central spindle further separates sister chromosomes by elongating the spindle (anaphase B). Experimental evidence in cells supports the sliding mechanism but contributions of the depolymerization mechanism remain unclear. We show that kMT depolymerization limits spindle elongation rather than moving chromosomes apart. We developed a chemical optogenetic approach to recruit microtubule depolymerases to kinetochores at anaphase onset, thereby increasing kMT depolymerization rates without perturbing earlier stages of mitosis. We find that increased depolymerization slows the velocity at which spindle poles move apart without changing kinetochore separation velocities. Our findings support a model in which kinetochores selectively couple to central spindle microtubules parallel to their kMTs, such that antiparallel sliding drives chromosome segregation while kMT depolymerization pulls poles inward.