Kinetochore size scales with chromosome size in bimodal karyotypes of Agavoideae

Abstract

Background and Aims In eukaryotes, the total kinetochore size (defined as a chromosomal region containing CENH3-positive nucleosomes) per nucleus strongly correlates with genome size, a relationship that has been hypothesized to stem from general intracellular scaling principles. However, it could also come from the mechanics of the cell division, if larger chromosomes within a karyotype required larger kinetochores to move properly. Methods We selected seven species of the plant subfamily Agavoideae whose karyotypes are characterized by the presence of small and very large chromosomes. We visualized the kinetochore regions and chromosomes by immunolabeling with an anti-CENH3 antibody and DAPI staining. Then, we employed 2D widefield and 3D super-resolution microscopy to measure chromosome and kinetochore areas and volumes, respectively. To assess the scaling relationship of kinetochore size to chromosome size inside a karyotype, we log-transformed the data and analyzed them with linear mixed models which allowed us to control for the inherent hierarchical structure of the dataset (metaphases within slides and species). Key Results We found a positive intra-karyotype relationship between kinetochore and chromosome size. The slope of the regression line of the observed relationship (0.277 for areas, 0.247 for volumes) was very close to the theoretical slope of 0.25 for chromosome width based on the expected physics of chromosome passage through the cytoplasm during cell division. We obtained similar results by reanalyzing available data from human and maize. Conclusions Our findings suggest that the total kinetochore size to genome size scaling observed across eukaryotes may also originate from the cell division mechanics. Moreover, the potential causal link between kinetochore and chromosome size indicates that evolutionary mechanisms capable of leading kinetochore size changes to fixation, such as centromere drive, could promote the size evolution of entire chromosomes and genomes.

Super-resolution microscopy reveals the number and distribution of topoisomerase IIα and CENH3 molecules within barley metaphase chromosomes

“…Species with large genomes and few chromosomes have the largest centromeres (e.g., rye), while species with small genomes and many chromosomes have the smallest centromeres (e.g., rice) (Zhang and Dawe 2012). Although not as obvious as between species, a positive correlation between kinetochore size and chromosome size was also observed in human (Irvine et al 2004) and maize (Wang et al 2021), and within bimodal karyotypes as demonstrated for Agavoideae species (Plačková et al 2022).…”

“…A positive correlation exists between kinetochore and chromosome size, and the adequate number of attached microtubule spindle fibers are important for correct chromosome segregation during cell division. Larger chromosomes require more microtubules, and thus larger kinetochores to move them with the same velocity as small ones (Nicklas 1965;Plačková et al 2022). The microtubule-binding capacity increases with kinetochore size in Indian muntjac chromosomes (Drpic et al 2018) and in rat-kangaroo PtK1 cells, and it was demonstrated that the chromosome size determines the number of microtubules (McEwen et al 1998).…”

Breakups and Hookups: a Markov model for karyotype evolution

“…Although there are general trends in the distribution of (relative) chromosome sizes, the true physical length of a chromosome may not be the main factor that determines the rearrangement dynamics but rather its genomic content. Firstly, kinetochore length (and thereby strength of attachment of the centromere to the mitotic spindle) does not scale linearly with chromosome size (Plačková et al, 2022). Indeed, variation in centromere strength may influence which karyotype changes fix in a population through meiotic drive (Chmátal et al, 2014).…”