Chromosome (mis)segregation is biased by kinetochore size

Abstract

Aneuploidy, the gain or loss of chromosomes, arises through problems in chromosome segregation during mitosis or meiosis and has been implicated in cancer and developmental abnormalities in humans [1]. Possible routes to aneuploidy include a compromised spindle assembly checkpoint (SAC), cohesion defects, centrosome amplification, as well as improper kinetochore-microtubule attachments [2]. However, none of these established routes takes into account the intrinsic features of the kinetochore -the critical chromosomal interface with spindle microtubules. Kinetochore size and respective microtubule binding capacity varies between different animal and plant species [3][4][5][6][7][8][9][10], among different chromosomes from the same species (including humans) [3,[11][12][13][14][15], and in response to microtubule attachments throughout mitosis [16][17][18]. How kinetochore size impacts chromosome segregation remains unknown. Addressing this fundamental question in human cells is virtually impossible, because most of the 23 pairs of chromosomes cannot be morphologically distinguished, while detection of 2-3 fold differences in kinetochore size is limited by diffraction and cannot be resolved by conventional light microscopy in living cells. Here we used the unique cytological attributes of female Indian muntjac, the mammal with the lowest known chromosome number (n=3), to track individual chromosomes with distinct kinetochore sizes throughout mitosis. We found that chromosomes with larger kinetochores bi-orient more easily and are biased to congress to the equator in a motor-independent manner. However, they are also more prone to establish erroneous merotelic attachments and lag behind during anaphase. Thus, we uncovered an intrinsic kinetochore feature -size -as an important determinant of chromosome segregation fidelity.3 Results and Discussion:Kinetochore size is generally determined by the length of α-satellite DNA, the presence of a CENP-B-box, and the proportional incorporation of CENP-A at centromeres [19][20][21][22]. Additional size changes are due to an expandable module formed by CENP-C and outer kinetochore proteins involved in SAC signaling, as well as motor proteins, such as CENP-E and cytoplasmic dynein [12,17, 23]. In humans, the length of α-satellite DNA arrays at centromeres ranges from 200 kb on the Y chromosome, to >5 Mb on chromosome 18 [24], leading to an 3 fold variability in the amount of centromeric CENP-A and respective kinetochore size among different chromosomes [11][12][13][14][19][20][21]. To investigate the relevance of kinetochore size for chromosome congression and segregation during mitosis we took advantage from the unique cytological features of the Indian muntjac (IM), a small deer whose females have the lowest known chromosome number (n=3) in mammals [25]. As the result of tandem fusions during evolution, IM chromosomes are large and morphologically distinct (one metacentric and two acrocentric pairs). Specifically relevant for our purposes, one of the acrocentric chromosomes ...

Human chromosome‐specific aneuploidy is influenced by DNA ‐dependent centromeric features

“…Recently, it has been shown that the unusually large centromeres of the Indian muntjac deer chromosomes [covering up to 26% of whole chromosome length (Levy et al , )] display proportional kinetochore size which, however, negatively impacts on the segregation fidelity due to a higher chance of incorrect attachment (Drpic et al , ). Human chromosomes do not carry this extremely high diversity in centromere length and kinetochore size and, differently from what happens in the Indian muntjac deer, we demonstrated that lower levels of centromere components lead to increased chromosome mis‐segregation.…”

“…Differences in centromere features such as sequence variation (Alexandrov et al, 2001;Aldrup-MacDonald et al, 2016;Contreras-Galindo et al, 2017) and centromere length (Rudd & Willard, 2004;Contreras-Galindo et al, 2017;Dumont & Fachinetti, 2017) could modulate the abundance of centromeric and kinetochore components, as shown for CENP-A and Ndc80 (a subunit of the kinetochore; Irvine et al, 2004;Sullivan et al, 2011;Contreras-Galindo et al, 2017;Drpic et al, 2017), and, thus, have a direct impact on chromosome segregation fidelity. A direct correlation between centromere size and bias in chromosome segregation was demonstrated in mouse asymmetric female meiosis, a phenomenon defined as centromere drive (Henikoff & Malik, 2002).…”