Abstract
Centromeres are chromosomal domains essential for kinetochore assembly and correct chromosome segregation. Inconsistent in their underlying DNA sequences, centromeres are defined epigenetically by the presence of the centromere-specific histone H3 variant CenH3. Most of the analyzed eukaryotes have monocentric chromosomes in which CenH3 proteins deposit into a single, primary constriction visible at metaphase chromosomes. Contrary to monocentrics, evolutionary sporadic holocentric chromosomes lack a primary constriction and have kinetochore activity distributed along the entire chromosome length. In this work, we identified cCENH3 protein, the centromeric H3 histone of the coleopteran model beetle Tribolium castaneum. By ChIP-seq analysis we disclosed that cCENH3 chromatin assembles upon a repertoire of repetitive DNAs. cCENH3 in situ mapping revealed unusually elongated T. castaneum centromeres that comprise approximately 40% of the chromosome length. Being the longest insect regional centromeres evidenced so far, T. castaneum centromeres are characterized by metapolycentric structure composed of several individual cCENH3-containing domains. We suggest that the model beetle T. castaneum with its metapolycentromeres could represent an excellent model for further studies of non-canonical centromeres in insects.
Highlights
Centromeres are chromosomal loci essential for chromosome pairing and accurate chromosome segregation during cell division
Eukaryotic species studied to date mostly possess monocentric chromosomes with a functional centromere sited at a single locus, but there are species with holocentric chromosomes whose centromeres stretch throughout the entire length of the chromosome
By investigating centromere-specific variant of the histone protein H3 and its associated centromeric DNA in the model beetle Tribolium castaneum, we discovered that T. castaneum centromeres comprise several functional domains merged into one remarkably extended
Summary
Centromeres are chromosomal loci essential for chromosome pairing and accurate chromosome segregation during cell division. They represent a base upon which the kinetochore, a proteinaceous complex and the attachment site for spindle microtubules, is assembled. From structural point of view, eukaryotic chromosomes are mainly monocentric, having functional centromere located within a single, cytologically distinct primary constriction. Holocentricity is less commonly found in eukaryotes studied so far, but it is assumed that it has arisen in different plant and animal lineages in multiple independent events [4]. A novel, possibly intermediate type of centromere structure has recently been identified in the plant genera Pisum [7] and Lathyrus [8], whose metapolycentric chromosomes comprise several centromere domains in a single, but remarkably elongated primary constriction
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