Sequence comparisons between human alpha satellite monomers have led to the description of up to seventeen different alpha satellite families, or monomer types. In pericentromeres, a second type of organization, called monomeric and involving arrays of single alpha satellite monomers which are less well conserved (70–90% sequence identity), can coexist with HORs. This organization is typically found as very long arrays of alpha satellites at the centromere core of all human chromosomes. In the so-called higher order repeat (HOR) organizational pattern, highly conserved repeat units (97–100% sequence identity), each made of multiple 171 bp monomers (up to more than 30), are found as an homogenized array that can extend over a multimegabase-sized region. In human, alpha satellite DNA has been shown to adopt two different organizations. Nevertheless, over the last 30 years, the systematic cloning and sequencing of many alpha satellite DNAs, combined with fluorescence in situ hybridization (FISH) experiments, has provided a thorough knowledge of alpha satellite DNA diversity and organization patterns in the human genome and, to a much lesser extent, in other primates. The highly identical composition of successive repeats represents a technical challenge that has thwarted the complete assembly of centromeric DNA so far. In the human genome, individual monomers share between 60 and 100% sequence identity.
Alpha satellite DNA is made of tandemly repeated AT-rich monomers that are about 170 bp in length and organized in head-to-tail orientation. Alpha satellite DNA was originally isolated as a highly repetitive component of the Chlorocebus aethiops (also called African green monkey) genome homologous repeats were then described throughout the Primate order including apes, Old World and New World monkeys. Īlpha satellite DNA is the most abundant satellite DNA in Primates and is found both at the site of centromere attachment and in neighboring heterochromatic regions, referred to as pericentromeric regions.
The remarkable variation of satellite DNAs between species has been an enigma ever since their discovery and different important roles have been ascribed to these sequences, from the imperative centromeric function in mitosis and meiosis to regulatory functions. In almost all eukaryotes, the DNA underlying centromeres is made of large tracts of nearly identical tandem DNA repeats, known as satellite DNA. Applying this approach to other species will open new perspectives regarding the integration of satellite DNA into comparative genomic and cytogenetic studies.Ĭentromeres are chromosomal regions that control chromosome segregation during cell division in eukaryotes, through kinetochore assembly and microtubule attachment. We consider these data with respect to previously known alpha satellite families and to potential mechanisms for satellite DNA evolution. Our new approach provides an unprecedented and comprehensive view of the diversity and organization of alpha satellites in a species outside the hominoid group. Fluorescence in situ hybridization using oligonucleotide probes that are able to target each family in a specific way showed that the different families had distinct distributions on chromosomes and were not homogeneously distributed between chromosomes. While previous studies had suggested that alpha satellites in Old World monkeys were poorly diversified, our analysis provides evidence for the existence of at least four distinct families of sequences within the studied species and of higher order organizational patterns. Computational approaches were used to infer the existence of sequence families and to study how these families are organized with respect to each other. We carried out the targeted high-throughput sequencing of alpha satellite monomers and dimers from the Cercopithecus solatus genome, an Old World monkey from the Cercopithecini tribe. The limited amount of information available in non-human primates is a restriction to the understanding of the evolutionary dynamics of alpha satellite DNA. Evolution of these tandemly repeated sequences has led to the existence of numerous families of monomers exhibiting specific organizational patterns. Alpha satellite is the major repeated DNA element of primate centromeres.
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