Podium: Functional Organization and Inheritance of Satellite-Less Equid Centromeric Domains

The centromere is the site of kinetochore assembly required for correct chromosome segregation during cell division. At centromeres, despite the evolutionary conservation of proteins, DNA sequences are highly variable, even among related species. This paradox is now explained by the knowledge that the centromeric function is epigenetically specified.

This chromatin domain has so far escaped comprehensive molecular analysis due to its typical association with highly repetitive DNA (satellite DNA). Although satellite DNA is a common feature of mammalian centromeres, we proved that several equid centromeres are completely satellite-free, thus representing a unique model for studying this epigenetically specified locus.

In previous work, the functional organization of the single-copy centromere of horse chromosome 11 was analysed  by ChIP-on-chip with an antibody against CENP-A, the centromeric histone-H3 variant. Inter-individual positional variation of CENP-A domains was observed, giving rise to “epialleles" and proving that centromeric domains are autonomous relative to the underlying DNA and are characterized by positional instability.

ChIP-seq experiments with anti-CENP-A antibodies were performed in Grevy's zebra and donkey. The sequences of several satellite-less centromeres from these species were de novo assembled, allowing us to perform a comparative analysis between centromeric and orthologous non-centromeric DNA. The inheritance of centromeric domains in hybrid families (horses, donkeys and mules) was also analysed. The possible role of DNA breakage, methylation, transcription and heterochromatic marks in the establishment and function of the centromere will be discussed

The satellite-less equid centromeres represent a powerful system to study the molecular organization and evolution of mammalian centromeres.