Mapping protein architecture in centromeres of Equus asinus

Abstract

The centromere is a genetic locus present once per chromosome that specifies the site of kinetochore formation and is vital for chromosomal segregation. With the exception of Saccharomyces cerevisiae, whose ‘point’ centromeres are a defined 125bp sequence and Trypanosomes, most other eukaryotic centromeres are determined epigenetically. Eukaryotic centromeres are typically associated with highly repetitive, tandem repeats of alpha satellite DNA, varying greatly in span. Reports of instances of neocentromere formation, whereby the centromere has moved to a new non repetitive region of the chromosome has been reported in humans, equids, primates, birds and rice supporting the epigenetic status of centromere identity, independent of DNA sequence. The common feature shared by almost all centromeres is the presence of the “epigenetic placeholder” histone H3 variant CENPA. Centromeres and pericentric heterochromatin have been shown to contain an abundance of transposable elements in a number of phylogenetic species. Transposable elements, such as Long Interspersed Nuclear Elements (LINEs) have been implicated in the recruitment of CENP-A to new genomic loci forming neocentromeres. Transposons play a large role in shaping the genome, from maize to humans, these ‘jumping genes’ have been shown to play a role in gene regulation and genomic evolution. In this thesis we utilize the Equus asinus, which contains 16 naturally occurring unique sequence centromeres to gain insight into centromere dynamics. We identify inter-individual and interspecies sequence anomalies associated with these unique sequence centromeres as well as start the process of identifying the location of the inner centromere at the linear one-dimensional primary sequence level.