Histone repertoire changes are associated with changes in genome organisation: Loss of CenH3 in lolocentric insects

Our lab focusses on the evolution of centromeres, specialized chromosomal regions that fulfill critical roles during cell division. In all eukaryotes centromeres enable the assembly of the kinetochore protein complex and the attachment of spindle microtubules to ensure the faithful segregation of sister chromatids into the two daughter cells. Given this essential function it is surprising that different strategies of centromere organization have evolved. Among those, the evolutionary transition from monocentromeres (where spindle attachment is restricted to a single chromosomal region) to holocentromeres (where spindle microtubules attach along the entire length of the chromosome) represents the most dramatic change in centromeric architecture. We recently found that CenH3 (CENP-A) presumed to be the defining component of centromeres is lost in lineages associated with all independent transitions to holocentric chromosomes in insects. Using genomic, evolutionary and biochemical approaches we are characterizing this novel CenH3 independent chromosomes segregation and kinetochore assembly pathway in holocentric cell line systems. We aim to understand how CenH3 that is otherwise essential for centromere function in most eukaryotes, could have become dispensable in holocentric insect. In addition, these studies will also provide the first insights into the evolutionary transition from a monocentromere to a holocentromere.