Organization of centromeric chromatin in C. elegans
The centromere is a defining feature of eukaryotic chromosomes and is essential for the segregation of chromosomes during cell division, as it organizes the proteinaceous kinetochore for attachment to the spindle apparatus at mitosis. Aberrant centromere formation leads to aberrant chromosome segregation and aneuploidy, which is a widespread characteristic of cancer cells. C. elegans centromeres are different from most other organisms in that chromosomes are holocentric, and centromeric nucleosomes are localized to discrete sites that are distributed along the length of the chromosomes. These features make C. elegans an attractive model to study centromeric chromatin, as the low abundance of tandem repeats allows mapping of centromeric nucleosomes, and the interaction between centromeric nucleosomes and the kinetochore can be analyzed. By studying centromeres in this model organism, we aim to understand the mechanism by which centromeric chromatin is formed and maintained during development and from one generation to the next.
Identity and function of H3.3 in development and disease
Histone H3.3 is a replication-independent variant of histone H3 with important roles in roles in development, differentiation and fertility. The C. elegans genome contains five genes expressing H3.3. Interestingly, expression of two of these genes is restricted to the germline, suggesting a role in the transmission of chromatin states at the maternal zygotic transition. In contrast to other animal models, C. elegans lacking H3.3 are viable, but show increased embryonic lethality and susceptibility to temperature stress. We found that loss of H3.3 results in embryonic replication defects, and in impaired activation of heat shock genes in adults. The germline association and the viability of H3.3 mutant enable us to study the epigenetic contributions of this major histone variant to developmental processes.
Mutation of lysine 27 to methionine in histone H3.3 has recently been discovered as a driver mutation of pediatric glioblastoma. Worms carrying the H3.3K27M mutation show ectopic activation of DNA replication and a cancer-like phenotype in the proximal germline. H3.3K27M inhibits PRC2 activity and causes a major redistribution of polycomb silencing. This leads to expression changes of hundreds of genes, but we recently showed that only specific pathways are linked to the aberrant cell cycle progression. We aim to exploit the nematode system as a model for the cancer driver mutation to elucidate how repressed chromatin is formed and inherited, and to identify potential drug targets for the treatment of this devastating disease.