Determining the Mechanisms of De Novo Centromere Formation in C. elegans Embryos

Abstract

The centromere is the single, specialized chromosomal domain responsible for directing chromosome segregation. Maintaining one centromere per chromosome ensures chromosome stability. However, new centromeres can form at ectopic, non-centromeric locations in cancer cells or after chromosomal rearrangements, suggesting that centromere activity can be regulated by non-sequence-based (epigenetic) mechanisms. New centromeres can also form after introduction of purified DNA containing centromeric sequence into cells, generating autonomously segregating artificial chromosomes (ACs). This suggests that certain sequence characteristics of centromeric DNA may be preferred for new centromere formation. Based on these studies, we hypothesize that centromere activity is regulated both by epigenetic pathways and DNA sequence characteristics. However, the mechanism of centromere establishment has been challenging to study because new centromeres are often identified long after their initial formation. We have developed a model to study centromere formation by injecting DNA into the germline of Caenorhabditis elegans. This leads to formation of ACs in embryos, which efficiently form centromeres, permitting mechanistic study of centromere formation by live-cell imaging. We can monitor the frequency of equal AC segregation as an indicator of new functional centromere formation. We are employing the C. elegans AC system to decipher the roles of epigenetic factors, such as specific histone modifications, and DNA sequence characteristics, such as repetitiveness, AT contents and expression patterns, in centromere establishment. Our recent work revealed that, heterochromatin, an epigenetic mark for compact chromatin, antagonizes centromere formation. This system can uncover the requirements of new centromere formation.