The Impact of Retroelement Expression on Centromere Determination in Marsupials

University Of Connecticut, Storrs CT

Investigators

Abstract

The centromere is a cytologically defined entity with a conserved and restricted function in the chromosome: it is the site of kinetochore assembly and spindle attachment during cell division. Proper centromere function is essential to the equal segregation of genetic material at every cell division in all eukaryotes. In addition to its defined cytological role, the centromere is likely to be a key player in karyotypic change coincident with the divergence of species. Its importance in evolution is clearly evidenced by centromeric instability in cases of hybrid dysgenesis and by instances where karyotypic distinctiveness of species is defined exclusively by centromere character and position. Despite its essential function, the centromere is a surprisingly mutable portion of the chromosome, exhibiting little sequence conservation in the few organisms in which it has been studied. This region of the genome remains largely uncharted in most model organisms. Centromeres have long been thought to comprise non-coding and transcriptionally inactive DNA. Surprising new evidence suggests that active retroelements residing in centromeres and the transcripts they produce may play a critical role in centromere structure, function and evolution. This project will investigate the genomic features associated with centromere competence. Preliminary studies indicate that the centromeres of the wallaby Macropus eugenii are small and tractable with respect to BAC mapping and contiguous sequence development. The centromeres of this species carry actively transcribed retroelements and repeated sequences that may facilitate centromere function. This research will focus specifically on the centromere of chromosome 7 of the tammar wallaby, Macropus eugenii and will directly test hypotheses addressing the involvement of retroelements in centromere determination and maintenance, and ultimately chromosome evolution. As the field of genomics has shifted from a focus on the small percentage of DNA that codes for proteins to the large percentage of DNA that does not, there has been a corresponding shift from traditional genetic studies to a completely different paradigm: comparative genomics. The application of comparative studies involving genomic sequences of evolutionarily distinct and informative taxa has led to remarkable advances in identification of regulatory domains within conserved sequences. For the first time, the opportunity exists to examine a conserved, centromere-specific retroelement in the context of its domestication for use in centromere function in mammals. The power of this approach is underscored by the fact that comparative methods are now targeting analyses of functionally important genomic elements in non-coding regions across several vertebrate genome projects. Evolutionary comparisons are equally critical in advancing an understanding of regions of the genome, like the centromere, that are conserved in function but are comprised of widely divergent non-coding DNA. In addition, this proposal includes integration of a significant education component in its research endeavor that targets students at various education levels. Graduate and undergraduate students will directly participate in this research, including contributions to scientific workshops and conferences and involvement in the Research Experience for Undergraduates program. Novel curriculum development will be supported by this proposed work. Several technical approaches in the research design will be incorporated into modular laboratory courses, developed in the previous award period, for students enrolled in the Professional Sloan Masters program in Applied Genomics. The research outlined in this proposal supports outreach activities through the participation of two to four high school students each summer. This will be implemented in collaboration with the UCONN Mentor Connection program, which allows participants to join this laboratory and conduct research under the mentoring of the principal investigator.