Hybrid de novo genome assembly and centromere characterization of the gray mouse lemur (Microcebus murinus).

Research in the Sullivan Lab is focused on chromosome organization, with a specific emphasis on the genomics and epigenetics of the chromosomal locus called the centromere. The centromere is a specialized chromosomal site involved in chromosome architecture and movement, and when defective, is linked to cancer, birth defects, and infertility. The lab has described a unique type of chromatin (CEN chromatin) that forms exclusively at the centromere by replacement of core histone H3 by the centromeric histone variant CENP-A. Their studies also explore the composition of CEN chromatin and its relationship to the underlying highly repetitive alpha satellite DNA at the centromere. The Sullivan lab also discovered that genomic variation within alpha satellite DNA affects where the centromere is built and how well it functions. The Sullivan lab was part of the Telomere-to-Telomere T2T Consortium that used ultra long read sequencing and optical mapping to completely assemble each human chromosome, including through millions of basepairs of alpha satellite DNA at each centromere. Dr. Sullivan's group also builds human artificial chromosomes (HACs), using them as tools to test components required for a viable, transmissible chromosome and to study centromeric transcription and chromosome stability. The lab also studies formation and fate of chromosome abnormalities associated with birth defects, reproductive abnormalities, and cancer. Specifically, they study chromosomal abnormalities with two centromeres, called dicentric chromosomes. Originally described by Nobelist Barbara McClintock in the 1930s, dicentrics in most organisms are considered inherently unstable chromosomes because they trigger genome instability. However, dicentric chromosomes in humans are very stable and are often transmitted through multiple generations of a family. Using several approaches to experimentally reproduce dicentric chromosomes in human cells, the lab explores mechanisms of dicentric formation and their long-term fate.

My work integrates field inventory activities with molecular phylogenetic techniques and geospatial analysis to investigate Madagascar, an area of the world that is biologically complex, poorly understood, and urgently threatened. Madagascar has been designated as one of the most critical geographic priorities for conservation action, retaining less than 10% of the natural habitats that existed before human colonization. It is critical that information be obtained as quickly as possible to document the biota that occurs in the remaining and highly threatened forested areas of western Madagascar, to gain an understanding of the evolutionary processes and associated distributional patterns that have shaped this diversity, and to use this information to help set conservation priorities. Phylogenetic and biogeographic analysis of Malagasy vertebrates, each with unique life-history and dispersal characteristics, are conducted to identify areas of high endemism potentially associated with underlying geological features, and also to test for the role that geographic features have played in generating patterns of vertebrate diversity and distribution. My lab also has a significant focus on capacity-building through the education and training of both American and Malagasy students. Research opportunities for American graduate students are enhanced by the formation of Malagasy/American partnerships.