PROJECT SUMMARY
Chromatin structure and organization are critical to establishing developmentally appropriate gene expression
programs for each cell type, and aberrations in these processes lead to developmental abnormalities and
disease. Our research program’s long-term goal is to define how a specialized molecular machine called
condensin can restructure chromosomes to regulate genes in interphase as well as to promote chromosome
segregation in mitosis. Condensin mutations have been reported in patients with microcephaly and various
cancers. Therefore, findings from this project will have direct relevance to human health. Condensin complexes
are conserved from yeast to human, and while their roles in mitosis are relatively well defined, their function in
interphase gene regulation is not well understood. Regulation of X chromosome-wide gene expression in C.
elegans provides us with an opportunity to uncover condensin’s interphase roles. In this organism, in a process
called sex chromosome dosage compensation, a specialized condensin complex binds both X chromosomes
of XX hermaphrodites to downregulate gene expression by half thereby equalizing X-linked gene expression
between the sexes. Condensin-mediated gene repression involves altering X chromosome structure on
multiple levels, including posttranslational modifications of histones, looping of the chromatin fiber,
chromosome compaction, and nuclear organization. The first major project will determine how mutations in
conserved domains affect condensin’s interphase roles compared to its mitotic roles. The effect of the
phosphorylation, which is known to modulate condensin’s activity in mitosis, will also be investigated. The
second project centers on the roles of histone modifiers which cooperate with condensin in the process of
dosage compensation. These histone modifiers perform additional functions in the germline. The project will
characterize the dual functionality of this cellular machinery to reveal how the same activity can be co-opted to
fulfill different biological functions in different tissues. The third project examines how developmental regulators
can coordinate sex chromosome dosage compensation with developmental transitions. Defining the regulation
of key dosage compensation proteins at two key transitions, loss of the pluripotent state and then terminal
differentiation, will reveal the mechanistic link between these processes. Precise genome editing techniques
and tissue and developmental stage-specific protein depletion techniques will be employed to reveal the
mechanism of action and regulation of condensin in gene regulation. State-of-the art microscopy techniques
will be combined with genomic methods and bioinformatics to identify chromosome and chromatin structure
changes that are linked to gene repression.