The biology of syncytial cells: Dissecting the mechanisms and functions of nuclear differentiation inside skeletal muscle syncytium – SyncyNucDiff

Due to their cellular anatomy, syncytial cells face many unique challenges that mono-nucleated cells do not.
One of them is how syncytial cells organize gene expression among many nuclei in a shared cytoplasm. How
such property is linked to their biological functions remains poorly understood. Using the skeletal muscle as a
paradigm and single-nucleus transcriptomics, I recently uncovered previously unrecognized diversity and
dynamics of myonuclear transcriptional programs. This conceptualized the syncytial muscle cell itself as an
analog of multi-cellular tissue where individual nuclei are counterparts of differentiated cell types. My findings
raise two important and unanswered questions. 1) How are the diverse nuclear identities specified and
maintained? And 2) What are the functional contributions of the diverse nuclear subtypes in health and disease?
I will first focus on the nuclei at the neuromuscular junction (NMJ) and myotendinous junction (MTJ),
which are responsible for initiation of contraction and dissipation of contractile force, respectively. Despite
their well-established functions, the mechanisms that specify or maintain them are sparsely understood. I will
investigate how chromatin architecture and transcriptional regulators govern their identities. I will then
characterize the upstream signalling pathways from motor neuron or tendon cells that activate the specific
transcriptional programs. So far, genetic manipulation of myofibers have targeted entire muscle nuclei. To
overcome this limit, I will develop tools that allow genetic manipulation in specific nuclear subtypes. Previous
works had identified a new nuclear subtype associated with muscular dystrophy and a transient time window
during postnatal development. I will characterize the function of these nuclei using a method that abolishes
their transcriptional activities. The approaches to be developed here will pave the way to understanding the
pathophysiology of syncytial cells in the future.