PROJECT SUMMARY
The ability of the heart to contract continuously is vital to the organism and is dictated in part by the sarcomeres,
the functional units of the contractile apparatus. Consequently, any errors in the formation, composition or
homeostasis of the sarcomere structure lead to congenital heart defects (CHD) or various forms of
cardiomyopathy. While the highly complex structure of the cardiac sarcomere and its function have been studied
extensively for decades, comparatively little remains known about how the sarcomere structure is established in
the first place, during de novo sarcomerogenesis. Current knowledge is largely qualitative as in depth
mechanistic studies are challenging at such early stages of development. Here we will use human pluripotent
stem cell-derived cardiomyocytes (hPSC-CMs) to interrogate our hypothesis that de novo sarcomerogenesis
occurs via a mode of assembly that involves formation of membrane-less organelles (MLOs) with distinct
biophysical properties. In Aim 1 we will interrogate the biophysical properties of Z-bodies and Z-discs during
early heart development and identify individual candidates and biological processes that dictate Z-body formation.
We will use super-resolution and time-lapse microscopy, FRAP analysis and transmission electron microscopy.
To identify drivers of Z-body formation we will use CRISPRi for candidates identified in the ACTN2 interactome
and likely to be involved in formation of MLOs. Lastly, we will assess if Z-bodies possess distinct biochemical
functions, including the presence of specific mRNA transcrips and/or local translational activity. In Aim 2 we will
determine the mechanisms that underlie Z-body initiation at the onset of de novo sarcomerogenesis. We have
described a role for WNT and RHO signaling in Z-body formation and we will identify additional mechanisms
using small molecule screening. The successful completion of this comprehensive and detailed mechanistic
study of Z-bodies holds the promise of delivering an unprecedented level of characterization of this critical stage
of de novo sarcomerogenesis. It will encompass a thorough understanding of the formation and function of Z-
bodies as a biomolecular condensates, as well as the identification of novel candidates involved in this process
and their role in cardiac function.