Nascent Polypeptide Associated Complex–alphaand Signal Recognition Particle are required for cardiac development and remodeling

Congenital Heart Disease (CHD) is driven by a strong genetic predisposition, yet only a small subset of patients (∼20%) are diagnosed with a precise genetic cause. Therefore, expanding the pool of genes associated with CHD and establishing the functional relationships between genes can assemble a more comprehensive genetic network to better understand cardiac development and pathogenesis. In our studies, we identified protein biogenesis cofactors Nascent polypeptide Associated Complex (NAC) and Signal Recognition Particle (SRP) that bind disparate subsets of emerging nascent polypeptides at the ribosome exit site to direct polypeptide fates, as novel regulators of cell differentiation and cardiac morphogenesis. Knockdown (KD) of the alpha-(Nacα)or beta- subunit (bicaudal, bic)of NAC in the developingDrosophilaheart led to disruption of cardiac remodeling during pupal stages resulting in an adult fly with no heart. Heart loss was rescued by combined KD ofNacαwith theHoxgeneAbd-B.Consistent with a central role for this interaction in the regulation of cardiogenesis, KD ofNacαin Cardiac Progenitors derived from human iPSCs impaired cardiac differentiation while co-KD with mammalianHoxgenesHOXC12 and HOXD12rescued this phenotype. The effect ofNacαKD on the fly heart was temporally regulated, in that KD in embryo or in pupae caused only a partial loss of the heart, whereas KD during both stages led to heart loss similar to continuous KD throughout life. This suggests thatNacαKD already in the embryo may reprogram cells leading to aberrant cardiac remodeling during pupal stages. Lastly, KD of several SRP subunits individually in the fly heart produced a range of cardiac phenotypes that targeted specific segments and cell types, indicating spatially regulated activities of SRP components in the heart. Together, these data suggest that despite NAC and SRP ubiquitous presence, they displayed spatially and temporally fine-tuned activities for proper cardiac morphogenesis.Nacα’sinteraction with cardiac-specificHoxgene functions builds upon the novel role of this pathway and expands our understanding of the complex genetic networks involved in cardiac development and pathogenesis.