Enhancer of zeste homolog 2 (Ezh2) is required in mouse Isl1-expressing progenitors for proper development of cardiac and skeletal hindlimb structures

Enhancer of zeste homolog 2 (EZH2), the catalytic subunit of Polycomb Repressive Complex 2, catalyzes H3K27 trimethylation and directs lineage development programs, yet its function in early multipotent progenitors remains incompletely understood. ISL1 marks cardiopharyngeal and neural crest progenitors that contribute to second heart field derivatives and to craniofacial and limb morphogenesis. Here, Isl1-cre lineage tracing showed that lineage derivatives populated the cardiopharyngeal region and the posteromedial hindlimb bud during mid-gestation, and contributed extensively to the developing right ventricle, outflow tract, and hindlimb. Loss of Ezh2 in Isl1-expressing progenitors resulted in a high incidence of congenital heart defects, dominated by incomplete atrial and ventricular septation and outflow tract malformations, including double outlet right ventricle and persistent truncus arteriosus. These defects were accompanied by ventricular wall thickening at birth. In parallel, Ezh2 mutants exhibited hindlimb skeletal abnormalities, including pelvic and tarsal malformations with impaired ossification. These abnormalities were associated with cyanosis and perinatal demise. Together, these findings identify a requirement for EZH2 in Isl1-lineage contribution to heart and hindlimb development.