PPP1R12A encodes myosin light chain phosphatase target subunit 1 (MYPT1), a key regulatory component of the myosin phosphatase complex that dephosphorylates myosin light chains and other substrates 1. As a regulatory subunit of protein phosphatase 1 (PP1), PPP1R12A mediates PP1 binding to myosin and participates in dephosphorylation of multiple targets including PLK1 and MKLP1/KIF23 during cytokinesis 2. The gene undergoes complex alternative splicing producing 11 protein-coding transcripts with tissue-specific expression patterns; endothelial and smooth muscle cells predominantly express full-length variants, while platelets favor E14-skipped isoforms 1. PPP1R12A localizes to recycling endosomes where it facilitates YAP dephosphorylation and activation, promoting cancer cell proliferation 3. Disease associations include persistent Müllerian duct syndrome (PMDS), caused by truncation mutations disrupting Müllerian regression independently of AMH signaling 4, and genitourinary/brain malformation syndrome (GUBS) from haploinsufficiency 5. Variants are associated with hypertensive disorders of pregnancy susceptibility 6 and altered vascular smooth muscle cell contractility in abdominal aortic aneurysm 7. A circular RNA derivative, circPPP1R12A, encodes a functional 73-amino acid protein that promotes colorectal cancer progression via Hippo-YAP pathway activation 8.