MYL12B (myosin light chain 12B) is a regulatory subunit of non-muscle myosin II that plays a critical role in cellular contractility and cytoskeletal dynamics. As a regulatory light chain, MYL12B binds to myosin heavy chains (MYH9 and MYH10) and is essential for maintaining myosin II structural integrity and function 1. Phosphorylation of MYL12B enhances the Mg2+-ATPase activity of myosin heavy chains, triggering actin polymerization in smooth muscle and non-muscle cells 2. The protein participates in fundamental cellular processes including cytokinesis, cell migration, and adhesion through its role in stress fiber organization and myosin II complex assembly 1. MYL12B dysregulation has emerged as a biomarker in multiple disease contexts. Elevated MYL12B expression is associated with active juvenile idiopathic arthritis (JIA), showing strong diagnostic predictive power (AUC = 0.757) 3. Increased MYL12B expression occurs in post-traumatic intervertebral disc degeneration, where it participates in pathological focal adhesion and extracellular matrix remodeling pathways 4. Notably, TAD (topologically associating domain) reorganization can down-regulate MYL12B transcription in tumor cells through disruption of intrachromosomal looping 5. MYL12B has been identified as a prognostic gene in nasopharyngeal carcinoma and tongue squamous cell carcinoma, suggesting roles in cancer progression and invasion 6, 7.