TMEM131L is a membrane-associated transmembrane protein that functions as a negative regulator of canonical Wnt signaling during thymopoiesis and immune development. Mechanistically, TMEM131L antagonizes Wnt/β-catenin signaling by triggering lysosome-dependent degradation of phosphorylated LRP6, a key Wnt coreceptor 1. This degradation depends on TMEM131L's conserved extracellular domain rather than its cytoplasmic portion 1. TMEM131L regulates thymocyte proliferation through stage-specific surface translocation, preventing inappropriate immature single-positive thymocyte expansion via mixed Wnt-dependent and -independent mechanisms 1. Additionally, TMEM131L function is evolutionarily conserved and involves Notch signaling inhibition; overexpression decreases susceptibility to Notch1 ligation and impairs T lineage commitment 2. Disease relevance: TMEM131L has been implicated in type 1 diabetes pathogenesis, with variants identified through linkage analysis in Kuwaiti families showing significant genetic enrichment in affected individuals 3. The gene's role in regulating both Wnt and Notch signaling suggests involvement in immune tolerance mechanisms, with dysregulation potentially contributing to autoimmune disease susceptibility.