EID1 (EP300 interacting inhibitor of differentiation 1) is a transcriptional corepressor that inhibits histone acetyltransferase activity of CBP/p300 complexes 1. EID1 interacts with RB1 and acts as a repressor of MYOD1 transactivation, coupling cell cycle exit to differentiation gene activation 1. Its protein abundance is tightly regulated through proteasomal degradation via the SCF(FBXO21) ubiquitin ligase complex 23, and its stability is further controlled by the Pcid2-mediated suppression of MDM2-dependent ubiquitination 1. EID1 functions extend beyond myogenesis to adipocyte biology, where it promotes beige adipocyte differentiation and thermogenic gene expression (PGC1α, UCP1, TFAM) in human subcutaneous adipose tissue 4. In reproductive biology, EID1 promotes trophoblast cell proliferation and invasion through Akt/b-catenin signaling activation; decreased EID1 expression in pre-eclampsia placental tissues correlates with disease severity and fetal growth restriction 5. Neurologically, increased EID1 nuclear localization in Alzheimer's disease neurons impairs CBP/p300-mediated histone acetylation, disrupting synaptic plasticity and spatial memory 6. EID1 also functions as a transcriptional corepressor for the orphan nuclear receptor SHP, utilizing a conserved N-terminal binding interface distinct from classical nuclear receptor cofactor sites 7.