MPHOSPH8 (M-phase phosphoprotein 8) is a heterochromatin component that functions as an H3K9me3 reader, specifically recognizing and binding methylated histone H3 lysine 9 to promote epigenetic repression 1. As a core member of the HUSH complex (alongside TASOR and PPHLN1), MPHOSPH8 mediates recruitment of repressive machinery including the histone methyltransferase SETDB1 and chr13 remodeler MORC2 to maintain transcriptional silencing 1. The HUSH complex primarily silences LINE-1 retrotransposons located within transcriptionally active euchromatic regions, with silencing events often occurring within gene introns and reducing host gene expression 2. MPHOSPH8 also facilitates silencing of unintegrated retroviral DNA and integrase-deficient retroviruses through recruitment to target loci 3. As part of the HUSH2 complex, MPHOSPH8 suppresses interferon-stimulated genes and represses protocadherin gene clusters in the nervous system, influencing brain development and neuronal identity 4. In S phase, MPHOSPH8 interacts with DNA polymerase ε to promote asymmetric H3K9me3 distribution at head-on LINE elements 5. Clinically, MPHOSPH8 loss reactivates L1 retrotransposons in acute myeloid leukemia, inducing DNA damage and cell cycle exit, revealing unexpected tumor-suppressive functions 6. Genetic variants in MPHOSPH8 are implicated in Ménière's disease pathogenesis 7.