Serving as a host factor for human immunodeficiency virus (HIV) integration,LEDGF/p75 has been under extensive study as a potential target for therapy.However,as a highly conserved protein,its physiological function remains to be thoroughly elucidated.Here,we characterize the molecular function of dP75,the Drosophila homolog of LEDGF/p75,during oogenesis.dP75 binds to transcriptionally active chromatin with its PWWP domain.The C-terminus integrase-binding domain-containing region of dP75 physically interacts with the histone kinase Jil-1 and stabilizes it in vivo.Together with Jil-1,dP75 prevents the spreading of the heterochromatin mark-H3K9me2-onto genes required for oogenesis and piRNA production.Without dP75,ectopical silencing of these genes disrupts oogenesis,activates transposons,and causes animal sterility.We propose that dP75,the homolog of an HIV host factor in Drosophila,partners with and stabilizes Jil-1 to ensure gene expression during oogenesis by preventing ectopic heterochromatin spreading.