Parental expression of the chromodomain protein Pdd1p is required for completion of programmed DNA elimination and nuclear differentiation

Thousands of DNA elimination events occur during somatic differentiation of many ciliated protozoa. In Tetrahymena, the eliminated DNA aggregates into submacronuclear structures containing the protein Pdd1p, a member of the c hromodomain family. We disrupted somatic copies of PDD1, eliminating parent al expression of the gene early in the sexual phase of the life cycle. Even though zygotic expression, from the undisrupted germline PDD1 copy, is act ivated before DNA elimination normally occurs, the somatic knockout cells s uffer defects in DNA elimination, genome endoduplication, and nuclear resor ption, and eventually die, demonstrating that PDD1 is essential and suggest ing Pdd1p is directly involved in establishing a chromatin structure requir ed for DNA elimination.