SEQUENCE-SPECIFIC EPIGENETIC EFFECTS OF THE MATERNAL SOMATIC GENOME ON DEVELOPMENTAL REARRANGEMENTS OF THE ZYGOTIC GENOME IN PARAMECIUM-PRIMAURELIA

In ciliates, the germ line genome is extensively rearranged during the development of the somatic macronucleus from a mitotic product of the zygotic nucleus. Germ line chromosomes are fragmented in specific reg ions, and a large number of internal sequence elements are eliminated. It was previously shown that transformation of the vegetative macronu cleus of Paramecium primaurelia with a plasmid containing a subtelomer ic surface antigen gene can affect the processing of the homologous ge rm line genomic region during development of a new macronucleus in sex ual progeny of transformed clones. The gene and telomere-proximal flan king sequences are deleted from the new macronuclear genome, although the germ line genome remains wild type. Here we show that plasmids con taining nonoverlapping segments of the same genomic region are able to induce similar terminal deletions; the locations of deletion end poin ts depend on the particular sequence used. Transformation of the mater nal macronucleus with a sequence internal to a macronuclear chromosome also causes the occurrence of internal deletions between short direct repeats composed of alternating thymines and adenines. The epigenetic influence of maternal macronuclear sequences on developmental rearran gements of the zygotic genome thus appears to be both sequence specifi c and general, suggesting that this trans-nucleus effect is mediated b y pairing of homologous sequences.