Article Abstract:
Nongenic, bidirectional transcription has been found to precede developmental DNA deletion in Tetrahymena thermophila, one of the ciliated protozoa, and it may promote it as well. It has been shown that many of the noncoding DNAs are transcribed during nuclear development. Germline-limited sequences excised from the somatic nucleus in the development of the organism have been studied. Transcription seems to target the germline-limited sequences for elimination by altering chromatin to ensure accessibility to excision machinery.
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Article Abstract:
Asynchronous replication timing of imprinted loci has been found to be independent of DNA methylation, but is consistent with differential subnuclear localization. Replication timing in Dnmt1- an d Dnmt3L-deficient embryonic stem (ES) cells was analyzed. The ES cells lack differential DNA methylation and imprinted gene expression, but maintain asynchronous replication .
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Article Abstract:
Excision of micronuclear-specific DNA in Tetrahymena thermophila, a binuclear ciliate, is discussed. It requires parental expression of Pdd2p, a polypeptide, and it occurs independently of DNA replication. Pdd2p is in a small set of Tetrahymena polypeptides for which the time of synthesis, nuclear localization and physical association with sequences to be eliminated suggest involvement in the DNA elimination process. Loss of parental expression of Pdd2p leads to perturbing of several DNA rearrangement processes in developing zygotic macronuclei.
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