Nongenic, bidirectional transcription precedes and may promote developmental DNA deletion in Tetrahymena thermophila.
A large number of DNA segments are excised from the chromosomes of the somatic nucleus during development of Tetrahymena thermophila. How these germline-limited sequences are recognized and excised is still poorly understood. We have found that many of these noncoding DNAs are transcribed during nuclear development. Transcription of the germline-limited M element occurs from both DNA strands and results in heterogeneous transcripts of < 200 b to > 1 kb. Transcripts are most abundant when developing micro- and macronuclei begin their differentiation. Transcription is normally restricted to unrearranged DNA of micronuclei and/or developing nuclei, but germline-limited DNAs can induce their own transcription when placed into somatic macronuclei. Brief actinomycin D treatment of conjugating cells blocked M-element excision, providing evidence that transcription is important for efficient DNA rearrangement. We propose that transcription targets these germline-limited sequences for elimination by altering chromatin to ensure their accessibility to the excision machinery.
Chalker
D L
DL
Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA. dchalker@biology.wustl.edu
Yao
M C
MC
D000818:Animals; D015152:Blotting, Northern; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D004247:DNA / Q000032:analysis; D021901:DNA, Intergenic / Q000235:genetics* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D015321:Gene Rearrangement / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017384:Sequence Deletion; D016808:Tetrahymena thermophila / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
D002843:Chromatin; D021901:DNA, Intergenic; D012333:RNA, Messenger; D004247:DNA