Cell cycle regulated transcription of heterochromatin in mammals vs. fission yeast: functional conservation or coincidence?
Although it is tempting to speculate that the transcription-dependent heterochromatin assembly pathway found in fission yeast may operate in higher mammals, transcription of heterochromatin has been difficult to substantiate in mammalian cells. We recently demonstrated that transcription from the mouse pericentric heterochromatin major (gamma) satellite repeats is under cell cycle control, being sharply downregulated at the metaphase to anaphase transition and resuming in late G(1)-phase dependent upon passage through the restriction point. The highest rates of transcription were in early S-phase and again in mitosis with different RNA products detected at each of these times.(1) Importantly, differences in the percentage of cells in G(1)-phase can account for past discrepancies in the detection of major satellite transcripts and suggest that pericentric heterochromatin transcription takes place in all proliferating mammalian cells. A similar cell cycle regulation of heterochromatin transcription has now been shown in fission yeast,(2,3) providing further support for a conserved mechanism. However, there are still fundamental differences between these two systems that preclude the identification of a functional or mechanistic link.
Lu
Junjie
J
Department of Biological Science, Florida State University, Tallahassee, Florida 32306-4295, USA.
Gilbert
David M
DM
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D060565:Argonaute Proteins; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D042002:Chromatin Assembly and Disassembly; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D053487:DEAD-box RNA Helicases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004722:Endoribonucleases / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D006570:Heterochromatin / Q000378:metabolism*; D051379:Mice; D046912:Multiprotein Complexes / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D043244:Ribonuclease III; D012568:Schizosaccharomyces / Q000378:metabolism; D015398:Signal Transduction; D013004:Somatostatin / Q000031:analogs & derivatives / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
C526735:Ago2 protein, mouse; D060565:Argonaute Proteins; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D015852:Eukaryotic Initiation Factor-2; D006570:Heterochromatin; D046912:Multiprotein Complexes; D010446:Peptide Fragments; D014157:Transcription Factors; C108312:condensin complexes; D013004:Somatostatin; C043819:somatostatin, cyclic hexapeptide(Phe-Phe-Trp-Lys-Thr-Phe)-; D004722:Endoribonucleases; C509781:Dicer1 protein, mouse; D043244:Ribonuclease III; D000251:Adenosine Triphosphatases; D053487:DEAD-box RNA Helicases