title: A CpG-rich RNA and an RNA helicase tightly associated with the DNA demethylation complex are present mainly in dividing chick embryo cells.
abstract: In the developing chicken embryo, active DNA demethylation requires both RNA and proteins (Nucleic Acids Res. 25, 2375-2380, 1997; ibid. 25, 4545-4550, 1997, FEBS Lett. 449, 251-254, 1999a). In vitro assays indicate that in the 5- and 12-day-old embryos the highest specific activity of 5-methylcytosine DNA glycosylase is found in the brain, the eyes and the skin. In situ hybridization with antisense CpG-rich RNA tightly associated to the DNA demethylation complex shows a restricted expression pattern only in proliferating tissues such as the neuroepithelia of the brain in 5-day-old embryos. The RNA is absent in differentiated tissues like the skeletal and heart muscle, liver and the crystallin-producing cells in the lens. The CpG-rich RNA is transcribed in a developmental stage-specific rather than in a cell-specific manner. In contrast transcripts of DNA methyltransferase are found in dividing and quiescent cells. In situ hybridization with a probe of a RNA helicase which is also associated with the DNA demethylation complex shows a very similar localization in mitotically active tissues as the CpG-rich RNA. The content of 5-methylcytosine in individual cells was determined with a specific monoclonal antibody and cytometric analysis on tissue sections. The results indicate that proliferating cells have on the average 15% more methylated cytosines than non-dividing cells. This represents roughly 3x10(6) more methylation sites per haploid genome.
authors.affiliation: Friedrich-Miescher-Institut, Basel/Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Schwarz
authors.forename: C
authors.initials: C
authors.lastname: Bourgeois
authors.forename: F
authors.initials: F
authors.lastname: Soussaline
authors.forename: C
authors.initials: C
authors.lastname: Homsy
authors.forename: A
authors.initials: A
authors.lastname: Podestà
authors.forename: J P
authors.initials: JP
authors.lastname: Jost
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D001973:Bromodeoxyuridine / Q000378:metabolism; D002455:Cell Division; D002642:Chick Embryo; D002645:Chickens; D018899:CpG Islands; D045647:DNA Glycosylases; D019175:DNA Methylation; D015536:Down-Regulation; D005123:Eye / Q000378:metabolism; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008856:Microscopy, Fluorescence; D008938:Mitosis; D009699:N-Glycosyl Hydrolases / Q000096:biosynthesis* / Q000378:metabolism; D009693:Nucleic Acid Hybridization; D020365:RNA Helicases / Q000096:biosynthesis* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012867:Skin / Q000378:metabolism; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D012333:RNA, Messenger; C093335:5-methylcytosine-DNA glycosylase; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D020365:RNA Helicases; D001973:Bromodeoxyuridine