Clonal variation in gene methylation: c-H-ras and alpha-hCG regions vary independently in human fibroblast lineages.
The stability of DNA methylation has been followed in clonal lineages of human diploid fibroblasts, for the gene regions encoding the c-H-ras proto-oncogene and the alpha subunit of human chorionic gonadotropin (alpha-hCG). Although methylation losses predominated, both de novo gains and losses of cytosine methylation were observed in subclones and sub-subclones, at frequencies which differed between individual clonal lineages, and between the 2 gene regions compared. Methylation of these loci varied independently among clones; e.g., a lineage which showed frequent methylation loss in the c-H-ras gene region remained highly methylated for alpha-hCG, and vice versa. Thus, the fidelity with which DNA methylation is inherited in specific endogenous gene regions must be governed by a clone-specific property affecting local chromatin structure, but apparently not by gene expression per se. Late in the replicative life-span of diploid fibroblasts, as cell replication slowed, restriction patterns for methylation-sensitive enzymes became simpler and more discrete, while those for other enzymes did not change. This is interpreted as a consequence of 'clonal succession', in which the fastest-replicating or longest-lived clones/subclones eventually predominate in a cell population; it could also reflect a decreased rate or a non-random selection of methylation changes in late-passage cells.
Shmookler Reis
R J
RJ
Department of Medicine, University of Arkansas for Medical Sciences, Little Rock.
Finn
G K
GK
Smith
K
K
Goldstein
S
S
D002470:Cell Survival; D006063:Chorionic Gonadotropin / Q000235:genetics*; D002999:Clone Cells; D003596:Cytosine / Q000378:metabolism; D004247:DNA / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D015342:DNA Probes; D004262:DNA Restriction Enzymes; D004587:Electrophoresis, Agar Gel; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D011905:Genes, ras; D014644:Genetic Variation; D006801:Humans; D008745:Methylation; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras); D015183:Restriction Mapping
D006063:Chorionic Gonadotropin; D015342:DNA Probes; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D003596:Cytosine; D004247:DNA; D004262:DNA Restriction Enzymes; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)