DNA replication asynchrony between the paternal and maternal alleles of imprinted genes does not straddle the R/G transition.
Imprinted autosomal loci apparently reside in very large chromosomal domains that exhibit asynchrony in replication of homologous alleles during the DNA synthesis phase. Replication asynchrony can be cytogenetically visualized by a replication-banding discordance between homologous bands of a given pair of chromosomal homologs. The replication time of a chromosomal band at high resolution can be determined by blocking DNA synthesis at the R/G-band transition and using replication banding. The R/G transition reflects the transition from early (R-) to late (G- and C-) band DNA replication. We studied discordance between two groups of homologous chromosomal bands: (a) four bands, 6q26-27, 11p13, 11p15.5 and 15q11.2-12, each containing at least one imprinted gene; and (b) nine bands containing no known imprinted genes. Fifty pairs of chromosomes were analyzed at high resolution after R/G transition blocking and late 5-bromo-2'-deoxyuridine incorporation. The rate of discordance was the same for bands containing imprinted genes and for control bands. Both homologous bands of a pair replicate either before or after the R/G transition and do not straddle the R/G transition. Repression associated with imprinting does not appear to involve late replication at the band level of resolution. Tissue-specific inactivation is associated with DNA methylation and late replication, whereas allele-specific inactivation is associated with DNA methylation but not with delayed or late replication.
Drouin
R
R
Unité de Recherche en Génétique Humaine et Moléculaire, Centre de Recherche, Pavillon Saint-François d'Assise, CHUQ, 10 rue de l'Espinay, Universit-e Laval, Qu-ebec, Canada G1L 3L5.
Boutouil
M
M
Fetni
R
R
Holmquist
G P
GP
Scott
P
P
Richer
C L
CL
Lemieux
N
N
D000328:Adult; D000483:Alleles; D002871:Chromosome Banding / Q000379:methods*; D002877:Chromosomes, Human / Q000235:genetics; D004261:DNA Replication / Q000235:genetics*; D005260:Female; D018392:Genomic Imprinting / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016196:S Phase