DNA replication analysis of FMRI, XIST, and factor 8C Loci by FISH shows nontranscribed X-linked genes replicate late

Journal Article · Fri Jul 01 04:00:00 EDT 1994 · American Journal of Human Genetics; (United States)

OSTI ID:6822555

Torchia, B S; Call, L M; Migeon, B R ^[1]

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1. John Hopkins Univ. School of Medicine, Baltimore, MD (United States)

The relationship between the transcriptional state of a locus and the time when it replicates during DNA synthesis is increasingly apparent. Active autosomal genes tend to replicate early, whereas inactive ones are more permissive and frequently replicate later. Although the inactive X chromosome replicates later than its active homologue, little is known about the replication of X-linked genes. The authors have used FISH to examine the replication of loci on the active X chromosome that are not transcribed, either because the tissue analyzed was not the expressing tissue (F8C), because the locus is silent on all active X chromosomes (XIST), or because it has been mutated by expansion and methylation of a CpG island (FMR1). In this assay, an unreplicated locus is characterized by a single hybridization signal, and a replicated locus is characterized by a doublet hybridization signal. The percentage of doublets is used as a measure of relative time of replication in S phase. The results show that the FMR1 gene replicates relatively later in fragile X(fraX) males with the full mutation than in normal males, irrespective of the probe used. The F8C locus is late replicating in both normal and fraX males and replicates at nearly the same time on active and inactive X in females. The XIST locus replicates late in all the males studied and asynchronously in female cells. From the late replication of the locus on the active X in males, the authors deduce that the locus on the active X is the later replicating locus in female cells. They conclude that (1) the expansion of the FMR1 locus leads to late replication, (2) silence of the XIST gene in males is associated with late replication of the locus, and (3) this assay will be useful for further studies of the relationship between transcription and replication. 32 refs., 2 figs., 5 tabs.

• OSTI ID: 6822555
• Journal Information: American Journal of Human Genetics; (United States), Journal Name: American Journal of Human Genetics; (United States) Vol. 55:1; ISSN AJHGAG; ISSN 0002-9297
• Country of Publication: United States
• Language: English

Related Subjects

550400* -- Genetics
59 BASIC BIOLOGICAL SCIENCES
CHROMOSOMES
DNA REPLICATION
GENE REGULATION
HETEROCHROMOSOMES
HUMAN CHROMOSOMES
HUMAN X CHROMOSOME
NUCLEIC ACID REPLICATION
TIME DEPENDENCE
TRANSCRIPTION
X CHROMOSOME