title: Heritable gene silencing in lymphocytes delays chromatid resolution without affecting the timing of DNA replication.
abstract: Temporal control of DNA replication has been implicated in epigenetic regulation of gene expression on the basis of observations that certain tissue-specific genes replicate earlier in expressing than non-expressing cells. Here, we show evidence that several leukocyte-specific genes replicate early in lymphocytes regardless of their transcription and also in fibroblasts, where these genes are never normally expressed. Instead, the heritable silencing of some genes (Rag-1, TdT, CD8alpha and lambda5) and their spatial recruitment to heterochromatin domains within the nucleus of lymphocytes resulted in a markedly delayed resolution of sister chromatids into doublet signals discernable by 3D fluorescence in situ hybridization (FISH). Integration of transgenes within heterochromatin (in cis) did, however, confer late replication and this was reversed after variegated transgene expression. These findings emphasise that chromosomal location is important for defining the replication timing of genes and show that retarded sister-chromatid resolution is a novel feature of inactive chromatin.
authors.affiliation: Lymphocyte Development Group, MRC Clinical Sciences Centre, Imperial College School of Medicine, Hammersmith Hospital, Du Cane Road, London W12 ONN, UK. v.azuara@csc.mrc.ac.uk
authors.forename: Véronique
authors.initials: V
authors.lastname: Azuara
authors.forename: Karen E
authors.initials: KE
authors.lastname: Brown
authors.forename: Ruth R E
authors.initials: RR
authors.lastname: Williams
authors.forename: Natasha
authors.initials: N
authors.lastname: Webb
authors.forename: Niall
authors.initials: N
authors.lastname: Dillon
authors.forename: Richard
authors.initials: R
authors.lastname: Festenstein
authors.forename: Veronica
authors.initials: V
authors.lastname: Buckle
authors.forename: Matthias
authors.initials: M
authors.lastname: Merkenschlager
authors.forename: Amanda G
authors.initials: AG
authors.lastname: Fisher
mesh_terms: D000818:Animals; D016827:CD8 Antigens / Q000235:genetics / Q000378:metabolism; D002453:Cell Cycle / Q000235:genetics*; D002460:Cell Line; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D002556:Cerebrospinal Fluid Proteins / Q000235:genetics / Q000378:metabolism; D002842:Chromatids / Q000235:genetics*; D004253:DNA Nucleotidylexotransferase / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication / Q000235:genetics*; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000235:genetics*; D020868:Gene Silencing / Q000502:physiology*; D006570:Heterochromatin / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008214:Lymphocytes / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D019076:Transgenes / Q000235:genetics
chemical_list: D016827:CD8 Antigens; C431698:CD8alpha antigen; D002556:Cerebrospinal Fluid Proteins; D006570:Heterochromatin; D018398:Homeodomain Proteins; C046525:gamma 5 protein, human; C064658:RAG-1 protein; D004253:DNA Nucleotidylexotransferase