title: Chromosomal dynamics at the Shh locus: limb bud-specific differential regulation of competence and active transcription.
abstract: The expression of Sonic hedgehog (Shh) in mouse limb buds is regulated by a long-range enhancer 1 Mb upstream of the Shh promoter. We used 3D-FISH and chromosome conformation capture assays to track changes at the Shh locus and found that long-range promoter-enhancer interactions are specific to limb bud tissues competent to express Shh. However, the Shh locus loops out from its chromosome territory only in the posterior limb bud (zone of polarizing activity or ZPA), where Shh expression is active. Notably, while Shh mRNA is detected throughout the ZPA, enhancer-promoter interactions and looping out were only observed in small fractions of ZPA cells. In situ detection of nascent Shh transcripts and unstable EGFP reporters revealed that active Shh transcription is likewise only seen in a small fraction of ZPA cells. These results suggest that chromosome conformation dynamics at the Shh locus allow transient pulses of Shh transcription.
authors.affiliation: Mammalian Genetics Laboratory, Genetic Strains Research Center, National Institute of Genetics, Mishima, Shizuoka, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Amano
authors.forename: Tomoko
authors.initials: T
authors.lastname: Sagai
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Tanabe
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Mizushina
authors.forename: Hiromi
authors.initials: H
authors.lastname: Nakazawa
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Shiroishi
mesh_terms: D000818:Animals; D002875:Chromosomes / Q000378:metabolism / Q000648:ultrastructure; D004742:Enhancer Elements, Genetic; D018507:Gene Expression Regulation, Developmental; D017930:Genes, Reporter; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism; D017404:In Situ Hybridization, Fluorescence; D018878:Limb Buds / Q000033:anatomy & histology / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009024:Morphogenesis; D012322:RNA Precursors / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D053823:Hedgehog Proteins; D012322:RNA Precursors; C465570:Shh protein, mouse