title: The A- and B-type nuclear lamin networks: microdomains involved in chromatin organization and transcription.
abstract: The nuclear lamins function in the regulation of replication, transcription, and epigenetic modifications of chromatin. However, the mechanisms responsible for these lamin functions are poorly understood. We demonstrate that A- and B-type lamins form separate, but interacting, stable meshworks in the lamina and have different mobilities in the nucleoplasm as determined by fluorescence correlation spectroscopy (FCS). Silencing lamin B1 (LB1) expression dramatically increases the lamina meshwork size and the mobility of nucleoplasmic lamin A (LA). The changes in lamina mesh size are coupled to the formation of LA/C-rich nuclear envelope blebs deficient in LB2. Comparative genomic hybridization (CGH) analyses of microdissected blebs, fluorescence in situ hybridization (FISH), and immunofluorescence localization of modified histones demonstrate that gene-rich euchromatin associates with the LA/C blebs. Enrichment of hyperphosphorylated RNA polymerase II (Pol II) and histone marks for active transcription suggest that blebs are transcriptionally active. However, in vivo labeling of RNA indicates that transcription is decreased, suggesting that the LA/C-rich microenvironment induces promoter proximal stalling of Pol II. We propose that different lamins are organized into separate, but interacting, microdomains and that LB1 is essential for their organization. Our evidence suggests that the organization and regulation of chromatin are influenced by interconnections between these lamin microdomains.
authors.affiliation: Department of Cell and Molecular Biology, Northwestern University, Feinberg School of Medicine, Chicago, Illinois 60611, USA.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Shimi
authors.forename: Katrin
authors.initials: K
authors.lastname: Pfleghaar
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Kojima
authors.forename: Chan-Gi
authors.initials: CG
authors.lastname: Pack
authors.forename: Irina
authors.initials: I
authors.lastname: Solovei
authors.forename: Anne E
authors.initials: AE
authors.lastname: Goldman
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Adam
authors.forename: Dale K
authors.initials: DK
authors.lastname: Shumaker
authors.forename: Masataka
authors.initials: M
authors.lastname: Kinjo
authors.forename: Thomas
authors.initials: T
authors.lastname: Cremer
authors.forename: Robert D
authors.initials: RD
authors.lastname: Goldman
mesh_terms: D002843:Chromatin / Q000235:genetics* / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000235:genetics*; D004257:DNA Polymerase II / Q000378:metabolism; D005786:Gene Expression Regulation; D020868:Gene Silencing; D006367:HeLa Cells; D006801:Humans; D034904:Lamin Type A / Q000235:genetics*; D034881:Nuclear Lamina / Q000378:metabolism
chemical_list: C114988:CKAP2 protein, human; D002843:Chromatin; D003598:Cytoskeletal Proteins; C494847:LMNA protein, human; D034904:Lamin Type A; D004257:DNA Polymerase II