Cell Nuclei Spin in the Absence of Lamin B1

Abstract

Mutations of the nuclear lamins cause a wide range of human diseases, including Emery-Dreifuss muscular dystrophy and Hutchinson-Gilford progeria syndrome. Defects in A-type lamins reduce nuclear structural integrity and affect transcriptional regulation, but few data exist on the biological role of B-type lamins. To assess the functional importance of lamin B1, we examined nuclear dynamics in fibroblasts from Lmnb1 ⌬/⌬ and wild-type littermate embryos by time-lapse videomicroscopy. Here, we report that Lmnb1 ⌬/⌬ cells displayed striking nuclear rotation, with ϳ90% of Lmnb1 ⌬/⌬ nuclei rotating at least 90°during an 8-h period. The rotation involved the nuclear interior as well as the nuclear envelope. The rotation of nuclei required an intact cytoskeletal network and was eliminated by expressing lamin B1 in cells. Nuclear rotation could also be abolished by expressing larger nesprin isoforms with long spectrin repeats. These findings demonstrate that lamin B1 serves a fundamental role within the nuclear envelope: anchoring the nucleus to the cytoskeleton.Mutations in nuclear lamins and lamin-associated proteins cause a panoply of human diseases (laminopathies) including Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy with conduction system disease, Dunnigan-type familial partial lipodystrophy, limb-girdle muscular dystrophy, Charcot-Marie tooth disorder type 2, and Hutchinson-Gilford progeria syndrome (1-7). The mechanism by which these ubiquitously expressed proteins cause such diverse phenotypes is unclear. This is not particularly surprising, though, because the functions of the nuclear lamins themselves are currently incompletely understood.Lamins are the principal components of the nuclear lamina, an intermediate filament meshwork that lines the inner nuclear membrane (8, 9). Lamins are associated with chromatin, other integral proteins of the inner nuclear membrane, inner portions of the nuclear pore complexes (NPCs), 2 and several transcription factors such as SREBP1, retinoblastoma protein, and MOK (10). Thus, lamins are critical for the structural integrity of the nucleus and also play a role in DNA replication, chromatin organization, and transcriptional regulation (11).In mammalian cells, the major A-type lamins, lamins A and C, are alternatively spliced products of LMNA, whereas the major B-type lamins, lamin B1 and lamin B2, are encoded by two distinct genes, LMNB1 and LMNB2, respectively (12). Although the A-and B-type lamins share a similar structure, they differ in their behavior during cell division and their patterns of expression. B-type lamins are found in all cell types and are expressed throughout development, whereas A-type lamins are not present in early embryos (13). Within the nucleus, lamin B1 binds directly to chromatin and histones (14) and interacts with several chromatin-binding inner nuclear membrane proteins (e.g. lamina-associated proteins, lamin B receptor (LBR), and the nuclear pore protein nucleoporin 153) (15). Following mitosis, B-type lamins assemble first into t...

Abnormal development of the cerebral cortex and cerebellum in the setting of lamin B2 deficiency

“…For example, Lammerding and coworkers (31) showed that the nuclei of cells spin in the absence of lamin B1, strongly suggesting that lamin B1 helps to anchor the nucleus to the cytoskeleton. Although the current studies focused entirely on Lmnb2-deficient mice, the involvement of lamin B1 in nuclear-cytoskeletal interactions raises the question of whether lamin B1 might also be important for neuronal migration in the brain.…”

Nuclear lamins and laminopathies

“…These morphological alterations depend upon cell type, lamin protein sequence, protein expression levels in transfected cells and culture conditions. Along with altered nuclear morphology, deficiencies of A-and B-type lamins and expression of certain lamin A variants lead to abnormalities in nuclear mechanics and cellular mechanotransduction [70][71][72][73][74]. Lack of A-type lamins and expression of variants in striated muscle diseases also cause abnormal positioning of nuclei in migrating fibroblasts, which likely results from defective connections between the nucleus and cytoplasm [74,75].…”

Lamins at a glance

“…The protein complex formed by nesprins and SUN proteins is often referred to as the linker of nucleoskeleton and cytoskeleton (LINC) complex (Crisp et al, 2006) and is essential for intracellular force transmission, cell migration and cell polarization (Méjat and Misteli, 2010). Loss of either type of lamin impairs nucleo-cytoskeletal coupling: cells that lack A-type lamins have defects in nuclear positioning and disturbed cytoskeletal organization, with reduced stiffness (Broers et al, 2004;Folker et al, 2011;Hale et al, 2008;Lammerding et al, 2004;Lee et al, 2007;Luxton et al, 2011); B-type lamins are required for nuclear movement in neuronal migration (Coffinier et al, 2010;Kim et al, 2011) and lamin-B1-deficient cells display sustained spontaneous nuclear rotation (Ji et al, 2007).…”