The integrity of a lamin-B1-dependent nucleoskeleton is a fundamental determinant of RNA synthesis in human cells

Abstract

Spatial organisation of nuclear compartments is an important regulator of chromatin function, yet the molecular principles that maintain nuclear architecture remain ill-defined. We have used RNA interference to deplete key structural nuclear proteins, the nuclear lamins. In HeLa cells, we show that reduced expression of lamin B1, but not lamin A/C, severely inhibits RNA synthesis – first by RNA polymerase II and later by RNA polymerase I. Declining levels of transcription correlate with different morphological changes in major nuclear compartments, nucleoli and nuclear speckles. Ultimately, nuclear changes linked to the loss of synthetic activity result in expansion of the inter-chromatin domain and corresponding changes in the structure and spatial organisation of chromosome territories, which relocate towards the nuclear periphery. These results show that a lamin B1-containing nucleoskeleton is required to maintain RNA synthesis and that ongoing synthesis is a fundamental determinant of global nuclear architecture in mammalian cells.

The B-type lamin is required for somatic repression of testis-specific gene clusters

“…The derepression of testis-specific gene clusters upon ablation of LamDm 0 in somatic cells was selective because a number of other genes not included in such clusters were not affected. This effect was different from the global down-regulation of RNA polymerase activity previously reported in the Lamin B1-ablated mammalian cells (62). Such difference is probably due to the high mortality caused by the Lamin B1 ablation (62), whereas in our experiments the reduced levels of LamDm 0 were physiologically acceptable as evidenced by the survival of the Lam 04643 /Lam ari3 mutants through adulthood.…”

“…This effect was different from the global down-regulation of RNA polymerase activity previously reported in the Lamin B1-ablated mammalian cells (62). Such difference is probably due to the high mortality caused by the Lamin B1 ablation (62), whereas in our experiments the reduced levels of LamDm 0 were physiologically acceptable as evidenced by the survival of the Lam 04643 /Lam ari3 mutants through adulthood. Thus, our studies, which took advantage of Drosophila that can tolerate severe changes in the B-type lamin dosage, provided unique direct experimental evidence that this major component of nuclear lamina is involved in repression of tissue-specific multigenic domains.…”

An Absence of Nuclear Lamins in Keratinocytes Leads to Ichthyosis, Defective Epidermal Barrier Function, and Intrusion of Nuclear Membranes and Endoplasmic Reticulum into the Nuclear Chromatin

“…An RNA interference (RNAi) knockdown of lamin B1 and lamin B2 was reported to lead to mitotic arrest and apoptosis (6). Other studies reported that B-type lamins were important for chromatin organization and proper gene expression (7,8).…”

“…An RNA interference (RNAi) knockdown of lamin B1 and lamin B2 was reported to lead to mitotic arrest and apoptosis (6). Other studies reported that B-type lamins were important for chromatin organization and proper gene expression (7,8).The view that B-type lamins play crucial roles in the cell nucleus likely dampened enthusiasm for testing the importance of B-type lamins in knockout mice. Ultimately, however, Yang et al (9) created conditional knockout alleles for both Lmnb1 and Lmnb2 and used those alleles to generate keratinocyte-specific Lmnb1 Lmnb2 knockout mice.…”

“…T he B-type lamins, which are expressed in virtually all cells from the earliest stages of development, have been assumed to play vital functions in the cell nucleus (1)(2)(3)(4)(5)(6)(7)(8). Multiple studies contributed to this view.…”