Prelamin A and lamin A appear to be dispensable in the nuclear lamina
Loren G. Fong, … , Martin O. Bergo, Stephen G. Young
Loren G. Fong, … , Martin O. Bergo, Stephen G. Young
Published March 1, 2006
Citation Information: J Clin Invest. 2006;116(3):743-752. https://doi.org/10.1172/JCI27125.
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Research Article Genetics

Prelamin A and lamin A appear to be dispensable in the nuclear lamina

Abstract

Lamin A and lamin C, both products of Lmna, are key components of the nuclear lamina. In the mouse, a deficiency in both lamin A and lamin C leads to slow growth, muscle weakness, and death by 6 weeks of age. Fibroblasts deficient in lamins A and C contain misshapen and structurally weakened nuclei, and emerin is mislocalized away from the nuclear envelope. The physiologic rationale for the existence of the 2 different Lmna products lamin A and lamin C is unclear, although several reports have suggested that lamin A may have particularly important functions, for example in the targeting of emerin and lamin C to the nuclear envelope. Here we report the development of lamin C–only mice (Lmna+/+), which produce lamin C but no lamin A or prelamin A (the precursor to lamin A). Lmna+/+ mice were entirely healthy, and Lmna+/+ cells displayed normal emerin targeting and exhibited only very minimal alterations in nuclear shape and nuclear deformability. Thus, at least in the mouse, prelamin A and lamin A appear to be dispensable. Nevertheless, an accumulation of farnesyl–prelamin A (as occurs with a deficiency in the prelamin A processing enzyme Zmpste24) caused dramatically misshapen nuclei and progeria-like disease phenotypes. The apparent dispensability of prelamin A suggested that lamin A–related progeroid syndromes might be treated with impunity by reducing prelamin A synthesis. Remarkably, the presence of a single LmnaLCO allele eliminated the nuclear shape abnormalities and progeria-like disease phenotypes in Zmpste24–/– mice. Moreover, treating Zmpste24–/– cells with a prelamin A–specific antisense oligonucleotide reduced prelamin A levels and significantly reduced the frequency of misshapen nuclei. These studies suggest a new therapeutic strategy for treating progeria and other lamin A diseases.

Authors

Loren G. Fong, Jennifer K. Ng, Jan Lammerding, Timothy A. Vickers, Margarita Meta, Nathan Coté, Bryant Gavino, Xin Qiao, Sandy Y. Chang, Stephanie R. Young, Shao H. Yang, Colin L. Stewart, Richard T. Lee, C. Frank Bennett, Martin O. Bergo, Stephen G. Young

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Figure 1

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Production of a mutant Lmna allele, LmnaLCO. (A) A sequence-replacement ...
Production of a mutant Lmna allele, LmnaLCO. (A) A sequence-replacement vector was used to remove intron 11 and the last 150 nucleotides of exon 11. Unexpectedly, this mutation eliminated the splicing event required to produce prelamin A. Exons are shown as boxes. Locations of the PCR primers (i and ii) and the 5′ flanking probe for Southern blots are shown. tk, thymidine kinase gene (for negative selection). (B) Southern blot detection of the LmnaLCO (LCO/+) allele in EcoRI-cleaved genomic DNA from ES cells. (C) PCR identification of wild-type and LmnaLCO alleles. Shown are results with wild-type (A10, C12) and LmnaLCO/+ (B10, B11, B12) ES cell clones from gene-targeting experiments. (D) Northern blot of total RNA from Lmna+/+ (+/+), LmnaLCO/+ (LCO/+), and Lmna+/+ (LCO/LCO) fibroblasts; the blot was hybridized with a mouse Lmna cDNA probe that detects both prelamin A and lamin C transcripts and a mouse Lmnb1 cDNA probe that detects lamin B1, a closely related lamin protein. (E) Western blots of 3 different wild-type, 2 heterozygous, and 1 homozygous primary fibroblast cell lines at the same passage number with a polyclonal antibody against lamin A/C and actin. A minor form of lamin A lacking exon 10 has been reported previously in some human cells (43). It is conceivable that this minor lamin could be synthesized, but this would require splicing from exon 9 to the exon 11–12 fusion. We have not identified this minor splice variant in the lamin C–only fibroblasts.