Direct synthesis of lamin A, bypassing prelamin a processing, causes misshapen nuclei in fibroblasts but no detectable pathology in mice.
Lamin A, a key component of the nuclear lamina, is generated from prelamin A by four post-translational processing steps: farnesylation, endoproteolytic release of the last three amino acids of the protein, methylation of the C-terminal farnesylcysteine, and finally, endoproteolytic release of the last 15 amino acids of the protein (including the farnesylcysteine methyl ester). The last cleavage step, mediated by ZMPSTE24, releases mature lamin A. This processing scheme has been conserved through vertebrate evolution and is widely assumed to be crucial for targeting lamin A to the nuclear envelope. However, its physiologic importance has never been tested. To address this issue, we created mice with a "mature lamin A-only" allele (Lmna(LAO)), which contains a stop codon immediately after the last codon of mature lamin A. Thus, Lmna(LAO/LAO) mice synthesize mature lamin A directly, bypassing prelamin A synthesis and processing. The levels of mature lamin A in Lmna(LAO/LAO) mice were indistinguishable from those in "prelamin A-only" mice (Lmna(PLAO/PLAO)), where all of the lamin A is produced from prelamin A. Lmna(LAO/LAO) exhibited normal body weights and had no detectable disease phenotypes. A higher frequency of nuclear blebs was observed in Lmna(LAO/LAO) embryonic fibroblasts; however, the mature lamin A in the tissues of Lmna(LAO/LAO) mice was positioned normally at the nuclear rim. We conclude that prelamin A processing is dispensable in mice and that direct synthesis of mature lamin A has little if any effect on the targeting of lamin A to the nuclear rim in mouse tissues.
Coffinier
Catherine
C
Department of Medicine, University of California, Los Angeles, CA 90095, USA. coffinie@ucla.edu
Jung
Hea-Jin
HJ
Li
Ziwei
Z
Nobumori
Chika
C
Yun
Ui Jeong
UJ
Farber
Emily A
EA
Davies
Brandon S
BS
Weinstein
Michael M
MM
Yang
Shao H
SH
Lammerding
Jan
J
Farahani
Javad N
JN
Bentolila
Laurent A
LA
Fong
Loren G
LG
Young
Stephen G
SG
D000818:Animals; D015153:Blotting, Western; D002467:Cell Nucleus / Q000473:pathology*; D017124:Conserved Sequence; D003433:Crosses, Genetic; D004622:Embryo, Mammalian; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism / Q000473:pathology*; D007438:Introns; D034904:Lamin Type A / Q000096:biosynthesis* / Q000235:genetics; D008745:Methylation; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D046188:Protein Modification, Translational; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D014714:Vertebrates
D034904:Lamin Type A; D009687:Nuclear Proteins; D011498:Protein Precursors; C090764:prelamin A