Revisiting the truncated lamin A produced by a commonly used strain of Lmna knockout mice

ABSTRACT

The Lmna knockout mouse (Lmna^–/–) created by Sullivan and coworkers in 1999 has been widely used to examine lamin A/C function. The knockout allele contains a deletion of Lmna intron 7–exon 11 sequences and was reported to be a null allele. Later, Jahn and coworkers discovered that the mutant allele produces a 54-kDa truncated lamin A and identified, by RT-PCR, a Lmna cDNA containing exon 1–7 + exon 12 sequences. Because exon 12 encodes prelamin A’s CaaX motif, the mutant lamin A is assumed to be farnesylated. In the current study, we found that the truncated lamin A in Lmna^–/– mouse embryonic fibroblasts (MEFs) was predominantly nucleoplasmic rather than at the nuclear rim, leading us to hypothesize that it was not farnesylated. Our study revealed that the most abundant Lmna transcripts in Lmna^–/– MEFs contain exon 1–7 but not exon 12 sequences. Exon 1–7 + exon 12 transcripts were detectable by PCR but in trace amounts. We suspect that these findings explain the nucleoplasmic distribution of the truncated lamin A in Lmna^–/– MEFs, and subsequent cell transduction experiments support this suspicion. A truncated lamin A containing exon 1–7 sequence was nucleoplasmic, whereas a lamin A containing exon 1–7 + exon 12 sequences was located along the nuclear rim. Our study explains the nucleoplasmic targeting of truncated lamin A in Lmna^–/– MEFs and adds to our understanding of a commonly used strain of Lmna^–/– mice.

KEYWORDS:

• Lamins
• LMNA deficiency
• lmna transcripts
• nuclear envelope
• nuclear lamina
• protein farnesylation

Acknowledgments

Virus production and transduction were performed by the IMTC/UCLA Vector Core, which is supported by CURE/P30 DK041301. Flow cytometry was performed in the UCLA Jonsson Comprehensive Cancer Center (JCCC) and Center for AIDS Research Flow Cytometry Core Facility that is supported by the National Institutes of Health awards P30 CA016042 and 5P30 AI028697, and by the JCCC, the UCLA AIDS Institute, the David Geffen School of Medicine at UCLA, the UCLA Chancellor’s Office, and the UCLA Vice Chancellor’s Office of Research.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data supporting the findings of this study are available within the article and its supplementary materials from Supplementary file 1 and Supplementary file 2.

Author contributions

J.R.K. and S.G.Y. designed research; J.R.K., P.H.K., A.S., and Y.T. performed research; J.R.K. and S.G.Y. analyzed data; and J.R.K. and S.G.Y. wrote the paper.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/19491034.2023.2262308

Additional information

Funding

The author(s) reported that there is no funding associated with the work featured in this article.