Functions and dysfunctions of the nuclear lamin Ig-fold domain in nuclear assembly, growth, and Emery–Dreifuss muscular dystrophy

doi:10.1073/pnas.0507612102

Functions and dysfunctions of the nuclear lamin Ig-fold domain in nuclear assembly, growth, and Emery–Dreifuss muscular dystrophy

^*Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, 303 East Chicago Avenue, Chicago, IL 60611; and ^‡Division Molecular Genetics, German Cancer Research Center, D-69120 Heidelberg, Germany

Communicated by Laszlo Lorand, Feinberg School of Medicine, Northwestern University, Chicago, IL, August 31, 2005 (received for review June 5, 2005)

Abstract

The non-α-helical C terminus of Xenopus lamin B3 (LB3T) inhibits the polymerization of lamin B3 in vitro and prevents the assembly of nuclei in Xenopus egg interphase extracts. To more precisely define the functions of LB3T in nuclear assembly, we have expressed subdomains of LB3T and determined their effects on nuclear assembly in Xenopus extracts. The results demonstrate that the Ig-fold motif (LB3T-Ig) is sufficient to inhibit lamin polymerization in vitro. Addition of the LB3T-Ig to egg extracts before the introduction of chromatin prevents chromatin decondensation and the assembly of the lamina, membranes, and pore complexes comprising the nuclear envelope. When added to assembled nuclei, LB3T-Ig prevents the further incorporation of lamin B3 into the endogenous lamina and blocks nuclear growth. The introduction of a point mutation in LB3T-Ig (R454W; LB3T-IgRW), known to cause Emery–Dreifuss muscular dystrophy when present in lamin A, does not inhibit lamin polymerization, chromatin decondensation, or nuclear assembly and growth. These results shed light on the specific alterations in lamin functions attributable to a known muscular dystrophy mutation and provide an experimental framework for revealing the effects of other mutations causing a wide range of laminopathies.

Footnotes

↵ § To whom correspondence should be addressed. E-mail: r-goldman{at}northwestern.edu.
↵ † D.K.S. and R.I.L.-S. contributed equally to this work.
Author contributions: D.K.S., R.I.L.-S., and R.D.G. designed research; D.K.S. and R.I.L.-S. performed research; S.A.A., H.H., R.D.M., and T.P.S. contributed new reagents/analytic tools; D.K.S., R.I.L.-S., and R.D.G. analyzed data; and D.K.S., R.I.L.-S., and R.D.G. wrote the paper.
Abbreviations: LB3T, C-terminal domain of Xenopus lamin B3; LA, lamin A; PB, protein buffer; FLAG-LB3, FLAG-tagged lamin B3; LB3T-Ig, lamin B3 Ig-fold; LB3T-IgRW, lamin B3 with point mutation R454W; NWB, nuclear wash buffer; LAB, lamin assembly buffer; EDMD, Emery–Dreifuss muscular dystrophy; NLS, nuclear localization signal.
Freely available online through the PNAS open access option.