The truncated prelamin A in Hutchinson-Gilford progeria syndrome alters segregation of A-type and B-type lamin homopolymers.
Hutchinson-Gilford progeria syndrome (HGPS) is a dominant autosomal premature aging syndrome caused by the expression of a truncated prelamin A designated progerin (Pgn). A-type and B-type lamins are intermediate filament proteins that polymerize to form the nuclear lamina network apposed to the inner nuclear membrane of vertebrate somatic cells. It is not known if in vivo both type of lamins assemble independently or co-assemble. The blebbing and disorganization of the nuclear envelope and adjacent heterochromatin in cells from patients with HGPS is a hallmark of the disease, and the ex vivo reversal of this phenotype is considered important for the development of therapeutic strategies. Here, we investigated the alterations in the lamina structure that may underlie the disorganization caused in nuclei by Pgn expression. We studied the polymerization of enhanced green fluorescent protein- and red fluorescent protein-tagged wild-type and mutated lamins in the nuclear envelope of living cells by measuring fluorescence resonance energy transfer (FRET) that occurs between the two fluorophores when tagged lamins interact. Using time domain fluorescence lifetime imaging microscopy that allows a quantitative analysis of FRET signals, we show that wild-type lamins A and B1 polymerize in distinct homopolymers that further interact in the lamina. In contrast, expressed Pgn co-assembles with lamin B1 and lamin A to form a mixed heteropolymer in which A-type and B-type lamin segregation is lost. We propose that such structural lamina alterations may be part of the primary mechanisms leading to HGPS, possibly by impairing functions specific for each lamin type such as nuclear membrane biogenesis, signal transduction, nuclear compartmentalization and gene regulation.
Département de Biologie Cellulaire, Institut Jacques Monod, CNRS, Université Paris 6 and 7, 2 Place Jussieu Tour 43, 75251 Paris Cedex 05, France.
Erwan
E
Delbarre
Marc
M
Tramier
Maïté
M
Coppey-Moisan
Claire
C
Gaillard
Jean-Claude
JC
Courvalin
Brigitte
B
Buendia
D000818:Animals; D002478:Cells, Cultured; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D034904:Lamin Type A / Q000235:genetics / Q000378:metabolism*; D034921:Lamin Type B / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence / Q000379:methods; D008954:Models, Biological; D008957:Models, Genetic; D032446:Myoblasts / Q000166:cytology / Q000378:metabolism; D009685:Nuclear Envelope / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011371:Progeria / Q000378:metabolism*; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D034904:Lamin Type A; D034921:Lamin Type B; D009687:Nuclear Proteins; D011498:Protein Precursors; C485184:enhanced green fluorescent protein; C090764:prelamin A; D049452:Green Fluorescent Proteins