The lamin CxxM motif promotes nuclear membrane growth.
We analyzed the influence of lamins on nuclear envelope growth in cultured Xenopus A6 cells by the overexpression of human lamin A, Xenopus and zebrafish lamins B2 and Drosophila lamins Dm0 and C as GFP fusion proteins. Lamins containing a CxxM motif in their primary sequence (lamins A, B2, Dm0) induced the formation of lobulated nuclei with multi-membrane-layered, highly folded nuclear membranes and intranuclear membrane assemblies, as observed by electron microscopy. Such morphological alterations were not observed with Drosophila lamin C, a lamin without this motif or with a lamin B2 mutant (B2-SxxM) where the cysteine of the CxxM motif is replaced by a serine. Drosophila lamin C mutants containing a CxxM motif behaved like B-type lamins thus confirming that this tetrapeptide is directly involved in the morphological changes we observed. Nuclear membrane proliferation could also be induced by lamin B2 in COS-7 cells and in zebrafish embryos but not by human lamin A in COS-7 cells. We speculate that the human lamin A is incompletely processed in Xenopus A6 cells and therefore behaves in this cell line like a B-type lamin. Our results indicate that the CxxM motif of B-type lamins has a dual function: it mediates lamin targeting to the inner nuclear membrane thereby promoting nuclear membrane growth.
Prüfert
Kristina
K
Division of Electron Microscopy, Biocenter of the University of Würzburg, Am Hubland, 97074 Würzburg, Germany.
Vogel
Annette
A
Krohne
Georg
G
D020816:Amino Acid Motifs; D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D049109:Cell Proliferation; D003545:Cysteine / Q000737:chemistry; D004330:Drosophila / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D034904:Lamin Type A / Q000737:chemistry* / Q000235:genetics*; D034921:Lamin Type B / Q000737:chemistry / Q000235:genetics*; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009154:Mutation; D009685:Nuclear Envelope / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D014158:Transcription, Genetic; D014162:Transfection; D014981:Xenopus; D015027:Zebrafish
D034904:Lamin Type A; D034921:Lamin Type B; C440308:lamin C; D049452:Green Fluorescent Proteins; D003545:Cysteine