Filaments made from A- and B-type lamins differ in structure and organization

Abstract

vertebrate lamin filaments in vitro. Therefore, we have used the oocyte system, where exogenously expressed somatic B-type and A-type lamins assemble into filaments. Expression of Btype lamins induces the formation of intranuclear membranes that are covered by single filament layers. LIII filaments appear identical to the endogenous lamina, whereas lamin B2 assembles into filaments that are organized less precisely. Lamin A induces sheets of thicker filaments on the endogenous lamina and significantly increases the rigidity of the nuclear envelope.

Flaw Tolerance of Nuclear Intermediate Filament Lamina under Extreme Mechanical Deformation

“…13,15 It is noted that so far only amphibian oocytes' nuclear lamina has been shown to form a rather regular lattice, 1,13,15 while the structure of nuclear lamina in other cells is likely more disordered and more tightly associated with chromatin. 13 Thus it is important to note that the model we study here may only represent a first approximation to the structure of other nuclear laminas. Figure 1a illustrates the hierarchical structure of this nuclear lamina.…”

“…1,[12][13][14] Defects in the lamina can also be caused by localized forces from cytoskeletal structures or by atomic-scale defects due to the imperfect assembly of the meshwork, leading to void formation in the meshwork. 1,12,13,15 Another source of imperfections is generated by the clustering of lamin-associated nuclear pore complexes, which can grow rather large and are naturally present in virtually all cells. 13,14,16 Other possible factors include ionizing radiation that results in the breakage of covalent or noncovalent bonds within protein structures and thus results in structural defects.…”

“…1,12,13,15 Another source of imperfections is generated by the clustering of lamin-associated nuclear pore complexes, which can grow rather large and are naturally present in virtually all cells. 13,14,16 Other possible factors include ionizing radiation that results in the breakage of covalent or noncovalent bonds within protein structures and thus results in structural defects. [17][18][19] It has been shown that continuous radiation, as experienced for example during space flight, causes cracks to occur around nuclear pores which leads to a complete fragmentation of nuclear envelopes once a critical defect concentration is reached 17 (see Figure S2 in the Supporting Information).…”

Molecular characterization of Xenopus lamin LIV reveals differences in the lamin composition of sperms in amphibians and mammals

“…On the surface of these membranes, they form IF-like filaments with morphologies characteristic for each particular lamin. 35 To analyze how the insertion of the 40 amino acid residues in lamin LIV might influence filament formation, lamin LIV was expressed in oocytes and nuclear envelope spreads were analyzed by feSEM. The spreads were compared to spreads of oocytes overexpressing lamin LIII.…”

“…35,50 This approach allowed us to analyze the filament forming capabilities of the germ line-specific lamins B3 and LIV ex vivo. In striking contrast to somatic lamins and lamin LIII neither human lamin B3 nor Xenopus lamin LIV formed IF-like filaments in this experimental system.…”