title: Annulate lamellae play only a minor role in the storage of excess nucleoporins in Drosophila embryos.
abstract: The nuclear pore complexes (NPCs), multiprotein assemblies embedded in the nuclear envelope, conduct nucleo-cytoplasmic traffic of macromolecules. Mimics of NPCs, called annulate lamellae pore complexes (ALPCs), are usually found in cytoplasmic membranous stacks in oocytes and early embryonic cells. They are believed to constitute storage compartments for excess premade nucleoporins. To evaluate the extent to which ALPCs store nucleoporins in early embryonic cells we took advantage of syncytial Drosophila embryos, containing both AL and rapidly proliferating nuclei in the common cytoplasm. Electron microscopic morphometric analysis showed that the number of ALPCs did not decrease to compensate for the growing number of NPCs during syncytial development. We performed Western blot analysis to quantify seven different nucleoporins and analyzed their intraembryonal distribution by confocal microscopy and subcellular fractionation. Syncytial embryos contained a large maternally contributed stockpile of nucleoporins. However, even during interphases, only a small fraction of the excess nucleoporins was assembled into ALPCs, whereas the major fraction was soluble and contained at least one phosphorylated nucleoporin. We conclude that in Drosophila embryos ALPCs play only a minor role in storing the excess maternally contributed nucleoporins. Factors that may prevent nucleoporins from assembly into ALPCs are discussed.
authors.affiliation: Section for Natural Sciences, Södertörns University College, SE-14189. Huddinge, Sweden.
authors.forename: Evgeny A
authors.initials: EA
authors.lastname: Onischenko
authors.forename: Natalia V
authors.initials: NV
authors.lastname: Gubanova
authors.forename: Thomas
authors.initials: T
authors.lastname: Kieselbach
authors.forename: Elena V
authors.initials: EV
authors.lastname: Kiseleva
authors.forename: Einar
authors.initials: E
authors.lastname: Hallberg
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D003593:Cytoplasm / Q000378:metabolism; D004331:Drosophila melanogaster / Q000166:cytology* / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000166:cytology* / Q000378:metabolism*; D015726:Giant Cells / Q000737:chemistry / Q000378:metabolism; D037102:Lectins / Q000378:metabolism; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D022022:Nuclear Pore / Q000276:immunology / Q000378:metabolism*; D028861:Nuclear Pore Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D016415:Sequence Alignment; D012995:Solubility; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013347:Subcellular Fractions
chemical_list: D000911:Antibodies, Monoclonal; D037102:Lectins; D028861:Nuclear Pore Complex Proteins