Biomedical subjects

Peter Askjaer

Publications and source records attributed to Peter Askjaer.

3 recordsLinked to original sources

PubMed2003

Caenorhabditis elegans nucleoporins Nup93 and Nup205 determine the limit of nuclear pore complex size exclusion in vivo.

Nuclear pore complexes (NPCs) span the nuclear envelope and mediate communication between the nucleus and the cytoplasm. To obtain insight into the structure and function of NPCs of multicellular organisms, we have initiated an extensive analysis of Caenorhabditis elegans nucleoporins. Of 20 assigned C. elegans nucleoporin genes, 17 were found to be essential for embryonic development either alone or in combination. In several cases, depletion of nucleoporins by RNAi caused severe defects in nuclear appearance. More specifically, the C. elegans homologs of vertebrate Nup93 and Nup205 were each found to be required for normal NPC distribution in the nuclear envelope in vivo. Depletion of Nup93 or Nup205 caused a failure in nuclear exclusion of nonnuclear macromolecules of approximately 70 kDa without preventing active nuclear protein import or the assembly of the nuclear envelope. The defects in NPC exclusion were accompanied by abnormal chromatin condensation and early embryonic arrest. Thus, the contribution to NPC structure of Nup93 and Nup205 is essential for establishment of normal NPC function and for cell viability.

Animals↗

PubMed2003

RanGTP mediates nuclear pore complex assembly.

In metazoa, the nuclear envelope breaks down and reforms during each cell cycle. Nuclear pore complexes (NPCs), which serve as channels for transport between the nucleus and cytoplasm, assemble into the reforming nuclear envelope in a sequential process involving association of a subset of NPC proteins, nucleoporins, with chromatin followed by the formation of a closed nuclear envelope fenestrated by NPCs. How chromatin recruitment of nucleoporins and NPC assembly are regulated is unknown. Here we demonstrate that RanGTP production is required to dissociate nucleoporins Nup107, Nup153 and Nup358 from Importin beta, to target them to chromatin and to induce association between separate NPC subcomplexes. Additionally, either an excess of RanGTP or removal of Importin beta induces formation of NPC-containing membrane structures--annulate lamellae--both in vitro in the absence of chromatin and in vivo. Annulate lamellae formation is strongly and specifically inhibited by an excess of Importin beta. The data demonstrate that RanGTP triggers distinct steps of NPC assembly, and suggest a mechanism for the spatial restriction of NPC assembly to the surface of chromatin.

Amino Acid Substitution↗

PubMed2002

Ran GTPase cycle and importins alpha and beta are essential for spindle formation and nuclear envelope assembly in living Caenorhabditis elegans embryos.

The small GTPase Ran has been found to play pivotal roles in several aspects of cell function. We have investigated the role of the Ran GTPase cycle in spindle formation and nuclear envelope assembly in dividing Caenorhabditis elegans embryos in real time. We found that Ran and its cofactors RanBP2, RanGAP, and RCC1 are all essential for reformation of the nuclear envelope after cell division. Reducing the expression of any of these components of the Ran GTPase cycle by RNAi leads to strong extranuclear clustering of integral nuclear envelope proteins and nucleoporins. Ran, RanBP2, and RanGAP are also required for building a mitotic spindle, whereas astral microtubules are normal in the absence of these proteins. RCC1(RNAi) embryos have similar abnormalities in the initial phase of spindle formation but eventually recover to form a bipolar spindle. Irregular chromatin structures and chromatin bridges due to spindle failure were frequently observed in embryos where the Ran cycle was perturbed. In addition, connection between the centrosomes and the male pronucleus, and thus centrosome positioning, depends upon the Ran cycle components. Finally, we have demonstrated that both IMA-2 and IMB-1, the homologues of vertebrate importin alpha and beta, are essential for both spindle assembly and nuclear formation in early embryos.

Aneuploidy↗