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.