Abstract
ABSTRACTThe nuclear pore complex (NPC), a gateway for nucleocytoplasmic trafficking, is composed of ∼30 different proteins called nucleoporins. It remains unknown whether the NPCs within a species are homogeneous or vary depending on the cell type or physiological condition. Here, we present evidence for compositionally distinct NPCs that form within a single cell in a binucleated ciliate. In Tetrahymena thermophila, each cell contains both a transcriptionally active macronucleus (MAC) and a germline micronucleus (MIC). By combining in silico analysis, mass spectrometry analysis for immuno-isolated proteins and subcellular localization analysis of GFP-fused proteins, we identified numerous novel components of MAC and MIC NPCs. Core members of the Nup107–Nup160 scaffold complex were enriched in MIC NPCs. Strikingly, two paralogs of Nup214 and of Nup153 localized exclusively to either the MAC or MIC NPCs. Furthermore, the transmembrane components Pom121 and Pom82 localize exclusively to MAC and MIC NPCs, respectively. Our results argue that functional nuclear dimorphism in ciliates is likely to depend on the compositional and structural specificity of NPCs.
Highlights
Ciliated protozoa maintain two distinct nuclei within the same cytoplasm: a somatic macronucleus (MAC) and a germline micronucleus (MIC) (Fig. 1A) (Eisen et al, 2006; Orias et al, 2011; Karrer, 2012)
In T. thermophila, we previously identified homologs for Nup93 (TtNup93; Gene Model identifier TTHERM_00622800) and Nup155 (TtNup155; TTHERM_00760460), and found both of them distributed to both MAC and MIC nuclear pore complex (NPC) (Iwamoto et al, 2009)
When either the Blast search or the expression profile analysis found similarities to any known Nups, we examined its subcellular localization in T. thermophila by ectopically expressing GFP-fused proteins
Summary
Ciliated protozoa maintain two distinct nuclei within the same cytoplasm: a somatic macronucleus (MAC) and a germline micronucleus (MIC) (Fig. 1A) (Eisen et al, 2006; Orias et al, 2011; Karrer, 2012). The polyploid MAC is transcriptionally active, and its acentromeric chromosomes segregate during cell division by a spindle-independent amitotic process. The diploid MIC has transcriptionally inert, centromeric chromosomes that segregate by canonical mitosis. In Tetrahymena thermophila, DNA replication in the MIC and MAC occurs during non-overlapping periods in the cell cycle. Nuclear dimorphism in ciliates involves nonequivalent regulation of multiple activities in two distinct nuclei (Orias, 2000; Goldfarb and Gorovsky, 2009).
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