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Nuclear pore complex evolution: A trypanosome Mlp analog functions in chromosomal segregation but lacks transcriptional barrier activity

ABSTRACT: The nuclear pore complex (NPC) has dual roles in nucleocytoplasmic transport and chromatin organisation. In many eukaryotes the coiled coil Mlp/Tpr proteins of the NPC nuclear basket have specific roles in interactions with chromatin and defining specialised regions of active transcription, while Mlp2 associates with the mitotic spindle in a cell-cycle dependent manner. We previously identified two putative Mlp-related proteins in African trypanosomes, TbNup110 and TbNup92, the latter of which associates with the spindle. We now provide evidence for independent ancestry for TbNup92/TbNup110 and Mlp/Tpr proteins. However, TbNup92 is required for correct chromosome segregation, with knockout cells exhibiting microaneuploidy and low fidelity telomere segregation. Further, TbNup92 is intimately associated with the mitotic spindle and spindle anchor site, but apparently has minimal roles in the control of gene transcription, indicating that TbNup92 lacks major barrier activity. TbNup92 therefore acts as a functional analog of Mlp/Tpr proteins, and together with the lamina analog NUP-1, represents a cohort of novel proteins operating at the nuclear periphery of trypanosomes, uncovering complex evolutionary trajectories for the NPC and nuclear lamina.

ORGANISM(S): Trypanosoma brucei

PROVIDER: GSE56436 | GEO | 2014/04/03

SECONDARY ACCESSION(S): PRJNA243315

REPOSITORIES: GEO

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Project description:Nup133 belongs to the Y-complex, a key component of the nuclear pore complex (NPC) scaffold. Studies on a null mutation in mice previously revealed that Nup133 is essential for embryonic development but not for mouse embryonic stem cells (mESCs) proliferation. Using single pore detection and average NE-fluorescence intensity, we find that Nup133 is dispensable for interphase and postmitotic NPC scaffold assembly in pluripotent mESCs. However, loss of Nup133 specifically perturbs the formation of the nuclear basket as manifested by the absence of Tpr in about half of the NPCs combined with altered dynamics of Nup153. Nup153 is a large multifunctional protein that interacts with both the Y-complex and Tpr through its N-terminal NPC-targeting domain (NTD, [aa 1-339]) (Hase and Cordes, 2003; Vasu et al., 2001). To explore the possibility that the interaction between Nup153-NTD and the Y-complex or Tpr requires Nup133, we performed pull down assays on whole protein extracts from WT and Nup133-/- mESCs using recombinant Nup153-NTD [aa 1-339] as bait. Nup153 [aa 1-245], lacking the binding domains for the Y-complex and Tpr served as control. Western blot and quantitative mass spectrometry analyses detected Nup133 only in WT samples and documented its specific enrichment, along with other tested Y-Nups and Tpr, in the Nup153-NTD [aa 1-339] bound fraction. These analyses also revealed a similar enrichment of Tpr and Y-complex proteins in Nup153-NTD [aa 1-339]-purified extracts from either WT or Nup133-/- mESCs. These data show that in the context of whole cell lysates containing NPCs as dissociated subcomplexes, the lack of Nup133 neither precludes nor appreciably affects the biochemical interaction between Nup153-NTD and the Y-complex or Tpr. This differs from the in vivo situation that revealed a measurable impact of Nup133 on Nup153 dynamics and Tpr localization in the context of assembled NPCs. This apparent discrepancy between our in vitro and in vivo data indicates that the structural integrity of the NPC is likely required to visualize the contribution of Nup133 to the binding of Nup153 to Tpr or to the Y-complex. Hase, M.E., and Cordes, V.C. (2003). Direct interaction with nup153 mediates binding of Tpr to the periphery of the nuclear pore complex. Mol Biol Cell 14, 1923-1940. Vasu, S., Shah, S., Orjalo, A., Park, M., Fischer, W.H., and Forbes, D.J. (2001). Novel vertebrate nucleoporins Nup133 and Nup160 play a role in mRNA export. J Cell Biol 155, 339-354.

Project description:In Saccharomyces cerevisiae, specific genes physically relocate from the nucleoplasm to the nuclear periphery concomitant with transcriptional activation, where they associate with the nuclear pore complex (NPC). We took a genomics approach in order to gain insight into the universality and physiological relevance of the interaction between active genes and the NPC. Using synthetic genetic array (SGA) approach, we identified interactions between components of the SAGA histone acetyltransferase complex and the Mlp and Nup60 subunits of the NPC. Cells lacking these SAGA and NPC components display growth defects under optimal growth conditions, in which cells are grown on rich medium containing the preferred sugar glucose as a carbon source and incubated at their optimal temperature. That growth defects were observed under these non-stress conditions suggests that these interactions are indicative of defects in normal cell physiology. These results are consistent with a model where physical interactions between the NPC and SAGA are important for transcription of constitutively expressed genes. To test this hypothesis, we used microarray analysis to assess changes global transcript levels in the absence of Nup60, Ada2, or Nup60 and Ada2. Microarray analysis reveals that the growth defect in these double mutants is correlated with a synthetic reduction in steady-state transcript levels for numerous genes that are strongly expressed in wildtype cells. These results suggest that SAGA and Nup60 cooperate in transcriptional regulation, and are consistent with a model for global regulation of SAGA-dependent transcription at the NPC. Wildype, single deletion, and double deletion cells were inoculated to equal starting ODs in 50 mL YEPD media and grown at 30C with shaking. Cells were collected at mid-log phase, washed with chilled water, and stored at -80C for later processing. RNA was isolated using TRIzol reagent according to the manufacturer's protocol, with modification for yeast cells.

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Nuclear pore complex evolution: A trypanosome Mlp analog functions in chromosomal segregation but lacks transcriptional barrier activity

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