NUP-1 Is a Large Coiled-Coil Nucleoskeletal Protein in Trypanosomes with Lamin-Like Functions

Department of Pathology, University of Cambridge, Cambridge, United Kingdom.
PLoS Biology (Impact Factor: 9.34). 03/2012; 10(3):e1001287. DOI: 10.1371/journal.pbio.1001287
Source: PubMed


A unifying feature of eukaryotic nuclear organization is genome segregation into transcriptionally active euchromatin and transcriptionally repressed heterochromatin. In metazoa, lamin proteins preserve nuclear integrity and higher order heterochromatin organization at the nuclear periphery, but no non-metazoan lamin orthologues have been identified, despite the likely presence of nucleoskeletal elements in many lineages. This suggests a metazoan-specific origin for lamins, and therefore that distinct protein elements must compose the nucleoskeleton in other lineages. The trypanosomatids are highly divergent organisms and possess well-documented but remarkably distinct mechanisms for control of gene expression, including polycistronic transcription and trans-splicing. NUP-1 is a large protein localizing to the nuclear periphery of Trypanosoma brucei and a candidate nucleoskeletal component. We sought to determine if NUP-1 mediates heterochromatin organization and gene regulation at the nuclear periphery by examining the influence of NUP-1 knockdown on morphology, chromatin positioning, and transcription. We demonstrate that NUP-1 is essential and part of a stable network at the inner face of the trypanosome nuclear envelope, since knockdown cells have abnormally shaped nuclei with compromised structural integrity. NUP-1 knockdown also disrupts organization of nuclear pore complexes and chromosomes. Most significantly, we find that NUP-1 is required to maintain the silenced state of developmentally regulated genes at the nuclear periphery; NUP-1 knockdown results in highly specific mis-regulation of telomere-proximal silenced variant surface glycoprotein (VSG) expression sites and procyclin loci, indicating a disruption to normal chromatin organization essential to life-cycle progression. Further, NUP-1 depletion leads to increased VSG switching and therefore appears to have a role in control of antigenic variation. Thus, analogous to vertebrate lamins, NUP-1 is a major component of the nucleoskeleton with key roles in organization of the nuclear periphery, heterochromatin, and epigenetic control of developmentally regulated loci.

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    • "However, the critical functions performed by lamins and their partners in metazoan cells (see above) are fulfilled in the plant cell. Hence, the plant lamina must be established by proteins that evolved separately to those in metazoans, as is the case of the NUP-1-based lamina in trypanosomids (Figure 1; Rout and Field, 2001; Dubois et al., 2012). Similarly, such proteins would represent functional plant homologs of lamins, with similar characteristics rather than sequences. "
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    ABSTRACT: The nuclear lamina is a complex protein mesh attached to the inner nuclear membrane (INM), which is also associated with nuclear pore complexes. It provides mechanical support to the nucleus and nuclear envelope, and as well as facilitating the connection of the nucleoskeleton to the cytoskeleton, it is also involved in chromatin organization, gene regulation, and signaling. In metazoans, the nuclear lamina consists of a polymeric layer of lamins and other interacting proteins responsible for its association with the INM and chromatin. In plants, field emission scanning electron microscopy of nuclei, and thin section transmission electron microscopy of isolated nucleoskeletons, reveals the lamina to have a similar structure to that of metazoans. Moreover, although plants lack lamin genes and the genes encoding most lamin-binding proteins, the main functions of the lamina are fulfilled in plants. Hence, it would appear that the plant lamina is not based on lamins and that other proteins substitute for lamins in plant cells. The nuclear matrix constituent proteins are the best characterized structural proteins in the plant lamina. Although these proteins do not display strong sequence similarity to lamins, their predicted secondary structure and sub-nuclear distribution, as well as their influence on nuclear size and shape, and on heterochromatin organization, suggest they could be functional lamin analogs. In this review we shall summarize what is currently known about the organization and composition of the plant nuclear lamina and its interacting complexes, and we will discuss the activity of this structure in the plant cell and its nucleus.
    Frontiers in Plant Science 04/2014; 5:166. DOI:10.3389/fpls.2014.00166 · 3.95 Impact Factor
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    • "Putative lamin analogs have been identified in Arabidopsis thaliana while a small family of coiled-coil LINC proteins are associated with the A. thaliana nucleus and nuclear periphery and appear to control nuclear size and chromosomal segregation (Dittmer et al., 2007), but these proteins also seem to be land plant specific. Recently NUP-1, a large coiled-coil protein was described in trypanosomes, which performs many of the roles ascribed to lamins, including maintaining nuclear structure and defining heterochromatin (DuBois et al., 2012). While similarities between NUP-1 and lamin functions are striking, in silico analysis has not identified NUP-1 orthologs outside of the kinetoplastida, or common ancestry with unikont lamins or plant LINC proteins. "
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    Critical Reviews in Biochemistry and Molecular Biology 07/2013; 48(4):373-396. DOI:10.3109/10409238.2013.821444 · 7.71 Impact Factor
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    • "Thus, it is of interest to identify functional analogues of lamin in non-metazoans (Peter and Stick, 2012) and indeed, two lamin-like proteins were recently described in unicellular eukaryotes. The Dictyostelium NE81 protein is considered an evolutionary precursor of metazoan lamins (Kruger et al., 2012), while the large coiled-coil nucleoskeletal protein NUP1 of Trypanosoma fulfils lamin functions but it is otherwise unrelated to lamins (Dubois et al., 2012). Plants lack genes that encode lamins but they have a fibrous structure similar to the animal lamina (also called plamina) underlying the inner nuclear membrane (Fiserova et al., 2009; Moreno Díaz de la Espina, 2009). "
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    ABSTRACT: The nucleoskeleton of plants contains a peripheral lamina (also called plamina) and, even though lamins are absent in plants, their roles are still fulfilled in plant nuclei. One of the most intriguing topics in plant biology concerns the identity of lamin protein analogues in plants. Good candidates to play lamin functions in plants are the members of the NMCP (nuclear matrix constituent protein) family, which exhibit the typical tripartite structure of lamins. This paper describes a bioinformatics analysis and classification of the NMCP family based on phylogenetic relationships, sequence similarity and the distribution of conserved regions in 76 homologues. In addition, NMCP1 in the monocot Allium cepa characterized by its sequence and structure, biochemical properties, and subnuclear distribution and alterations in its expression throughout the root were identified. The results demonstrate that these proteins exhibit many similarities to lamins (structural organization, conserved regions, subnuclear distribution, and solubility) and that they may fulfil the functions of lamins in plants. These findings significantly advance understanding of the structural proteins of the plant lamina and nucleoskeleton and provide a basis for further investigation of the protein networks forming these structures.
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