The Spliceosome-Activating Complex: Molecular Mechanisms Underlying the Function of a Pleiotropic Regulator

Department of Plant Developmental Biology, Max-Planck Institute for Plant Breeding Research Cologne, Germany.
Frontiers in Plant Science (Impact Factor: 3.95). 01/2012; 3:9. DOI: 10.3389/fpls.2012.00009
Source: PubMed


Correct interpretation of the coding capacity of RNA polymerase II transcribed eukaryotic genes is determined by the recognition and removal of intronic sequences of pre-mRNAs by the spliceosome. Our current knowledge on dynamic assembly and subunit interactions of the spliceosome mostly derived from the characterization of yeast, Drosophila, and human spliceosomal complexes formed on model pre-mRNA templates in cell extracts. In addition to sequential structural rearrangements catalyzed by ATP-dependent DExH/D-box RNA helicases, catalytic activation of the spliceosome is critically dependent on its association with the NineTeen Complex (NTC) named after its core E3 ubiquitin ligase subunit PRP19. NTC, isolated recently from Arabidopsis, occurs in a complex with the essential RNA helicase and GTPase subunits of the U5 small nuclear RNA particle that are required for both transesterification reactions of splicing. A compilation of mass spectrometry data available on the composition of NTC and spliceosome complexes purified from different organisms indicates that about half of their conserved homologs are encoded by duplicated genes in Arabidopsis. Thus, while mutations of single genes encoding essential spliceosome and NTC components lead to cell death in other organisms, differential regulation of some of their functionally redundant Arabidopsis homologs permits the isolation of partial loss of function mutations. Non-lethal pleiotropic defects of these mutations provide a unique means for studying the roles of NTC in co-transcriptional assembly of the spliceosome and its crosstalk with DNA repair and cell death signaling pathways.

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Available from: Zsuzsa Koncz, Oct 13, 2015
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    • "Here, we report on the identification of a meristem changed root 1 (mcr1) mutation, which reduces root meristem size and stem cell niche activity. The mcr1 mutation proved to be allelic with the prl1 mutation, which inactivates the Pleiotropic Regulatory Locus 1 (PRL1) that codes for a conserved WD40-repeat protein subunit of the nuclear spliceosome-activating Nineteen Complex (NTC) (Koncz et al., 2012). PRL1 was originally identified as an important pleiotropic regulator of plant responses to sugars, multiple hormones including auxin, ABA, cytokinin, and ethylene; cold stress and defense responses to bacterial and fungal pathogens (N emeth et al., 1998; Palma et al., 2007). "
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    ABSTRACT: The stem cell niche in the root meristem maintains pluripotent stem cells to ensure a constant supply of cells for root growth. Despite extensive progress, the molecular mechanisms through which root stem cell fates and stem cell niche activity are determined remain largely unknown. In Arabidopsis thaliana, the Pleiotropic Regulatory Locus 1 (PRL1) encodes a WD40-repeat protein subunit of the spliceosome-activating Nineteen complex (NTC) that plays a role in multiple stress, hormone and developmental signaling pathways. Here, we show that PRL1 is involved in the control of root meristem size and root stem cell niche activity. PRL1 is strongly expressed in the root meristem and its loss of function mutation results in disorganization of the quiescent center (QC), premature stem cell differentiation, aberrant cell division, and reduced root meristem size. Our genetic studies indicate that PRL1 is required for confined expression of the homeodomain transcription factor WOX5 in the QC and acts upstream of the transcription factor PLETHORA (PLT) in modulating stem cell niche activity and root meristem size. These findings define a role for PRL1 as an important determinant of PLT signaling that modulates maintenance of the stem cell niche and root meristem size.This article is protected by copyright. All rights reserved.
    The Plant Journal 11/2014; 81(3). DOI:10.1111/tpj.12733 · 5.97 Impact Factor
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    • "Loss of two different spliceosomal components, Prp19 and U2A, through RNAi knockdown creates distinct NC chromatin defects that differ from the canonical 5-blob phenotype. Prp19 is a putative scaffolding protein for the Nineteen Complex; although it is not found to be a specific component of the spliceosome, it is required for both steps of intron removal in the lariat pathway through spliceosomal conformational changes [47], [48]. After stage 6, the NC nuclei retain some semi-blob characteristics, but change into the ‘bowl’ phenotype from stage 9 onwards, in which the nucleolus does not disperse, but remains clustered in an interchromatin space (reminiscent of smnA073 stage-10 germ-line clones [49]; Fig. S6C-C″), correlating defects in spliceosomal activation with NC chromatin-morphology defects. "
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    ABSTRACT: During Drosophila oogenesis, the endopolyploid nuclei of germ-line nurse cells undergo a dramatic shift in morphology as oogenesis progresses; the easily-visible chromosomes are initially polytenic during the early stages of oogenesis before they transiently condense into a distinct '5-blob' configuration, with subsequent dispersal into a diffuse state. Mutations in many genes, with diverse cellular functions, can affect the ability of nurse cells to fully decondense their chromatin, resulting in a '5-blob arrest' phenotype that is maintained throughout the later stages of oogenesis. However, the mechanisms and significance of nurse-cell (NC) chromatin dispersal remain poorly understood. Here, we report that a screen for modifiers of the 5-blob phenotype in the germ line isolated the spliceosomal gene peanuts, the Drosophila Prp22. We demonstrate that reduction of spliceosomal activity through loss of peanuts promotes decondensation defects in NC nuclei during mid-oogenesis. We also show that the Prp38 spliceosomal protein accumulates in the nucleoplasm of nurse cells with impaired peanuts function, suggesting that spliceosomal recycling is impaired. Finally, we reveal that loss of additional spliceosomal proteins impairs the full decondensation of NC chromatin during later stages of oogenesis, suggesting that individual spliceosomal subcomplexes modulate expression of the distinct subset of genes that are required for correct morphology in endopolyploid nurse cells.
    PLoS ONE 11/2013; 8(11):e79048. DOI:10.1371/journal.pone.0079048 · 3.23 Impact Factor
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    • "In this review we will refer to the complex as NTC/Prp19C and to its subunit as Prp19. NTC/Prp19C is a large protein complex consisting of eight core proteins and up to 19 associated proteins in Saccharomyces cerevisiae and more than 30 proteins in higher eukaryotes including animals and plants (see Table 1; [1] [2] and references therein). "
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    ABSTRACT: The conserved Prp19 complex (Prp19C) - also known as NineTeen Complex (NTC) -functions in several processes of paramount importance for cellular homeostasis. NTC/Prp19C was discovered as a complex that functions in splicing and more specifically during the catalytic activation of the spliceosome. More recent work revealed that NTC/Prp19C plays a role in transcription elongation in S. cerevisiae and in genome maintenance in higher eukaryotes. In addition, mouse PRP19 might ubiquitylate proteins targeted for degradation and guide them to the proteasome. Furthermore, NTC/Prp19C has been implicated in lipid droplet biogenesis. In the future, the molecular function of NTC/Prp19C in all of these processes needs to be refined or elucidated. Most of NTC/Prp19C's functions have been shown in only one or few organisms. However, since this complex is highly conserved it is likely that it has the same functions across all species. Moreover, one NTC/Prp19C or different subcomplexes could function in the above-mentioned processes. Intriguingly, NTC/Prp19C might link these different processes to ensure an optimal coordination of cellular processes. Thus, many important questions about the functions of this interesting complex remain to be investigated. In this review we discuss the different functions of NTC/Prp19C focusing on the novel and emerging ones as well as open questions.
    Biochimica et Biophysica Acta 06/2013; 1833(10). DOI:10.1016/j.bbamcr.2013.05.023 · 4.66 Impact Factor
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