Analysis of alternative splicing of cassette exons at single-cell level using two fluorescent proteins

Alternative splicing plays a major role in increasing proteome complexity and regulating gene expression. Here, we developed a new fluorescent protein-based approach to quantitatively analyze the alternative splicing of a target cassette exon (skipping or inclusion), which results in an open-reading frame shift. A fragment of a gene of interest is cloned between red and green fluorescent protein (RFP and GFP)-encoding sequences in such a way that translation of the normally spliced full-length transcript results in expression of both RFP and GFP. In contrast, alternative exon skipping results in the synthesis of RFP only. Green and red fluorescence intensities can be used to estimate the proportions of normal and alternative transcripts in each cell. The new method was successfully tested for human PIG3 (p53-inducible gene 3) cassette exon 4. Expected pattern of alternative splicing of PIG3 minigene was observed, including previously characterized effects of UV light irradiation and specific mutations. Interestingly, we observed a broad distribution of normal to alternative transcript ratio in individual cells with at least two distinct populations with ∼45% and >95% alternative transcript. We believe that this method is useful for fluorescence-based quantitative analysis of alternative splicing of target genes in a variety of biological models

Plants with genetically encoded autoluminescence

Autoluminescent plants engineered to express a bacterial bioluminescence gene cluster in plastids have not been widely adopted because of low light output. We engineered tobacco plants with a fungal bioluminescence system that converts caffeic acid (present in all plants) into luciferin and report self-sustained luminescence that is visible to the naked eye. Our findings could underpin development of a suite of imaging tools for plants

Systematic Comparison of Plant Promoters in <i>Nicotiana</i> spp. Expression Systems

We report a systematic comparison of 19 plant promoters and 20 promoter-terminator combinations in two expression systems: agroinfiltration in Nicotiana benthamiana leaves, and Nicotiana tabacum BY-2 plant cell packs. The set of promoters tested comprised those not present in previously published work, including several computationally predicted synthetic promoters validated here for the first time. The expression of EGFP driven by different promoters varied by more than two orders of magnitude and was largely consistent between two tested Nicotiana systems. We confirmed previous reports of significant modulation of expression by terminators, as well as synergistic effects of promoters and terminators. Additionally, we observed non-linear effects of gene dosage on expression level. The dataset presented here can inform the design of genetic constructs for plant engineering and transient expression assays

Domain Truncation in Hispidin Synthase Orthologs from Non-Bioluminescent Fungi Does Not Lead to Hispidin Biosynthesis

Hispidin is a polyketide found in plants and fungi. In bioluminescent fungi, hispidin serves as a precursor of luciferin and is produced by hispidin synthases. Previous studies revealed that hispidin synthases differ in orthologous polyketide synthases from non-bioluminescent fungi by the absence of two domains with predicted ketoreductase and dehydratase activities. Here, we investigated the hypothesis that the loss of these domains in evolution led to the production of hispidin and the emergence of bioluminescence. We cloned three orthologous polyketide synthases from non-bioluminescent fungi, as well as their truncated variants, and assessed their ability to produce hispidin in a bioluminescence assay in yeast. Interestingly, expression of the full-length enzyme hsPKS resulted in dim luminescence, indicating that small amounts of hispidin are likely being produced as side products of the main reaction. Deletion of the ketoreductase and dehydratase domains resulted in no luminescence. Thus, domain truncation by itself does not appear to be a sufficient step for the emergence of efficient hispidin synthases from orthologous polyketide synthases. At the same time, the production of small amounts of hispidin or related compounds by full-length enzymes suggests that ancestral fungal species were well-positioned for the evolution of bioluminescence

Genetically encodable bioluminescent system from fungi

Bioluminescence is found across the entire tree of life, conferring a spectacular set of visually oriented functions from attracting mates to scaring off predators. Half a dozen different luciferins, molecules that emit light when enzymatically oxidized, are known. However, just one biochemical pathway for luciferin biosynthesis has been described in full, which is found only in bacteria. Here, we report identification of the fungal luciferase and three other key enzymes that together form the biosynthetic cycle of the fungal luciferin from caffeic acid, a simple and widespread metabolite. Introduction of the identified genes into the genome of the yeast Pichia pastoris along with caffeic acid biosynthesis genes resulted in a strain that is autoluminescent in standard media. We analyzed evolution of the enzymes of the luciferin biosynthesis cycle and found that fungal bioluminescence emerged through a series of events that included two independent gene duplications. The retention of the duplicated enzymes of the luciferin pathway in nonluminescent fungi shows that the gene duplication was followed by functional sequence divergence of enzymes of at least one gene in the biosynthetic pathway and suggests that the evolution of fungal bioluminescence proceeded through several closely related stepping stone nonluminescent biochemical reactions with adaptive roles. The availability of a complete eukaryotic luciferin biosynthesis pathway provides several applications in biomedicine and bioengineering.This research was supported by Planta LLC and Evrogen JSC. IVIS imaging and animal experiments were carried out using the equipment of the Center for Collective Usage “Medical Nanobiotechologies” located in the Russian National Research Medical University. Experiments were partially carried out using the equipment provided by the Institute of Bioorganic Chemistry of the Russian Academy of Sciences Сore Facility (CKP IBCH; supported by Russian Ministry of Education and Science Grant RFMEFI62117X0018). T.G. and M.M.-H. acknowledge support from Spanish Ministry of Economy and Competitiveness Grant BFU2015-67107 cofounded by the European Regional Development Fund, European Research Council (ERC) Grant ERC-2012-StG-310325 under the European Union’s Seventh Framework Programme FP7/2007-2013, and the European Union’s Horizon 2020 Research and Innovation Programme under Marie Sklodowska-Curie Grant H2020-MSCA-ITN-2014-642095. F.A.K. acknowledges the support of HHMI International Early Career Scientist Program 55007424, the Spanish Ministry of Economy and Competitiveness (MINECO) Grants BFU2012-31329 and BFU2015-68723-P, MINECO Centro de Excelencia Severo Ochoa 2013-2017 Grant SEV-2012-0208, Secretaria d’Universitats i Recerca del Departament d’Economia i Coneixement de la Generalitat’s Agency for Management of University and Research Grants Program 2014 SGR 0974, the Centres de Recerca de Catalunya Programme of the Generalitat de Catalunya, and ERC Grant 335980_EinME under the European Union’s Seventh Framework Programme FP7/2007-2013. H.E.W., A.G.O., and C.V.S. acknowledge support from São Paulo Research Foundation Fundação de Amparo à Pesquisa do Estado de São Paulo Grants 11/10507-0 (to H.E.W.), 10/11578-5 (to A.G.O.), and 13/16885-1 (to C.V.S.)