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Hoh C, Salzberg SL. Discovering Intron Gain Events in Humans through Large-Scale Evolutionary Comparisons. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.02.592247. [PMID: 38746259 PMCID: PMC11092651 DOI: 10.1101/2024.05.02.592247] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
The rapid growth in the number of sequenced genomes makes it possible to search for the appearance of entirely new introns in the human lineage. In this study, we compared the genomic sequences for 19,120 human protein-coding genes to a collection of 3493 vertebrate genomes, mapping the patterns of intron alignments onto a phylogenetic tree. This mapping allowed us to trace many intron gain events to precise locations in the tree, corresponding to distinct points in evolutionary history. We discovered 584 intron gain events, all of them relatively recent, in 514 distinct human genes. Among these events, we explored the hypothesis that intronization was the mechanism responsible for intron gain. Intronization events were identified by locating instances where human introns correspond to exonic sequences in homologous vertebrate genes. Although apparently rare, we found three compelling cases of intronization, and for each of those we compared the human protein sequence and structure to homologous genes that lack the introns.
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Affiliation(s)
- Celine Hoh
- Department of Computer Science, Johns Hopkins University, Baltimore, MD 21218, USA
- Center for Computational Biology, Johns Hopkins University, Baltimore, MD 21211, USA
| | - Steven L Salzberg
- Department of Computer Science, Johns Hopkins University, Baltimore, MD 21218, USA
- Center for Computational Biology, Johns Hopkins University, Baltimore, MD 21211, USA
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21211, USA
- Department of Biostatistics, Johns Hopkins University, Baltimore, MD 21205, USA
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Hertzler PL, Devries EJ, DeBoer RA. The Hedgehog pathway in penaeid shrimp: developmental expression and evolution of splice junctions in Pancrustacea. Genetica 2022; 150:87-96. [PMID: 35129716 DOI: 10.1007/s10709-022-00151-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Accepted: 01/27/2022] [Indexed: 11/25/2022]
Abstract
Penaeid shrimp embryos undergo holoblastic division, gastrulation by invagination, and hatching as a nauplius larva. Posterior segments form and differentiate during larval development. Hedgehog (Hh) pathway genes from penaeid shrimp and other pancrustaceans were identified by in silico analysis of genomes and transcriptomes, and mapped onto a recent pancrustacean phylogeny to determine patterns of intron gains and losses. Penaeus vannamei, P. japonicus, and P. monodon Hh proteins were encoded by four exons. Amphipod, isopod, and ostracod hh were also encoded by four exons, but hh from other arthropod groups contained three conserved exons. The novel hh intron is hypothesized to have arisen independently in the malacostracan ancestor and Ostracoda by a transposon insertion. Shared patterns of ptc, smo, and ci exon structure were found for Malacostraca, Branchiopoda + Hexapoda, Hexanauplia (Thecostraca + Copepoda), Multicrustacea (Thecostraca + Copepoda + Malacostraca), and Pancrustacea minus Oligostraca. mRNA expression of P. vannamei of hh, ptc, and ci from developmental transcriptomes of zygotes through postlarvae showed low expression from zygote to gastrula, which increased at limb bud, peaked at unhatched nauplius, and declined in nauplius and later larval stages. smo expression was found in zygotes, peaked in gastrula, and declined in limb bud and later stages. These results are consistent with a role for Hh signaling during segmentation in penaeid shrimp.
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Affiliation(s)
- Philip L Hertzler
- Department of Biology, Central Michigan University, Mount Pleasant, MI, 48859, USA.
| | - Emma J Devries
- Department of Biology, Central Michigan University, Mount Pleasant, MI, 48859, USA
| | - Rachel A DeBoer
- Department of Biology, Central Michigan University, Mount Pleasant, MI, 48859, USA
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Exploring the Impact of Cleavage and Polyadenylation Factors on Pre-mRNA Splicing Across Eukaryotes. G3-GENES GENOMES GENETICS 2017; 7:2107-2114. [PMID: 28500052 PMCID: PMC5499120 DOI: 10.1534/g3.117.041483] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
In human, mouse, and Drosophila, the spliceosomal complex U1 snRNP (U1) protects transcripts from premature cleavage and polyadenylation at proximal intronic polyadenylation signals (PAS). These U1-mediated effects preserve transcription integrity, and are known as telescripting. The watchtower role of U1 throughout transcription is clear. What is less clear is whether cleavage and polyadenylation factors (CPFs) are simply patrolled or if they might actively antagonize U1 recruitment. In addressing this question, we found that, in the introns of human, mouse, and Drosophila, and of 14 other eukaryotes, including multi- and single-celled species, the conserved AATAAA PAS—a major target for CPFs—is selected against. This selective pressure, approximated using DNA strand asymmetry, is detected for peripheral and internal introns alike. Surprisingly, it is more pronounced within—rather than outside—the action range of telescripting, and particularly intense in the vicinity of weak 5′ splice sites. Our study uncovers a novel feature of eukaryotic genes: that the AATAAA PAS is universally counter-selected in spliceosomal introns. This pattern implies that CPFs may attempt to access introns at any time during transcription. However, natural selection operates to minimize this access. By corroborating and extending previous work, our study further indicates that CPF access to intronic PASs might perturb the recruitment of U1 to the adjacent 5′ splice sites. These results open the possibility that CPFs may impact the splicing process across eukaryotes.
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Abstract
Introns inserted within introns are commonly referred to as twintrons, however the original definition for twintron implied that splicing of the external member of the twintron could only proceed upon splicing of the internal member. This review examines the various types of twintron-like arrangements that have been reported and assigns them to either nested or twintron categories that are subdivided further into subtypes based on differences of their mode of splicing. Twintron-like arrangements evolved independently by fortuitous events among different types of introns but once formed they offer opportunities for the evolution of new regulatory strategies and/or novel genetic elements.
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Affiliation(s)
- Mohamed Hafez
- a Department of Biochemistry ; Faculty of Medicine; University of Montreal ; Montréal , QC Canada.,b Department of Botany and Microbiology ; Faculty of Science; Suez University ; Suez , Egypt
| | - Georg Hausner
- c Department of Microbiology ; University of Manitoba ; Winnipeg , MB Canada
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Ma MY, Lan XR, Niu DK. Intron gain by tandem genomic duplication: a novel case in a potato gene encoding RNA-dependent RNA polymerase. PeerJ 2016; 4:e2272. [PMID: 27547574 PMCID: PMC4974935 DOI: 10.7717/peerj.2272] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Accepted: 06/29/2016] [Indexed: 01/15/2023] Open
Abstract
The origin and subsequent accumulation of spliceosomal introns are prominent events in the evolution of eukaryotic gene structure. However, the mechanisms underlying intron gain remain unclear because there are few proven cases of recently gained introns. In an RNA-dependent RNA polymerase (RdRp) gene, we found that a tandem duplication occurred after the divergence of potato and its wild relatives among other Solanum plants. The duplicated sequence crosses the intron-exon boundary of the first intron and the second exon. A new intron was detected at this duplicated region, and it includes a small previously exonic segment of the upstream copy of the duplicated sequence and the intronic segment of the downstream copy of the duplicated sequence. The donor site of this new intron was directly obtained from the small previously exonic segment. Most of the splicing signals were inherited directly from the parental intron/exon structure, including a putative branch site, the polypyrimidine tract, the 3' splicing site, two putative exonic splicing enhancers, and the GC contents differed between the intron and exon. In the widely cited model of intron gain by tandem genomic duplication, the duplication of an AGGT-containing exonic segment provides the GT and AG splicing sites for the new intron. Our results illustrate that the tandem duplication model of intron gain should be diverse in terms of obtaining the proper splicing signals.
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Affiliation(s)
- Ming-Yue Ma
- MOE Key Laboratory for Biodiversity Science and Ecological Engineering and Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Sciences, Beijing Normal University , Beijing , China
| | - Xin-Ran Lan
- MOE Key Laboratory for Biodiversity Science and Ecological Engineering and Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Sciences, Beijing Normal University , Beijing , China
| | - Deng-Ke Niu
- MOE Key Laboratory for Biodiversity Science and Ecological Engineering and Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Sciences, Beijing Normal University , Beijing , China
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Zhou K, Salamov A, Kuo A, Aerts AL, Kong X, Grigoriev IV. Alternative splicing acting as a bridge in evolution. Stem Cell Investig 2015; 2:19. [PMID: 27358887 DOI: 10.3978/j.issn.2306-9759.2015.10.01] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Accepted: 10/15/2015] [Indexed: 12/15/2022]
Abstract
BACKGROUND Alternative splicing (AS) regulates diverse cellular and developmental functions through alternative protein structures of different isoforms. Alternative exons dominate AS in vertebrates; however, very little is known about the extent and function of AS in lower eukaryotes. To understand the role of introns in gene evolution, we examined AS from a green algal and five fungal genomes using a novel EST-based gene-modeling algorithm (COMBEST). METHODS AS from each genome was classified with COMBEST that maps EST sequences to genomes to build gene models. Various aspects of AS were analyzed through statistical methods. The interplay of intron 3n length, phase, coding property, and intron retention (RI) were examined with Chi-square testing. RESULTS With 3 to 834 times EST coverage, we identified up to 73% of AS in intron-containing genes and found preponderance of RI among 11 types of AS. The number of exons, expression level, and maximum intron length correlated with number of AS per gene (NAG), and intron-rich genes suppressed AS. Genes with AS were more ancient, and AS was conserved among fungal genomes. Among stopless introns, non-retained introns (NRI) avoided, but major RI preferred 3n length. In contrast, stop-containing introns showed uniform distribution among 3n, 3n+1, and 3n+2 lengths. We found a clue to the intron phase enigma: it was the coding function of introns involved in AS that dictates the intron phase bias. CONCLUSIONS Majority of AS is non-functional, and the extent of AS is suppressed for intron-rich genes. RI through 3n length, stop codon, and phase bias bridges the transition from functionless to functional alternative isoforms.
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Affiliation(s)
- Kemin Zhou
- 1 US Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598, USA ; 2 Roche Molecular Diagnostics, 4300 Hacienda Drive, Pleasanton, CA 94588, USA ; 3 Department of Clinical Medicine, Kunming University of Science and Technology, Kunming 650031, China
| | - Asaf Salamov
- 1 US Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598, USA ; 2 Roche Molecular Diagnostics, 4300 Hacienda Drive, Pleasanton, CA 94588, USA ; 3 Department of Clinical Medicine, Kunming University of Science and Technology, Kunming 650031, China
| | - Alan Kuo
- 1 US Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598, USA ; 2 Roche Molecular Diagnostics, 4300 Hacienda Drive, Pleasanton, CA 94588, USA ; 3 Department of Clinical Medicine, Kunming University of Science and Technology, Kunming 650031, China
| | - Andrea L Aerts
- 1 US Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598, USA ; 2 Roche Molecular Diagnostics, 4300 Hacienda Drive, Pleasanton, CA 94588, USA ; 3 Department of Clinical Medicine, Kunming University of Science and Technology, Kunming 650031, China
| | - Xiangyang Kong
- 1 US Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598, USA ; 2 Roche Molecular Diagnostics, 4300 Hacienda Drive, Pleasanton, CA 94588, USA ; 3 Department of Clinical Medicine, Kunming University of Science and Technology, Kunming 650031, China
| | - Igor V Grigoriev
- 1 US Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598, USA ; 2 Roche Molecular Diagnostics, 4300 Hacienda Drive, Pleasanton, CA 94588, USA ; 3 Department of Clinical Medicine, Kunming University of Science and Technology, Kunming 650031, China
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