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Rey C, Launay C, Wenger E, Delattre M. Programmed DNA elimination in Mesorhabditis nematodes. Curr Biol 2023; 33:3711-3721.e5. [PMID: 37607549 DOI: 10.1016/j.cub.2023.07.058] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2023] [Revised: 07/04/2023] [Accepted: 07/26/2023] [Indexed: 08/24/2023]
Abstract
Some species undergo programmed DNA elimination (PDE), whereby portions of the genome are systematically destroyed in somatic cells. PDE has emerged independently in several phyla, but its function is unknown. Although the mechanisms are partially solved in ciliates, PDE remains mysterious in metazoans because the study species were not yet amenable to functional approaches. We fortuitously discovered massive PDE in the free-living nematode genus Mesorhabditis, from the same family as C. elegans. As such, these species offer many experimental advantages to start elucidating the PDE mechanisms in an animal. Here, we used cytology to describe the dynamics of chromosome fragmentation and destruction in early embryos. Elimination occurs once in development, at the third embryonic cell division in the somatic blastomeres. Chromosomes are first fragmented during S phase. Next, some of the fragments fail to align on the mitotic spindle and remain outside the re-assembled nuclei after mitosis. These fragments are gradually lost after a few cell cycles. The retained fragments form new mini chromosomes, which are properly segregated in the subsequent cell divisions. With genomic approaches, we found that Mesorhabditis mainly eliminate repeated regions and also about a hundred genes. Importantly, none of the eliminated protein-coding genes are shared between closely related Mesorhabditis species. Our results strongly suggest PDE has not been selected for regulating genes with important biological functions in Mesorhabditis but rather mainly to irreversibly remove repeated sequences in the soma. We propose that PDE may target genes, provided their elimination in the soma is invisible to selection.
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Affiliation(s)
- Carine Rey
- Laboratory of Biology and Modeling of the Cell, Ecole Normale Superieure de Lyon, CNRS UMR5239, Inserm U1293, University Claude Bernard Lyon 1, Lyon, France
| | - Caroline Launay
- Laboratory of Biology and Modeling of the Cell, Ecole Normale Superieure de Lyon, CNRS UMR5239, Inserm U1293, University Claude Bernard Lyon 1, Lyon, France
| | - Eva Wenger
- Laboratory of Biology and Modeling of the Cell, Ecole Normale Superieure de Lyon, CNRS UMR5239, Inserm U1293, University Claude Bernard Lyon 1, Lyon, France
| | - Marie Delattre
- Laboratory of Biology and Modeling of the Cell, Ecole Normale Superieure de Lyon, CNRS UMR5239, Inserm U1293, University Claude Bernard Lyon 1, Lyon, France.
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Blanc C, Saclier N, Le Faou E, Marie-Orleach L, Wenger E, Diblasi C, Glemin S, Galtier N, Delattre M. Cosegregation of recombinant chromatids maintains genome-wide heterozygosity in an asexual nematode. SCIENCE ADVANCES 2023; 9:eadi2804. [PMID: 37624896 PMCID: PMC10456839 DOI: 10.1126/sciadv.adi2804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2023] [Accepted: 07/27/2023] [Indexed: 08/27/2023]
Abstract
In asexual animals, female meiosis is modified to produce diploid oocytes. If meiosis still involves recombination, this is expected to lead to a rapid loss of heterozygosity, with adverse effects on fitness. Many asexuals, however, have a heterozygous genome, the underlying mechanisms being most often unknown. Cytological and population genomic analyses in the nematode Mesorhabditis belari revealed another case of recombining asexual being highly heterozygous genome-wide. We demonstrated that heterozygosity is maintained despite recombination because the recombinant chromatids of each chromosome pair cosegregate during the unique meiotic division. A theoretical model confirmed that this segregation bias is necessary to account for the observed pattern and likely to evolve under a wide range of conditions. Our study uncovers an unexpected type of non-Mendelian genetic inheritance involving cosegregation of recombinant chromatids.
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Affiliation(s)
- Caroline Blanc
- Laboratory of Biology and Modeling of the Cell, Ecole Normale Supérieure de Lyon, CNRS UMR 5239, Inserm U1293, University Claude Bernard Lyon 1, Lyon, France
| | - Nathanaelle Saclier
- Institut des Sciences de l'Evolution, Université Montpellier, Institut de Recherche pour le Développement, 34090 Montpellier, France
| | - Ehouarn Le Faou
- University of Rennes, CNRS, ECOBIO (Ecologie, Biodiversité, Evolution)–UMR 6553, F-35000 Rennes, France
| | - Lucas Marie-Orleach
- University of Rennes, CNRS, ECOBIO (Ecologie, Biodiversité, Evolution)–UMR 6553, F-35000 Rennes, France
| | - Eva Wenger
- Laboratory of Biology and Modeling of the Cell, Ecole Normale Supérieure de Lyon, CNRS UMR 5239, Inserm U1293, University Claude Bernard Lyon 1, Lyon, France
| | - Celian Diblasi
- Institut des Sciences de l'Evolution, Université Montpellier, Institut de Recherche pour le Développement, 34090 Montpellier, France
| | - Sylvain Glemin
- University of Rennes, CNRS, ECOBIO (Ecologie, Biodiversité, Evolution)–UMR 6553, F-35000 Rennes, France
- Department of Ecology and Genetics, Evolutionary Biology Centre, Uppsala University, 75236 Uppsala, Sweden
| | - Nicolas Galtier
- Institut des Sciences de l'Evolution, Université Montpellier, Institut de Recherche pour le Développement, 34090 Montpellier, France
| | - Marie Delattre
- Laboratory of Biology and Modeling of the Cell, Ecole Normale Supérieure de Lyon, CNRS UMR 5239, Inserm U1293, University Claude Bernard Lyon 1, Lyon, France
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Cutter AD. Speciation and development. Evol Dev 2023; 25:289-327. [PMID: 37545126 DOI: 10.1111/ede.12454] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2023] [Revised: 06/13/2023] [Accepted: 07/20/2023] [Indexed: 08/08/2023]
Abstract
Understanding general principles about the origin of species remains one of the foundational challenges in evolutionary biology. The genomic divergence between groups of individuals can spawn hybrid inviability and hybrid sterility, which presents a tantalizing developmental problem. Divergent developmental programs may yield either conserved or divergent phenotypes relative to ancestral traits, both of which can be responsible for reproductive isolation during the speciation process. The genetic mechanisms of developmental evolution involve cis- and trans-acting gene regulatory change, protein-protein interactions, genetic network structures, dosage, and epigenetic regulation, all of which also have roots in population genetic and molecular evolutionary processes. Toward the goal of demystifying Darwin's "mystery of mysteries," this review integrates microevolutionary concepts of genetic change with principles of organismal development, establishing explicit links between population genetic process and developmental mechanisms in the production of macroevolutionary pattern. This integration aims to establish a more unified view of speciation that binds process and mechanism.
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Affiliation(s)
- Asher D Cutter
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
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Ryss AY, Subbotin SA. New Records of Wood- and Bark-Inhabiting Nematodes from Woody Plants with a Description of Bursaphelenchus zvyagintsevi sp. n. (Aphelenchoididae: Parasitaphelenchinae) from Russia. PLANTS (BASEL, SWITZERLAND) 2023; 12:382. [PMID: 36679095 PMCID: PMC9860568 DOI: 10.3390/plants12020382] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 01/11/2023] [Accepted: 01/11/2023] [Indexed: 06/17/2023]
Abstract
Wood- and bark-inhabiting parasitic nematodes are of great economic importance. Nematodes can cause wilt diseases in conifers and deciduous trees. In 2014-2022, during nematology surveys conducted in different regions of Russia and Belarus, adults and dauer juveniles of nematodes were collected from wood, bark and beetle vectors. Using traditional morphological taxonomic characters integrated with molecular criteria, we identified in the studied samples the following nematode species: Aphelenchoides heidelbergi, Bursaphelenchus eremus, B. fraudulentus, B. michalskii, B. mucronatus, B. willibaldi, Deladenus posteroporus, Diplogasteroides nix and Laimaphelenchus hyrcanus, several unidentified species: Aphelenchoides sp.1 and sp.2, Cryptaphelenchus sp.1, sp.2 and sp.3, Laimaphelenchus sp.1, Micoletzkya sp.1, Parasitaphelenchus sp.1, Parasitorhabditis sp.1, three unidentified tylenchid nematodes and a new species, Bursaphelenchus zvyagintsevi sp.n. Morphological descriptions and molecular characterization are provided for B. zvyagintsevi sp. n. belonging to the Abietinus group and B. michalskii belonging to the Eggersi group. Findings of Aphelenchoides heidelbergi, Bursaphelenchus eremus, B. michalskii, Deladenus posteroporus, Diplogasteroides nix and Laimaphelenchus hyrcanus are new records for Russia. Phylogenetic positions of studied species were reconstructed using D2-D3 expansion segments of 28S rRNA gene sequence analysis. The data obtained in this study may help to detect the refugia of opportunistic plant pests and find possible native biocontrol nematode agents of insect vectors causing diseases.
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Affiliation(s)
- Alexander Y. Ryss
- Zoological Institute, Russian Academy of Sciences, Universitetskaya Emb. 1, 199034 Saint Petersburg, Russia
| | - Sergei A. Subbotin
- Plant Pest Diagnostic Centre, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832, USA
- Department of Entomology and Nematology, Hutchison Hall, University of California, Davis, CA 95616, USA
- Centre of Parasitology, A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Leninskii Prospect 33, 117071 Moscow, Russia
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HODDA M. Phylum Nematoda: trends in species descriptions, the documentation of diversity, systematics, and the species concept. Zootaxa 2022; 5114:290-317. [DOI: 10.11646/zootaxa.5114.1.2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Indexed: 11/04/2022]
Abstract
This paper summarizes the trends in nematode species description and systematics emerging from a comparison of the latest comprehensive classification and census of Phylum Nematoda (Hodda 2022a, b) with earlier classifications (listed in Hodda 2007). It also offers some general observations on trends in nematode systematics emerging from the review of the voluminous literature used to produce the classification. The trends in nematodes can be compared with developments in the systematics of other organisms to shed light on many of the general issues confronting systematists now and into the future.
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Van Goor J, Shakes DC, Haag ES. Fisher vs. the Worms: Extraordinary Sex Ratios in Nematodes and the Mechanisms that Produce Them. Cells 2021; 10:1793. [PMID: 34359962 PMCID: PMC8303164 DOI: 10.3390/cells10071793] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Revised: 07/08/2021] [Accepted: 07/13/2021] [Indexed: 01/20/2023] Open
Abstract
Parker, Baker, and Smith provided the first robust theory explaining why anisogamy evolves in parallel in multicellular organisms. Anisogamy sets the stage for the emergence of separate sexes, and for another phenomenon with which Parker is associated: sperm competition. In outcrossing taxa with separate sexes, Fisher proposed that the sex ratio will tend towards unity in large, randomly mating populations due to a fitness advantage that accrues in individuals of the rarer sex. This creates a vast excess of sperm over that required to fertilize all available eggs, and intense competition as a result. However, small, inbred populations can experience selection for skewed sex ratios. This is widely appreciated in haplodiploid organisms, in which females can control the sex ratio behaviorally. In this review, we discuss recent research in nematodes that has characterized the mechanisms underlying highly skewed sex ratios in fully diploid systems. These include self-fertile hermaphroditism and the adaptive elimination of sperm competition factors, facultative parthenogenesis, non-Mendelian meiotic oddities involving the sex chromosomes, and environmental sex determination. By connecting sex ratio evolution and sperm biology in surprising ways, these phenomena link two "seminal" contributions of G. A. Parker.
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Affiliation(s)
- Justin Van Goor
- Department of Biology, University of Maryland, College Park, MD 20742, USA;
| | - Diane C. Shakes
- Department of Biology, William and Mary, Williamsburg, VA 23187, USA;
| | - Eric S. Haag
- Department of Biology, University of Maryland, College Park, MD 20742, USA;
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