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Smith CH, Mejia-Trujillo R, Breton S, Pinto BJ, Kirkpatrick M, Havird JC. Mitonuclear Sex Determination? Empirical Evidence from Bivalves. Mol Biol Evol 2023; 40:msad240. [PMID: 37935058 PMCID: PMC10653589 DOI: 10.1093/molbev/msad240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Revised: 10/04/2023] [Accepted: 10/26/2023] [Indexed: 11/09/2023] Open
Abstract
Genetic elements encoded in nuclear DNA determine the sex of an individual in many animals. In certain bivalve lineages that possess doubly uniparental inheritance (DUI), mitochondrial DNA (mtDNA) has been hypothesized to contribute to sex determination. In these cases, females transmit a female mtDNA to all offspring, while male mtDNA (M mtDNA) is transmitted only from fathers to sons. Because M mtDNA is inherited in the same way as Y chromosomes, it has been hypothesized that mtDNA may be responsible for sex determination. However, the role of mitochondrial and nuclear genes in sex determination has yet to be validated in DUI bivalves. In this study, we used DNA, RNA, and mitochondrial short noncoding RNA (sncRNA) sequencing to explore the role of mitochondrial and nuclear elements in the sexual development pathway of the freshwater mussel Potamilus streckersoni (Bivalvia: Unionida). We found that the M mtDNA sheds a sncRNA partially within a male-specific mitochondrial gene that targets a pathway hypothesized to be involved in female development and mitophagy. RNA-seq confirmed the gene target was significantly upregulated in females, supporting a direct role of mitochondrial sncRNAs in gene silencing. These findings support the hypothesis that M mtDNA inhibits female development. Genome-wide patterns of genetic differentiation and heterozygosity did not support a nuclear sex-determining region, although we cannot reject that nuclear factors are involved with sex determination. Our results provide further evidence that mitochondrial loci contribute to diverse, nonrespiratory functions and additional insights into an unorthodox sex-determining system.
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Affiliation(s)
- Chase H Smith
- Department of Integrative Biology, University of Texas at Austin, Austin, TX, USA
| | | | - Sophie Breton
- Department of Biological Sciences, University of Montreal, Montreal, Canada
| | - Brendan J Pinto
- School of Life Sciences, Arizona State University, Tempe, AZ, USA
- Center for Evolution and Medicine, Arizona State University, Tempe, AZ, USA
- Department of Zoology, Milwaukee Public Museum, Milwaukee, WI, USA
| | - Mark Kirkpatrick
- Department of Integrative Biology, University of Texas at Austin, Austin, TX, USA
| | - Justin C Havird
- Department of Integrative Biology, University of Texas at Austin, Austin, TX, USA
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Zwonitzer KD, Iverson ENK, Sterling JE, Weaver RJ, Maclaine BA, Havird JC. Disentangling Positive Selection from Relaxed Selection in Animal Mitochondrial Genomes. Am Nat 2023; 202:E121-E129. [PMID: 37792916 PMCID: PMC10955554 DOI: 10.1086/725805] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/06/2023]
Abstract
AbstractDisentangling different types of selection is a common goal in molecular evolution. Elevated dN/dS ratios (the ratio of nonsynonymous to synonymous substitution rates) in focal lineages are often interpreted as signs of positive selection. Paradoxically, relaxed purifying selection can also result in elevated dN/dS ratios, but tests to distinguish these two causes are seldomly implemented. Here, we reevaluated seven case studies describing elevated dN/dS ratios in animal mitochondrial DNA (mtDNA) and their accompanying hypotheses regarding selection. They included flightless lineages versus flighted lineages in birds, bats, and insects and physiological adaptations in snakes, two groups of electric fishes, and primates. We found that elevated dN/dS ratios were often not caused by the predicted mechanism, and we sometimes found strong support for the opposite mechanism. We discuss reasons why energetic hypotheses may be confounded by other selective forces acting on mtDNA and caution against overinterpreting singular molecular signals, including elevated dN/dS ratios.
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Affiliation(s)
- Kendra D. Zwonitzer
- Department of Integrative Biology, University of Texas at Austin, Austin, Texas 78712
| | - Erik N. K. Iverson
- Department of Integrative Biology, University of Texas at Austin, Austin, Texas 78712
| | - Jess E. Sterling
- Department of Integrative Biology, University of Texas at Austin, Austin, Texas 78712
| | - Ryan J. Weaver
- Department of Ecology, Evolution, and Organismal Biology and Department of Natural Resource Ecology and Management, Iowa State University, Ames, Iowa 50011
| | - Bradley A. Maclaine
- Department of Human Development and Family Sciences, University of Texas at Austin, Austin, Texas 78712
| | - Justin C. Havird
- Department of Integrative Biology, University of Texas at Austin, Austin, Texas 78712
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Smith CH, Mejia-Trujillo R, Breton S, Pinto BJ, Kirkpatrick M, Havird JC. Mitonuclear sex determination? Empirical evidence from bivalves. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.05.547839. [PMID: 37461691 PMCID: PMC10349986 DOI: 10.1101/2023.07.05.547839] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 07/24/2023]
Abstract
Genetic elements encoded in nuclear DNA determine the sex of an individual in many animals. In bivalves, however, mitochondrial DNA (mtDNA) has been hypothesized to contribute to sex determination in lineages that possess doubly uniparental inheritance (DUI). In these cases, females transmit a female mtDNA (F mtDNA) to all offspring, while male mtDNA (M mtDNA) is transmitted only from fathers to sons. Because M mtDNA is inherited in the same way as Y chromosomes, it has been hypothesized that mtDNA may be responsible for sex determination. However, the role of mitochondrial and nuclear genes in sex determination has yet to be validated in DUI bivalves. In this study, we used DNA, RNA, and mitochondrial short non-coding RNA (sncRNA) sequencing to explore the role of mitochondrial and nuclear elements in the sexual development pathway of the freshwater mussel Potamilus streckersoni (Bivalvia: Unionida). We found that the M mtDNA shed a sncRNA partially within a male-specific mitochondrial gene that targeted pathways hypothesized to be involved in female development and mitophagy. RNA-seq confirmed the gene target was significantly upregulated in females, supporting a direct role of mitochondrial sncRNAs in gene silencing. These findings support the hypothesis that M mtDNA inhibits female development. Genome-wide patterns of genetic differentiation and heterozygosity did not support a nuclear sex determining region, although we cannot reject that nuclear factors are involved with sex determination. Our results provide further evidence that mitochondrial loci contribute to diverse, non-respiratory functions and provide a first glimpse into an unorthodox sex determining system.
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Affiliation(s)
- Chase H. Smith
- Department of Integrative Biology, University of Texas at Austin, Austin, TX, USA
| | | | - Sophie Breton
- Department of Biological Sciences, University of Montreal, Montreal, Canada
| | - Brendan J. Pinto
- School of Life Sciences, Arizona State University, Tempe, AZ USA
- Center for Evolution and Medicine, Arizona State University, Tempe, AZ USA
- Department of Zoology, Milwaukee Public Museum, Milwaukee, WI USA
| | - Mark Kirkpatrick
- Department of Integrative Biology, University of Texas at Austin, Austin, TX, USA
| | - Justin C. Havird
- Department of Integrative Biology, University of Texas at Austin, Austin, TX, USA
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Smith CH, Pinto BJ, Kirkpatrick M, Hillis DM, Pfeiffer JM, Havird JC. A tale of two paths: The evolution of mitochondrial recombination in bivalves with doubly uniparental inheritance. J Hered 2023; 114:199-206. [PMID: 36897956 PMCID: PMC10212130 DOI: 10.1093/jhered/esad004] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2022] [Accepted: 01/19/2023] [Indexed: 03/12/2023] Open
Abstract
In most animals, mitochondrial DNA is strictly maternally inherited and non-recombining. One exception to this pattern is called doubly uniparental inheritance (DUI), a phenomenon involving the independent transmission of female and male mitochondrial genomes. DUI is known only from the molluskan class Bivalvia. The phylogenetic distribution of male-transmitted mitochondrial DNA (M mtDNA) in bivalves is consistent with several evolutionary scenarios, including multiple independent gains, losses, and varying degrees of recombination with female-transmitted mitochondrial DNA (F mtDNA). In this study, we use phylogenetic methods to test M mtDNA origination hypotheses and infer the prevalence of mitochondrial recombination in bivalves with DUI. Phylogenetic modeling using site concordance factors supported a single origin of M mtDNA in bivalves coupled with recombination acting over long evolutionary timescales. Ongoing mitochondrial recombination is present in Mytilida and Venerida, which results in a pattern of concerted evolution of F mtDNA and M mtDNA. Mitochondrial recombination could be favored to offset the deleterious effects of asexual inheritance and maintain mitonuclear compatibility across tissues. Cardiida and Unionida have gone without recent recombination, possibly due to an extension of the COX2 gene in male mitochondrial DNA. The loss of recombination could be connected to the role of M mtDNA in sex determination or sexual development. Our results support that recombination events may occur throughout the mitochondrial genomes of DUI species. Future investigations may reveal more complex patterns of inheritance of recombinants, which could explain the retention of signal for a single origination of M mtDNA in protein-coding genes.
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Affiliation(s)
- Chase H Smith
- Department of Integrative Biology, University of Texas, Austin, TX, United States
| | - Brendan J Pinto
- Center for Evolutionary Medicine & Public Health, Arizona State University, Tempe, AZ, United States
- Department of Zoology, Milwaukee Public Museum, Milwaukee, WI, United States
| | - Mark Kirkpatrick
- Department of Integrative Biology, University of Texas, Austin, TX, United States
| | - David M Hillis
- Department of Integrative Biology, University of Texas, Austin, TX, United States
| | - John M Pfeiffer
- Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC, United States
- Department of Integrative Biology, University of Texas, Austin, TX, United States
| | - Justin C Havird
- Department of Integrative Biology, University of Texas, Austin, TX, United States
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Xu R, Martelossi J, Smits M, Iannello M, Peruzza L, Babbucci M, Milan M, Dunham JP, Breton S, Milani L, Nuzhdin SV, Bargelloni L, Passamonti M, Ghiselli F. Multi-tissue RNA-Seq Analysis and Long-read-based Genome Assembly Reveal Complex Sex-specific Gene Regulation and Molecular Evolution in the Manila Clam. Genome Biol Evol 2022; 14:6889380. [PMID: 36508337 PMCID: PMC9803972 DOI: 10.1093/gbe/evac171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2022] [Revised: 11/26/2022] [Accepted: 11/30/2022] [Indexed: 12/14/2022] Open
Abstract
The molecular factors and gene regulation involved in sex determination and gonad differentiation in bivalve molluscs are unknown. It has been suggested that doubly uniparental inheritance (DUI) of mitochondria may be involved in these processes in species such as the ubiquitous and commercially relevant Manila clam, Ruditapes philippinarum. We present the first long-read-based de novo genome assembly of a Manila clam, and a RNA-Seq multi-tissue analysis of 15 females and 15 males. The highly contiguous genome assembly was used as reference to investigate gene expression, alternative splicing, sequence evolution, tissue-specific co-expression networks, and sexual contrasting SNPs. Differential expression (DE) and differential splicing (DS) analyses revealed sex-specific transcriptional regulation in gonads, but not in somatic tissues. Co-expression networks revealed complex gene regulation in gonads, and genes in gonad-associated modules showed high tissue specificity. However, male gonad-associated modules showed contrasting patterns of sequence evolution and tissue specificity. One gene set was related to the structural organization of male gametes and presented slow sequence evolution but high pleiotropy, whereas another gene set was enriched in reproduction-related processes and characterized by fast sequence evolution and tissue specificity. Sexual contrasting SNPs were found in genes overrepresented in mitochondrial-related functions, providing new candidates for investigating the relationship between mitochondria and sex in DUI species. Together, these results increase our understanding of the role of DE, DS, and sequence evolution of sex-specific genes in an understudied taxon. We also provide resourceful genomic data for studies regarding sex diagnosis and breeding in bivalves.
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Affiliation(s)
- Ran Xu
- Corresponding authors: E-mail: (R.X.); E-mail: (F.G.)
| | | | | | | | - Luca Peruzza
- Department of Comparative Biomedicine and Food Science, University of Padova, Padova, Italy
| | - Massimiliano Babbucci
- Department of Comparative Biomedicine and Food Science, University of Padova, Padova, Italy
| | - Massimo Milan
- Department of Comparative Biomedicine and Food Science, University of Padova, Padova, Italy
| | - Joseph P Dunham
- Program in Molecular and Computational Biology, University of Southern California, Los Angeles, CA, USA,SeqOnce Biosciences Inc., Pasadena, CA, USA
| | - Sophie Breton
- Department of Biological Sciences, University of Montreal, Montreal, Canada
| | - Liliana Milani
- Department of Biological, Geological, and Environmental Sciences, University of Bologna, Bologna, Italy
| | - Sergey V Nuzhdin
- Program in Molecular and Computational Biology, University of Southern California, Los Angeles, CA, USA
| | - Luca Bargelloni
- Department of Comparative Biomedicine and Food Science, University of Padova, Padova, Italy
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