Mitochondrial DNA maintenance in vertebrates

Muscle metabolic resilience and enhanced exercise adaptation by Esr1-induced remodeling of mitochondrial cristae-nucleoid architecture in males

Reduced estrogen action is associated with obesity and insulin resistance. However, the cell and tissue-specific actions of estradiol in maintaining metabolic health remain inadequately understood, especially in men. We observed that skeletal muscle ESR1/Esr1 (encodes estrogen receptor α [ERα]) is positively correlated with insulin sensitivity and metabolic health in humans and mice. Because skeletal muscle is a primary tissue involved in oxidative metabolism and insulin sensitivity, we generated muscle-selective Esr1 loss- and gain-of-expression mouse models. We determined that Esr1 links mitochondrial DNA replication and cristae-nucleoid architecture with metabolic function and insulin action in the skeletal muscle of male mice. Overexpression of human ERα in muscle protected male mice from diet-induced disruption of metabolic health and enhanced mitochondrial adaptation to exercise training intervention. Our findings indicate that muscle expression of Esr1 is critical for the maintenance of mitochondrial function and metabolic health in males and that tissue-selective activation of ERα can be leveraged to combat metabolic-related diseases in both sexes.

Comprehensive mitochondrial genomics of Fasciola gigantica from Sudan: insights into genetic diversity, evolutionary dynamics, and host adaptation

Introduction

This study presents a comprehensive analysis of the complete mitochondrial genomes of Fasciola gigantica isolated from cattle, sheep, and goats in Sudan, aiming to provide new insights into genetic diversity, evolutionary dynamics, and host adaptation.

Methods

Mitochondrial genomes were sequenced using high-throughput Illumina MiSeq technology, yielding sequences of 14,483 bp, slightly longer than the reference genome (14,478 bp). A sliding window analysis was conducted to assess nucleotide diversity, and phylogenetic analyses were performed using complete mitochondrial sequences, including and excluding non-coding regions.

Results

Key genetic variations were observed, including a non-canonical start codon (GTG) in the ND5 gene and an alternative stop codon (TAA) in ND4. Length polymorphisms in ND4L and cox1 suggested potential mitochondrial efficiency adaptations. Non-coding regions showed minor length differences, with the long non-coding region extending by 20 bp and the short by 4 bp. Sliding window analysis identified ND4 and ND5 as the most variable genes, while cox1, nd1, and cox2 were the most conserved. Phylogenetic analysis showed distinct clustering of Sudanese F. gigantica isolates with strong bootstrap support. Excluding the D-loop preserved phylogenetic structure, while D-loop-specific analysis revealed high variability, particularly in the sheep isolate.

Discussion

These findings highlight significant genetic variation and evolutionary divergence among F. gigantica isolates in Sudan. The observed diversity, particularly within non-coding and variable coding regions, underscores the influence of regional evolutionary pressures and host-associated adaptations. This work enhances understanding of F. gigantica's genetic landscape and supports the development of more targeted molecular surveillance and control strategies for fascioliasis in endemic regions.

Structural Basis for Promoter Recognition and Transcription Factor Binding and Release in Human Mitochondria

Transcription in human mitochondria is driven by a core apparatus consisting of a Pol A family RNA polymerase (mtRNAP), the initiation factors TFAM and TFB2M, and the elongation factor TEFM. While earlier structures of initiation and elongation complexes provided valuable snapshots, they represent isolated stages of a highly dynamic and multistep process. Critical aspects of mitochondrial transcription-such as DNA recognition and melting, promoter escape, and the release of initiation factors-remain poorly understood. Here, we present a series of cryo-EM structures that capture the transcription complex as it transitions from the initial open promoter complex to the processive elongation complex through intermediate stages. Our data reveal new determinants of promoter specificity, the sequential disengagement of mtRNAP from TFAM and the promoter, the release of TFB2M, and the recruitment of TEFM. Together, these findings provide a detailed molecular mechanism underlying transcription in human mitochondria.

An updated compendium and reevaluation of the evidence for nuclear transcription factor occupancy over the mitochondrial genome

In most eukaryotes, mitochondrial organelles contain their own genome, usually circular, which is the remnant of the genome of the ancestral bacterial endosymbiont that gave rise to modern mitochondria. Mitochondrial genomes are dramatically reduced in their gene content due to the process of endosymbiotic gene transfer to the nucleus; as a result most mitochondrial proteins are encoded in the nucleus and imported into mitochondria. This includes the components of the dedicated mitochondrial transcription and replication systems and regulatory factors, which are entirely distinct from the information processing systems in the nucleus. However, since the 1990s several nuclear transcription factors have been reported to act in mitochondria, and previously we identified 8 human and 3 mouse transcription factors (TFs) with strong localized enrichment over the mitochondrial genome using ChIP-seq (Chromatin Immunoprecipitation) datasets from the second phase of the ENCODE (Encyclopedia of DNA Elements) Project Consortium. Here, we analyze the greatly expanded in the intervening decade ENCODE compendium of TF ChIP-seq datasets (a total of 6,153 ChIP experiments for 942 proteins, of which 763 are sequence-specific TFs) combined with interpretative deep learning models of TF occupancy to create a comprehensive compendium of nuclear TFs that show evidence of association with the mitochondrial genome. We find some evidence for chrM occupancy for 50 nuclear TFs and two other proteins, with bZIP TFs emerging as most likely to be playing a role in mitochondria. However, we also observe that in cases where the same TF has been assayed with multiple antibodies and ChIP protocols, evidence for its chrM occupancy is not always reproducible. In the light of these findings, we discuss the evidential criteria for establishing chrM occupancy and reevaluate the overall compendium of putative mitochondrial-acting nuclear TFs.

Complete mitochondrial genomes of Sinonovacularivularis and Novaculinachinensis and their phylogenetic relationships within family Pharidae

Pharidae is one of the most ecologically and commercially significant families of marine Bivalvia; however, the taxonomy and phylogeny of Pharidae has been ongoing for quite some time and remains a contentious issue. Here, to resolve some problematical relationships among this family, the complete mitochondrial genomes (mitogenomes) of Sinonovacularivularis (17,159 bp) and Novaculinachinensis (15,957 bp) were assembled, and a comparative mitochondrial genomic analysis was conducted. Both mitogenomes contain 12 protein-coding genes, 22 transfer RNA genes, and two ribosomal RNA genes. Among the published Pharidae mitogenomes, N.chinensis exhibited the smallest genome size but the highest AT content. The results of the phylogenetic trees confirmed the monophyly of the family Solenoidea, and indicated that N.chinensis and Sinonovacula (S.constricta and S.rivularis) were closely related in the family Pharidae. From the CREx analysis, we found that transposition and tandem duplication random losses (TDRLs) might have occurred between Pharidae and Solenidae. Moreover, positive selection was detected in nad5 of the foreground N.chinensis, and divergent evolution occurred at site 144 in the freshwater and marine lineages. Overall, our findings provide new molecular data on the phylogenetic and evolutionary relationships of Pharidae, and contribute to unraveling the salinity adaptations of Pharidae.

A DNP-Supported Solid-State NMR Approach to Study Nucleic Acids In Situ Reveals Berberine-Stabilized Hoogsteen Structures in Mitochondria

Mitochondria are central to cellular bioenergetics, with the unique ability to translate and transcribe a subset of their own proteome. Given the critical importance of energy production, mitochondria seem to utilize higher-order nucleic acid structures to regulate gene expression, much like nuclei. Herein, we introduce a tailored approach to probe the formation of such structures, specifically G-quadruplexes, within intact mitochondria by using sensitivity-enhanced dynamic nuclear polarization-supported solid-state NMR (DNP-ssNMR). We acquired NMR spectra on isolated intact isotopically labeled mitochondria treated with berberine, a known high-affinity G-quadruplex stabilizer. The DNP-ssNMR data revealed spectral changes in nucleic acid sugar correlations, increased signal intensity for guanosine carbons, and enhanced Hoogsteen hydrogen bond formation, providing evidence of in vivo G-quadruplex formation in mitochondria. Together, our workflow enables the study of mitochondrial nucleic acid-ligand interactions at endogenous concentrations within biologically relevant environments by DNP-ssNMR, thus paving the way for future research into mitochondrial diseases and their potential treatments.

FAM43A coordinates mtDNA replication and mitochondrial biogenesis in response to mtDNA depletion

Mitochondrial retrograde signaling (MRS) pathways relay the functional status of mitochondria to elicit homeostatic or adaptive changes in nuclear gene expression. Budding yeast have "intergenomic signaling" pathways that sense the amount of mitochondrial DNA (mtDNA) independently of oxidative phosphorylation (OXPHOS), the primary function of genes encoded by mtDNA. However, MRS pathways that sense the amount of mtDNA in mammalian cells remain poorly understood. We found that mtDNA-depleted IMR90 cells can sustain OXPHOS for a significant amount of time, providing a robust model system to interrogate human intergenomic signaling. We identified FAM43A, a largely uncharacterized protein, as a CHK2-dependent early responder to mtDNA depletion. Depletion of FAM43A activates a mitochondrial biogenesis program, resulting in an increase in mitochondrial mass and mtDNA copy number via CHK2-mediated upregulation of the p53R2 form of ribonucleotide reductase. We propose that FAM43A performs a checkpoint-like function to limit mitochondrial biogenesis and turnover under conditions of mtDNA depletion or replication stress.

DNA repair pathways in the mitochondria

Mitochondria contain their own small, circular genome that is present in high copy number. The mitochondrial genome (mtDNA) encodes essential subunits of the electron transport chain. Mutations in the mitochondrial genome are associated with a wide range of mitochondrial diseases and the maintenance and replication of mtDNA is crucial to cellular health. Despite the importance of maintaining mtDNA genomic integrity, fewer DNA repair pathways exist in the mitochondria than in the nucleus. However, mitochondria have numerous pathways that allow for the removal and degradation of DNA damage that may prevent accumulation of mutations. Here, we briefly review the DNA repair pathways present in the mitochondria, sources of mtDNA mutations, and discuss the passive role that mtDNA mutagenesis may play in cancer progression.

Mitochondrial DNA alterations in precision oncology: Emerging roles in diagnostics and therapeutics

Mitochondria are dynamic organelles essential for vital cellular functions, including ATP production, apoptosis regulation, and calcium homeostasis. Increasing research has highlighted the significance of mitochondrial DNA (mtDNA) content and alterations in the development and progression of various diseases, including cancer. The high mutation rate and vulnerability of mtDNA to damage make these alterations valuable biomarkers for cancer diagnosis, monitoring disease progression, detecting metastasis, and predicting treatment resistance across different tumor types. This review explores the emerging roles of mtDNA alterations in precision oncology, emphasizing their potential in theranostics. The authors explore the mechanisms by which mtDNA mutations contribute to tumorigenesis and therapy resistance, the impact of heteroplasmy in cancer biology, and the integration of mtDNA-based diagnostics with current therapeutic strategies. Additionally, the authors highlight the experimental tools and models currently used to investigate mtDNA alterations in cancer, including advanced sequencing technologies and animal models.

KAS-ATAC reveals the genome-wide single-stranded accessible chromatin landscape of the human genome

Gene regulation in most eukaryotes involves two fundamental processes: alterations in genome packaging by nucleosomes, with active cis-regulatory elements (CREs) generally characterized by open-chromatin configuration, and transcriptional activation. Mapping these physical properties and biochemical activities, through profiling chromatin accessibility and active transcription, is a key tool for understanding the logic and mechanisms of transcription and its regulation. However, the relationship between these two states has not been accessible to simultaneous measurement. To this end, we developed KAS-ATAC, a combination of the kethoxal-assisted ssDNA sequencing (KAS-seq) and assay for transposase-accessible chromatin using sequencing (ATAC-seq) methods for mapping single-stranded DNA (and thus active transcription) and chromatin accessibility, respectively, enabling the genome-wide identification of DNA fragments that are simultaneously accessible and contain ssDNA. We use KAS-ATAC to evaluate levels of active transcription over different CRE classes, to estimate absolute levels of transcribed accessible DNA over CREs, to map nucleosomal configurations associated with RNA polymerase activities, and to assess transcription factor association with transcribed DNA through transcription factor binding site (TFBS) footprinting. We observe lower levels of transcription over distal enhancers compared with promoters and distinct nucleosomal configurations around transcription initiation sites associated with active transcription. We find that most TFs associate equally with transcribed and nontranscribed DNA, but a few factors specifically do not exhibit footprints over ssDNA-containing fragments. We anticipate KAS-ATAC to continue to derive useful insights into chromatin organization and transcriptional regulation in other contexts in the future.

Characterization of Complete Mitochondrial Genome and Phylogeny of Three Echeneidae Species

Species of the family Echeneidae are renowned for their capacity to adhere to various hosts using a sucking disc. This study aimed to examine the mitochondrial genome characteristics of three fish species (Echeneis naucrates, Remora albescens, and Remora remora) within the family Echeneidae and determine their phylogenetic relationships. The findings revealed that the mitochondrial genome lengths of the three species were 16,611 bp, 16,648 bp, and 16,623 bp, respectively, containing 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs), and a D-loop region. Most PCGs utilized ATG as the initiation codon, while only cox I used the GTG as the initiation codon. Additionally, seven genes employed incomplete termination codons (T and TA). The majority of PCGs in the three species displayed negative AT-skew and GC-skew values, with the GC-skew amplitude being greater than the AT-skew. The Ka/Ks ratios of the 13 PCGs did not exceed 1, demonstrating these species had been subjected to purification selection. Furthermore, only tRNA-Ser (GCT) lacked the D arm, while other tRNAs exhibited a typical cloverleaf secondary structure. Bayesian inference (BI) and maximum likelihood (ML) methods were utilized to construct a phylogenetic tree of the three species based on the 13 PCGs. Remora remora was identified as a distinct group, while R. osteochir and R. brachyptera were classified as sister taxa. This study contributes to the mitochondrial genome database of the family Echeneidae and provides a solid foundation for further systematic classification research in this fish group.

D-loop mutations in mitochondrial DNA are a risk factor for chemotherapy resistance in esophageal cancer

Esophageal cancer is a highly aggressive disease, and acquired resistance to chemotherapy remains a significant hurdle in its treatment. mtDNA, crucial for cellular energy production, is prone to mutations at a higher rate than nuclear DNA. These mutations can accumulate and disrupt cellular function; however, mtDNA mutations induced by chemotherapy in esophageal cancer remain unexplored. We aimed to identify such mutations in esophageal cancer, pre- and post-chemotherapy, and explore the relationship between them and clinicopathological factors associated with chemotherapy resistance. We investigated mtDNA mutations in Human esophageal squamous cell carcinoma (ESCC) cancer cell lines (TE8 and TE11) and patient samples (27 pre- and post-chemotherapy, and 96 post-chemotherapy) using next-generation sequencing. Our analysis revealed a rise in mtDNA mutations following chemotherapy, particularly within the D-loop region. Moreover, mutations in a specific D-loop segment (hypervariable segment 1; HVS1) were associated with lower mtDNA copy number, poorer response to chemotherapy, and decreased five-year survival rates. These findings suggest that HVS1 mutations in mtDNA acquired after chemotherapy may contribute to treatment resistance and poorer clinical outcomes in patients with esophageal cancer. This study sheds light on the mechanisms of chemotherapy resistance and provides valuable insights for future research to overcome this challenge.

Complete mitochondrial genome of Lepidocephalichthysberdmorei and its phylogenetic status within the family Cobitidae (Cypriniformes)

In this study, the complete mitochondrial genome of Lepidocephalichthysberdmorei was first determined by the primer walking sequence method. The complete mitochondrial genome was 16,574 bp in length, including 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes, and a control region (D-loop). The gene arrangement pattern was identical to that of other teleosts. The overall base composition was 29.9% A, 28.5% T, 25.5% C, and 16.1% G, with an A+T bias of 58.4%. Furthermore, phylogenetic analyses were conducted based on 13 PCGs from the mitochondrial genomes of 18 cobitid species using with three different methods (Neighbor-joining, Maximum likelihood, and Bayesian inference). All methods consistently showed that the four species of the genus Lepidocephalichthys form a monophyletic group. This study would provide effective molecular information for the Lepidocephalichthys species as well as novel genetic marker for the study of species identification.

The clinical and genetic spectrum of mitochondrial diseases in China: A multicenter retrospective cross-sectional study

Mitochondrial diseases (MtDs) present diverse clinical phenotypes, yet large-scale studies are hindered by their rarity. This retrospective, multicenter study, conducted across five Chinese hospitals' neurology departments from 2009 to 2019, aimed to address this gap. Nationwide, 1351 patients were enrolled, with a median onset age of 14.0 (18.5) years. The predominant phenotype was mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) (45.0%). Mitochondrial DNA (mtDNA) mutations were prevalent (87.4%), with m.3243A>G being the most common locus (48.7%). Meanwhile, POLG mutations in nuclear DNA (nDNA) accounted for 16.5%. Comparative analysis based on age groups (with a cut-off at 14 years) revealed the highest prevalence of MELAS, with Leigh syndrome (LS) and chronic progressive external ophthalmoplegia (CPEO) being the second most common phenotypes in junior and senior groups, respectively. Notably, the most commonly mutated nuclear genes varied across age groups. In conclusion, MELAS predominated in this Chinese MtD cohort, underscored by m.3243A>G and POLG as principal mtDNA mutations and pathogenic nuclear genes. The phenotypic and genotypic disparities observed among different age cohorts highlight the complex nature of MtDs.

Characterization and phylogenetic implications of newly sequenced mitochondrial genomes of cobitid fish Acantopsis Rungthipae (Boyd, Nithirojpakdee & Page, 2017)

BACKGROUND

Acantopsis rungthipae has significant ornamental and ecological value. This study aimed at structurally characterizing the A. rungthipae mitochondrial genome and elucidate its phylogenetic position in Cobitidae.

METHODS AND RESULTS

High-throughput sequencing technology was used to obtain the complete sequence of the mitochondrial genome of A. rungthipae and reconstruct a Cobitidae phylogenetic tree based on the sequence of 13 protein-coding genes. The entire mitochondrial genome of A. rungthipae was 16,600 bp, containing 22 tRNA genes, 13 protein-coding genes, 2 rRNAs, and 2 non-coding regions (D-loop and OL). The base composition showed a significant AT preference, with the highest A + T content (67.1%) in the D-loop region. Among the protein-coding genes, 12 had ATG as a typical starting codon, while only COXI had GTG as a special starting codon. Twenty-one of the tRNA genes exhibited clover structure, and only tRNA-Ser (GCT) could not fold into a clover structure because of the absence of DHU arms. The phylogenetic tree was reconstructed using the Bayesian and maximum likelihood methods and showed that A. rungthipae and Acantopsis choirorhynchos converged into one branch, and their phylogenetic relationships were relatively close.

CONCLUSIONS

Our findings supplement basic data on the A. rungthipae mitochondrial genome and deepen the understanding of the evolutionary relationships of the genus Acantopsis. Clarifying the evolutionary relationships between different species in Acantopsis lays a solid foundation for subsequent research on fish adaptation and selection pressure.

Comparative mitogenomic analysis and phylogeny of Veneridae with doubly uniparental inheritance

Doubly uniparental inheritance (DUI) is an atypical animal mtDNA inheritance system, reported so far only in bivalve species, in which two mitochondrial lineages exist: one transmitted through the egg (F-type) and the other through the sperm (M-type). Although numerous species exhibit this unusual organelle inheritance, it is primarily documented in marine and freshwater mussels. The distribution, function and molecular evolutionary implications of DUI in the family Veneridae, however, remain unclear. Here, we investigated 17 species of Veneridae, compared mitochondrial genomes of DUI species and reconstructed their phylogenetic framework. Different sex-linked mitochondrial genomes have been identified in the male gonads and adductor muscles of 7 venerids, indicating the presence of DUI in these species. Analysis of the unassigned regions (URs) of the mitochondrial genome in DUI species revealed that 13 out of 44 URs contained repetitive sequences, with nine being long unassigned regions (LURs). All LURs were capable of forming secondary structures, and most of them exhibited patterns of significant sequence similarity to elements known to have specific functions in the control regions of sea urchins and mammals. The F/M phylogeny showed that DUI venerids exhibit both taxon-specific patterns and gender-specific patterns, with Gafrarium dispar experiencing masculinization events.

Unraveling the Mitogenomic Characteristics and Phylogenetic Implications of Leuciscus merzbacheri (Zugmayer, 1912), an Endangered Fish in the Junggar Basin of Xinjiang, Northwest China

BACKGROUND

Leuciscus merzbacheri is a rare and endangered fish in Xinjiang, China. As a representative species of the fauna in the Junggar Basin, it is of high economic and scientific value. The genetic data are still limited, and the mitochondrial genomic characteristics remain unexplored.

METHODS

A high-throughput sequencing method was used to obtain the complete mitogenome of L. merzbacheri.

RESULTS

The full length of the circular DNA was 16,609 bp, and it consisted of 13 protein-coding genes (PCGs), 22 tRNAs, 2 rRNAs and 2 non-coding regions. The overall nucleotide compositions of both the mitogenome and PCGs showed an obvious AT preference with percentages of 54.20% and 53.60%, respectively. Three commonly used amino acids were Leu (16.43%), Ala (8.95%) and Thr (7.85%) in turn. All tRNAs could form the typical clover structures excluding tRNA-Ser AGY. The presumed secondary structures of two rRNAs contained several stem-loop domains, and the structure of 12S rRNA seemed to be more stable than that of 16S rRNA. Extended termination sequence regions (ETASs), central conserved regions (CSB-F, CSB-E and CSB-D), and conserved sequence regions (CSB-1, CSB-2 and CSB-3) were identified in the control region. The phylogenetic tree showed that L. merzbacheri was recovered with strong supports as a sister to the other members of the genus. The location in the outermost branch implied that it might be a relatively ancient species among its congeners.

CONCLUSIONS

This study would complement the genetic data on L. merzbacheri and contribute to a better understanding of molecular evolution in Leuciscus as well.

Characterization of the Complete Mitochondrial Genome of the Central Highland Grey-Shanked Douc Langur (Pygathrix cinerea), a Critically Endangered Species Endemic to Vietnam (Mammalia: Primates)

The grey-shanked douc langur (Pygathrix cinerea) is a recently described, critically endangered primate, endemic to Vietnam. In this study, we describe the Central Highland species' complete mitochondrial genome (mitogenome-mtDNA). It is a circular molecule with a length of 16,541 base pairs (bp). The genome consists of 37 genes, consistent with those found in most other vertebrates, including 13 protein coding genes, 22 transfer RNAs, and two ribosomal RNAs. A comparison with the mitogenomes of more than 50 primates showed that the mitogenome of Vietnamese Central Highland Pygathrix cinerea has a conservative gene order. We identified 43 nucleotide differences when comparing this genome with a previously published mitogenome of Pygathrix cinerea. It is evident that there are distinct differences between the Pygathrix cinerea we are currently studying and other Pygathrix cinerea specimens. These differences are unlikely to be solely the result of sequencing errors, as the mitogenomes were generated using high-quality methods. The genetic divergence observed between the two Pygathrix cinerea mitogenomes implies the potential existence of at least two distinct lineages or forms of this primate species within its native range in Vietnam.

Mitochondrial endogenous substance transport-inspired nanomaterials for mitochondria-targeted gene delivery

Mitochondrial genome (mtDNA) independent of nuclear gene is a set of double-stranded circular DNA that encodes 13 proteins, 2 ribosomal RNAs and 22 mitochondrial transfer RNAs, all of which play vital roles in functions as well as behaviors of mitochondria. Mutations in mtDNA result in various mitochondrial disorders without available cures. However, the manipulation of mtDNA via the mitochondria-targeted gene delivery faces formidable barriers, particularly owing to the mitochondrial double membrane. Given the fact that there are various transport channels on the mitochondrial membrane used to transfer a variety of endogenous substances to maintain the normal functions of mitochondria, mitochondrial endogenous substance transport-inspired nanomaterials have been proposed for mitochondria-targeted gene delivery. In this review, we summarize mitochondria-targeted gene delivery systems based on different mitochondrial endogenous substance transport pathways. These are categorized into mitochondrial steroid hormones import pathways-inspired nanomaterials, protein import pathways-inspired nanomaterials and other mitochondria-targeted gene delivery nanomaterials. We also review the applications and challenges involved in current mitochondrial gene editing systems. This review delves into the approaches of mitochondria-targeted gene delivery, providing details on the design of mitochondria-targeted delivery systems and the limitations regarding the various technologies. Despite the progress in this field is currently slow, the ongoing exploration of mitochondrial endogenous substance transport and mitochondrial biological phenomena may act as a crucial breakthrough in the targeted delivery of gene into mitochondria and even the manipulation of mtDNA.

Decoding mitochondria's role in immunity and cancer therapy

The functions of mitochondria, including energy production and biomolecule synthesis, have been known for a long time. Given the rising incidence of cancer, the role of mitochondria in cancer has become increasingly popular. Activated by components released by mitochondria, various pathways interact with each other to induce immune responses to protect organisms from attack. However, mitochondria play dual roles in the progression of cancer. Abnormalities in proteins, which are the elementary structures of mitochondria, are closely linked with oncogenesis. Both the aberrant accumulation of intermediates and mutations in enzymes result in the generation and progression of cancer. Therefore, targeting mitochondria to treat cancer may be a new strategy. Several drugs aimed at inhibiting mutated enzymes and accumulated intermediates have been tested clinically. Here, we discuss the current understanding of mitochondria in cancer and the interactions between mitochondrial functions, immune responses, and oncogenesis. Furthermore, we discuss mitochondria as hopeful targets for cancer therapy, providing insights into the progression of future therapeutic strategies.

Our current understanding of the biological impact of endometrial cancer mtDNA genome mutations and their potential use as a biomarker

Endometrial cancer (EC) is a devastating and common disease affecting women's health. The NCI Surveillance, Epidemiology, and End Results Program predicted that there would be >66,000 new cases in the United States and >13,000 deaths from EC in 2023, and EC is the sixth most common cancer among women worldwide. Regulation of mitochondrial metabolism plays a role in tumorigenesis. In proliferating cancer cells, mitochondria provide the necessary building blocks for biosynthesis of amino acids, lipids, nucleotides, and glucose. One mechanism causing altered mitochondrial activity is mitochondrial DNA (mtDNA) mutation. The polyploid human mtDNA genome is a circular double-stranded molecule essential to vertebrate life that harbors genes critical for oxidative phosphorylation plus mitochondrial-derived peptide genes. Cancer cells display aerobic glycolysis, known as the Warburg effect, which arises from the needs of fast-dividing cells and is characterized by increased glucose uptake and conversion of glucose to lactate. Solid tumors often contain at least one mtDNA substitution. Furthermore, it is common for cancer cells to harbor mixtures of wild-type and mutant mtDNA genotypes, known as heteroplasmy. Considering the increase in cancer cell energy demand, the presence of functionally relevant carcinogenesis-inducing or environment-adapting mtDNA mutations in cancer seems plausible. We review 279 EC tumor-specific mtDNA single nucleotide variants from 111 individuals from different studies. Many transition mutations indicative of error-prone DNA polymerase γ replication and C to U deamination events were present. We examine the spectrum of mutations and their heteroplasmy and discuss the potential biological impact of recurrent, non-synonymous, insertion, and deletion mutations. Lastly, we explore current EC treatments, exploiting cancer cell mitochondria for therapy and the prospect of using mtDNA variants as an EC biomarker.

An updated compendium and reevaluation of the evidence for nuclear transcription factor occupancy over the mitochondrial genome

In most eukaryotes, mitochondrial organelles contain their own genome, usually circular, which is the remnant of the genome of the ancestral bacterial endosymbiont that gave rise to modern mitochondria. Mitochondrial genomes are dramatically reduced in their gene content due to the process of endosymbiotic gene transfer to the nucleus; as a result most mitochondrial proteins are encoded in the nucleus and imported into mitochondria. This includes the components of the dedicated mitochondrial transcription and replication systems and regulatory factors, which are entirely distinct from the information processing systems in the nucleus. However, since the 1990s several nuclear transcription factors have been reported to act in mitochondria, and previously we identified 8 human and 3 mouse transcription factors (TFs) with strong localized enrichment over the mitochondrial genome using ChIP-seq (Chromatin Immunoprecipitation) datasets from the second phase of the ENCODE (Encyclopedia of DNA Elements) Project Consortium. Here, we analyze the greatly expanded in the intervening decade ENCODE compendium of TF ChIP-seq datasets (a total of 6,153 ChIP experiments for 942 proteins, of which 763 are sequence-specific TFs) combined with interpretative deep learning models of TF occupancy to create a comprehensive compendium of nuclear TFs that show evidence of association with the mitochondrial genome. We find some evidence for chrM occupancy for 50 nuclear TFs and two other proteins, with bZIP TFs emerging as most likely to be playing a role in mitochondria. However, we also observe that in cases where the same TF has been assayed with multiple antibodies and ChIP protocols, evidence for its chrM occupancy is not always reproducible. In the light of these findings, we discuss the evidential criteria for establishing chrM occupancy and reevaluate the overall compendium of putative mitochondrial-acting nuclear TFs.

Between good and evil: Complexation of the human cathelicidin LL-37 with nucleic acids

The innate immune system provides a crucial first line of defense against invading pathogens attacking the body. As the only member of the human cathelicidin family, the antimicrobial peptide LL-37 has been shown to have antiviral, antifungal, and antibacterial properties. In complexation with nucleic acids, LL-37 is suggested to maintain its beneficial health effects while also acting as a condensation agent for the nucleic acid. Complexes formed by LL-37 and nucleic acids have been shown to be immunostimulatory with a positive impact on the human innate immune system. However, some studies also suggest that in some circumstances, LL-37/nucleic acid complexes may be a contributing factor to autoimmune disorders such as psoriasis and systemic lupus erythematosus. This review provides a comprehensive discussion of research highlighting the beneficial health effects of LL-37/nucleic acid complexes, as well as discussing observed detrimental effects. We will emphasize why it is important to investigate and elucidate structural characteristics, such as condensation patterns of nucleic acids within complexation, and their mechanisms of action, to shed light on the intricate physiological effects of LL-37 and the seemingly contradictory role of LL-37/nucleic acid complexes in the innate immune response.

Characterization and Molecular Phylogenetic Analysis of Subfamily Erebinae (Lepidoptera: Noctuoidea: Erebidae) Using Five Complete Mitochondrial Genomes

In this study, the complete mitogenomes of Sympis rufibasis, Lacera noctilio, Oxyodes scrobiculata, Mocis undata, and Artena dotata were newly sequenced to bring up-to-date the database using the next-generation sequencing methods. The gene order of all sequenced mitogenomes was identical consisting of 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs), and a non-coding A+T-rich region, which were common to other Lepidopteran insects. All protein-coding genes (PCGs) initiated with a canonical ATN codon and ended with TAN or an incomplete stop codon, single T. The A+T-rich region of S. rufibasis, L. noctilio, O. scrobiculata, M. undata, and A. dotata are 406 bp, 462 bp, 372 bp, 410 bp, and 406 bp long, respectively, containing number of characteristics that are distinctive to Noctuoidea moths. We analyzed concatenated amino acid sequences of protein-coding genes not including rRNAs, using Maximum Likelihood and Bayesian Inference methods. The phylogenetic analyses indicated that the tribe relationships within Erebinae were reconstructed as (Sypnini+((Erebini 1+Poaphilini 1)+((Euclidiini+Catocalini+(Hypopyrini+Erebini 2))+((Hulodini+(Poaphilini 2+Ophiusini))))). Phylogenetic analyses supported and confirmed the monophyly of the subfamilies' relationships as follows: (Hypeninae+Lymantriinae)+((Scoliopterginae+((Calpinae+Erebinae)+((Herminiinae+Aganainae)+Arctiinae)))) within Erebidae.

Directional selection, not the direction of selection, affects telomere length and copy number at ribosomal RNA loci

Many fisheries exert directional selection on traits such as body size and growth rate. Whether directional selection impacts regions of the genome associated with traits related to growth is unknown. To address this issue, we characterised copy number variation in three regions of the genome associated with cell division, (1) telomeric DNA, (2) loci transcribed as ribosomal RNA (rDNA), and (3) mitochondrial DNA (mtDNA), in three selection lines of zebrafish reared at three temperatures (22 °C, 28 °C, and 34 °C). Selection lines differed in (1) the direction of selection (two lines experienced directional selection for large or small body size) and (2) whether they experienced any directional selection itself. Lines that had experienced directional selection were smaller, had lower growth rate, shorter telomeres, and lower rDNA copy number than the line that experiencing no directional selection. Neither telomere length nor rDNA copy number were affected by temperature. In contrast, mtDNA content increased at elevated temperature but did not differ among selection lines. Though directional selection impacts rDNA and telomere length, direction of such selection did not matter, whereas mtDNA acts as a stress marker for temperature. Future work should examine the consequences of these genomic changes in natural fish stocks.

Genetic analysis of Octopus cyanea reveals high gene flow in the South-West Indian Ocean

Octopus cyanea (Gray, 1849), abundant in the South-West Indian Ocean (SWIO), constitutes a vital resource for both subsistence and commercial fisheries. However, despite this socioeconomic importance, and recent indications of overfishing, little is known about the population structure of O. cyanea in the region. To inform sustainable management strategies, this study assessed the spatio-temporal population structure and genetic variability of O. cyanea at 20 sites in the SWIO (Kenya, Tanzania, Mozambique, Madagascar, Mauritius, Rodrigues, and the Seychelle Islands) by complementary analysis of mitochondrial DNA (mtDNA) noncoding region (NCR) sequences and microsatellite markers. MtDNA analysis revealed a shallow phylogeny across the region, with demographic tests suggesting historic population fluctuations that could be linked to glacial cycles. Contrary to expectations, NCR variation was comparable to other mtDNA regions, indicating that the NCR is not a hypervariable region. Both nuclear and mtDNA marker types revealed a lack of genetic structure compatible with high gene flow throughout the region. As adults are sedentary, this gene flow likely reflects connectivity by paralarval dispersal. All samples reported heterozygote deficits, which, given the overall absence of structure, likely reflect ephemeral larval recruitment variability. Levels of mtDNA and nuclear variability were similar at all locations and congruent with those previously reported for harvested Octopodidae, implying resilience to genetic erosion by drift, providing current stock sizes are maintained. However, as O. cyanea stocks in the SWIO represent a single, highly connected population, fisheries may benefit from additional management measures, such as rotational closures aligned with paralarval ecology and spanning geopolitical boundaries.

Mitochondrial deoxyguanosine kinase is required for female fertility in mice

Mitochondrial homeostasis plays a pivotal role in oocyte maturation and embryonic development. Deoxyguanosine kinase (DGUOK) is a nucleoside kinase that salvages purine nucleosides in mitochondria and is critical for mitochondrial DNA replication and homeostasis in non-proliferating cells. Dguok loss-of-function mutations and deletions lead to hepatocerebral mitochondrial DNA deletion syndrome. However, its potential role in reproduction remains largely unknown. In this study, we find that Dguok knockout results in female infertility. Mechanistically, DGUOK deficiency hinders ovarian development and oocyte maturation. Moreover, DGUOK deficiency in oocytes causes a significant reduction in mitochondrial DNA copy number and abnormal mitochondrial dynamics and impairs germinal vesicle breakdown. Only few DGUOK-deficient oocytes can extrude their first polar body during in vitro maturation, and these oocytes exhibit irregular chromosome arrangements and different spindle lengths. In addition, DGUOK deficiency elevates reactive oxygen species levels and accelerates oocyte apoptosis. Our findings reveal novel physiological roles for the mitochondrial nucleoside salvage pathway in oocyte maturation and implicate DGUOK as a potential marker for the diagnosis of female infertility.

Comprehensive Analysis of Phylogenetic Relationship and Optimal Codons in Mitochondrial Genomes of the Genus Pseudogastromyzon

As indicator organisms for water pollution detection, Pseudogasteromyzon species play a vital role in aquatic environment monitoring. We have successfully sequenced the mitogenomes of P. fasciatus jiulongjiangensis and P. myersi and downloaded the mitogenomes of nine other Pseudogastromyzon fish on GenBank to conduct a detailed comparative analysis of their phylogenetic relationships and evolutionary history. The findings revealed a conservation in both gene composition and gene order. Except for the trnS1 gene lacking dihydrouracil arms, the other 21 tRNAs showed the typical clover-leaf secondary structure. According to the ΔRSCU method, we identified the seven most abundant optimal codons: CUA, GUA, CCA, CAA, GAA, AGC, and GGC. The construction of maximum parsimony, maximum likelihood, and Bayes trees yielded congruent topologies, and the 11 Pseudogastromyzon species were clustered into two major clusters. Among them, one of which was composed of P. fangi, P. changtingensis changtingensis, and P. changtingensis tungpeiensis, while the remaining eight species formed another cluster, further subdivided into five smaller clusters. Distinct clusters formed between P. fasciatus jiulongjiangensis and P. meihuashanensis, P. cheni and P. peristictus, and P. laticeps and P. lianjiangensis, and the remaining two species were clustered separately, thereby enhancing our understanding of them. Furthermore, our analysis results of divergence times revealed that these 11 Pseudogasteromyzon species underwent rapid differentiation in the Pleistocene epochs. Overall, our study sheds light on the phylogenetic relationship and evolutionary history of Pseudogasteromyzon species, providing a necessary knowledge foundation for further understanding the intricacies of an ecosystem health assessment.

Multiple independent origins of duplicated mitochondrial control regions indicate an apomorphy in the Thysanoptera (Insecta)

The mitochondrial genome (mitogenome) of thrips is characterized by the presence of control region (CR) duplication. However, the evolution pattern of duplicated CRs in thrips is still unclear. In this study, the multiple independent origins of duplicated CR indicated that the CR duplication was not an ancestral state for Thysanoptera. The macroevolutionary pattern suggested that the earliest CR duplication event occurred in the middle Cretaceous (94.85 Ma) coincided with rearrangement events forming the ancestors of Aeolothripidae, but much later than that forming the ancestors of the suborder Terebrantia. The mitogenome with duplicated CRs showed a higher rate of gene rearrangement. The sequence similarity of the CR copies and divergence time were negatively correlated, indicating age-related deterioration of mitochondrial function. No significant differences were found in the mitochondrial DNA, the P123 and P4FD between the single and multiple-CR charactered mitogenomes, which suggested that the duplicated CRs may not affect the replication process in thrip mitogenome. The mitogenomes with duplicated CRs (mean: 0.0088 subs/s/my) show a significantly increased evolutionary rate than that with a single one (mean: 0.0058 subs/s/my). However, it seems that this higher evolutionary rate did not have adaptive mechanisms in Terebrantia. We speculated that the duplicated CRs may cause a more intense production of energy by mitochondria, and an accelerated mutation and substitution rate is expected in such mitogenomes. Our study provided new insights into the presence of CR duplications and their evolution in the mitogenomes of thrips.

Molecular mechanisms underlying sarcopenia in heart failure

The loss of skeletal muscle, also known as sarcopenia, is an aging-associated muscle disorder that is disproportionately present in heart failure (HF) patients. HF patients with sarcopenia have poor outcomes compared to the overall HF patient population. The prevalence of sarcopenia in HF is only expected to grow as the global population ages, and novel treatment strategies are needed to improve outcomes in this cohort. Multiple mechanistic pathways have emerged that may explain the increased prevalence of sarcopenia in the HF population, and a better understanding of these pathways may lead to the development of therapies to prevent muscle loss. This review article aims to explore the molecular mechanisms linking sarcopenia and HF, and to discuss treatment strategies aimed at addressing such molecular signals.

Effects of Lactiplantibacillus plantarum on oxidative stress, mitophagy, and NLRP3 inflammasome activation in broiler breast meat

Poultry meat has a high polyunsaturated fatty acids content, making it vulnerable to oxidative stress. Mitophagy participates in the regulation of oxidative stress and the nucleotide-binding and oligomerization domain (NOD)-like receptor family as well as pyrin domain-containing protein 3 (NLRP3) inflammasome activation. Lactiplantibacillus plantarum P8 (P8) is a probiotic strain with an antioxidant capacity. In the present study, we investigated the effects of P8 on oxidative stress, mitochondrial function, mitophagy, and NLRP3 inflammasome in the breast meat of oxidatively stressed broilers. Four hundred 1-day-old male broilers were assigned to a 2 × 2 factorial design with 2 P8 levels (0 or 1 × 108 cfu/g), either with or without dexamethasone (DEX) injection, for a 21-day experimental period. DEX was injected intraperitoneally once daily from d 16 to 21. The breast meat was collected on d 21. The results showed that P8 supplementation decreased malondialdehyde (MDA) levels, increased superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and activated the Keap1-Nrf2 pathway in DEX-injected broilers. Moreover, P8 supplementation downregulated mitochondrial DNA (mtDNA) copy number and increased the expressions of peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), silent information regulator 1 (SIRT1), mitochondrial fusion protein 1 (Mfn1), and optic atrophy protein 1 (OPA1) in DEX-treated broilers. In addition, the decreased mitophagy level in DEX-treated broilers was elevated with P8 supplementation, as reflected by the increased gene expression of autophagy-related gene 5 (ATG5), Bcl-2-interacting protein (Becline-1), Parkin, PTEN-induced kinase 1 (PINK1), light chain 3 II (LC3II)/LC31, and the protein expression of Parkin as well as decreased p62 expression. In addition, P8 supplementation inhibited NLRP3 inflammasome activation by decreasing the transcription of NLRP3, IL-18, cysteinyl aspartate-specific proteinase-1 (Caspase-1), and the expression of NLRP3 and IL-18 in DEX-treated broilers. In conclusion, dietary P8 supplementation alleviates oxidative stress, improves mitophagy, and inhibits NLRP3 inflammasome activation in the breast meat of oxidatively stressed broilers.

Comparative Mitogenomics Reveals Cryptic Species in Sillago ingenuua McKay, 1985 (Perciformes: Sillaginidae)

It is unreliable to identify marine fishes only by external morphological features. Species misidentification brings great challenges to fishery research, resource monitoring and ecomanagement. Sillago ingenuua is an important part of commercial marine fishes, and in which, the morphological differences between different groups are not obvious. Here, we compared different geographical groups of S. ingenuua which were collected from Xiamen, Dongshan, Keelung, Songkhla and Java. The results showed that all samples of S. ingenuua were similar in external morphological characteristics and the shape of the swim bladder, but there were two distinctive lineages which were flagged as cryptic species based on DNA barcoding. The comparative mitogenomic results showed that S. ingenuua A and S. ingenuua B were identical in structural organization and gene arrangement. Their nucleotide composition and codon usage were also similar. A phylogenetic analysis was performed based on 13 concatenated PCGs from eight Sillago species. The results showed that the genetic distance between S. ingenuua A and S. ingenuua B was large (D = 0.069), and this genetic distance was large enough to reveal that S. ingenuua A and S. ingenuua B might be different species.

Decoding mitochondrial-nuclear (epi)genome interactions: the emerging role of ncRNAs

Bidirectional communication between the mitochondria and the nucleus is required for several physiological processes, and the nuclear epigenome is a key mediator of this relationship. ncRNAs are an emerging area of discussion for their roles in cellular function and regulation. In this review, we highlight the role of mitochondrial-encoded ncRNAs as mediators of communication between the mitochondria and the nuclear genome. We focus primarily on retrograde signaling, a process in which the mitochondrion relays ncRNAs to translate environmental stress signals to changes in nuclear gene expression, with implications on stress responses that may include disease(s). Other biological roles of mitochondrial-encoded ncRNAs, such as mitochondrial import of proteins and regulation of cell signaling, will also be discussed.

Variants in the mitochondrial genome sequence of Oryctes rhinoceros (Coleoptera: Scarabaeidae) infected with Oryctes rhinoceros nudivirus in oil palm and coconut plantations

The CRB (coconut rhinoceros beetle) haplotype was classified into CRB-S and CRB-G, based on the presence of single nucleotide polymorphisms (SNPs) in the mitochondrial cox1 gene. Mitochondrial genomes (mitogenomes) are the most widely used genetic resources for molecular evolution, phylogenetics, and population genetics in relation to insects. This study presents the mitogenome CRB-G and CRB-S which were collected in Johor, Malaysia. The mitogenome of CRB-G collected from oil palm plantations in 2020 and 2021, and wild coconut palms in 2021 was 15,315 bp, 15,475 bp, and 17,275 bp, respectively. The CRB-S was discovered in coconut and oil palms in 2021, and its mitogenome was 15,484 bp and 17,142 bp, respectively. All the mitogenomes have 37 genes with more than 99% nucleotide sequence homology, except the CRB-G haplotype collected from oil palm in 2021 with 89.24% nucleotide sequence homology. The mitogenome of Johor CRBs was variable in the natural population due to its elevated mutation rate. Substitutions and indels in cox1, cox2, nad2 and atp6 genes were able to distinguish the Johor CRBs into two haplotypes. The mitogenome data generated in the present study may provide baseline information to study the infection and relationship between the two haplotypes of Johor CRB and OrNV in the field. This study is the first report on the mitogenomes of mixed haplotypes of CRB in the field.

Mitochondria in health, disease, and aging

Mitochondria are well known as organelles responsible for the maintenance of cellular bioenergetics through the production of ATP. Although oxidative phosphorylation may be their most important function, mitochondria are also integral for the synthesis of metabolic precursors, calcium regulation, the production of reactive oxygen species, immune signaling, and apoptosis. Considering the breadth of their responsibilities, mitochondria are fundamental for cellular metabolism and homeostasis. Appreciating this significance, translational medicine has begun to investigate how mitochondrial dysfunction can represent a harbinger of disease. In this review, we provide a detailed overview of mitochondrial metabolism, cellular bioenergetics, mitochondrial dynamics, autophagy, mitochondrial damage-associated molecular patterns, mitochondria-mediated cell death pathways, and how mitochondrial dysfunction at any of these levels is associated with disease pathogenesis. Mitochondria-dependent pathways may thereby represent an attractive therapeutic target for ameliorating human disease.

Two-Fold ND5 Genes, Three-Fold Control Regions, lncRNA, and the "Missing" ATP8 Found in the Mitogenomes of Polypedates megacephalus (Rhacophridae: Polypedates)

In prior research on the mitochondrial genome (mitogenome) of Polypedates megacephalus, the one copy of ND5 gene was translocated to the control region (CR) and the ATP8 gene was not found. Gene loss is uncommon among vertebrates. However, in this study, we resequenced the mitogenomes of P. megacephalus from different regions using a "primer bridging" approach with Sanger sequencing technologies, which revealed the "missing" ATP8 gene in P. megacephalus as well as three other previously published Polypedates. The mitogenome of this species was found to contain two copies of the ND5 genes and three copies of the control regions. Furthermore, multiple tandem repeats were identified in the control regions. Notably, we observed that there was no correlation between genetic divergence and geographic distance. However, using the mitogenome, gene expression analysis was performed via RT-qPCR of liver samples and it was thus determined that COIII, ND2, ND4, and ND6 were reduced to 0.64 ± 0.24, 0.55 ± 0.34, 0.44 ± 0.21 and 0.65 ± 0.17, respectively, under low-temperature stress (8 °C) as compared with controls (p < 0.05). Remarkably, the transcript of long non-coding RNA (lncRNA) between positions 8029 and 8612 decreased significantly with exposure to low-temperature stress (8 °C). Antisense ND6 gene expression showed a downward trend, but this was not significant. These results reveal that modulations of protein-coding mitochondrial genes and lncRNAs of P. megacephalus play a crucial role in the molecular response to cold stress.

The mitochondrial genome of the mountain wooly tapir, Tapirus pinchaque and a formal test of the effect of altitude on the adaptive evolution of mitochondrial protein coding genes in odd-toed ungulates

BACKGROUND

The harsh conditions of high-altitude environments are known to drive the evolution of physiological and morphological traits in endothermic animals. These conditions are expected to result in the adaptive evolution of protein coding genes encoded in mitochondrial genomes that are vital for the oxidative phosphorylation pathway. In this study, we formally tested for signatures of adaptive evolution on mitochondrial protein coding genes in Tapirus pinchaque and other odd-toed ungulates inhabiting high-elevation environments.

RESULTS

The AT-rich mitochondrial genome of T. pinchaque is 16,750 bp long. A phylomitogenomic analysis supports the monophyly of the genus Tapirus and families in the Perissodactyla. The ratio of non-synonymous to synonymous substitutions demonstrated that all mitochondrial genes undergo purifying selection in T. pinchaque and other odd ungulates living at high elevations. Over this negative background selection, Branch Models suggested that cox3 and nad6 might be undergoing stronger purifying selection than other mitochondrial protein coding genes. Furthermore, Site Models suggested that one and four sites in nad2 and nad5, respectively, could be experiencing positive selection. However, these results were supported by Likelihood Ratio Tests but not Bayesian Empirical Bayes posterior probabilities. Additional analyses (in DataMonkey) indicated a relaxation of selection strength in nad6, evidence of episodic diversifying selection in cob, and revealed episodic positive/diversifying selection signatures for two sites in nad1, and one site each in nad2 and nad4.

CONCLUSION

The mitochondrial genome of T. pinchaque is an important genomic resource for conservation of this species and this study contributes to the understanding of adaptive evolution of mitochondrial protein coding genes in odd-toed ungulates inhabiting high-altitude environments.

Mitochondrial DNA Release in Innate Immune Signaling

According to the endosymbiotic theory, most of the DNA of the original bacterial endosymbiont has been lost or transferred to the nucleus, leaving a much smaller (∼16 kb in mammals), circular molecule that is the present-day mitochondrial DNA (mtDNA). The ability of mtDNA to escape mitochondria and integrate into the nuclear genome was discovered in budding yeast, along with genes that regulate this process. Mitochondria have emerged as key regulators of innate immunity, and it is now recognized that mtDNA released into the cytoplasm, outside of the cell, or into circulation activates multiple innate immune signaling pathways. Here, we first review the mechanisms through which mtDNA is released into the cytoplasm, including several inducible mitochondrial pores and defective mitophagy or autophagy. Next, we cover how the different forms of released mtDNA activate specific innate immune nucleic acid sensors and inflammasomes. Finally, we discuss how intracellular and extracellular mtDNA release, including circulating cell-free mtDNA that promotes systemic inflammation, are implicated in human diseases, bacterial and viral infections, senescence and aging.

The complete mitochondrial genomes of the Leuciscus baicalensis and Rutilus rutilus: a detailed genomic comparison among closely related species of the Leuciscinae subfamily

Cyprinidae is the largest family in the order of freshwater fish Cypriniformes. Increased subfamily members of Cyprinidae have been suggested to be re-classified for decades. In this study, we sequenced the mitochondrial genomes (mitogenomes) of Leuciscus baicalensis and Rutilus rutilus collected from northwest China and compared with other closely related species to determine their associated family or subfamily. We used Illumina NovaSeq to sequence the entire mitochondrial genomes of Leuciscus baicalensis and Rutilus rutilus and characterized the mitogenomes by the gene structure, gene order, and the secondary structures of the 22 tRNA genes. We compared mitogenome features of Leuciscinae with other subfamilies in Cyprinidae. We used the analytic Bayesian Information and Maximum Likelihood methods to determine phylogenetic trees of 13 PCGs. The mitogenomes of Leuciscus baicalensis and Rutilus rutilus were 16,607 bp and 16,606 bp, respectively. Organization and location of these genes were consistent with already studied Leuciscinae fishes. Synonymous codon usage was conservative in Leuciscinae as compared with other subfamilies in Cyprinidae. Phylogenetic analysis indicated that Leuciscinae was a monophyletic group, and genus Leuciscus was a paraphyletic group. Our approach, for the first time, of studying comparative mitochondrial genomics and phylogenetics together provided a supportive platform to the analysis of population genetics and phylogeny for Leuciscinae. Our results indicated a promising potential of comparative mitochondrial genomics in the manifestation of phylogenetic relationships between fishes, leading us to a suggestion that mitogenomes should be routinely considered in clarifying phylogenetics of family and subfamily members of fish.

Comparative mitogenome analyses of twelve non-biting flies and provide insights into the phylogeny of Chironomidae (Diptera: Culicomorpha)

The family Chironomidae is represented by seven subfamilies in China, among which Chironominae and Orthocladiinae are the most diverse. To gain a better understanding of the architecture and evolution of the mitogenomes of Chironomidae, we sequenced mitogenomes of twelve species (including two published species) of the two subfamilies Chironominae and Orthocladiinae, and comparative mitogenomic analyses were performed. Thus, we identified highly conserved genome organization of twelve species with regard to genome content, nucleotide and amino acid composition, codon usage, and gene characteristics. The K_a/K_s values of most protein-coding genes were far smaller than 1, indicating that these genes were evolving under purifying selection. Phylogenetic relationships between the family Chironomidae were reconstructed using 23 species representing six subfamilies, based on protein-coding genes and rRNAs using Bayesian Inference and Maximum Likelihood. Our results suggested the following relationship within the Chironomidae: (Podonominae + Tanypodinae) + (Diamesinae + (Prodiamesinae + (Orthocladiinae + Chironominae))). This study contributes to the mitogenomic database of Chironomidae, which will be significant for studing the mitogenome evolution of Chironomidae.

Homo cerevisiae-Leveraging Yeast for Investigating Protein-Protein Interactions and Their Role in Human Disease

Understanding how genetic variation affects phenotypes represents a major challenge, particularly in the context of human disease. Although numerous disease-associated genes have been identified, the clinical significance of most human variants remains unknown. Despite unparalleled advances in genomics, functional assays often lack sufficient throughput, hindering efficient variant functionalization. There is a critical need for the development of more potent, high-throughput methods for characterizing human genetic variants. Here, we review how yeast helps tackle this challenge, both as a valuable model organism and as an experimental tool for investigating the molecular basis of phenotypic perturbation upon genetic variation. In systems biology, yeast has played a pivotal role as a highly scalable platform which has allowed us to gain extensive genetic and molecular knowledge, including the construction of comprehensive interactome maps at the proteome scale for various organisms. By leveraging interactome networks, one can view biology from a systems perspective, unravel the molecular mechanisms underlying genetic diseases, and identify therapeutic targets. The use of yeast to assess the molecular impacts of genetic variants, including those associated with viral interactions, cancer, and rare and complex diseases, has the potential to bridge the gap between genotype and phenotype, opening the door for precision medicine approaches and therapeutic development.

Description of the Three Complete Mitochondrial Genomes of Sitta (S. himalayensis, S. nagaensis, and S. yunnanensis) and Phylogenetic Relationship (Aves: Sittidae)

Nuthatches (genus Sitta; family Sittidae) are a passerine genus with a predominantly Nearctic and Eurasian distribution. To understand the phylogenetic position of Sitta and phylogenetic relations within this genus, we sequenced the complete mitochondrial genomes of three Sitta species (S. himalayensis, S. nagaensis, and S. yunnanensis), which were 16,822–16,830 bp in length and consisted of 37 genes and a control region. This study recovered the same gene arrangement found in the mitogenomes of Gallus gallus, which is considered the typical ancestral avian gene order. All tRNAs were predicted to form the typical cloverleaf secondary structures. Bayesian inference and maximum likelihood phylogenetic analyses of sequences of 18 species obtained a well-supported topology. The family Sittidae is the sister group of Troglodytidae, and the genus Sitta can be divided into three major clades. We demonstrated the phylogenetic relationships within the genus Sitta (S. carolinensis + ((S. villosa + S. yunnanensis) + (S. himalayensis + (S. europaea + S. nagaensis)))).

Gene Editing Technologies Targeting TFAM and Its Relation to Mitochondrial Diseases

Mitochondria are organelles present in the cytoplasm of eukaryotic cells; they play a key role in adenosine triphosphate (ATP) synthesis and oxidative phosphorylation. Mitochondria have their own DNA, mitochondrial DNA (mtDNA), keeping the function of the mitochondria. Mitochondrial transcription factor A (TFAM) is a member of the HMGB subfamily that binds to mtDNA promoters is and considered essential in mtDNA replication and transcription. More recently, TFAM has been shown to play a central role in the maintenance and regulation of mitochondrial copy number, inflammatory response, expression regulation, and mitochondrial genome activity. Gene editing tools such as the CRISPR-Cas 9 technique, TALENs, and other gene editing tools have been used to investigate the role of TFAM in mitochondrial mechanics and biogenesis as well as its correlation to mitochondrial disorders. Thus this chapter brings a summary of mitochondria function, dysfunction, the importance of TFAM in the maintenance of mitochondria, and state of the art of gene editing tools involving TFAM and mtDNA.

The N-terminal domain of human mitochondrial helicase Twinkle has DNA-binding activity crucial for supporting processive DNA synthesis by polymerase γ

Twinkle is the ring-shaped replicative helicase within the human mitochondria with high homology to bacteriophage T7 gp4 helicase-primase. Unlike many orthologs of Twinkle, the N-terminal domain (NTD) of human Twinkle has lost its primase activity through evolutionarily acquired mutations. The NTD has no demonstrated activity thus far; its role has remained unclear. Here, we biochemically characterize the isolated NTD and C-terminal domain (CTD) with linker to decipher their contributions to full-length Twinkle activities. This novel CTD construct hydrolyzes ATP, has weak DNA unwinding activity, and assists DNA polymerase γ (Polγ)-catalyzed strand-displacement synthesis on short replication forks. However, CTD fails to promote multikilobase length product formation by Polγ in rolling-circle DNA synthesis. Thus, CTD retains all the motor functions but struggles to implement them for processive translocation. We show that NTD has DNA-binding activity, and its presence stabilizes Twinkle oligomerization. CTD oligomerizes on its own, but the loss of NTD results in heterogeneously sized oligomeric species. The CTD also exhibits weaker and salt-sensitive DNA binding compared with full-length Twinkle. Based on these results, we propose that NTD directly contributes to DNA binding and holds the DNA in place behind the central channel of the CTD like a "doorstop," preventing helicase slippages and sustaining processive unwinding. Consistent with this model, mitochondrial single-stranded DNA-binding protein (mtSSB) compensate for the NTD loss and partially restore kilobase length DNA synthesis by CTD and Polγ. The implications of our studies are foundational for understanding the mechanisms of disease-causing Twinkle mutants that lie in the NTD.

Complete Mitogenome of Oreolalax Omeimontis Reveals Phylogenetic Status and Novel Gene Arrangement of Archaeobatrachia

Species of the genus Oreolalax displayed crucial morphological characteristics of vertebrates transitioning from aquatic to terrestrial habitats; thus, they can be regarded as a representative vertebrate genus for this landing phenomenon. But the present phylogenetic status of Oreolalax omeimontis has been controversial with morphological and molecular approaches, and specific gene rearrangements were discovered in all six published Oreolalax mitogenomes, which are rarely observed in Archaeobatrachia. Therefore, this study determined the complete mitogenome of O. omeimontis with the aim of identifying its precise phylogenetic position and novel gene arrangement in Archaeobatrachia. Phylogenetic analysis with Bayesian inference and maximum likelihood indicates O. omeimontis is a sister group to O. lichuanensis, which is consistent with previous phylogenetic analysis based on morphological characteristics, but contrasts with other studies using multiple gene fragments. Moreover, although the duplication of trnM occurred in all seven Oreolalax species, the translocation of trnQ and trnM occurred differently in O. omeimontis to the other six, and this unique rearrangement would happen after the speciation of O. omeimontis. In general, this study sheds new light on the phylogenetic relationships and gene rearrangements of Archaeobatrachia.

Complete Mitogenomes of Polypedates Tree Frogs Unveil Gene Rearrangement and Concerted Evolution within Rhacophoridae

New developments in sequencing technology and nucleotide analysis have allowed us to make great advances in reconstructing anuran phylogeny. As a clade of representative amphibians that have radiated from aquatic to arboreal habitats, our understanding of the systematic status and molecular biology of rhacophorid tree frogs is still limited. We determined two new mitogenomes for the genus Polypedates (Rhacophoridae): P. impresus and P. mutus. We conducted comparative and phylogenetic analyses using our data and seven other rhacophorid mitogenomes. The mitogenomes of the genera Polypedates, Buergeria, and Zhangixalus were almost identical, except that the ATP8 gene in Polypedates had become a non-coding region; Buergeria maintained the legacy "LTPF" tRNA gene cluster compared to the novel "TLPF" order in the other two genera; and B. buergeri and Z. dennysi had no control region (CR) duplication. The resulting phylogenetic relationship supporting the above gene rearrangement pathway suggested parallel evolution of ATP8 gene loss of function (LoF) in Polypedates and CR duplication with concerted evolution of paralogous CRs in rhacophorids. Finally, conflicting topologies in the phylograms of 185 species reflected the advantages of phylogenetic analyses using multiple loci.

The Nursehound Scyliorhinus stellaris Mitochondrial Genome—Phylogeny, Relationships among Scyliorhinidae and Variability in Waters of the Balearic Islands

The complete mitochondrial DNA sequence of the Nursehound Scyliorhinus stellaris has been determined for the first time and compared with congeneric species. The mitogenome sequence was 16,684 bp in length. The mitogenome is composed of 13 PCGs, 2 rRNAs, 22 transfer RNA genes and non-coding regions. The gene order of the newly sequenced mitogenome is analogous to the organization described in other vertebrate genomes. The typical conservative blocks in the control region were indicated. The phylogenetic analysis revealed a monophyletic origin of the Scyliorhininae subfamily, and within it, two subclades were identified. A significant divergence of Scyliorhinus spp. together with Poroderna patherinum in relation to the group of Cephaloscyllium spp. was observed, except for Scyliorhinus torazame, more related to this last cited clade. A hypothesis of a divergent evolution consequent to a selective pressure in different geographic areas, which lead to a global latitudinal diversity gradient, has been suggested to explain this phylogenetic reconstruction. However, convergent evolution on mitochondrial genes could also involve different species in some areas of the world.

Molecular mechanism of two functional protein structure changes under 2,3-butanedione-induced oxidative stress and apoptosis effects in the hepatocytes

Food security has become closely watched with the occurrence of a series of food safety incidents in recent years. The widespread adoption of 2,3-butanedione (BUT), as a food additive, is an unpreventable significant risk factor to food security. Based on this, mouse hepatocyte AML-12 cells and two functional proteins (bovine serum albumin and lysozyme) were utilized as targeted receptors to study the adverse effects of BUT at the cellular and molecular levels. Results suggested that BUT could disrupt the redox balance of AML-12 cells, reducing glutathione (GSH) activity fell to 87.18 %, which cannot offset the production of reactive oxygen species (ROS). Meanwhile, the increasement of lipid peroxidation and malondialdehyde (MDA) levels were observed. The mitochondrial membrane function was also abnormal due to the excessive accumulation of ROS and eventually leads to cell apoptosis and death. At the molecular level, the exposure of BUT could alter the skeleton and secondary structure of bovine serum albumin (BSA) and lysozyme (LYZ), and it could statically quench the intrinsic fluorescence of proteins. The combined experiments confirmed proved the potentially toxic effects of BUT accumulation on the detoxification organ, providing theoretical support for the liver diseases caused by BUT exposure, and a reference for the risk assessment of occupational exposure of BUT.

Heterozygous p.Y955C mutation in DNA polymerase γ leads to alterations in bioenergetics, complex I subunit expression, and mtDNA replication

In human cells, ATP is generated using oxidative phosphorylation machinery, which is inoperable without proteins encoded by mitochondrial DNA (mtDNA). The DNA polymerase gamma (Polγ) repairs and replicates the multicopy mtDNA genome in concert with additional factors. The Polγ catalytic subunit is encoded by the POLG gene, and mutations in this gene cause mtDNA genome instability and disease. Barriers to studying the molecular effects of disease mutations include scarcity of patient samples and a lack of available mutant models; therefore, we developed a human SJCRH30 myoblast cell line model with the most common autosomal dominant POLG mutation, c.2864A>G/p.Y955C, as individuals with this mutation can present with progressive skeletal muscle weakness. Using on-target sequencing, we detected a 50% conversion frequency of the mutation, confirming heterozygous Y955C substitution. We found mutated cells grew slowly in a glucose-containing medium and had reduced mitochondrial bioenergetics compared with the parental cell line. Furthermore, growing Y955C cells in a galactose-containing medium to obligate mitochondrial function enhanced these bioenergetic deficits. Also, we show complex I NDUFB8 and ND3 protein levels were decreased in the mutant cell line, and the maintenance of mtDNA was severely impaired (i.e., lower copy number, fewer nucleoids, and an accumulation of Y955C-specific replication intermediates). Finally, we show the mutant cells have increased sensitivity to the mitochondrial toxicant 2′-3′-dideoxycytidine. We expect this POLG Y955C cell line to be a robust system to identify new mitochondrial toxicants and therapeutics to treat mitochondrial dysfunction.

Unraveling mitochondrial piRNAs in mouse embryonic gonadal cells

Although mitochondria are widely studied organelles, the recent interest in the role of mitochondrial small noncoding RNAs (sncRNAs), miRNAs, and more recently, piRNAs, is providing new functional perspectives in germ cell development and differentiation. piRNAs (PIWI-interacting RNAs) are single-stranded sncRNAs of mostly about 20-35 nucleotides, generated from the processing of pre-piRNAs. We leverage next-generation sequencing data obtained from mouse primordial germ cells and somatic cells purified from early-differentiating embryonic ovaries and testis from 11.5 to 13.5 days postcoitum. Using bioinformatic tools, we elucidate (i) the origins of piRNAs as transcribed from mitochondrial DNA fragments inserted in the nucleus or from the mitochondrial genome; (ii) their levels of expression; and (iii) their potential roles, as well as their association with genomic regions encoding other sncRNAs (such as tRNAs and rRNAs) and the mitochondrial regulatory region (D-loop). Finally, our results suggest how nucleo-mitochondrial communication, both anterograde and retrograde signaling, may be mediated by mitochondria-associated piRNAs.