Degradation of paternal mitochondria after fertilization: implications for heteroplasmy, assisted reproductive technologies and mtDNA inheritance

Bottom-up approach to deciphering the targets of the ubiquitin-proteasome system in porcine sperm capacitation

Capacitation is an essential post-testicular maturation event endowing spermatozoa with fertilizing capacity within the female reproductive tract, significant for fertility, reproductive health, and contraception. By using a human-relevant large animal model, the domestic boar, this study focuses on furthering our understanding of the involvement of the ubiquitin-proteasome system (UPS) in sperm capacitation. The UPS is a universal, evolutionarily conserved, cellular proteome-wide degradation and recycling machinery, that has been shown to play a significant role in reproduction during the past two decades. Herein, we have used a bottom-up proteomic approach to (i) monitor the capacitation-related changes in the sperm protein levels, and (ii) identify the targets of UPS regulation during sperm capacitation. Spermatozoa were capacitated under proteasomal activity-permissive and inhibiting conditions and extracted sperm proteins were subjected to high-resolution mass spectrometry. We report that 401 individual proteins differed at least two-fold in abundance (P < 0.05) after in vitro capacitation (IVC) and 13 proteins were found significantly different (P < 0.05) between capacitated spermatozoa with proteasomal inhibition compared to the vehicle control. These proteins were associated with biological processes including sperm capacitation, sperm motility, metabolism, binding to zona pellucida, and proteasome-mediated catabolism. Changes in RAB2A, CFAP161, and TTR during IVC were phenotyped by immunocytochemistry, image-based flow cytometry, and Western blotting. We conclude that (i) the sperm proteome is subjected to extensive remodeling during sperm capacitation, and (ii) the UPS has a narrow range of distinct protein substrates during capacitation. This knowledge highlights the importance of the UPS in sperm capacitation and offers opportunities to identify novel pharmacological targets to modulate sperm fertilizing ability for the benefit of human reproductive health, assisted reproductive therapy, and contraception, as well as reproductive management in food animal agriculture.

Mitochondrial DNA: Inherent Complexities Relevant to Genetic Analyses

Mitochondrial DNA (mtDNA) exhibits distinct characteristics distinguishing it from the nuclear genome, necessitating specific analytical methods in genetic studies. This comprehensive review explores the complex role of mtDNA in a variety of genetic studies, including genome-wide, epigenome-wide, and phenome-wide association studies, with a focus on its implications for human traits and diseases. Here, we discuss the structure and gene-encoding properties of mtDNA, along with the influence of environmental factors and epigenetic modifications on its function and variability. Particularly significant are the challenges posed by mtDNA's high mutation rate, heteroplasmy, and copy number variations, and their impact on disease susceptibility and population genetic analyses. The review also highlights recent advances in methodological approaches that enhance our understanding of mtDNA associations, advocating for refined genetic research techniques that accommodate its complexities. By providing a comprehensive overview of the intricacies of mtDNA, this paper underscores the need for an integrated approach to genetic studies that considers the unique properties of mitochondrial genetics. Our findings aim to inform future research and encourage the development of innovative methodologies to better interpret the broad implications of mtDNA in human health and disease.

Identification of candidate mitochondrial inheritance determinants using the mammalian cell-free system

The degradation of sperm-borne mitochondria after fertilization is a conserved event. This process known as post-fertilization sperm mitophagy, ensures exclusively maternal inheritance of the mitochondria-harbored mitochondrial DNA genome. This mitochondrial degradation is in part carried out by the ubiquitin-proteasome system. In mammals, ubiquitin-binding pro-autophagic receptors such as SQSTM1 and GABARAP have also been shown to contribute to sperm mitophagy. These systems work in concert to ensure the timely degradation of the sperm-borne mitochondria after fertilization. We hypothesize that other receptors, cofactors, and substrates are involved in post-fertilization mitophagy. Mass spectrometry was used in conjunction with a porcine cell-free system to identify other autophagic cofactors involved in post-fertilization sperm mitophagy. This porcine cell-free system is able to recapitulate early fertilization proteomic interactions. Altogether, 185 proteins were identified as statistically different between control and cell-free-treated spermatozoa. Six of these proteins were further investigated, including MVP, PSMG2, PSMA3, FUNDC2, SAMM50, and BAG5. These proteins were phenotyped using porcine in vitro fertilization, cell imaging, proteomics, and the porcine cell-free system. The present data confirms the involvement of known mitophagy determinants in the regulation of mitochondrial inheritance and provides a master list of candidate mitophagy co-factors to validate in the future hypothesis-driven studies.

The Ubiquitin-Proteasome System Participates in Sperm Surface Subproteome Remodeling during Boar Sperm Capacitation

Sperm capacitation is a complex process endowing biological and biochemical changes to a spermatozoon for a successful encounter with an oocyte. The present study focused on the role of the ubiquitin-proteasome system (UPS) in the remodeling of the sperm surface subproteome. The sperm surface subproteome from non-capacitated and in vitro capacitated (IVC) porcine spermatozoa, with and without proteasomal inhibition, was selectively isolated. The purified sperm surface subproteome was analyzed using high-resolution, quantitative liquid chromatography-mass spectrometry (LC-MS) in four replicates. We identified 1680 HUGO annotated proteins, out of which we found 91 to be at least 1.5× less abundant (p < 0.05) and 141 to be at least 1.5× more abundant (p < 0.05) on the surface of IVC spermatozoa. These proteins were associated with sperm capacitation, hyperactivation, metabolism, acrosomal exocytosis, and fertilization. Abundances of 14 proteins were found to be significantly different (p < 0.05), exceeding a 1.5-fold abundance between the proteasomally inhibited (100 µM MG132) and vehicle control (0.2% ethanol) groups. The proteins NIF3L1, CSE1L, NDUFB7, PGLS, PPP4C, STK39, and TPRG1L were found to be more abundant; while BPHL, GSN, GSPT1, PFDN4, STYXL1, TIMM10, and UBXN4 were found to be less abundant in proteasomally inhibited IVC spermatozoa. Despite the UPS having a narrow range of targets, it modulated sperm metabolism and binding by regulating susceptible surface proteins. Changes in CSE1L, PFDN4, and STK39 during in vitro capacitation were confirmed using immunocytochemistry, image-based flow cytometry, and Western blotting. The results confirmed the active participation of the UPS in the extensive sperm surface proteome remodeling that occurs during boar sperm capacitation. This work will help us to identify new pharmacological mechanisms to positively or negatively modulate sperm fertilizing ability in food animals and humans.

OXIDATIVE STRESS AND REPRODUCTIVE FUNCTION: Oxidative stress and in vitro ageing of the post-ovulatory oocyte: an update on recent advances in the field

In brief

Post-ovulatory ageing of oocytes leads to poor oocyte and embryo quality as well as abnormalities in offspring. This review provides an update on the contributions of oxidative stress to this process and discusses the current literature surrounding the use of antioxidant media to delay post-ovulatory oocyte ageing.

Abstract

Following ovulation, the metaphase II stage oocyte has a limited functional lifespan before succumbing to a process known as post-ovulatory oocyte ageing. This progressive demise occurs both in vivo and in vitro and is accompanied by a deterioration in oocyte quality, leading to a well-defined sequelae of reduced fertilisation rates, poor embryo quality, post-implantation errors, and abnormalities in the offspring. Although the physiological consequences of post-ovulatory oocyte ageing have largely been characterised, less is known regarding the molecular mechanisms that drive this process. This review presents an update on the established relationships between the biochemical changes exhibited by the ageing oocyte and the myriad of symptoms associated with the ageing phenotype. In doing so, we consider the molecular events that are potentially involved in orchestrating post-ovulatory ageing with a particular focus on the role of oxidative stress. We highlight the mounting evidence that oxidative stress acts as an initiator for a cascade of events that create the aged oocyte phenotype. Specifically, oxidative stress has the capacity to disrupt mitochondrial function and directly damage multiple intracellular components of the oocyte such as lipids, proteins, and DNA. Finally, this review addresses emerging strategies for delaying post-ovulatory oocyte ageing with emphasis placed on the promise afforded by the use of selected antioxidants to guide the development of media tailored for the preservation of oocyte integrity during in vitro fertilisation procedures.

Comparative Ubiquitome Analysis Reveals Deubiquitinating Effects Induced by Wolbachia Infection in Drosophila melanogaster

The endosymbiotic Wolbachia bacteria frequently cause cytoplasmic incompatibility (CI) in their insect hosts, where Wolbachia-infected males cross with uninfected females, leading to no or fewer progenies, indicating a paternal modification by Wolbachia. Recent studies have identified a Wolbachia protein, CidB, containing a DUB (deubiquitylating enzyme) domain, which can be loaded into host sperm nuclei and involved in CI, though the DUB activity is not necessary for CI in Drosophila melanogaster. To investigate whether and how Wolbachia affect protein ubiquitination in testes of male hosts and are thus involved in male fertility, we compared the protein and ubiquitinated protein expressions in D. melanogaster testes with and without Wolbachia. A total of 643 differentially expressed proteins (DEPs) and 309 differentially expressed ubiquitinated proteins (DEUPs) were identified to have at least a 1.5-fold change with a p-value of <0.05. Many DEPs were enriched in metabolic pathway, ribosome, RNA transport, and post-translational protein modification pathways. Many DEUPs were involved in metabolism, ribosome, and proteasome pathways. Notably, 98.1% DEUPs were downregulated in the presence of Wolbachia. Four genes coding for DEUPs in ubiquitin proteasome pathways were knocked down, respectively, in Wolbachia-free fly testes. Among them, Rpn6 and Rpn7 knockdown caused male sterility, with no mature sperm in seminal vesicles. These results reveal deubiquitylating effects induced by Wolbachia infection, suggesting that Wolbachia can widely deubiquitinate proteins that have crucial functions in male fertility of their hosts, but are not involved in CI. Our data provide new insights into the regulatory mechanisms of endosymbiont/host interactions and male fertility.

Inheritance as Evolved and Evolving Physiological Processes

In this paper, we adopt a physiological perspective in order to produce an intelligible overview of biological transmission in all its diversity. This allows us to put forward the analysis of transmission mechanisms, with the aim of complementing the usual focus on transmitted factors. We underline the importance of the structural, dynamical, and functional features of transmission mechanisms throughout organisms' life cycles in order to answer to the question of what is passed on across generations, how and why. On this basis, we propose a vision of biological transmission as networks of heterogeneous physiological mechanisms, not restricted to transmission mechanisms stricto sensu. They prove to be themselves suited candidates for evolutionary explanations. They are processes both necessary for evolution to happen and resulting themselves from evolution. This leads us to call for a strategy of endogenization to account for transmission, and more specifically inheritance, as evolved and evolving physiological mechanisms.

Mitochondrial Modulations, Autophagy Pathways Shifts in Viral Infections: Consequences of COVID-19

Mitochondria are vital intracellular organelles that play an important role in regulating various intracellular events such as metabolism, bioenergetics, cell death (apoptosis), and innate immune signaling. Mitochondrial fission, fusion, and membrane potential play a central role in maintaining mitochondrial dynamics and the overall shape of mitochondria. Viruses change the dynamics of the mitochondria by altering the mitochondrial processes/functions, such as autophagy, mitophagy, and enzymes involved in metabolism. In addition, viruses decrease the supply of energy to the mitochondria in the form of ATP, causing viruses to create cellular stress by generating ROS in mitochondria to instigate viral proliferation, a process which causes both intra- and extra-mitochondrial damage. SARS-COV2 propagates through altering or changing various pathways, such as autophagy, UPR stress, MPTP and NLRP3 inflammasome. Thus, these pathways act as potential targets for viruses to facilitate their proliferation. Autophagy plays an essential role in SARS-COV2-mediated COVID-19 and modulates autophagy by using various drugs that act on potential targets of the virus to inhibit and treat viral infection. Modulated autophagy inhibits coronavirus replication; thus, it becomes a promising target for anti-coronaviral therapy. This review gives immense knowledge about the infections, mitochondrial modulations, and therapeutic targets of viruses.

The perspective of the incompatible of nucleus and mitochondria in interspecies somatic cell nuclear transfer for endangered species

Taking into account the latest Red List of the International Union for Conservation of Nature in which 25% of all mammals are threatened with extinction, somatic cell nuclear transfer (SCNT) could be a beneficial tool and holds a lot of potential for aiding the conservation of endangered, exotic or even extinct animal species if somatic cells of such animals are available. In the case of shortage and sparse amount of wild animal oocytes, interspecies somatic cell nuclear transfer (iSCNT), where the recipient ooplasm and donor nucleus are derived from different species, is the alternative SCNT technique. The successful application of iSCNT, resulting in the production of live offspring, was confirmed in several combination of closely related species. When nucleus donor cells and recipient oocytes have been used in many other combinations, very often with a very distant taxonomical relation iSCNT resulted only in the very early stages of cloned embryo development. Problems encountered during iSCNT related to mitochondrial DNA (mtDNA)/genomic DNA incompatibility, mtDNA heteroplasmy, embryonic genome activation of the donor nucleus by the recipient oocyte and availability of suitable foster mothers for iSCNT embryos. Implementing assisted reproductive technologies, including iSCNT, to conservation programmes also raises concerns that the production of genetically identical populations might cause problems with inbreeding. The article aims at presenting achievements, limitations and perspectives of iSCNT in maintaining animal biodiversity.

In Vitro Development and Mitochondrial Gene Expression in Brown Brocket Deer (Mazama gouazoubira) Embryos Obtained by Interspecific Somatic Cell Nuclear Transfer

The genetic diversity of Neotropical deer is increasingly jeopardized, owing to declining population size. Thus, the formation of cryobanking of somatic cells is important for the preservation of these species using cloning. The transformation of these cells into viable embryos has been hampered by a lack of endangered species oocytes. Accordingly, the aim of this study was to produce brown brocket deer embryos by interspecific somatic cell nuclear transfer (iSCNT), using goat or cattle oocytes as cytoplasts, and to elucidate embryo mitochondrial activity by measuring the expression levels of ATP6, COX3, and ND5. Cattle embryos produced by in vitro fertilization (IVF) were used as a control. There were no differences in the development of embryos produced by traditional SCNT and iSCNT when using either the goat cytoplasts (38.4% vs. 25.0% cleaved and 40.0% vs. 50.0% morula rates, respectively) or cattle cytoplast (72.8% vs. 65.5% cleaved and 11.3% vs. 5.9% blastocyst rates, respectively). Concerning the gene expression, no significant difference was observed when goat oocytes were used as cytoplasts. However, when using cattle oocytes and 16S as a reference gene, the iSCNT upregulated COX3, when compared with SCNT group. In contrast, when GAPDH was used as a reference gene, all the evaluated genes were upregulated in the iSCNT group, when compared with the IVF group. When compared with the SCNT group, only the expression of ATP6 was statistically different. In conclusion, it was demonstrated that interspecific nuclear transfer is a potentially useful tool for conservation programs of endangered similar deer species.

Causes and consequences of sperm mitochondrial dysfunction

Mitochondria have multiple functions, including synthesis of adenine triphosphate, production of reactive oxygen species, calcium signalling, thermogenesis and apoptosis. Mitochondria have a significant contribution in regulating the various physiological aspects of reproductive function, from spermatogenesis up to fertilisation. Mitochondrial functionality and intact mitochondrial membrane potential are a pre-requisite for sperm motility, hyperactivation, capacitation, acrosin activity, acrosome reaction and DNA integrity. Optimal mitochondrial activity is therefore crucial for human sperm function and semen quality. However, the precise role of mitochondria in spermatozoa remains to be fully explored. Defects in sperm mitochondrial function severely impair the maintenance of energy production required for sperm motility and may be an underlying cause of asthenozoospermia. Sperm mtDNA is susceptible to oxidative damage and mutations that could compromise sperm function leading to infertility. Males with abnormal semen parameters have increased mtDNA copy number and reduced mtDNA integrity. This review discusses the role of mitochondria in sperm function, along with the causes and impact of its dysfunction on male fertility. Greater understanding of sperm mitochondrial function and its correlation with sperm quality could provide further insights into their contribution in the assessment of the infertile male.

Porcine model for the study of sperm capacitation, fertilization and male fertility

Mammalian fertilization remains a poorly understood event with the vast majority of studies done in the mouse model. The purpose of this review is to revise the current knowledge about semen deposition, sperm transport, sperm capacitation, gamete interactions and early embryonic development with a focus on the porcine model as a relevant, alternative model organism to humans. The review provides a thorough overview of post-ejaculation events inside the sow's reproductive tract including comparisons with humans and implications for human fertilization and assisted reproductive therapy (ART). Porcine methodology for sperm handling, preservation, in vitro capacitation, oocyte in vitro maturation, in vitro fertilization and intra-cytoplasmic sperm injection that are routinely used in pig research laboratories can be successfully translated into ART to treat human infertility. Last, but not least, new knowledge about mitochondrial inheritance in the pig can provide an insight into human mitochondrial diseases and new knowledge on polyspermy defense mechanisms could contribute to the development of new male contraceptives.

Application of extracellular flux analysis for determining mitochondrial function in mammalian oocytes and early embryos

Mitochondria provide the major source of ATP for mammalian oocyte maturation and early embryo development. Oxygen Consumption Rate (OCR) is an established measure of mitochondrial function. OCR by mammalian oocytes and embryos has generally been restricted to overall uptake and detailed understanding of the components of OCR dedicated to specific molecular events remains lacking. Here, extracellular flux analysis (EFA) was applied to small groups of bovine, equine, mouse and human oocytes and bovine early embryos to measure OCR and its components. Using EFA, we report the changes in mitochondrial activity during the processes of oocyte maturation, fertilisation, and pre-implantation development to blastocyst stage in response to physiological demands in mammalian embryos. Crucially, we describe the real time partitioning of overall OCR to spare capacity, proton leak, non-mitochondrial and coupled respiration – showing that while activity changes over the course of development in response to physiological demand, the overall efficiency is unchanged. EFA is shown to be able to measure mitochondrial function in small groups of mammalian oocytes and embryos in a manner which is robust, rapid and easy to use. EFA is non-invasive and allows real-time determination of the impact of compounds on OCR, facilitating an assessment of the components of mitochondrial activity. This provides proof-of-concept for EFA as an accessible system with which to study mammalian oocyte and embryo metabolism.

Associations of sperm mitochondrial DNA copy number and deletion rate with fertilization and embryo development in a clinical setting

STUDY QUESTION

Are sperm mitochondrial DNA copy number (mtDNAcn) and deletion rate (mtDNAdel) associated with odds of fertilization and high embryo quality at Days 3 and 5?

SUMMARY ANSWER

Higher sperm mtDNAcn and mtDNAdel were associated with lower odds of high quality Day 3 embryos and transfer quality Day 5 embryos, both of which were primarily driven by lowered odds of fertilization.

WHAT IS KNOWN ALREADY

Sperm mtDNAcn and mtDNAdel have been previously associated with poor semen parameters and clinical male infertility. One prior study has shown that mtDNAdel is associated with lower fertilization rates. However, it is unknown whether these characteristics are linked with ART outcomes.

STUDY DESIGN, SIZE, DURATION

This prospective observational study included 119 sperm samples collected from men undergoing ART in Western Massachusetts. ART outcomes were observed through to Day 5 post-insemination.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

As part of the Sperm Environmental Epigenetics and Development Study (SEEDS), 119 sperm samples were collected from men undergoing ART in Western Massachusetts. Sperm mtDNAcn and mtDNAdel were measured via triplex probe-based qPCR. Fertilization, Day 3 embryo quality and Day 5 embryo quality measures were fitted with mtDNAcn and mtDNAdel using generalized estimating equations.

MAIN RESULTS AND THE ROLE OF CHANCE

After adjusting for male age and measurement batches, higher sperm mtDNAcn and mtDNAdel were associated with lower odds of fertilization (P = 0.01 and P < 0.01), high quality Day 3 embryos (P = 0.02 for both) and transfer quality Day 5 embryos (P = 0.01 and P = 0.09). However, the associations of mtDNAcn and mtDNAdel with Day 3 high quality status and Day 5 transfer quality status were attenuated in models restricted to fertilized oocytes. Sperm mtDNAcn and mtDNAdel remained statistically significant in models adjusted for both male age and semen parameters, although models including both mtDNA markers generally favoured mtDNAdel.

LIMITATIONS, REASONS FOR CAUTION

Our sample only included oocytes and embryos from 119 couples and thus large diverse cohorts are necessary to confirm the association of sperm mtDNA biomarkers with embryo development.

WIDER IMPLICATIONS OF THE FINDINGS

To our knowledge, our study is the first to assess the associations of sperm mtDNAcn and mtDNAdel with fertilization and embryo quality. The biological mechanism(s) underlying these associations are unknown. Multivariable models suggest that sperm mtDNAcn and mtDNAdel provide discrimination independent of age and semen parameters; therefore, future investigation of the utility of sperm mtDNA as a biomarker for ART outcomes is warranted.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by Grant (K22-ES023085) from the National Institute of Environmental Health Sciences. The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Mitochondrial DNA: Distribution, Mutations, and Elimination

Mitochondrion harbors its own DNA (mtDNA), which encodes many critical proteins for the assembly and activity of mitochondrial respiratory complexes. mtDNA is packed by many proteins to form a nucleoid that uniformly distributes within the mitochondrial matrix, which is essential for mitochondrial functions. Defects or mutations of mtDNA result in a range of diseases. Damaged mtDNA could be eliminated by mitophagy, and all paternal mtDNA are degraded by endonuclease G or mitophagy during fertilization. In this review, we describe the role and mechanism of mtDNA distribution and elimination. In particular, we focus on the regulation of paternal mtDNA elimination in the process of fertilization.

RNA-seq coupled to proteomic analysis reveals high sperm proteome variation between two closely related marine mussel species

Speciation mechanisms in marine organisms have attracted great interest because of the apparent lack of substantial barriers to genetic exchange in marine ecosystems. Marine mussels of the Mytilus edulis species complex provide a good model to study mechanisms underlying species formation. They hybridise extensively at many localities and both pre- and postzygotic isolating mechanisms may be operating. Mussels have external fertilisation and sperm cells should show specific adaptations for survival and successful fertilisation. Sperm thus represent key targets in investigations of the molecular mechanisms underlying reproductive isolation. We undertook a deep transcriptome sequencing (RNA-seq) of mature male gonads and a 2DE/MS-based proteome analysis of sperm from Mytilus edulis and M. galloprovincialis raised in a common environment. We provide evidence of extensive expression differences between the two mussel species, and general agreement between the transcriptomic and proteomic results in the direction of expression differences between species. Differential expression is marked for mitochondrial genes and for those involved in spermatogenesis, sperm motility, sperm-egg interactions, the acrosome reaction, sperm capacitation, ATP reserves and ROS production. Proteins and their corresponding genes might thus be good targets in further genomic analysis of reproductive barriers between these closely related species. SIGNIFICANCE: Model systems for the study of fertilization include marine invertebrates with external fertilisation, such as abalones, sea urchins and mussels, because of the ease with which large quantities of gametes released into seawater can be collected after induced spawning. Unlike abalones and sea urchins, hybridisation has been reported between mussels of different Mytilus spp., which thus makes them very appealing for the study of reproductive isolation at both pre- and postzygotic levels. There is a lack of empirical proteomic studies on sperm samples comparing different Mytilus species, which could help to advance this study. A comparative analysis of sperm proteomes across different taxa may provide important insights into the fundamental molecular processes and mechanisms involved in reproductive isolation. It might also contribute to a better understanding of sperm function and of the adaptive evolution of sperm proteins in different taxa. There is now growing evidence from genomics studies that multiple protein complexes and many individual proteins might have important functions in sperm biology and the fertilisation process. From an applied perspective, the identification of sperm-specific proteins could also contribute to the improved understanding of fertility problems and as targets for fertility control.

Influence of Maternal Aging on Mitochondrial Heterogeneity, Inheritance, and Function in Oocytes and Preimplantation Embryos

Contrasting the equal contribution of nuclear genetic material from maternal and paternal sources to offspring, passage of mitochondria, and thus mitochondrial DNA (mtDNA), is uniparental through the egg. Since mitochondria in eggs are ancestral to all somatic mitochondria of the next generation and to all cells of future generations, oocytes must prepare for the high energetic demands of maturation, fertilization and embryogenesis while simultaneously ensuring that their mitochondrial genomes are inherited in an undamaged state. Although significant effort has been made to understand how the mtDNA bottleneck and purifying selection act coordinately to prevent silent and unchecked spreading of invisible mtDNA mutations through the female germ line across successive generations, it is unknown if and how somatic cells of the immediate next generation are spared from inheritance of detrimental mtDNA molecules. Here, we review unique aspects of mitochondrial activity and segregation in eggs and early embryos, and how these events play into embryonic developmental competency in the face of advancing maternal age.

Clonorchis sinensis and Clonorchiasis: The Relevance of Exploring Genetic Variation

Parasitic trematodes (flukes) cause substantial mortality and morbidity in humans. The Chinese liver fluke, Clonorchis sinensis, is one of the most destructive parasitic worms in humans in China, Vietnam, Korea and the Russian Far East. Although C. sinensis infection can be controlled relatively well using anthelmintics, the worm is carcinogenic, inducing cholangiocarcinoma and causing major suffering in ~15 million people in Asia. This chapter provides an account of C. sinensis and clonorchiasis research-covering aspects of biology, epidemiology, pathogenesis and immunity, diagnosis, treatment and control, genetics and genomics. It also describes progress in the area of molecular biology (genetics, genomics, transcriptomics and proteomics) and highlights challenges associated with comparative genomics and population genetics. It then reviews recent advances in the sequencing and characterisation of the mitochondrial and nuclear genomes for a Korean isolate of C. sinensis and summarises salient comparative genomic work and the implications thereof. The chapter concludes by considering how advances in genomic and informatics will enable research on the genetics of C. sinensis and related parasites, as well as the discovery of new fluke-specific intervention targets.

Lack of effects of ooplasm transfer on early development of interspecies somatic cell nuclear transfer bison embryos

Background

Successful development of iSCNT (interspecies somatic cell nuclear transfer) embryos depends on complex interactions between ooplasmic and nuclear components, which can be compromised by genetic divergence. Transfer of ooplasm matching the genetic background of the somatic cell in iSCNT embryos is a valuable tool to study the degree of incompatibilities between nuclear and ooplasmic components. This study investigated the effects of ooplasm transfer (OT) on cattle (Bos taurus) and plains bison (Bison bison bison) embryos produced by iSCNT and supplemented with or without ooplasm from cattle or plains bison oocytes.

Results

Embryos in all groups were analysed for developmental competence that included cleavage rates, ATP content, and expression of nuclear- and mitochondrial- encoded genes at 8–16 cell stage. Interestingly, no significant differences were observed in embryo development, ATP content, and expression of nuclear respiratory factor 2 (NRF2), mitochondrial transcription factor A (TFAM) and mitochondrial subunit 2 of cytochrome c oxidase (mt-COX2) among groups. Thus, although OT did not result in any detrimental effects on the reconstructed embryos due to invasive manipulation, significant benefits of OT were not observed up to the 8–16 cell stage.

Conclusions

This study showed that a viable technique for OT + SCNT is possible, however, further understanding of the effects of OT on blastocyst development is necessary.

Autophagy and ubiquitin-proteasome system contribute to sperm mitophagy after mammalian fertilization

Maternal inheritance of mitochondria and mtDNA is a universal principle in human and animal development, guided by selective ubiquitin-dependent degradation of the sperm-borne mitochondria after fertilization. However, it is not clear how the 26S proteasome, the ubiquitin-dependent protease that is only capable of degrading one protein molecule at a time, can dispose of a whole sperm mitochondrial sheath. We hypothesized that the canonical ubiquitin-like autophagy receptors [sequestosome 1 (SQSTM1), microtubule-associated protein 1 light chain 3 (LC3), gamma-aminobutyric acid receptor-associated protein (GABARAP)] and the nontraditional mitophagy pathways involving ubiquitin-proteasome system and the ubiquitin-binding protein dislocase, valosin-containing protein (VCP), may act in concert during mammalian sperm mitophagy. We found that the SQSTM1, but not GABARAP or LC3, associated with sperm mitochondria after fertilization in pig and rhesus monkey zygotes. Three sperm mitochondrial proteins copurified with the recombinant, ubiquitin-associated domain of SQSTM1. The accumulation of GABARAP-containing protein aggregates was observed in the vicinity of sperm mitochondrial sheaths in the zygotes and increased in the embryos treated with proteasomal inhibitor MG132, in which intact sperm mitochondrial sheaths were observed. Pharmacological inhibition of VCP significantly delayed the process of sperm mitophagy and completely prevented it when combined with microinjection of autophagy-targeting antibodies specific to SQSTM1 and/or GABARAP. Sperm mitophagy in higher mammals thus relies on a combined action of SQSTM1-dependent autophagy and VCP-mediated dislocation and presentation of ubiquitinated sperm mitochondrial proteins to the 26S proteasome, explaining how the whole sperm mitochondria are degraded inside the fertilized mammalian oocytes by a protein recycling system involved in degradation of single protein molecules.

Structural and functional biology of arachidonic acid 15-lipoxygenase-1 (ALOX15)

Lipoxygenases (LOX) form a family of lipid peroxidizing enzymes, which have been implicated in a number of physiological processes and in the pathogenesis of inflammatory, hyperproliferative and neurodegenerative diseases. They occur in two of the three domains of terrestrial life (bacteria, eucarya) and the human genome involves six functional LOX genes, which encode for six different LOX isoforms. One of these isoforms is ALOX15, which has first been described in rabbits in 1974 as enzyme capable of oxidizing membrane phospholipids during the maturational breakdown of mitochondria in immature red blood cells. During the following decades ALOX15 has extensively been characterized and its biological functions have been studied in a number of cellular in vitro systems as well as in various whole animal disease models. This review is aimed at summarizing the current knowledge on the protein-chemical, molecular biological and enzymatic properties of ALOX15 in various species (human, mouse, rabbit, rat) as well as its implication in cellular physiology and in the pathogenesis of various diseases.

Changes in Sperm Motility and Capacitation Induce Chromosomal Aberration of the Bovine Embryo following Intracytoplasmic Sperm Injection

Intracytoplasmic sperm injection (ICSI) has become the method of choice to treat human male infertility. One of the outstanding problems associated with this technique is our current lack of knowledge concerning the effect of sperm capacitation and motility upon the subsequent development of oocytes following ICSI. In the present study, we first examined the capacitation state of sperm exhibiting normal motility, along with sperm that had been activated, and examined the effect of reactive oxygen species (ROS) produced by these sperm types upon embryogenesis following bovine in vitro fertilization (IVF) and ICSI. Data showed that activated sperm reduced the chromosomal integrity of IVF/ICSI embryos at the blastocyst stage, while capacitated sperm produced ROS in capacitation media. Secondly, we treated sperm with carbonyl cyanide m-chlorophenyl hydrazine (CCCP), a chemical known to uncouple cell respiration within the mitochondria, and investigated the effect of this treatment upon blastocyst formation and chromosomal integrity at the blastocyst stage. Activated sperm in which the mitochondria had been treated with CCCP reduced levels of chromosomal aberration at the blastocyst stage following ICSI, by reducing mitochondrial activity in activated sperm. In conclusion, these findings suggest that capacitated sperm exhibiting activated motility induced chromosomal aberration during development to the blastocyst stage following ICSI. The injection of sperm exhibiting normal motility, or activated sperm in which mitochondrial activity had been reduced, improved the quality of ICSI-derived embryos. Therefore, the selection of sperm exhibiting progressive motility may not always be better for early embryo development and fetal growth following human ICSI, and that the use of a bovine model may contribute to a deeper understanding of sperm selection for human ICSI embryo development.

Developmental competence of 8?16-cell stage bison embryos produced by interspecies somatic cell nuclear transfer

Altered communication between nuclear and cytoplasmic components has been linked to impaired development in interspecies somatic cell nuclear transfer (iSCNT) embryos as a result of genetic divergence between the two species. This study investigated the developmental potential and mitochondrial function of cattle (Bos taurus), plains bison (Bison bison bison) and wood bison (Bison bison athabascae) embryos produced by iSCNT using domestic cattle oocytes as cytoplasts. Embryos in all groups were analysed for development, accumulation of ATP, apoptosis and gene expression of nuclear- and mitochondrial-encoded genes at the 8-16-cell stage. The results of this study showed no significant differences in the proportion of developed embryos at the 2-, 4- and 8-16-cell stages between groups. However, significantly higher ATP levels were observed in cattle SCNT embryos compared with bison iSCNT embryos. Significantly more condensed and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL)-positive nuclei were found in plains bison iSCNT embryos. No significant differences in the expression levels of nuclear respiratory factor 2 (NRF2) or mitochondrial subunit 2 of cytochrome c oxidase (mt-COX2) were found in any of the groups. However, mitochondrial transcription factor A (TFAM) expression significantly differed between groups. The results of this study provide insights into the potential causes that might lead to embryonic arrest in bison iSCNT embryos, including mitochondrial dysfunction, increased apoptosis and abnormal gene expression.

The impact of mitochondrial function/dysfunction on IVF and new treatment possibilities for infertility

Mitochondria play vital roles in oocyte functions and they are critical indicators of oocyte quality which is important for fertilization and development into viable offspring. Quality-compromised oocytes are correlated with infertility, developmental disorders, reduced blastocyst cell number and embryo loss in which mitochondrial dysfunctions play a significant role. Increasingly, women affected by metabolic disorders such as diabetes or obesity and oocyte aging are seeking treatment in IVF clinics to overcome the effects of adverse metabolic conditions on mitochondrial functions and new treatments have become available to restore oocyte quality. The past decade has seen enormous advances in potential therapies to restore oocyte quality and includes dietary components and transfer of mitochondria from cells with mitochondrial integrity into mitochondria-impaired oocytes. New technologies have opened up new possibilities for therapeutic advances which will increase the success rates for IVF of oocytes from women with compromised oocyte quality.

Germline energetics, aging, and female infertility

The role of metabolism in ovarian aging is poorly described, despite the fact that ovaries fail earlier than most other organs. Growing interest in ovarian function is being driven by recent evidence that mammalian females routinely generate new oocytes during adult life through the activity of germline stem cells. In this perspective, we overview the female reproductive system as a powerful and clinically relevant model to understand links between aging and metabolism, and we discuss new concepts for how oocytes and their precursor cells might be altered metabolically to sustain or increase ovarian function and fertility in women.

Transgenic pig carrying green fluorescent proteasomes

Among its many functions, the ubiquitin-proteasome system regulates substrate-specific proteolysis during the cell cycle, apoptosis, and fertilization and in pathologies such as Alzheimer's disease, cancer, and liver cirrhosis. Proteasomes are present in human and boar spermatozoa, but little is known about the interactions of proteasomal subunits with other sperm proteins or structures. We have created a transgenic boar with green fluorescent protein (GFP) tagged 20S proteasomal core subunit α-type 1 (PSMA1-GFP), hypothesizing that the PSMA1-GFP fusion protein will be incorporated into functional sperm proteasomes. Using direct epifluorescence imaging and indirect immunofluorescence detection, we have confirmed the presence of PSMA1-GFP in the sperm acrosome. Western blotting revealed a protein band corresponding to the predicted mass of PSMA1-GFP fusion protein (57 kDa) in transgenic spermatozoa. Transgenic boar fertility was confirmed by in vitro fertilization, resulting in transgenic blastocysts, and by mating, resulting in healthy transgenic offspring. Immunoprecipitation and proteomic analysis revealed that PSMA1-GFP copurifies with several acrosomal membrane-associated proteins (e.g., lactadherin/milk fat globule E8 and spermadhesin alanine-tryptophan-asparagine). The interaction of MFGE8 with PSMA1-GFP was confirmed through cross-immunoprecipitation. The identified proteasome-interacting proteins may regulate sperm proteasomal activity during fertilization or may be the substrates of proteasomal proteolysis during fertilization. Proteomic analysis also confirmed the interaction/coimmunoprecipitation of PSMA1-GFP with 13/14 proteasomal core subunits. These results demonstrate that the PSMA1-GFP was incorporated in the assembled sperm proteasomes. This mammal carrying green fluorescent proteasomes will be useful for studies of fertilization and wherever the ubiquitin-proteasome system plays a role in cellular function or pathology.

Mitophagy: mechanisms, pathophysiological roles, and analysis

Abstract Mitochondria are essential organelles that regulate cellular energy homeostasis and cell death. The removal of damaged mitochondria through autophagy, a process called mitophagy, is thus critical for maintaining proper cellular functions. Indeed, mitophagy has been recently proposed to play critical roles in terminal differentiation of red blood cells, paternal mitochondrial degradation, neurodegenerative diseases, and ischemia or drug-induced tissue injury. Removal of damaged mitochondria through autophagy requires two steps: induction of general autophagy and priming of damaged mitochondria for selective autophagic recognition. Recent progress in mitophagy studies reveals that mitochondrial priming is mediated either by the Pink1-Parkin signaling pathway or the mitophagic receptors Nix and Bnip3. In this review, we summarize our current knowledge on the mechanisms of mitophagy. We also discuss the pathophysiological roles of mitophagy and current assays used to monitor mitophagy.

Mitoplasticity: adaptation biology of the mitochondrion to the cellular redox state in physiology and carcinogenesis

Adaptation and transformation biology of the mitochondrion to redox status is an emerging domain of physiology and pathophysiology. Mitochondrial adaptations occur in response to accidental changes in cellular energy demand or supply while mitochondrial transformations are a part of greater program of cell metamorphosis. The possible role of mitochondrial adaptations and transformations in pathogenesis remains unexplored, and it has become critical to decipher the stimuli and the underlying molecular pathways. Immediate activation of mitochondrial function was described during acute exercise, respiratory chain injury, Endoplasmic Reticulum stress, genotoxic stress, or environmental toxic insults. Delayed adaptations of mitochondrial form, composition, and functions were evidenced for persistent changes in redox status as observed in endurance training, in fibroblasts grown in presence of respiratory chain inhibitors or in absence of glucose, in the smooth muscle of patients with severe asthma, or in the skeletal muscle of patients with a mitochondrial disease. Besides, mitochondrial transformations were observed in the course of human cell differentiation, during immune response activation, or in cells undergoing carcinogenesis. Little is known on the signals and downstream pathways that govern mitochondrial adaptations and transformations. Few adaptative loops, including redox sensors, kinases, and transcription factors were deciphered, but their implication in physiology and pathology remains elusive. Mitoplasticity could play a protective role against aging, diabetes, cancer, or neurodegenerative diseases. Research on adaptation and transformation could allow the design of innovative therapies, notably in cancer.

Mitochondrial DNA transmission and confounding mitochondrial influences in cloned cattle and pigs

Although somatic cell nuclear transfer (SCNT) is a powerful tool for production of cloned animals, SCNT embryos generally have low developmental competency and many abnormalities. The interaction between the donor nucleus and the enucleated ooplasm plays an important role in early embryonic development, but the underlying mechanisms that negatively impact developmental competency remain unclear. Mitochondria have a broad range of critical functions in cellular energy supply, cell signaling, and programmed cell death; thus, affect embryonic and fetal development. This review focuses on mitochondrial considerations influencing SCNT techniques in farm animals. Donor somatic cell mitochondrial DNA (mtDNA) can be transmitted through what has been considered a "bottleneck" in mitochondrial genetics via the SCNT maternal lineage. This indicates that donor somatic cell mitochondria have a role in the reconstructed cytoplasm. However, foreign somatic cell mitochondria may affect the early development of SCNT embryos. Nuclear-mitochondrial interactions in interspecies/intergeneric SCNT (iSCNT) result in severe problems. A major biological selective pressure exists against survival of exogenous mtDNA in iSCNT. Yet, mtDNA differences in SCNT animals did not reflect transfer of proteomic components following proteomic analysis. Further study of nuclear-cytoplasmic interactions is needed to illuminate key developmental characteristics of SCNT animals associated with mitochondrial biology.

An investigation of excess residual cytoplasm in human spermatozoa and its distinction from the cytoplasmic droplet

Recent studies have shown cytoplasmic droplets to be normal morphological occurrences in human male spermatozoa. When the cytoplasm around the sperm midpiece is present in large amounts, however, pathological effects may transpire. The cytoplasmic droplet then becomes known as excess residual cytoplasm, which can impair overall sperm function and produce higher levels of reactive oxygen species, potentially leading to male infertility. Though the distinction between cytoplasmic droplets and excess residual cytoplasm has been made, some studies fail to recognize the difference and incorrectly label the latter as a cytoplasmic droplet. This review attempts to clarify excess residual cytoplasm's effect on fertility, examine the enzymes responsible, and suggest tests and possible treatment options for those affected by this defect.

Essential role of ubiquitin C-terminal hydrolases UCHL1 and UCHL3 in mammalian oocyte maturation

Ubiquitin C-terminal hydrolases (UCHs) comprise a family of deubiquitinating enzymes that play a role in the removal of multi-ubiquitin chains from proteins that are posttranslationally modified by ubiquitination to be targeted for proteolysis by the 26S proteasome. The UCH-enzymes also generate free monomeric ubiquitin from precursor multi-ubiquitin chains and, in some instances, may rescue ubiquitinated proteins from degradation. This study examined the roles of two oocyte-expressed UCHs, UCHL1, and UCHL3 in murine and rhesus monkey oocyte maturation. The Uchl1 and Uchl3 mRNAs were highly expressed in GV and MII oocytes, and were associated with the oocyte cortex (UCHL1) and meiotic spindle (UCHL3). Microinjection of the UCH-family enzyme inhibitor, ubiquitin-aldehyde (UBAL) to GV oocytes prevented oocyte meiotic progression beyond metaphase I in a majority of treated oocytes and caused spindle and first polar body anomalies. Injection of antibodies against UCHL3 disrupted oocyte maturation and caused meiotic anomalies, including abnormally long meiotic spindles. A selective, cell permeant inhibitor of UCHL3, 4, 5, 6, 7-tetrachloroidan-1, 3-dione also caused meiotic defects and chromosome misalignment. Cortical granule localization in the oocyte cortex was disrupted by UBAL injected after oocyte maturation. We conclude that the activity of oocyte UCHs contributes to oocyte maturation by regulating the oocyte cortex and meiotic spindle.

Essential role of maternal UCHL1 and UCHL3 in fertilization and preimplantation embryo development

Post-translational protein modification by ubiquitination, a signal for lysosomal or proteasomal proteolysis, can be regulated and reversed by deubiquitinating enzymes (DUBs). This study examined the roles of UCHL1 and UCHL3, two members of ubiquitin C-terminal hydrolase (UCH) family of DUBs, in murine fertilization and preimplantation development. Before fertilization, these proteins were associated with the oocyte cortex (UCHL1) and meiotic spindle (UCHL3). Intracytoplasmic injection of the general UCH-family inhibitor ubiquitin-aldehyde (UBAL) or antibodies against UCHL3 into mature metaphase II oocytes blocked fertilization by reducing sperm penetration of the zona pellucida and incorporation into the ooplasm, suggesting a role for cortical UCHL1 in sperm incorporation. Both UBAL and antibodies against UCHL1 injected at the onset of oocyte maturation (germinal vesicle stage) reduced the fertilizing ability of oocytes. The subfertile Uchl1(gad-/-) mutant mice showed an intriguing pattern of switched UCH localization, with UCHL3 replacing UCHL1 in the oocyte cortex. While fertilization defects were not observed, the embryos from homozygous Uchl1(gad-/-) mutant females failed to undergo morula compaction and did not form blastocysts in vivo, indicating a maternal effect related to UCHL1 deficiency. We conclude that the activity of oocyte UCHs contributes to fertilization and embryogenesis by regulating the physiology of the oocyte and blastomere cortex.

Numts help to reconstruct the demographic history of the ocellated lizard (Lacerta lepida) in a secondary contact zone

In northwestern Iberia, two largely allopatric Lacerta lepida mitochondrial lineages occur, L5 occurring to the south of Douro River and L3 to the north, with a zone of putative secondary contact in the region of the Douro River valley. Cytochrome b sequence chromatograms with polymorphisms at nucleotide sites diagnostic for the two lineages were detected in individuals in the region of the Douro River and further north within the range of L3. We show that these polymorphisms are caused by the presence of four different numts (I-IV) co-occurring with the L3 genome, together with low levels of heteroplasmy. Two of the numts (I and II) are similar to the mitochondrial genome of L5 but are quite divergent from the mitochondrial genome of L3 where they occur. We show that these numts are derived from the mitochondrial genome of L5 and were incorporated in L3 through hybridization at the time of secondary contact between the lineages. The additional incidence of these numts to the north of the putative contact zone is consistent with an earlier postglacial northward range expansion of L5, preceding that of L3. We show that genetic exchange between the lineages responsible for the origin of these numts in L3 after secondary contact occurred prior to, or coincident with, the northward expansion of L3. This study shows that, in the context of phylogeographic analysis, numts can provide evidence for past demographic events and can be useful tools for the reconstruction of complex evolutionary histories.

Mitochondrial biology in reproduction

Mitochondrial biology plays an important role in the reproductive process, with influence on germ cell development and quality as well as embryonic development and reproductive success. This review outlines the role of mitochondrial genetics and function in reproductive biology, including a discussion of general mitochondrial function, genetics and germline transmission. Also highlighted are the mitochondrial morphologic changes that occur during oogenesis and the role these changes play in the mitochondrial bottleneck that influences the distribution of deleterious mitochondrial genomes to offspring. The review covers the influence of mitochondria in embryonic stem cell and induced pluripotent stem cell biology and development. Lastly, the role of mitochondrial biology in assisted reproductive techniques is discussed.

Effect of age on the processing and import of matrix-destined mitochondrial proteins in skeletal muscle

Deregulation of muscle mitochondrial biogenesis may explain the altered mitochondrial properties associated with aging. Maintenance of the mitochondrial network requires the continuous incorporation of nascent proteins into their subcompartments via the protein import pathway. We examined whether this pathway was impaired in muscle of aged animals, focusing on the subsarcolemmal and intermyofibrillar mitochondrial populations. Our results indicate that the import of proteins into the mitochondrial matrix was unaltered with age. Interestingly, import assays supplemented with the cytosolic fraction illustrated an attenuation of protein import, and this effect was similar between age groups. We observed a 2.5-fold increase in protein degradation in the presence of the cytosolic fraction obtained from aged animals. Thus, the reduction of mitochondrial content and/or function observed with aging may not rely on altered activity of the import pathway but rather on the availability of preproteins that are susceptible to elevated rates of degradation by cytosolic factors.

Biparental inheritance of plastidial and mitochondrial DNA and hybrid variegation in Pelargonium

Plastidial (pt) and mitochondrial (mt) genes usually show maternal inheritance. Non-Mendelian, biparental inheritance of plastids was first described by Baur (Z Indukt Abstamm Vererbungslehre 1:330–351, 1909) for crosses between Pelargonium cultivars. We have analyzed the inheritance of pt and mtDNA by examining the progeny from reciprocal crosses of Pelargoniumzonale and P. inquinans using nucleotide sequence polymorphisms of selected pt and mt genes. Sequence analysis of the progeny revealed biparental inheritance of both pt and mtDNA. Hybrid plants exhibited variegation: our data demonstrate that the inquinans chloroplasts, but not the zonale chloroplasts bleach out, presumably due to incompatibility of the former with the hybrid nuclear genome. Different distribution of maternal and paternal sequences could be observed in different sectors of the same leaf, in different leaves of the same plant, and in different plants indicating random segregation and sorting-out of maternal and paternal plastids and mitochondria in the hybrids. The substantial transmission of both maternal and paternal mitochondria to the progeny turns Pelargonium into a particular interesting subject for studies on the inheritance, segregation and recombination of mt genes.

The fate of paternal mitochondria in marmoset pre-implantation embryos

BACKGROUND

Sperm-derived mitochondria are integrated into the oocyte at fertilization but seem to vanish during the early cleavage phase. The developmental potential of pre-implantation embryos seems to be closely related to their ability to induce degeneration of these mitochondria, but the mechanisms underlying their loss of function are not yet understood. This study focuses on the fate of paternal mitochondria in pre-implantation embryos.

METHODS

Stimulation, collection and in vitro culture of oocytes from Callithrix jacchus, allows the study of the destiny of paternal mitochondria by utilizing immunostaining of pre-implantation embryos, fluorescence and laserscanning microscopy. Live pre-implantation embryos were stained with a fluorescence indicator reflecting mitochondrial membrane potential.

RESULTS

Evidence indicating the loss of mitochondrial function was not found nor that apoptosis pathways were involved in the disappearance of paternally derived mitochondria.

CONCLUSIONS

These findings may have implications for mitochondrially inherited diseases and could lead to new strategies for improving assisted reproduction.

Analysis of heterogeneous mitochondria distribution in somatic cell nuclear transfer porcine embryos

We previously reported that translocation of mitochondria from the oocyte cortex to the perinuclear area indicates positive developmental potential that was reduced in porcine somatic cell nuclear transfer (SCNT) embryos compared to in vitro220.). The present study is focused on distribution of donor cell mitochondria in intraspecies (pig oocytes; pig fetal fibroblast cells) and interspecies (pig oocytes; mouse fibroblast cells) reconstructed embryos by using either pig fibroblasts with mitochondria-stained MitoTracker CMXRos or YFP-mitochondria 3T3 cells (pPhi-Yellow-mito) as donor cells. Transmission electron microscopy was employed for ultrastructural analysis of pig oocyte and donor cell mitochondria. Our results revealed donor cell mitochondrial clusters around the donor nucleus that gradually dispersed into the ooplasm at 3 h after SCNT. Donor-derived mitochondria distributed into daughter blastomeres equally (82.8%) or unequally (17.2%) at first cleavage. Mitochondrial morphology was clearly different between donor cells and oocytes in which various complex shapes and configurations were seen. These data indicate that (1) unequal donor cell mitochondria distribution is observed in 17.2% of embryos, which may negatively influence development; and (2) complex mitochondrial morphologies are observed in IVF and SCNT embryos, which may influence mitochondrial translocation and affect development.

Mitochondrial DNA inheritance after SCNT

Mitochondrial biogenesis and function is under dual genetic control and requires extensive interaction between biparentally inherited nuclear genes and maternally inherited mitochondrial genes. Standard SCNT procedures deprive an oocytes' mitochondrial DNA (mtDNA) of the corresponding maternal nuclear DNA and require it to interact with an entirely foreign nucleus that is again interacting with foreign somatic mitochondria. As a result, most SCNT embryos, -fetuses, and -offspring carry somatic cell mtDNA in addition to recipient oocyte mtDNA, a condition termed heteroplasmy. It is thus evident that somatic cell mtDNA can escape the selective mechanism that targets and eliminates intraspecific sperm mitochondria in the fertilized oocyte to maintain homoplasmy. However, the factors responsible for the large intra- and interindividual differences in heteroplasmy level remain elusive. Furthermore, heteroplasmy is probably confounded with mtDNA recombination. Considering the essential roles of mitochondria in cellular metabolism, cell signalling, and programmed cell death, future experiments will need to assess the true extent and impact of unorthodox mtDNA transmission on various aspects of SCNT success.

Efficient production of intersubspecific hybrid mice and embryonic stem cells by intracytoplasmic sperm injection

Recently, mice and embryonic stem (ES) cells with allelic polymorphisms have been used extensively in the field of genetics and developmental biology. In this study, we examined whether intersubspecific hybrid mice and ES cells with these genotypes can be efficiently produced by intracytoplasmic sperm injection (ICSI). Frozen-thawed spermatozoa from wild-derived strains, JF1 (Mus musculus molossinus), MSM (M. m. molossinus), HMI (M. m. castaneus), and SWN (M. m. spp.), were directly injected into mature oocytes from laboratory mice ([C57BL/6 x DBA2]F1; M. m. domesticus). The in vitro and in vivo developmental capacity of F1 embryos was not significantly different among the groups (P > 0.05), and term offspring were efficiently obtained in all groups (27%-34% of transferred embryos). However, the mean body and placental weights of the offspring differed significantly with genotype (P < 5 x 10(-10)), with the HMI hybrid greatest in both body and placental weights. In an application study using these F1 offspring, we analyzed their mitochondrial DNA using intersubspecific polymorphisms and found the consistent disappearance of sperm mitochondrial DNA in the F1 progeny. In a second series of experiments, we generated F1 blastocysts by injecting MSM spermatozoa into C57BL/6 oocytes and used them to generate hybrid ES cell lines. The ES cell lines were established at a high efficiency (9 lines from 20 blastocysts) and their allelic polymorphisms were confirmed. Thus, ICSI using cryopreserved spermatozoa allows the efficient and immediate production of a number of F1 hybrid mice and ES cell lines, which can be used for polymorphic analysis of mouse genetics.