RAC1 controls progressive movement and competitiveness of mammalian spermatozoa.

Mammalian spermatozoa employ calcium (Ca2+) and cyclic adenosine monophosphate (cAMP) signaling in generating flagellar beat. However, how sperm direct their movement towards the egg cells has remained elusive. Here we show that the Rho small G protein RAC1 plays an important role in controlling progressive motility, in particular average path velocity and linearity. Upon RAC1 inhibition of wild type sperm with the drug NSC23766, progressive movement is impaired. Moreover, sperm from mice homozygous for the genetically variant t-haplotype region (tw5/tw32), which are sterile, show strongly enhanced RAC1 activity in comparison to wild type (+/+) controls, and quickly become immotile in vitro. Sperm from heterozygous (t/+) males, on the other hand, display intermediate RAC1 activity, impaired progressive motility and transmission ratio distortion (TRD) in favor of t-sperm. We show that t/+-derived sperm consist of two subpopulations, highly progressive and less progressive. The majority of highly progressive sperm carry the t-haplotype, while most less progressive sperm contain the wild type (+) chromosome. Dosage-controlled RAC1 inhibition in t/+ sperm by NSC23766 rescues progressive movement of (+)-sperm in vitro, directly demonstrating that impairment of progressive motility in the latter is caused by enhanced RAC1 activity. The combined data show that RAC1 plays a pivotal role in controlling progressive motility in sperm, and that inappropriate, enhanced or reduced RAC1 activity interferes with sperm progressive movement. Differential RAC1 activity within a sperm population impairs the competitiveness of sperm cells expressing suboptimal RAC1 activity and thus their fertilization success, as demonstrated by t/+-derived sperm. In conjunction with t-haplotype triggered TRD, we propose that Rho GTPase signaling is essential for directing sperm towards the egg cells.

Human sperm tail proteome suggests new endogenous metabolic pathways.

Proteomic studies are contributing greatly to our understanding of the sperm cell, and more detailed descriptions are expected to clarify additional cellular and molecular sperm attributes. The aim of this study was to characterize the subcellular proteome of the human sperm tail and, hopefully, identify less concentrated proteins (not found in whole cell proteome studies). Specifically, we were interested in characterizing the sperm metabolic proteome and gaining new insights into the sperm metabolism issue. Sperm were isolated from normozoospermic semen samples and depleted of any contaminating leukocytes. Tail fractions were obtained by means of sonication followed by sucrose-gradient ultracentrifugation, and their purity was confirmed via various techniques. Liquid chromatography and tandem mass spectrometry of isolated sperm tail peptides resulted in the identification of 1049 proteins, more than half of which had not been previously described in human sperm. The categorization of proteins according to their function revealed two main groups: proteins related to metabolism and energy production (26%), and proteins related to sperm tail structure and motility (11%). Interestingly, a great proportion of the metabolic proteome (24%) comprised enzymes involved in lipid metabolism, including enzymes for mitochondrial beta-oxidation. Unexpectedly, we also identified various peroxisomal proteins, some of which are known to be involved in the oxidation of very long chain fatty acids. Analysis of our data using Reactome suggests that both mitochondrial and peroxisomal pathways might indeed be active in sperm, and that the use of fatty acids as fuel might be more preponderant than previously thought. In addition, incubation of sperm with the fatty acid oxidation inhibitor etomoxir resulted in a significant decrease in sperm motility. Contradicting a common concept in the literature, we suggest that the male gamete might have the capacity to obtain energy from endogenous pools, and thus to adapt to putative exogenous fluctuations.

Identification of proteins involved in human sperm motility using high-throughput differential proteomics.

Mammalian sperm motility is a prerequisite for in vivo fertilization, and alterations in this parameter are commonly observed in infertile males. However, we still do not have a complete understanding of the molecular mechanisms controlling it. The aim of this study was to identify proteins involved in human sperm motility deficiency by using TMT protein labeling and LC-MS/MS. Two complementary approaches were used: comparison between sperm samples differing in motility (asthenozoospermic versus normozoospermic) and comparison between sperm subpopulations of fractionated normozoospermic samples differing in motility (non-migrated versus migrated). LC-MS/MS resulted in the identification of 1157 and 887 proteins in the first and second approaches, respectively. Remarkably, similar proteomic alterations were detected in the two experiments, with 80 proteins differentially expressed in the two groups of samples and 93 differentially expressed in the two groups of subpopulations. The differential proteins were analyzed by GO, cellular pathways, and clustering analyses and resulted in the identification of core deregulated proteins and pathways associated with sperm motility dysfunction. These included proteins associated with energetic metabolism, protein folding/degradation, vesicle trafficking, and the cytoskeleton. Contrary to what is usually accepted, the outcomes support the hypothesis that several metabolic pathways (notably, mitochondrial-related ones) contribute toward regulating sperm motility.

Genomic and proteomic dissection and characterization of the human sperm chromatin.

The mammalian spermatozoon has a unique chromatin structure where the majority of DNA is packaged by protamines, while a small fraction (∼8%) remains associated with nucleosomes. However, the chromatin affinity and repertoire of the additional proteins constituting the different sperm chromatin fractions have not yet been explored. To address this we have carried out a genomic and proteomic characterization of human sperm samples subjected to chromatin fractionation using either 0.65 M NaCl extraction followed by EcoRI/BamHI DNA restriction enzyme digestion, or micrococcal nuclease digestion. DNA fractions corresponding to the nucleosome-packaged DNA were sequenced, confirming an appropriate dissection of the sperm chromatin. In addition we detected and sequenced a subnucleosomal particle. Although both fractions were highly enriched at gene promoters, some sequences were found to be exclusively associated with one of those. The results of the proteomic analyses demonstrate that there are two distinct sets of sperm proteins which differ in chromatin affinity. Histone variants, transcription factors, chromatin-associated and modifying proteins involved in regulatory roles were identified as weakly attached to the sperm DNA, whereas proteins with structural roles were identified in the condensed fraction. Many factors, such as the histone lysine demethylase PHF8 identified for the first time in the human sperm cell in this study, were identified exclusively in soluble fraction. Our results provide additional support to the possibility that all of these factors may constitute additional layers of sperm epigenetic information or have structural or regulatory roles transmitted by the sperm cell to the oocyte at fertilization.

High-throughput sperm differential proteomics suggests that epigenetic alterations contribute to failed assisted reproduction.

STUDY QUESTION: Are there quantitative alterations in the proteome of normozoospermic sperm samples that are able to complete IVF but whose female partner does not achieve pregnancy? SUMMARY ANSWER: Normozoospermic sperm samples with different IVF outcomes (pregnancy versus no pregnancy) differed in the levels of at least 66 proteins. WHAT IS KNOWN ALREADY: The analysis of the proteome of sperm samples with distinct fertilization capacity using low-throughput proteomic techniques resulted in the detection of a few differential proteins. Current high-throughput mass spectrometry approaches allow the identification and quantification of a substantially higher number of proteins. STUDY DESIGN, SIZE, DURATION: This was a case-control study including 31 men with normozoospermic sperm and their partners who underwent IVF with successful fertilization recruited between 2007 and 2008. PARTICIPANTS/MATERIALS, SETTING, METHODS: Normozoospermic sperm samples from 15 men whose female partners did not achieve pregnancy after IVF (no pregnancy) and 16 men from couples that did achieve pregnancy after IVF (pregnancy) were included in this study. To perform the differential proteomic experiments, 10 no pregnancy samples and 10 pregnancy samples were separately pooled and subsequently used for tandem mass tags (TMT) protein labelling, sodium dodecyl sulphate-polyacrylamide gel electrophoresis, liquid chromatography tandem mass spectrometry (LC-MS/MS) identification and peak intensity relative protein quantification. Bioinformatic analyses were performed using UniProt Knowledgebase, DAVID and Reactome. Individual samples (n = 5 no pregnancy samples; n = 6 pregnancy samples) and aliquots from the above TMT pools were used for western blotting. MAIN RESULTS AND THE ROLE OF CHANCE: By using TMT labelling and LC-MS/MS, we have detected 31 proteins present at lower abundance (ratio no pregnancy/pregnancy < 0.67) and 35 at higher abundance (ratio no pregnancy/pregnancy > 1.5) in the no pregnancy group. Bioinformatic analyses showed that the proteins with differing abundance are involved in chromatin assembly and lipoprotein metabolism (P values < 0.05). In addition, the differential abundance of one of the proteins (SRSF protein kinase 1) was further validated by western blotting using independent samples (P value < 0.01). LIMITATIONS, REASONS FOR CAUTION: For individual samples the amount of recovered sperm not used for IVF was low and in most of the cases insufficient for MS analysis, therefore pools of samples had to be used to this end. WIDER IMPLICATIONS OF THE FINDINGS: Alterations in the proteins involved in chromatin assembly and metabolism may result in epigenetic errors during spermatogenesis, leading to inaccurate sperm epigenetic signatures, which could ultimately prevent embryonic development. These sperm proteins may thus possibly have clinical relevance. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the Spanish Ministry of Economy and Competitiveness (Ministerio de Economia y Competividad; FEDER BFU 2009-07118 and PI13/00699) and Fundación Salud 2000 SERONO13-015. There are no competing interests to declare.

Mitochondria functionality and sperm quality.

Although mitochondria are best known for being the eukaryotic cell powerhouses, these organelles participate in various cellular functions besides ATP production, such as calcium homoeostasis, generation of reactive oxygen species (ROS), the intrinsic apoptotic pathway and steroid hormone biosynthesis. The aim of this review was to discuss the putative roles of mitochondria in mammalian sperm function and how they may relate to sperm quality and fertilisation ability, particularly in humans. Although paternal mitochondria are degraded inside the zygote, sperm mitochondrial functionality seems to be critical for fertilisation. Indeed, changes in mitochondrial integrity/functionality, namely defects in mitochondrial ultrastructure or in the mitochondrial genome, transcriptome or proteome, as well as low mitochondrial membrane potential or altered oxygen consumption, have been correlated with loss of sperm function (particularly with decreased motility). Results from genetically engineered mouse models also confirmed this trend. On the other hand, increasing evidence suggests that mitochondria derived ATP is not crucial for sperm motility and that glycolysis may be the main ATP supplier for this particular aspect of sperm function. However, there are contradictory data in the literature regarding sperm bioenergetics. The relevance of sperm mitochondria may thus be associated with their role in other physiological features, particularly with the production of ROS, which in controlled levels are needed for proper sperm function. Sperm mitochondria may also serve as intracellular Ca²âº stores, although their role in signalling is still unclear.

Energy metabolism in mammalian sperm motility.

Mammalian sperm, the only cells that achieve their purpose outside their organism of origin, have to swim vigorously within the female reproductive tract to reach an oocyte. Flagellar dyneins drive sperm motility, which accounts for the consumption of high amounts of ATP. The two main ATP-producing metabolic pathways are compartmentalized in sperm: oxidative phosphorylation in the midpiece and glycolysis in the principal piece. The relative preponderance of these pathways has been discussed for decades (the so-called sperm energy debate). The debate has been muddled by species-specific variances and by technical constraints. But recent findings suggest that sperm from most mammalian species employ a versatile metabolic strategy to maintain motility according to the physiological environment. Different metabolic pathways likely coordinate by using exogenous and/or endogenous substrates in order to produce ATP efficiently. Defects in any of these pathways (glycolysis, mitochondrial oxidative phosphorylation, Krebs cycle, fatty acids oxidation, and ketone bodies oxidation, among others) may disturb sperm motility and be at the origin of male infertility. Understanding sperm bioenergetics is thus crucial for building new diagnostic tools, and for the development of treatments for patients presenting with low sperm motility. Some of these patients may benefit from personalized metabolic supplementations and dietary interventions. This article is categorized under: Reproductive System Diseases > Molecular and Cellular Physiology.

Skin adhesive versus subcuticular suture for perineal skin repair after episiotomy--a randomized controlled trial.

OBJECTIVE: Surgical repair of perineal lesions after delivery is frequently associated with pain and discomfort, interfering with the normal activities of the puerperium. The aim of this study was to compare perineal skin repair after episiotomy with adhesive glue versus a subcuticular suture, regarding the incidence of pain and wound complications. STUDY DESIGN: Randomized clinical trial. SETTING: Tertiary care university hospital. MATERIAL AND METHODS: One hundred women having mediolateral episiotomy at vaginal delivery were enrolled. They were randomized to receive skin adhesive (n = 53) or subcuticular suture (n = 47) for closure of perineal skin. The main outcome measure was self-evaluated pain in the 30 days following delivery. Secondary outcome measures were technical difficulties reported with the procedure, duration of surgical repair, wound complications observed at 42-68 hours post-partum and re-initiation of sexual activity by 30 days post-partum. RESULTS: No significant differences were observed between the two groups in incidence of technical difficulties and failed procedures, pain during the procedure, wound complications at hospital discharge, self-evaluated measures of pain at 7 and 30 days or re-initiation of sexual activity by 30 days post-partum. The skin adhesive group had a significantly shorter mean duration of the procedure (four minutes less). CONCLUSION: Perineal skin closure using adhesive glue is faster than subcuticular suture, and associated with a similar incidence of complications and pain in the first 30 days.

Antioxidant Evaluation of Extracts of Pecan NutShell (Carya illinoensis) in Soybean Biodiesel B100.

Biodiesel is subject to radical reactions that promote degradation. To decrease the speed of these degradation reactions and increase oxidative stability, either natural or synthetic antioxidants are added to biodiesel. Thus, the objective of this study is to evaluate the effect of extracts of pecan nutshell (Carya illinoensis) as natural antioxidants derived from biomass using water, ethanol, and methanol/water (50/50) as a solvent for extraction. The addition of these antioxidants is performed during the soybean biodiesel washing process in an unconventional manner. The results obtained are statistically analyzed and compared to the control. The induction time (IT) for the biodiesel samples washed with ethanolic extract of pecan nutshell (5 g L-1), aqueous extract of pecan nutshell (12 g L-1) and methanol/water extract of pecan nutshell (12 g L-1), are, respectively, 9.46, 7.60, 7.43 h. The activation energy and the storage time of the biodiesel samples washed with the extracts are also studied. The order of reaction of the oxidation kinetics of biodiesel is first order.

Fungi in cake production chain: Occurrence and evaluation of growth potential in different cake formulations during storage.

This study aimed to determine the prevalence and populations of fungi in cake production chain. Besides, the growth potential of twelve fungal strains in different cake formulations was evaluated. Raw materials from two different batches (n=143), chocolate cakes (n=30), orange cakes (n=20), and processing environment air samples (n=147) were analyzed. Among the raw materials, wheat flour (3.2±0.3 log CFU per g) and corn meal (3.8±0.8 log CFU per g) belonging to batch #1 showed significant higher fungal counts (p<0.05). The fungal counts in the processing environment air reached up to 2.56 log CFU per m3 (p<0.05). The predominant fungi species in the industrialized cakes were Aspergillus flavus (28.15%), Penicillium citrinum (18.45%), Penicillium paxilli (14.56%), and Aspergillus niger (6.8%), which were also detected in the raw materials and processing environment air. Only Penicillium glabrum and Penicillium citrinum showed visible mycelium (>3mm) in the free of preservative cake formulation at 19th and 44th days of storage at 25°C, respectively. Revealing the biodiversity of fungi in ingredients, air and final products, as well as challenging final products with representative fungal strains may assist to implement effective controlling measures as well as to gather data for the development of more robust cake formulations.

The analysis of mitochondria and mitochondrial DNA in human embryonic stem cells.

As human embryonic stem cells (hESCs) undergo differentiation, they express genes characteristic of the lineage for which they are destined. However, fully differentiated individual cell types can be characterized by the number of mitochondria they possess and the copies of the mitochondrial genome per mitochondrion. These characteristics are indicative of a specific cell's requirement for adenosine triphosphate (ATP) and therefore cellular viability and function. Consequently, failure for an ESC to possess the full complement of mitochondria and mitochondrial DNA (mtDNA) could limit its final commitment to a particular fate. We describe a series of protocols that analyze the process of cellular mitochondrial and mtDNA differentiation during hESC differentiation. In addition, mtDNA transcription and replication are key events in cellular differentiation that require interaction between the nucleus and the mitochondrion. To this extent, we describe a series of protocols that analyze the initiation of these key events as hESCs progress from their undifferentiated state to the fully committed cell. Last, we describe real-time polymerase chain reaction protocols that allow both the identification of mtDNA copy number and determine whether mtDNA copy is uniform (homoplasmy) in its transmission or heterogeneous (heteroplasmy).

Simultaneous analysis of cytoskeletal patterns and chromosome positioning in human fertilization failures.

OBJECTIVE: To sequentially and reliably apply both tubulin immunocytochemistry (ICC) and fluorescence in situ hybridization (FISH) to human fertilization failures, thus providing a tool for a multiple analysis of arrest. DESIGN: Analysis of human fertilization failures at several stages of arrest. SETTING: Academic and clinical institutions. PATIENT(S): Consenting patients undergoing assisted reproduction technologies. INTERVENTION(S): Failed fertilizations displaying signs of activation without pronuclear development, or with the absence of polar body emission or cleavage 48 hours after insemination or microinjection were analyzed. Fertilization failures were fixed and processed for ICC. After data was collected the same samples were then subjected to FISH analysis using probes for chromosomes X, Y, and 18. MAIN OUTCOME MEASURE(S): Simultaneous ICC and FISH data on the same sample. RESULT(S): Sequential application of straightforward standard ICC and FISH techniques was not possible, as the morphologic features had been altered, microtubular patterns were not preserved, and many samples were rendered opaque. Only chromatin at the cell surface or outside the oocyte/zygote, such as metaphase II spindles or polar body nuclei, could be routinely probed for FISH after ICC. However, an increase in detergent-induced sample permeabilization as well as the removal of several steps usually performed for FISH made it possible to directly compare microtubular patterns and chromosome position, regardless of chromatin status. CONCLUSION(S): Analysis of specific proteins by immunocytochemistry and of chromosome status/positioning by FISH can be carried out sequentially in human fertilization failures, irrespective of the stage of arrest.

The combined human sperm proteome: cellular pathways and implications for basic and clinical science.

BACKGROUND: The human sperm cell is very well suited for proteomic studies, as it is accessible, can be easily purified and is believed to be transcriptionally and translationally silent. The recent use of advanced proteomic approaches is clearly challenging the understanding of sperm biology. The aims of this review are to discuss the various human sperm proteomic studies, to create a compiled list of all the sperm proteins described to date and to re-assess the potential functional implications. METHODS: A search of the scientific literature available in the PubMed/Medline database at 31 December 2012 was conducted for studies on human sperm proteomics. The complete list of proteins obtained was carefully analysed using different bioinformatics tools, including Reactome, a knowledgebase of biological pathways. RESULTS: A total of 30 studies were identified. The proteomics studies have resulted in the identification of 6198 different proteins, an important proportion of which (around 30%) are known to be expressed in the testis. The proteins were assigned to various functional pathways, including metabolism, apoptosis, cell cycle, meiosis and membrane trafficking, among others. Unexpectedly, the sperm cell also contains a range of proteins involved in RNA metabolism and translational regulation, as well as proteins usually located in organelles believed to be absent in sperm, such as cytoplasmatic ribosomes and peroxisomes. Additionally, some proteins whose levels seem to be altered in low-quality sperm might have clinical relevance. CONCLUSIONS: The analysis of the most complete sperm proteome available to date indicates the presence of several cellular protein pathways previously ignored in the male gamete. Confirming the activity of each of these pathways and understanding their biological significance will certainly boost the knowledge of human sperm and male fertility and infertility in the next years.

Aging and male reproductive function: a mitochondrial perspective.

Researching the effects of aging in the male reproductive system is not trivial. Not only are multiple changes at molecular, cellular and endocrine levels involved, but any findings must be discussed with variable individual characteristics, as well as with lifestyle and environmental factors. Age-related changes in the reproductive system include any aspect of reproductive function, from deregulation of the hypothalamic-pituitary-gonadal axis and of local auto/paracrine interactions, to effects on testicular stem cells, defects in testicular architecture and spermatogenesis, or sperm with decreased functionality. Several theories place mitochondria at the hub of cellular events related to aging, namely regarding the accumulation of oxidative damage to cells and tissues, a process in which these organelles play a prominent role, although alternative theories have also emerged. However, oxidative stress is not the only process involved in mitochondrial-related aging; mitochondrial energy metabolism, changes in mitochondrial DNA or in mitochondrial-dependent testosterone production are also important. Crucially, all these issues are likely interdependent. We will review evidence that suggests that mitochondria constitute a common link between aging and fertility loss.

Exogenous glucose improves long-standing human sperm motility, viability, and mitochondrial function.

A relevant fraction of human sperm can be maintained in simple phosphate-buffered saline (PBS) for more than 1 week at room temperature, a time that could be doubled if glucose was available. This does not seem to be directly due to sperm mitochondrial activity.

Not all sperm are equal: functional mitochondria characterize a subpopulation of human sperm with better fertilization potential.

Human sperm samples are very heterogeneous and include a low amount of truly functional gametes. Distinct strategies have been developed to characterize and isolate this specific subpopulation. In this study we have used fluorescence microscopy and fluorescence-activated cell sorting to determine if mitochondrial function, as assessed using mitochondrial-sensitive probes, could be employed as a criterion to obtain more functional sperm from a given ejaculate. We first determined that mitochondrial activity correlated with the quality of distinct human samples, from healthy donors to patients with decreased semen quality. Furthermore, using fluorescence-activated cell sorting to separate sperm with active and inactive mitochondria we found that this was also true within samples. Indeed, sperm with active mitochondria defined a more functional subpopulation, which contained more capacitated and acrosome intact cells, sperm with lower chromatin damage, and, crucially, sperm more able to decondense and participate in early development using both chemical induction and injection into mature bovine oocytes. Furthermore, cell sorting using mitochondrial activity produced a more functional sperm subpopulation than classic swim-up, both in terms of improvement in a variety of functional sperm parameters and in statistical significance. In conclusion, whatever the true biological role of sperm mitochondria in fertilization, mitochondrial activity is a clear hallmark of human sperm functionality.

Mitochondrial functionality in reproduction: from gonads and gametes to embryos and embryonic stem cells.

BACKGROUND: Mitochondria are multitasking organelles involved in ATP synthesis, reactive oxygen species (ROS) production, calcium signalling and apoptosis; and mitochondrial defects are known to cause physiological dysfunction, including infertility. The goal of this review was to identify and discuss common themes in mitochondrial function related to mammalian reproduction. METHODS: The scientific literature was searched for studies reporting on the several aspects of mitochondrial activity in mammalian testis, sperm, oocytes, early embryos and embryonic stem cells. RESULTS: ATP synthesis and ROS production are the most discussed aspects of mitochondrial function. Metabolic shifts from mitochondria-produced ATP to glycolysis occur at several stages, notably during gametogenesis and early embryo development, either reflecting developmental switches or substrate availability. The exact role of sperm mitochondria is especially controversial. Mitochondria-generated ROS function in signalling but are mostly described when produced under pathological conditions. Mitochondria-based calcium signalling is primarily important in embryo activation and embryonic stem cell differentiation. Besides pathologically triggered apoptosis, mitochondria participate in apoptotic events related to the regulation of spermatogonial cell number, as well as gamete, embryo and embryonic stem cell quality. Interestingly, data from knock-out (KO) mice is not always straightforward in terms of expected phenotypes. Finally, recent data suggests that mitochondrial activity can modulate embryonic stem cell pluripotency as well as differentiation into distinct cellular fates. CONCLUSIONS: Mitochondria-based events regulate different aspects of reproductive function, but these are not uniform throughout the several systems reviewed. Low mitochondrial activity seems a feature of 'stemness', being described in spermatogonia, early embryo, inner cell mass cells and embryonic stem cells.

The expression of polymerase gamma and mitochondrial transcription factor A and the regulation of mitochondrial DNA content in mature human sperm.

BACKGROUND: Human mitochondrial DNA (mtDNA) encodes 13 polypeptides of the electron transfer chain. Its replication is dependent on the nuclear-encoded polymerase gamma (POLG) and mitochondrial transcription factor A (TFAM). For POLG, only the polyglutamine tract, characterized by a series of CAG repeats, has been investigated in human sperm. However, TFAM is associated with the reduction in mtDNA content of testicular sperm. We have determined whether POLG and TFAM have functional roles in post-ejaculatory sperm mtDNA. METHODS: Sperm samples were categorized as: normals, samples with one or two abnormal sperm parameters and oligoasthenoteratozoospermics (OATs). These were analysed by fluorescent PCR to determine the number of CAG repeats, real-time PCR for mtDNA copy number and immunocytochemistry and western blotting for patterns of expression for POLG, TFAM and the mtDNA-encoded COXI. RESULTS: Only the OAT group presented with a significantly higher incidence of heterozygosity for CAG repeats, higher mtDNA content and a lower percentage of sperm expressing POLG and TFAM. Paradoxically, good-quality sperm had fewer mtDNA copies but significantly more sperm expressed POLG, TFAM and COXI. CONCLUSIONS: Our data support the original findings that an association between sperm quality and POLG CAG repeats does exist. However, the biological significance of these variants in male infertility remains unclear, as these do not seem to affect mtDNA maintenance. The reduction in mtDNA content in normal samples likely reflects normal spermiogenesis, whereas increases in POLG and TFAM expression possibly compensate for the low mtDNA content, maintaining mitochondrial homeostasis.

Sperm mitochondria and fertilisation.

Human mitochondrial DNA (mtDNA) is an extranuclear genome that encodes 13 of the polypeptides associated with the process of oxidative phosphorylation (OXPHOS). The role and importance of OXPHOS in sperm motility and function has been debated over the last few years. Here, we argue that sperm OXPHOS is important to sperm function in the light of clinical based evidence in the human where pathogenic mutations have also been described in sperm and are associated with varying degrees of male subfertility. We also discuss the importance of maintaining maternal inheritance of mtDNA and how sperm mtDNA might be eliminated during early embryogenesis in a manner similar to the process which decreases oocyte mtDNA to extremely low levels once it reaches the blastocyst stage of preimplantation development. Finally, we discuss the role of sperm mtDNA replication and why it may be prudent to considerably reduce sperm mtDNA numbers during the transition from spermatogenesis to spermiogenesis.