Lactic acid is a sperm motility inactivation factor in the sperm storage tubules

Revisiting the Injury Mechanism of Goat Sperm Caused by the Cryopreservation Process from a Perspective of Sperm Metabolite Profiles

Semen cryopreservation results in the differential remodeling of the molecules presented in sperm, and these alterations related to reductions in sperm quality and its physiological function have not been fully understood. Given this, this study aimed to investigate the cryoinjury mechanism of goat sperm by analyzing changes of the metabolic characteristics in sperm during the cryopreservation process. The ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS) technique was performed to explore metabolite profiles of fresh sperm (C group), equilibrated sperm (E group), and frozen-thawed sperm (F group). In total, 2570 metabolites in positive mode and 2306 metabolites in negative mode were identified, respectively. After comparative analyses among these three groups, 374 differentially abundant metabolites (DAMs) in C vs. E, 291 DAMs in C vs. F, and 189 DAMs in E vs. F were obtained in the positive mode; concurrently, 530 DAMs in C vs. E, 405 DAMs in C vs. F, and 193 DAMs in E vs. F were obtained in the negative mode, respectively. The DAMs were significantly enriched in various metabolic pathways, including 31 pathways in C vs. E, 25 pathways in C vs. F, and 28 pathways in E vs. F, respectively. Among them, 65 DAMs and 25 significantly enriched pathways across the three comparisons were discovered, which may be tightly associated with sperm characteristics and function. Particularly, the functional terms such as TCA cycle, biosynthesis of unsaturated fatty acids, sphingolipid metabolism, glycine, serine and threonine metabolism, alpha-linolenic acid metabolism, and pyruvate metabolism, as well as associated pivotal metabolites like ceramide, betaine, choline, fumaric acid, L-malic acid and L-lactic acid, were focused on. In conclusion, our research characterizes the composition of metabolites in goat sperm and their alterations induced by the cryopreservation process, offering a critical foundation for further exploring the molecular mechanisms of metabolism influencing the quality and freezing tolerance of goat sperm. Additionally, the impacts of equilibration at low temperature on sperm quality may need more attentions as compared to the freezing and thawing process.

The surprising complexity and diversity of sperm storage structures across Galliformes

In internal fertilisers, the precise timing of ovulation with the arrival of sperm at the site of fertilisation is essential for fertilisation success. In birds, mating is often not synchronised with ovulation, but instead females utilise specialised sperm storage tubules (SSTs) in the reproductive tract, which can ensure sperm are always available for fertilisation at the time of ovulation, whilst simultaneously providing a mechanism of post-copulatory sexual selection. Despite the clear importance of SSTs for fertilisation success, we know little about the mechanisms involved in sperm acceptance, storage, and release. Furthermore, most research has been conducted on only a small number of species, based on which SSTs are usually assumed to look and function in the same way across all species. Here, we conduct a comparative exploration of SST morphology across 26 species of Galliformes. We show that SSTs, and the surrounding tissue, can vary significantly in morphology across species. We provide observational evidence that Galliformes exhibit at least 5 distinct categories of tubule types, including distinctive coiled and multi-branched tubules, and describe 2 additional features of the surrounding tissue. We suggest functional explanations for variation in tubule morphology and propose next steps for future research. Our findings indicate that SSTs are likely to be far more variable than has previously been assumed, with potentially important consequences for our understanding of sperm storage in birds and post-copulatory sexual selection in general.

In vitro characteristics of X- and Y-bearing ram spermatozoa sorted by bovine serum albumin (BSA) column and TLR7/8 ligand R848

The quality of the separated fractions in sex-sorted semen is very important for the success of the artificial insemination. This study aimed to evaluate some in vitro characteristics (DNA quantity, kinematic parameters and enzymes activity) of X- and Y-bearing ram spermatozoa sorted by bovine serum albumin (BSA) column and toll-like receptors (TLR)7/8 ligand R848. The ejaculates from six rams were collected by artificial vagina and subjected to a computer-assisted semen analysis (CASA). Total motility and percentage of the sperms with rapid and medium progressivity or non-progressivity in whole ejaculates and in X and Y fractions were analyzed. Activity of the enzymes ALP, GGT, CK, LDH and accumulation of lactate in the seminal plasma of ejaculates and in the environmental fluid of sexed spermatozoa were measured by biochemical analyzer. DNA was isolated from precipitated spermatozoa, and its quantity was measured. For both protocols the DNA mass from X-bearing fractions was higher, than from Y-bearing fractions. The high total motility of X- and Y-bearing spermatozoa as well as greater percent sperms with progressive motility were observed after use of BSA protocol. The application of TLR7/8 ligand R848 protocol led to reducing of Y-sperm motility and enhancement of non-progressivity in both fractions, which corresponded to the determined high amount of the extracellular lactate. For both methods, the significantly reduced activity of enzymes in the X and Y spermatozoa environmental fluids was established. Both protocols produce X- and Y-sperm fractions with satisfactory quality (over 80% total motility and over 50% rapid and medium progressive spermatozoa in each fraction).

Arresting calcium-regulated sperm metabolic dynamics enables prolonged fertility in poultry liquid semen storage

The preservation of liquid semen is pivotal for both industrial livestock production and genetic management/conservation of species with sperm that are not highly cryo-tolerant. Nevertheless, with regard to poultry semen, even brief in vitro storage periods can lead to a notable decline in fertility, despite the in vivo capacity to maintain fertility for several weeks when within the hen's sperm storage tubules. For fertility in sperm, intracellular calcium ions ([Ca2+]i) play a key role in signaling towards modifying energy metabolism. While reducing [Ca2+]i has been found to enhance the preservation of sperm fertility in some mammals, the connection between semen fertility and calcium availability in avian sperm has received limited attention. In this study, we demonstrate that the use of extracellular and intracellular calcium chelators in liquid semen extenders, specifically EGTA and EGTA-AM, has distinct effects on prolonging the fertility of chicken sperm. These results were validated through in vivo fertility tests. Mechanistically, the effects observed were linked to coordination of mitochondrial metabolism and ATP catabolism. Despite both calcium chelators inducing hypoxia, they differentially regulated mitochondrial respiration and ATP accumulation. This regulation was closely linked to a bimodal control of dynein ATPase activity; a direct initial activation with reduction in [Ca2+]i, and subsequent suppression by cytoplasmic acidification caused by lactic acid. These findings not only contribute to advancing poultry liquid semen preservation techniques, but also elucidates biologically relevant mechanisms that may underlie storage within the female reproductive tract in birds.

In Vitro Storage of Functional Sperm at Room Temperature in Zebrafish and Medaka

The longevity of sperm in teleost such as zebrafish and medaka is short when isolated even in saline-balanced solution at a physiological temperature. In contrast, some internal fertilizers exhibit the long-term storage of sperm, >10 months, in the female reproductive tract. This evidence implies that sperm in teleost possesses the ability to survive for a long time under suitable conditions; however, these conditions are not well understood. In this study, we show that the sperm of zebrafish can survive and maintain fertility in L-15-based storage medium supplemented with bovine serum albumin, fetal bovine serum, glucose, and lactic acid for 28 days at room temperature. The fertilized embryos developed to normal fertile adults. This storage medium was effective in medaka sperm stored for 7 days at room temperature. These results suggest that sperm from external fertilizer zebrafish and medaka has the ability to survive for at least 4 and 1 week, respectively, in the body fluid-like medium at a physiological temperature. This sperm storage method allows researchers to ship sperm by low-cost methods and to investigate key factors for motility and fertile ability in those sperm.

Transcriptome analysis of the uterovaginal junction containing sperm storage tubules in heat-stressed breeder hens

Sperm storage tubules (SSTs) in the uterovaginal junction (UVJ) of the oviduct are major sites of sperm storage after artificial insemination or mating. Female birds may regulate sperm motility in the UVJ. Heat stress can decrease the reproductive ability of broiler breeder hens. However, its effects on UVJ remain unclear. Changes in gene expression aid in understanding heat stress-affected molecular mechanisms. Herein, we wanted to conduct a comparative transcriptomic analysis to identify the differentially expressed genes (DEGs) in the UVJ of breeder hens under thermoneutral (23°C) and heat stress (36°C for 6 h) conditions. The results indicated that cloacal temperatures and respiratory rates were significantly increased in heat-stressed breeder hens (P < 0.05). Total RNA was extracted from the hen UVJ tissues containing SSTs after heat exposure. Transcriptome analysis identified 561 DEGs, including 181 upregulated DEGs containing heat shock protein (HSP) transcripts and 380 downregulated DEGs containing immune-related genes, such as interleukin 4-induced 1, radical S-adenosyl methionine domain containing 2, and 2'-5'-oligoadenylate synthetase like, in heat-stressed hens. Gene Ontology analysis revealed the significantly enriched terms involving HSPs. Kyoto Encyclopedia of Genes and Genomes analysis identified 9 significant pathways, including the protein processing in endoplasmic reticulum (11 genes including HSPs), neuroactive ligand-receptor interaction (13 genes including luteinizing hormone/choriogonadotropin receptor), biosynthesis of amino acids (4 genes including tyrosine aminotransferase), ferroptosis (3 genes including heme oxygenase 1), and nitrogen metabolism (carbonic anhydrase [CA]-12 and CA6) pathways. Protein-protein interaction network analysis of DEGs revealed 2 large networks, one containing upregulated HSPs and the other containing downregulated interferon-stimulating genes. Overall, heat stress inhibits innate immunity in the UVJ tissues of broiler chickens, and heat-stressed chickens protect their cells by increasing the expression levels of HSPs. The identified genes are potential candidates for further exploration of the UVJ in heat-stressed hens. The identified molecular pathways and networks increase our understanding of the sperm storage reservoirs (UVJ containing SSTs) within the reproductive tract and may be used to prevent heat stress-induced fertility loss in breeder hens.

A novel protein encoded by circRsrc1 regulates mitochondrial ribosome assembly and translation during spermatogenesis

BACKGROUND

Circular RNAs (circRNAs) are a large class of mammalian RNAs. Several protein products translated by circRNAs have been reported to be involved in the development of various tissues and systems; however, their physiological functions in male reproduction have yet not been explored.

RESULTS

Here, we report an endogenous circRNA (circRsrc1) that encodes a novel 161-amino-acid protein which we named Rsrc1-161aa through circRNA sequencing coupled with mass spectrometry analysis on mouse testicular tissues. Deletion of Rsrc1-161aa in mice impaired male fertility with a significant decrease in sperm count and motility due to dysfunctions of mitochondrial energy metabolism. A series of in vitro rescue experiments revealed that circRsrc1 regulates mitochondrial functions via its encoded protein Rsrc1-161aa. Mechanistically, Rsrc1-161aa directly interacts with mitochondrial protein C1qbp and enhances its binding activity to mitochondrial mRNAs, thereby regulating the assembly of mitochondrial ribosomes and affecting the translation of oxidative phosphorylation (OXPHOS) proteins and mitochondrial energy metabolism.

CONCLUSIONS

Our studies reveal that Rsrc1-161aa protein encoded by circRsrc1 regulates mitochondrial ribosome assembly and translation during spermatogenesis, thereby affecting male fertility.

Long-term sperm storage in eusocial Hymenoptera

In internally fertilizing species, sperm transfer is not always immediately followed by egg fertilization, and female sperm storage (FSS) may occur. FSS is a phenomenon in which females store sperm in a specialized organ for periods lasting from a few hours to several years, depending on the species. Eusocial hymenopterans (ants, social bees, and social wasps) hold the record for FSS duration. In these species, mating takes place during a single nuptial flight that occurs early in adult life for both sexes; they never mate again. Males die quickly after copulation but survive posthumously as sperm stored in their mates' spermathecae. Reproductive females, also known as queens, have a much longer life expectancy, up to 20 years in some species. Here, we review what is currently known about the molecular adaptations underlying the remarkable FSS capacities in eusocial hymenopterans. Because sperm quality is crucial to the reproductive success of both sexes, we also discuss the mechanisms involved in sperm storage and preservation in the male seminal vesicles prior to ejaculation. Finally, we propose future research directions that should broaden our understanding of this unique biological phenomenon.

Abd Elhafeez H, S. Rutland C, M. El-Sherry T. The Relationship of Sperm Motility Pattern and Its Ability to Agglutinate with Vaginal Sperm Selection, Uptake in Sperm Storage Tubules and Competitiveness

To ensure survival, some unique features can be distinguished in birds that help them maintain reproduction. These features include the ability to store sperm for long periods within the utero-vaginal junction, a high sperm concentration per ejaculate, and polyspermy fertilization. Sperm face many challenges prior to fertilization. After copulation, most ejaculated sperm exit the female reproductive tract, and less than 1% continue in an attempt to achieve fertilization. In addition, egg size is substantially larger than sperm size because of the presence of the egg yolk. This results in a large number of sperm penetrating the egg away from the oocyte. These challenges have triggered evolutionary changes to maintain the existence of many species, such as the enormous relative size of the testis, which produces billions of sperm each day, and the ability to store viable sperm for long periods in the oviduct to ensure asynchronous fertilization. This chapter discusses several contemporary and sometimes controversial points regarding sperm behavior and their storage in the oviduct.

Transcriptome identification of genes associated with uterus-vagina junction epithelial folds formation in chicken hens

The development regulation of the uterine-vaginal junction (UVJ) epithelial folds during the sexual maturation of female birds played crucial roles in the adults' sperm storage duration and fertilization capability. However, there is a lack of studies on it in the breeding field of laying hens. In this study, White Leghorn was used for the morphological and developmental studies. According to the morphological characteristics, the development of the UVJ epithelial folds was classified into 4 stages (morphological stage T1-T4). Significant individual differences were observed simultaneously, which is one of the factors leading to the adults' UVJ morphological differences. Bulk RNA-seq suggested the different regulations of UVJ epithelial folds were classified into 3 stages (developmental stage S1-S3). Genes enriched in cell proliferation, differentiation, polarity, migration, adhesion and junction were supposed to regulate UVJ epithelial fold formation. Single-cell RNA-sequencing (scRNA-seq) showed significant differences between different types of cells within UVJ at the developmental stage S2. Immunohistochemical studies confirmed that the different proliferation rates between the epithelium and nonepithelium were one of the key factors leading to the formation of UVJ epithelial folds. Genes in the TGF-beta and WNT pathways may play roles in regulating the proliferation and differentiation of epithelium. Some factors, such as CHD2, CDC42, and carbonic anhydrases, were important participants in forming UVJ epithelial folds. This study will provide new thoughts on the differential regulation of fertilization traits from the developmental biology perspective.

Near-anoxia induces immobilization and sustains viability of sperm stored in ant queens

After copulation, insect females store sperm in a spermatheca for some duration until fertilization. At the beginning of their adult lives, ant queens can preserve numerous viable sperm cells from copulation for over ten years. However, the key factors influencing long-term sperm storage have not been identified. Here we show that the spermathecal environment is nearly anoxic, which induces sperm immobilization. Furthermore, mitochondrial respiratory inhibitors suppress sperm motility, suggesting that sperm immobilization may be caused by a shortage of ATP generated from only glycolysis under near-anoxic conditions. Sperm immobilization is not induced by acidification via glycolytic metabolism because the spermathecal fluid is not acidic. Finally, we show that artificial anoxic conditions rather than aerobic conditions sustain viable sperm cells. Therefore, near-anoxia is a key factor influencing long-term sperm storage in ant queens. The viability of sperm cells under artificial anoxia, however, is lower than that of those dissected immediately from queens. Moreover, the immotile sperm cells under more than 4 h of anoxia do not begin swimming after aerobic exposure, unlike those under anoxic conditions for less than 2 h. This finding indicates that factors other than anoxia are also necessary for long-term sperm preservation.

Supplementation of Schisandrin B in Semen Extender Improves Quality and Oxidation Resistance of Boar Spermatozoa Stored at 4 °C

During cold storage, boar spermatozoa undergo oxidative stress, which can impair sperm function and fertilizing capacity. The objective of the present study was to assess the effects of Schisandrin B (Sch B) in semen extenders on the quality of boar semen stored at hypothermia. Semen was collected from twelve Duroc boars and diluted in extenders supplemented with different concentrations of Sch B (0 μmol/L, 2.5 μmol/L, 5 μmol/L, 10 μmol/L, 20 μmol/L, and 40 μmol/L). Here, we demonstrated that 10 μmol/L Sch B provided the best effects on motility, plasma membrane integrity, acrosome integrity, sperm normality rate, average movement velocity, wobbility, mitochondrial membrane potential (MMP), and DNA integrity of sperm. The results of Sch B effects on antioxidant factors in boar sperm showed that Sch B significantly elevated the total antioxidant capacity (T-AOC) and markedly decreased the reactive oxygen species (ROS) and malondialdehyde (MDA) content of sperm. The expression of catalase (CAT) and superoxide dismutase (SOD) mRNA was increased, while the expression of glutathione peroxidase (GPx) mRNA demonstrated no change compared to non-treated boar sperm. Compared to the non-treated group, Sch B triggered a decrease in Ca²⁺/protein kinase A (PKA) and lactic acid content in boar sperm. Similarly, Sch B led to a statistically higher quantitative expression of AWN mRNA and a lower quantitative expression of porcine seminal protein I (PSP-I) and porcine seminal protein II (PSP-II) mRNA. In a further reverse validation test, no significant difference was observed in any of the parameters, including adhesion protein mRNA, calcium content, lactic acid content, PKA, and protein kinase G (PKG) activity after sperm capacitation. In conclusion, the current study indicates the efficient use of Sch B with a 10 μmol/L concentration in the treatment of boar sperm through its anti-apoptosis, antioxidative, and decapacitative mechanisms, suggesting that Sch B is a novel candidate for improving antioxidation and decapacitation factors in sperm in liquid at 4 °C.

Sperm storage by females across the animal phyla: A survey on the occurrence and biomolecules involved in sperm storage

Long-term sperm storage by females in various regions of the oviduct is documented across many invertebrate and vertebrate species. Although, many reports emphasize on the histology, histochemistry and ultrastructural features of sperm storage, very little is known about the mechanisms underlying the sperm storage. The current review documents the occurrence of sperm storage by females in a wide array of invertebrate and vertebrate species. This review also provides an insight on the presence of various molecular factors of the sperm storage tubules presumably responsible for the prolonged sperm storage with an emphasis on a model reptile, the Indian garden lizard, Calotes versicolor which contains a unique approximately 55-kDa protein in its utero-vaginal lavage and found to inhibit washed epididymal sperm motility in a concentration and time-dependent manner in a reversible fashion.

Pre-but not post-meiotic senescence affects sperm quality and reproductive success in the North African houbara bustard

Age-dependent reduction in reproductive success can arise due to multiple factors including a deterioration of reproductive physiology. Senescing males have been shown to produce ejaculates with poor sperm quality, which impinges on male reproductive success. In addition to individual age, gamete age can also affect male reproductive success. Accordingly, variance in male reproductive success can be due to pre-meiotic (referring to individual age) and post-meiotic senescence (sperm age). Here, we tested whether male senescence and sperm cell aging have additive or interactive effects on male reproductive success in a bird with a promiscuous mating system, the North African houbara bustard. To assess the effect of pre-meiotic aging, we compared male reproductive success between two age classes (3-6- and 12–16-year-old). To infer the effect of post-meiotic aging, male ejaculates were collected at three-time intervals following a common initial collection (day 1, 5, and 10). Therefore, day 1 ejaculates are supposed to contain younger sperm than day 5 and 10 ejaculates. Following controlled artificial inseminations, reproductive success was assessed using three fitness-linked traits (hatching success, chick growth rate and survival). In addition to reproductive output, we also assessed whether pre- and post-meiotic aging affected a wide range of sperm and ejaculate traits. In agreement with previous reports, we found that males in the older age class produced less sperm with poorer motility compared to young individuals. However, contrary to the prediction, we found that ejaculates collected at day 5 and 10 tended to have better sperm traits such as motility and velocity. The results on sperm traits were generally mirrored in the effect on reproductive success since young males produced offspring that grew faster and had better survival during the first month of life, and eggs fertilized by sperm collected at day 5 had the highest hatching success. In any of the models, there was evidence for interactive effects of male and sperm age. Overall, these results confirm the role of pre-meiotic aging on male reproductive success. The lack of evidence for sperm aging could come from the experimental design but might also reflect the pattern of mating frequency in a species with a lek-based mating system.

New insights into sperm rheotaxis, agglutination and bundle formation in Sharkasi chickens based on an in vitro study

Fertility in birds is dependent on their ability to store adequate populations of viable sperm for extended durations in sperm storage tubules (SSTs). The exact mechanisms by which sperm enter, reside, and egress from the SSTs are still controversial. Sharkasi chicken sperm showed a high tendency to agglutinate, forming motile thread-like bundles comprising many cells. Since it is difficult to observe sperm motility and behavior inside the opaque oviduct, we employed a microfluidic device with a microchannel cross-section resembling close to that of sperm glands allowing for the study of sperm agglutination and motility behavior. This study discusses how sperm bundles are formed, how they move, and what role they may have in extending sperm residency inside the SSTs. We investigated sperm velocity and rheotaxis behavior when a fluid flow was generated inside a microfluidic channel by hydrostatic pressure (flow velocity = 33 µm/s). Spermatozoa tended to swim against the flow (positive rheotaxis) and sperm bundles had significantly lower velocity compared to lonesome sperm. Sperm bundles were observed to swim in a spiral-like motion and to grow in length and thickness as more lonesome sperm are recruited. Sperm bundles were observed approaching and adhering to the sidewalls of the microfluidic channels to avoid being swept with fluid flow velocity > 33 µm/s. Scanning and transmission electron microscopy revealed that sperm bundles were supported by a copious dense substance. The findings show the distinct motility of Sharkasi chicken sperm, as well as sperm's capacity to agglutinate and form motile bundles, which provides a better understanding of long-term sperm storage in the SSTs.

In vitro storage of boar spermatozoa increases the demand of ATP for reactivation of motility

BACKGROUND

Prolonging the shelf-life of liquid-preserved semen without compromising its fertilizing capacity may increase the efficiency of artificial insemination in pigs. Many fertilization-relevant processes are ATP dependent. The impact of semen storage and rewarming to body temperature on the energy status of sperm are as yet unknown.

OBJECTIVES

To investigate the energy status of boar spermatozoa during storage and subsequent rewarming, and to reveal the potential role of mitochondrial function for reactivation and maintenance of sperm motility.

MATERIALS AND METHODS

Extended semen samples (n = 7 boars) were used. Spermatozoa were challenged by storage at 17°C for seven days and incubation at 38°C for 180 minutes. The ATP concentration and energy charge (EC) in semen samples and lactate concentration in the extracellular medium were assessed. Viability and mitochondrial activity were determined by flow cytometry, and clustered single cell analysis of motility parameters were performed.

RESULTS

The energy status was not affected by semen storage (p>0.05). Rewarming resulted in a net reduction in ATP concentration which increased with storage time (maximum Day 5: -24.2±10.3 %), but was not accompanied by a loss in viability, motility or mitochondrial activity. Blocking glycolysis with 2-Deoxy-D-glucose prevented re-establishing of motility and mitochondrial activity after rewarming. Mitochondrial activity gradually subsided in virtually all spermatozoa during incubation at 38°C, while ATP and EC remained high. Concomitantly, extracellular lactate levels rose and sperm populations with lower velocity, increased linearity, and low lateral head-displacement grew larger. Size changes for major sperm subpopulations correlated with the percentage of viable sperm with high mitochondrial activity (r = 0.44 to 0.70 for individual subpopulations, p<0.01).

CONCLUSION

Storage of boar spermatozoa increases the demand of ATP for reactivation of sperm towards fast, non-linear and hyperactivation-like motility patterns upon rewarming. Maintenance of glycolysis seems to be decisive for sperm function after long-term storage in vitro. This article is protected by copyright. All rights reserved.

Transcriptome analysis of inseminated sperm storage tubules throughout the duration of fertility in the domestic turkey, Meleagris gallopavo

Sperm storage tubules (SST) are specialized invaginations of the oviductal epithelium that permit avian species to store spermatozoa for extended periods of time, without compromising sperm fertilization capacity. The molecular and physiological mechanisms behind sperm storage tubule differentiation, sperm protection, and regression remain largely unknown, but most likely have potential implications for substantially improving hen fertility, sperm storage, and semen cryopreservation in commercial poultry species. RNA sequencing was performed on sperm storage tubules isolated from the epithelium of the uterovaginal junction (UVJ) from hens at d 1, 7, 30, 60, and 90 postinsemination (n = 4 per timepoint). Read mapping and differential expression analysis were performed using CLC Genomics Workbench. A total of 2,340 differentially expressed genes were subjected to pathway analysis through Ingenuity Pathway Analysis (IPA). Through functional annotation of differentially expressed genes during early, peak, and late egg production, novel insights regarding the role of innate and acquired immune response to sperm, lipid synthesis and transfer, steroid hormone signalling, cytoskeletal reorganization, and regulation of ion homeostasis in SST were obtained. Additionally, potential pathways were identified that could be involved with suppressing sperm motility while sperm reside within the SST. Upstream analysis identified potential regulatory roles for 18 upstream regulators that could modulate sperm storage tubule function, including suppression of sperm motility. Understanding sperm storage tubule function throughout the laying cycle, especially with regards to sperm preservation may allow for the development of industry-based protocols for semen storage and cryopreservation that mimic the sperm preservation capabilities of SST and improve fertility.

Effect of vitamin E supplementation on chicken sperm quality: A meta-analysis

Background and Aim:

Among several factors, the sperm quality of poultry is affected by the rooster’s body size and the availability of antioxidants like vitamin E. This study aimed to determine the effect of dietary vitamin E supplementation on rooster sperm quality through a meta-analysis.

Materials and Methods:

After verification and evaluation, a total of 19 articles were included in this study. Data, including dietary vitamin E, semen volume, concentration, total sperm cells, pH, motility, viability, percentage of dead and abnormal sperm, vitamin E sperm content, malondialdehyde (MDA) content, and testosterone levels, were tabulated in a database; these were subsequently analyzed using mixed modeling with vitamin E dose as a fixed effect and study identity as a random effect.

Results:

Dietary supplementation level of vitamin E significantly (p<0.001) affected sperm concentration, significantly affected motility (p<0.001), significantly affected sperm vitamin E (p<0.001), significantly affected viability (p<0.001), and significantly affected chicken sperm fertility (p=0.001). Vitamin E administration also significantly reduced the number of sperm cell deaths (p<0.001); however, increased dietary levels of vitamin E did not affect semen volume (p=0.853), pH (p=0.951), MDA (p=0.542), the percentage of abnormal sperm cells (p=0.343), nor testosterone levels (p=0.063).

Conclusion:

Dietary vitamin E supplementation is recommended for male chickens since it generally enhances the quality of their sperm.

Sperm Motility Regulation in Male and Female Bird Genital Tracts

Sperm drastically change their flagellar movement in response to the surrounding physical and chemical environment. Testicular sperm are immotile; however, they gain the competence to initiate motility during passage through the male reproductive tract. Once ejaculated, the sperm are activated and promptly initiate motility. Unlike mammals, ejaculated sperm in birds are stored in specialized tubular invaginations referred to as sperm storage tubules (SSTs), located between the vagina and uterus, before fertilization. The resident sperm in the SSTs are in a quiescent state and then re-activated after release from the SSTs. It is thought that avian sperm can undergo motility change from quiescent to active state twice; however, the molecular mechanism underlying sperm motility regulation is poorly understood. In this short review, we summarize the current understanding of sperm motility regulation in male and female bird reproductive tracts. We also describe signal transduction, which regulates sperm motility, mainly derived from in vitro studies.

A 150 kDa Protein Derived from Bull Seminal Plasma Extended the Survival Time of Kacang Goat Sperm Stored at 5°C

Artificial insemination has proven to be an effective method for increasing population size and genetic quality of Kacang goats. However, innovation is required to maintain the quality of Kacang goat semen in storage. This study aimed to examine the effects of supplementing the 150 kDa protein assumed as IGF-I complex derived from bull seminal plasma in skim milk-egg yolk extender on the quality of Kacang goat sperm stored at 5°C. Twelve ejaculates collected from three Kacang goats were divided into three groups. In the control group (T0), the ejaculates were extended with skim milk-egg yolk only. In the treatment groups (T1 and T2), the ejaculates were extended with skim milk-egg yolk supplemented with the IGF-I complex protein at 12 μg and 24 μg/100 mL, respectively. The extended semen was stored at 5°C, and the viability, motility, intactness of the plasma membrane, malondialdehyde concentration, and apoptotic sperm percentage were evaluated daily for five days. The results showed that the T1 was the most effective treatment for maintaining Kacang goat semen at a quality acceptable for artificial insemination over five days of storage at 5°C. However, the T0 and T2 groups retained acceptable qualities for only three days at 5°C. It could be concluded that supplementation of 12 μg of the 150 kDa protein derived from bull seminal plasma per 100 mL extender successfully extended the life span of Kacang goat sperm for five days.

Functional difference of ATP-generating pathways in rooster sperm (Gallus gallus domesticus)

Adenosine triphosphate (ATP) production via glycolysis and oxidative phosphorylation is essential for the maintenance of flagellar motility in sperm; however, the primary energy production pathways supporting fertilization vary among species. Inconsistency in thought exists regarding which pathways maintain ATP production and sperm motility in poultry. Glycolysis and mitochondrial oxidation contribute to flagellar motion in chicken sperm, but the relative dependence on these pathways for motility and penetrability into the inner perivitelline layer remains unclear. In the present study, there was use of various inhibitors and energy substrates to evaluate the relative contribution of anaerobic glycolysis and mitochondrial oxidation to chicken sperm flagellar motility, ATP production, and penetrating capacity through the perivitelline layer. Although both pathways contributed to these processes to varying extent, glucose was the primary substrate for sperm penetration into the inner perivitelline layer in chickens. Furthermore, results from metabolic stress analyses indicated that there was less perivitelline penetrability in response to pyruvate that was not due to changes in reactive oxygen species or intracellular pH. Overall, results from the present study indicate glycolysis and mitochondrial oxidation pathways have distinct functions in the flagellar motility and penetrability of the perivitelline membrane by rooster sperm. There, therefore, are new insights as a result of findings in the present study into the energy production system of sperm through which there is utilization of extracellular metabolic substrates for maintaining sperm fertilization capacity.

Physiological factors influencing female fertility in birds

Fertility is fundamental to reproductive success, but not all copulation attempts result in a fertilized embryo. Fertilization failure is especially costly for females, but we still lack a clear understanding of the causes of variation in female fertility across taxa. Birds make a useful model system for fertility research, partly because their large eggs are easily studied outside of the female's body, but also because of the wealth of data available on the reproductive productivity of commercial birds. Here, we review the factors contributing to female infertility in birds, providing evidence that female fertility traits are understudied relative to male fertility traits, and that avian fertility research has been dominated by studies focused on Galliformes and captive (relative to wild) populations. We then discuss the key stages of the female reproductive cycle where fertility may be compromised, and make recommendations for future research. We particularly emphasize that studies must differentiate between infertility and embryo mortality as causes of hatching failure, and that non-breeding individuals should be monitored more routinely where possible. This review lays the groundwork for developing a clearer understanding of the causes of female infertility, with important consequences for multiple fields including reproductive science, conservation and commercial breeding.

Effect of sperm surface oligosaccharides in sperm passage into sperm storage tubules in Japanese quail (Coturnix japonica)

In birds, the ejaculated spermatozoa do not directly pass to the site of fertilization but rather are stored initially in specialized structures, referred to as sperm storage tubules (SSTs), located in the utero-vaginal junction (UVJ) of the oviduct. The fertilizing capacity of spermatozoa in the SSTs is maintained for an extended period (i.e., several days to months). Although many studies have been conducted to ascertain the mechanisms involved in sperm storage, the understanding of the phenomenon is limited. In this study, there was investigation of the effects of sperm surface oligosaccharides in sperm passage into SSTs in Japanese quail. Results from lectin staining of ejaculated spermatozoa indicated galactose/N-Acetylgalactosamine (Gal/GalNAc), N-Acetylglucosamine (GlcNAc) or mannose/glucose (Man/Glc) moieties were present on the sperm surface, indicating the presence of glycoproteins/glycolipids containing these oligosaccharides. When ejaculated spermatozoa were co-incubated with UVJ explants, the lectins derived from Agaricus bisporus and Canavalia ensiformis had marked inhibitory effects on sperm passage into SSTs. Preincubation of UVJ explants with these lectins, however, had no effect indicating there were no effects of UVJ oligosaccharides in this process. Furthermore, none of these lectin had effects on values of sperm motility variables. These results indicate that O-glycans with terminal β-Gal or GalNAc and N-glycans with terminal α-D-Man or α-D-Glc may have functions in the process of sperm passage into SSTs.

Longer and faster sperm exhibit better fertilization success in Japanese quail

In birds, sperm storage tubules (SST) located in the utero-vaginal junction are thought to be a site of sperm selection; however, the exact mechanism of sperm selection is poorly understood. Here, we investigated sperm entry into the SST and subsequent fertilization success under a competitive situation created by artificial insemination of a sperm mixture obtained from 2 males. We employed 2 quail strains, a wild-type and a dominant black (DB) type, as this allows easy assessment of paternity by feather coloration. We found paternity of embryos was biased toward DB males when a sperm mix with similar sperm numbers from the 2 males strains was artificially inseminated into females. Our novel sperm staining method with 2 different fluorescent dyes showed that the DB-biased fertilization was because of the better ability of DB sperm to enter the SST. Moreover, we found that DB sperm had a longer flagellum and midpiece. These characteristics probably allow sperm to swim faster in a high viscosity medium, which may be a similar environment to the lumen of the female reproductive tract. Our results indicated that sperm competition occurs to win a place in the SST and that filling the SST with their own spermatozoa is a critical step to achieve better fertilization success for the male Japanese quail.

Association of the serum metabolomic profile by nuclear magnetic resonance spectroscopy with sperm parameters: a cross-sectional study of 325 men

OBJECTIVE

To determine whether 155 circulating metabolic measures relevant to lifestyle and metabolic health are associated with sperm parameters, as measured by concentration, motility, and total motile sperm count (TMSC).

STUDY DESIGN

Cross sectional.

SETTING

University hospital.

PATIENT(S)

Three hundred twenty-five men prospectively recruited between April 1, 2017 and March 31, 2019.

INTERVENTION(S)

Detailed demographic, lifestyle, fertility, medical history, and semen analysis with quantification of nonfasting serum lipids, lipoprotein subclasses, and low-molecular weight metabolites (including amino acids, glycolysis, and inflammatory markers) by nuclear magnetic resonance (NMR) spectroscopy.

MAIN OUTCOME MEASURE(S)

Association of serum metabolic profiles with sperm parameters.

RESULT(S)

The age of the participants was mean 37.2 years, with a median sperm concentration of 35 million/mL and median motility of 53%. Of these men, 76% had a TMSC >15 million, 10% had 5-15 million, and 14% had <5 million. In both univariate and confounder adjusted analyses, an extensive range of lipids and lipoproteins, glycolysis-related metabolites, amino acids, ketone bodies, creatinine, or albumin showed no strong statistically significant association with sperm concentration, motility, or the odds of having a reduced or low TMSC. Higher levels of glycolysis metabolites and ketone bodies were associated with an increased odds of TMSC <15 million compared with ≥15 million (odds ratios of ∼1.2-1.3), and several lipids/lipoprotein concentrations appeared to protect against very low TMSC (<5 million compared with ≥5 million) with odds ratios of ∼0.8 or greater.

CONCLUSION(S)

Several metabolites exhibited potentially clinically relevant strength of association with the odds of a low TMSC and warrant replication.

Effects in broiler hens of genetic lines differing in fertility, biotin supplementation, and age on relative abundance of oviductal transforming growth factor-β and carbonic anhydrase mRNA transcripts

There was evaluation of effects of biotin administration on oviductal abundance of transforming growth factor-β (TGF-β) and carbonic anhydrase (CA) mRNA transcript in younger and older broiler hens of relatively lesser and greater fertility lines. Additionally, effects of biotin supplementation on attenuation of age-related subfertility were evaluated. Hens from the relatively greater (Line D, n = 60) and lesser (Line B, n = 60) fertility rate line were randomly assigned to three treatment groups. Biotin was not or was administered in drinking water from 30 to 33 (younger age) and 53 to 56 (older age) wk of age to have access to no biotin (T₀), or 0.3 (T₁), or 0.45 (T₂) mg/L of biotin. There was assessment the relative oviductal abundances of TGF-β and CA mRNA transcript abundances. Supplemental biotin and age had no effect on the relative abundance of oviductal TGF-β mRNA transcript in hens of Line D. There, however, was a ten-fold greater abundance of TGF-β in hens of the T₀ group of Line B compared with Line D. Relative abundance of TGF-β mRNA transcript was greater in younger hens of Line B; however, biotin supplementation of older hens of the T₂ group of Line B resulted in a similar TGF-β abundance to that of younger hens. Inconstant with the TGF-β abundance, CA abundance in hens of Line B was not affected by supplemental biotin or bird age. Overall, differences in TGF-β or CA abundances did not affect fertility of broiler hens.

Detrimental effects of excessive fatty acid secretion on female sperm storage in chickens

Background

Female sperm storage (FSS), the maintenance of sperm inside the female reproductive tract for an extended period of time, is pervasive among organisms with internal fertilization. Because FSS enables asynchronous mating and fertilization, it could be extremely important to reproduction. However, the physiological mechanisms underlying prolonged preservation and maintenance are poorly understood. Here, we used chicken, a typical oviparous animal, to determine the mechanisms ensuring sperm functionality in sperm storage tubules (SSTs).

Results

We performed an insemination experiment on over two thousand hens at two periods, and found that the FSS capabilities varied widely among individuals. Except for the differences in the SST density between the two groups with distinct FSS abilities, we quantitatively profiled small-molecule metabolites derived from SST cells, and identified 28 metabolites with differential expression. In particular, high levels of lipids, fatty acids and lipid peroxidation product were observed in hens with low FSS capability. Pathway analysis showed that these differential metabolites were significantly enriched in the biosynthesis of unsaturated fatty acids. Moreover, we detected the total antioxidant capacity and lipid peroxidation level of SSTs, and found that chickens with a lower FSS ability had a significantly higher content of lipid peroxidation end-product, which was 2.4-fold greater than chickens with a higher FSS capability, and no significant difference was found in the total antioxidant capacity between these two groups.

Conclusions

Our findings reveal that the long-term storage of sperm and the maintenance of their function in the female reproductive tract require an adequate microenvironment. The superabundance of fatty acids secreted by SST cells had detrimental effects on sperm storage in the female reproductive tract. Lipid peroxidation produces toxic biological substances that may cause irreversible damage to resident spermatozoa, resulting in short-term sperm retention and decreased fertility. Our findings provide new avenues for studying sperm storage and sustaining fertility.

Expression of Transferrin and Albumin in the Sperm-Storage Tubules of Japanese Quail and their Possible Involvement in Long-Term Sperm Storage

Because of the presence of sperm storage tubules (SSTs) in the utero-vaginal junction (UVJ) in the oviduct, once ejaculated sperm enter the female reproductive tract, they can survive for a prolonged period in domestic birds; however, the specific mechanisms involved in sperm maintenance within the SST remain to be elucidated. In this study, we showed that transferrin (TF) and albumin (ALB) are expressed in SSTs. When UVJ extracts were subjected to size-exclusion column chromatography, we obtained fractions that extend sperm longevity in vitro. LC-MS/MS analysis of the two major proteins in the fractions identified these proteins as TF and ALB. Immunohistochemical analysis using specific antisera against TF and ALB indicated that both proteins were localized not only in the SSTs, but also in the surface epithelium of the UVJ. When the ejaculated sperm were incubated with either purified TF or ALB, sperm viability increased after 24 h. These results indicated that oviductal TF and ALB are involved in the process of sperm storage in SSTs and may open a new approach for technological improvement to prolong sperm longevity in vitro.

Transcriptome analysis and identification of genes associated with chicken sperm storage duration

The sperm storage tubules located in the mucosal folds of the uterovaginal junction (UVJ) are the primary site of sperm storage in chicken hens after natural mating or artificial insemination (AI). The short-term sperm storage (24 h after mating or AI) in hens was highly associated with immunity and pH-related pathway genes. However, the underlying mechanism of longer duration of sperm storage in female birds remains largely unclear. In the present study, transcriptome analysis was applied to uncover the dynamic gene expression changes in chicken UVJ tissues at two time points (day 3 and day 9) after AI. A total of 574 differentially expressed genes (DEG) were enriched, including 266 upregulated and 308 downregulated DEG. The validation of 5 DEG using quantitative PCR showed a similar expression tendency with RNA sequencing results. The gene ontology terms of DEG were highly enriched in heparin binding (9 genes including COMP, CTGF, and IMPG2), glycosaminoglycan binding (10 genes including PCOLCE, POSTN, and RSPO3), and response to estradiol and ion transport (AREG, RAMP3, SFRP1, and SSTR1). Kyoto encyclopedia of genes and genomes pathway-enrichment analyses of DEG revealed 10 significant pathways (P < 0.05) represented by calcium signaling pathway (7 genes including CACNA1G, PDE1C, PDGFRB, and SLC8A1) and glycosaminoglycan biosynthesis (B3GNT7, CSGALNACT1, GLCE, and ST3GAL1). Protein-protein interaction network of DEG established the connection-regulating epithelial cell or cell-matrix adhesion and migration. The enriched pathways and genes were highly correlated with temporary sperm storage in and possibly sequential sperm release from chicken UVJ overtime after AI. Of these, HIP1, PDE1C, and calcium-related genes were the most interesting candidates associated with sperm storage duration. This report provided a global gene expression profile of the chicken UVJ regarding the capacity of sperm storage overtime after AI. The outcome of this study will contribute to further understanding of the long-term sperm maintenance in avian females and eventually improving the duration of fertile egg performance by selected chicken breeding.

Sperm Gatekeeping: 3D Imaging Reveals a Constricted Entrance to Zebra Finch Sperm Storage Tubules

Females across many internally fertilizing taxa store sperm, often in specialized storage organs in their reproductive tracts. In birds, several hundred sperm storage tubules exist in the utero-vaginal junction of the oviduct, and there is growing evidence that sperm storage in these tubules is selective. The mechanisms underlying female sperm storage in birds remain unknown because of our limited ability to make three-dimensional, live observations inside the large, muscular avian oviduct. Here, we describe a new application of fluorescence selective plane illumination microscopy to optically section oviduct tissue from zebra finch Taeniopygia guttata females label free by harnessing tissue autofluorescence. Our data provide the first description of the three-dimensional structure of sperm storage organs in any vertebrate to the best of our knowledge and reveal the presence of gate-like constricted openings that may play a role in sperm selection.

Role of genome-wide mRNA-seq profiling in understanding the long-term sperm maintenance in the storage tubules of laying hens

Sperm storage function of the sperm storage tubules (SSTs) is directly correlated with the fertility of laying hens. SSTs are located at the utero-vaginal junction (UVJ) and infundibulum of the hen oviduct. However, little is known about the cellular and molecular mechanisms responsible for long-term sperm maintenance in the lumen of the SSTs. In this study, we profiled transcriptomes to detect the different gene expressions between infundibulum and UVJ using RNA-seq. As a result, we identified a total of 1382 differentially expressed genes (DEGs). GO analysis showed that fat acid metabolism, regulation of cell differentiation, regulation of transport, and immune response were enriched for these DEGs, and many of the pH-regulatory functions genes such as CAIV and SLC4A4 were highly expressed in UVJ, which inferred that SSTs could preserve sperm by regulating physiological functions in UVJ. Our results provide new insight to understand the specific function for SSTs to extend sperm life span in the oviduct of laying hens.

A new DNA marker of the TMIGD1 gene used to identify high fertilization rates in Tsaiya ducks (Anas platyrhynchos)

In a prior study, comparisons of individuals of Anas platyrhynchos with higher/lower reproductive performances showed that the expression of the transmembrane and immunoglobulin domain containing 1 (TMIGD1) gene significantly differed between the two groups. Here, we demonstrate that ducks with the TMIGD1 GG genotype have a significantly higher fertilization rate than other TMIGD1 genotypes. Primers designed based on the TMIGD1 sequence of Pekin duck were able to successfully amplify a TMIGD1 fragment from Tsaiya ducks, and sequencing results indicated that a single nucleotide polymorphism (SNP) of the TMIGD1 gene existed. We also developed a cost-effective method of restriction fragment length polymorphism. Using the above methods, ducks were classified into three genotypes. To identify the relationships between genotypes and traits, we recorded the ducks’ performance; to ensure the coverage of the entire duration of the fertile period, the egg collection period was extended to 18 days, and therefore, lower than usual fertilization rates were observed. Further assessment using a high-throughput system showed that the ducks with the GG genotype exhibited the highest fertilization rates among genotypes (P < 0.05). We suggest that TMIGD1 may affect the release of sperm protection factors from the female genital tract, and thus alter fertilization rate. In conclusion, the results of this study demonstrate that the TMIGD1 GG genotype can be used as a new DNA marker to identify animals with high fertilization rates at a young age, a process which could improve farming efficiency.

Insights into pH regulatory mechanisms in mediating spermatozoa functions

Regulation of pH in spermatozoa is a complex and dynamic process as sperm cells encounter different pH gradients during their journey from testes to the site of fertilization in female genital tract. The precise regulations of pH in sperm cells regulate the sperm functions such as motility, hyperactivity, capacitation, and acrosome reaction. Electrophysiological, pharmacological, and molecular studies have revealed the presence of different ion channels and exchanger systems which regulate intracellular pH in sperm cells as well as regulate sperm functions. Recent studies also have shown the potential involvement of pH in the regulation of fertility competence of sperm cells, and alterations in pH have shown to impede sperm functions. This mini-review discusses the probable mechanisms involved in pH regulation in sperm cells and how pH is involved in regulation of various sperm functions.

Expression of gonadotropin and sex steroid hormone receptor mRNA in the utero-vaginal junction containing sperm storage tubules of oviduct during sexual maturation in Japanese quail

Sex steroid hormones play an important role in reproductive tissue development of avian species. However, their role in Japanese quail is yet to be established. To understand the physiological role of hormones involved in the development of sperm storage tubules (SSTs) in quail, we investigated expression profiles of gonadotropin (LH-R and FSH-R) and sex steroid hormone (PR-R, ER-α and ER-β) receptors in the uterovaginal junction (UVJ) containing SSTs before and during sexual maturation i.e. four to eight weeks. Every week four birds were sacrificed to collect blood and UVJ for sex steroid hormone (progesterone and estrogen) estimation and gene expression profiling of sex steroid hormone (PR-R, ER-α and ER-β) and gonadotropin receptors (LH-R and FSH-R) using qRT-PCR. Receptor expression results showed that the expression of sex steroid receptor (PR-R, ER-α and ER-β) genes were upregulated significantly (P < .05) in SSTs with the advancement of age. The expression of gonadotropin receptors (LH-R and FSH-R) was only high at week 5 and 6 respectively. Serum hormone analysis indicated a significant (P < .05) rise in estradiol till 7th week and progesterone from 7th week onwards. These results suggest that the gonadotropin and sex steroid hormone receptors may have the role in the development and maintenance of UVJ that contains predominantly SSTs during sexual maturation.

Age-dependent changes in metabolic profile of turkey spermatozoa as assessed by NMR analysis

Metabolic profile of fresh turkey spermatozoa at three different reproductive period ages, namely 32, 44 and 56 weeks, was monitored by Nuclear Magnetic Resonance (NMR) spectroscopy and correlated to sperm quality parameters. The age-related decrease in sperm quality as indicated by reduction of sperm concentration, sperm mobility and osmotic tolerance was associated to variation in the level of specific water-soluble and liposoluble metabolites. In particular, the highest levels of isoleucine, phenylalanine, leucine, tyrosine and valine were found at 32 weeks of age, whereas aspartate, lactate, creatine, carnitine, acetylcarnitine levels increased during the ageing. Lipid composition also changed during the ageing: diunsaturated fatty acids level increased from 32 to 56 weeks of age, whereas a reduction of polyunsaturated fatty acids content was observed at 56 weeks. The untargeted approach attempts to give a wider picture of metabolic changes occurring in ageing suggesting that the reduction of sperm quality could be due to a progressive deficiency in mitochondrial energy producing systems, as also prompted by the negative correlation found between sperm mobility and the increase in certain mitochondrial metabolites.

Proteinaceous sperm motility inhibitory factor from the female Indian garden lizard Calotes versicolor

Female sperm storage is an intriguing adaptation exhibited by a wide array of both vertebrates and invertebrates. The mechanisms underlying female sperm storage have remained elusive. Using the Indian garden lizard Calotes versicolor as a model organism, we investigated the role of low and high molecular weight factors in this phenomenon. Previously, we demonstrated three distinct phases of the reproductive cycle in this animal with live, motile spermatozoa recovered from the uterovaginal region during the reproductive phase. In the present study, we analysed the uterovaginal contents using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and identified an abundant protein band corresponding to ~55 kDa regardless of the phase of the reproductive cycle. Analysis of the purified protein by liquid chromatography-tandem mass spectrometry suggested a unique protein without any homology to the National Center for Biotechnology Information database. Exogenous addition of this protein to washed spermatozoa derived from the epididymis reversibly inhibited sperm motility in a concentration- and time-dependent manner, suggesting it plays a key role in sperm storage. These studies are likely to offer new avenues to unravel the secrets of female sperm storage seen across the animal taxa and may have novel applications not only in reproductive biology, but also in general cell storage and preserving endangered animal species.

Metabolite availability as a window to view the early embryo microenvironment in vivo

A preimplantation embryo exists independent of blood supply, and relies on energy sources from its in vivo environment (e.g., oviduct and uterine fluid) to sustain its development. The embryos can survive in this aqueous environment because it contains amino acids, proteins, lactate, pyruvate, oxygen, glucose, antioxidants, ions, growth factors, hormones, and phospholipids-albeit the concentration of each component varies by species, stage of the estrous cycle, and anatomical location. The dynamic nature of this environment sustains early development from the one-cell zygote to blastocyst, and is reciprocally influenced by the embryo at each embryonic stage. Focusing on embryo metabolism allowed us to identify how the local environment was deliberately selected to meet the dynamic needs of the preimplantation embryo, and helped reveal approaches to improve the in vitro culture of human embryos for improved implantation rates and pregnancy outcome.

Evidence for Rapid Oxidative Phosphorylation and Lactate Fermentation in Motile Human Sperm by Hyperpolarized 13C Magnetic Resonance Spectroscopy

Poor sperm motility is a common cause of male infertility for which there are no empirical therapies. Sperm motility is powered by adenosine triphosphate but the relative importance of lactate fermentation and Oxidative Phosphorylation (OxPhos) is debated. To study the relationship between energy metabolism and sperm motility we used dissolution Dynamic Nuclear Polarization (dDNP) for the first time to show the rapid conversion of ¹³C₁-pyruvate to lactate and bicarbonate, indicating active glycolytic and OxPhos metabolism in sperm. The magnitude of both lactate and bicarbonate signals were positively correlated with the concentration of progressively motile sperm. After controlling for sperm concentration, increased progressive sperm motility generated more pyruvate conversion to lactate and bicarbonate. The technique of dDNP allows ‘snapshots’ of sperm metabolism to be tracked over the different stages of their life. This may provide help to uncover the causes of poor sperm motility and suggest new approaches for novel treatments or therapies.

Effects of a Protein Kinase Inhibitor on Sperm Motility in the Japanese Quail

Sperm motility is an essential trait for successful fertilization in animals. In birds, ejaculated sperm migrate into sperm storage tubules before fertilization and are stored in a quiescent state. We previously reported that this type of sperm's flagellar quiescence was induced by lactic acid through flagellar dynein ATPase inactivation following cytoplasmic acidification (<pH 6.0). However, signal transduction in the sperm cells leading to motility inactivation is not well understood. The aim of the present study was to investigate the role of protein kinases in putative signal transduction in quail spermatozoa motility in vitro. Following incubation with bisindolylmaleimide II (BisII), a potent-competitive protein kinase C (PKC) inhibitor, sperm motility decreased in a dose related-manner. However, no such inhibitory effect was found in sperm exposed to bisindolylmaleimide V, H-89, or LY294002, a weak inhibitor of PKC, a potent inhibitor of protein kinase A (PKA) and a selective inhibitor of phosphatidylinositol 3-kinase, respectively. BisII-treated sperm exhibited no significant differences in pH _i , [Ca²⁺] _i , mitochondrial activity, intracellular cAMP or ATP concentration, as well as dynein ATPase activity, compared to the control sperm. However, when the phosphorylated substrate proteins by PKC were detected by Western blot analysis, the intensity of the band in sperm incubated in the presence of BisII decreased. Moreover, immunoreactive PKCι and µ isoforms in the sperm lysates were also detected. These results indicated that the PKC signaling pathway may be involved in sperm motility regulation, and protein phosphorylation by PKC may be required to maintain flagellar movement in the Japanese quail.

Sneaker Male Squid Produce Long-lived Spermatozoa by Modulating Their Energy Metabolism

Spermatozoa released by males should remain viable until fertilization. Hence, sperm longevity is governed by intrinsic and environmental factors in accordance with the male mating strategy. However, whether intraspecific variation of insemination modes can impact sperm longevity remains to be elucidated. In the squid Heterololigo bleekeri, male dimorphism (consort and sneaker) is linked to two discontinuous insemination modes that differ in place and time. Notably, only sneaker male spermatozoa inseminated long before egg spawning can be stored in the seminal receptacle. We found that sneaker spermatozoa exhibited greater persistence in fertilization competence and flagellar motility than consort ones because of a larger amount of flagellar glycogen. Sneaker spermatozoa also showed higher capacities in glucose uptake and lactate efflux. Lactic acidosis was considered to stabilize CO2-triggered self-clustering of sneaker spermatozoa, thus establishing hypoxia-induced metabolic changes and sperm survival. These results, together with comparative omics analyses, suggest that postcopulatory reproductive contexts define sperm longevity by modulating the inherent energy levels and metabolic pathways.