Oxytocin receptor expression in stallion testes and epididymides

Changes in characteristics of spermatogonial stem cells in response to heat stress in stallions

Spermatogonial stem cells (SSCs) are essential for the maintenance of male fertility and survival of species. Environmental conditions, notably heat stress, have been identified as important causes of male infertility and have a negative impact on SSCs. Animals with cryptorchid testes (CT) are optimal models for the study of long-term heat stress-related changes in germ cells. The effect of heat stress on germ cells differs depending on the spermatogenesis stage. Thus, verifying whether the specific phase of spermatogenesis is dependent or independent of heat stress in stallions is important. We evaluated the heat stress-related response of SSCs by comparing the relative abundance of mRNA transcripts and expression patterns of the undifferentiated embryonic cell transcription factor 1 (UTF-1) and deleted in azoospermia-like (DAZL) in the seminiferous tubules of CT and normal testes (NT) of stallions using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), immunofluorescence, and western blotting. We also analyzed the relative abundance of mRNA of different proliferative markers, including minichromosome maintenance 2 (MCM2), marker of proliferation Ki-67 (MKI-67), and proliferating cell nuclear antigen (PCNA). Testicular tissues from four Thoroughbred unilateral cryptorchid postpubertal stallions were used in this study during the breeding season. The relative abundance of the mRNA transcripts of UTF-1 and MCM2 was significantly upregulated in the CT group than that of those in the NT group. In contrast, the relative abundance of the mRNA transcripts of DAZL was significantly downregulated in the CT group than that of those in the NT group. Western blot quantification showed that the relative intensity of UTF-1 protein bands was significantly higher, while that of DAZL protein bands was significantly lower in the CT group than in the NT group. Immunofluorescence studies showed that the number of germ cells immunostained with UTF-1 was significantly higher while immunostained with DAZL was significantly lower in the CT group than that in the NT group. The higher expression level of UTF-1 in the CT group shows that undifferentiated SSCs are not affected by long-term exposure to heat stress. These results also indicate that germ cells after differentiation phase are directly affected by heat-stress conditions, such as cryptorchidism, in stallions.

Systematic review of hormonal strategies to improve fertility in rams

Reviewing the current state of knowledge on reproductive performance and productive traits in rams has many advantages. First, the compilation of this information will serve as a literature resource for scientists conducting research around the world and will contribute to the understanding of the data collected and interpreted by researchers on the different hormonal strategies used to improve reproductive performance in rams. Second, it will allow scientists to identify current knowledge gaps and set future research priorities in ram reproduction. Rams play an important role in the global flock economy, but their reproductive analysis has been limited in the use of hormonal technologies to increase the productivity of sheep flocks. In this review, we cite the most important works on six hormones that, in one way or another, modify the hypothalamus-pituitary-gonadal axis, at different doses, in and out of the reproductive season, breeds, application methods, among other factors. The overall aim is to increase the reproductive efficiency of rams in different scenarios and, in some cases, of other species due to the lack of limited information on rams.

Expression pattern of germ cell markers in cryptorchid stallion testes

Cryptorchidism affects spermatogenesis and testis development, often resulting in stallion subfertility/infertility. This study aims to identify the specific germ cells impacted by cryptorchism in stallions. In a previous study, we found that PGP9.5 and VASA are molecular markers expressed in different germ cells within stallions. Herein, we assessed the heat stress-induced response of spermatogonial stem cells (SSCs) in the seminiferous tubules (ST) of cryptorchid stallion testes (CST) and normal stallion testes (NST). This goal was accomplished by comparing PGP9.5 and VASA expression patterns through reverse transcription quantitative PCR and immunofluorescence assays. We also compared the cross-sectional ST area between groups. Six post-pubertal Thoroughbred unilateral cryptorchid stallions were used. The relative abundance of the mRNA transcripts of PGP9.5 and VASA was significantly upregulated in the NST group than in the CST group. Additionally, the cross-sectional ST area and localization of PGP9.5 and VASA in germ cells were significantly higher in the NST group than in the CST group. Regarding Leydig cells, PGP9.5 staining was observed in both groups. Spermatogonia, primary spermatocytes and secondary spermatocytes were immunostained with VASA in the NST group, while immunostaining was only observed in spermatogonia in the CST group. These results indicate long-term exposure to heat stress conditions, such as cryptorchidism, directly impacts germ cell proliferation and differentiation, leading to impaired spermatogenesis and compromised fertility in stallions.

Transcriptomic analysis of the HPG axis-related tissues reveals potential candidate genes and regulatory pathways associated with testicular size in Hu sheep

Testicular size is an excellent proxy for selecting high-fertility rams. The hypothalamus-pituitary-gonadal (HPG) axis plays an important role in regulating reproductive capacity in vertebrates, while key genes and regulatory pathways within the HPG axis associated with testicular size remain largely unknown in sheep. This study comprehensively compared the transcriptomic profiles in the hypothalamus, pituitary and testis of rams after sexual maturity between the large-testis group (LTG, testicular weight = 454.29 ± 54.24 g) and the small-testis group (STG, testicular weight = 77.29 ± 10.76 g). In total, 914, 795 and 10518 differentially expressed genes (DEGs) were identified in the hypothalamus, pituitary and testis between LTG and STG, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that these DEGs were mainly involved in the biological processes of reproduction, biological regulation, and development process. Notably, the neuroactive ligand-receptor interaction and cAMP signaling pathways, commonly enriched by the DEGs in the hypothalamus and pituitary between two groups, were considered as two key signal pathways regulating testicular development through the HPGs axis. Weighted gene co-expression network analysis (WGCNA) identified two modules that were significantly associated with testicular size, and 97 key genes were selected with high module membership (MM) and gene significance (GS) in these two modules. Finally, a protein-protein interaction (PPI) network was constructed, and ten genes with the highest degree were represented as hub genes, including FOS, NPY, SST, F2, AGT, NTS, OXT, EDN1, VIP and TAC1. Taken together, these results provide new insights into the molecular mechanism underlying the HPG axis regulating testicular size of Hu sheep.

Embryo developmental toxicity in marine medaka (Oryzias melastigma) due to parental and embryonic 17α-ethinylestradiol exposure

The synthetic estrogen 17α-ethinylestradiol (EE2) is a common component of hormone therapy and oral contraceptives and has been widely used for nearly 60 years. Numerous studies have shown that exposure to EE2 can affect embryonic development in a number of fish species. The effects of parental and embryonic EE2 exposure on embryo developmental toxicity and the underlying molecular mechanisms, however, have rarely been examined. In this study, embryos collected from parental EE2-exposed adult fish were examined to assess EE2-induecd toxicity during embryo development. The rate of embryo development including heart rate, hatching rate, and larval locomotion were measured to assess embryo developmental toxicity. The embryonic transcriptome was used to delineate the related developmental toxicity pathways. Our results suggest that parental and embryonic EE2 exposure resulted in growth retardation including a reduction in embryo heart rate, a delay in the appearance eye pigmentation, decreased hatching rate and impaired larval locomotion. In addition, gene ontology (GO) enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and Ingenuity Pathway Analysis (IPA) of transcriptome revealed that these impairments are controlled by estrogen receptor and related to eye structure, neuronal and synaptic structure, and behaviour. The key factors identified, including PRKAA2, APOB, EPHB2, OXTR, NR2E3, and POU4F2, could serve as biomarkers for assessing EE2-induced embryo developmental toxicity. For the first time, our results show that eye pigmentation is a potentially sensitive marker of EE2-induced embryo developmental toxicity.

Functions of somatic cells for spermatogenesis in stallions

Spermatogenesis and testis development are highly structured physiological processes responsible for post-pubertal fertility in stallions. Spermatogenesis comprises spermatocytogenesis, meiosis, and spermiogenesis. Although germ cell degeneration is a continuous process, its effects are more pronounced during spermatocytogenesis and meiosis. The productivity and efficiency of spermatogenesis are directly linked to pubertal development, degenerated germ cell populations, aging, nutrition, and season of the year in stallions. The multiplex interplay of germ cells with somatic cells, endocrine and paracrine factors, growth factors, and signaling molecules contributes to the regulation of spermatogenesis. A cell-to-cell communication within the testes of these factors is a fundamental requirement of normal spermatogenesis. A noteworthy development has been made recently on discovering the effects of different somatic cells including Leydig, Sertoli, and peritubular myoid cells on manipulation the fate of spermatogonial stem cells. In this review, we discuss the self-renewal, differentiation, and apoptotic roles of somatic cells and the relationship between somatic and germ cells during normal spermatogenesis. We also summarize the roles of different growth factors, their paracrine/endocrine/autocrine pathways, and the different cytokines associated with spermatogenesis. Furthermore, we highlight important matters for further studies on the regulation of spermatogenesis. This review presents an insight into the mechanism of spermatogenesis, and helpful in developing better understanding of the functions of somatic cells, particularly in stallions and would offer new research goals for developing curative techniques to address infertility/subfertility in stallions.

Expression of oxytocin receptors and oxytocin assisted electroejaculation in the domestic cat (Felis catus)

Oxytocin is a peptide hormone that mainly functions to control the contractility of smooth muscles and sex related steroidogenesis in male reproductive tracts. However, specific information concerning this hormone in controlling the reproductive organs of cats is limited. This study aimed to investigate the expression of oxytocin receptors (OTRs) and their signal mediator via prostacyclin synthase (PTGIS) in reproductive structures following oxytocin assisted electroejaculation. In Experiment 1, the testis, cauda epididymis and vas deferens from five cats were examined by immunohistochemistry and quantitative polymerase chain reaction in order to study the responses of OTR and PTGIS mRNA to oxytocin injection. Experiment 2 examined the effect of oxytocin administration prior to electroejaculation on ejaculate characteristics and sperm quality in terms of motility, viability and fertilising ability. Immunohistochemistry revealed the expression of OTRs in Leydig's, peritubular myoid cells and some spermatogenic cells. The expression was found in the epithelium and smooth muscle of the epididymis and vas deferens. After oxytocin administration, the OTR mRNA was upregulated in the epididymis (p > 0.05) and vas deferens (p = 0.01). The expression level of PTGIS mRNA increased in the response to oxytocin treatment only for the vas deferens (p > 0.05). Oxytocin treatment before electroejaculation resulted in an approximately two-fold increase in sperm concentration and total sperm output/ejaculate, while this intervention did not significantly affect ejaculate volume, sperm quality or fertilising ability. This study concluded that the oxytocin cascade is locally present in the reproductive structures and plays a role in promoting sperm delivery during electroejaculation in cats.

Oxytocin in pig seminal plasma is positively related with in vivo fertility of inseminated sows

BACKGROUND

Identification of relevant in vivo biomarkers for fertility remains a challenge for the livestock industry. Concentrations of the small peptide hormone oxytocin (OXT), involved in male reproductive function and present in the seminal plasma (SP) of several species could be a robust one. This study characterized concentrations of SP-OXT in ejaculates from boars used in artificial insemination (AI) programs aiming to evaluate its relationship with sperm quality variables and in vivo fertility of their liquid-stored AI-semen. Seminal OXT concentrations (ng/mL) were measured in 169 ejaculates from 61 boars of the Duroc, Pietrain, Landrace and Large White breeds using a direct competitive immunoassay test based on AlphaLISA^® technology. Ejaculate (ejaculate volume, sperm concentration, total sperm count) and sperm parameters (motility, viability, intracellular generation of reactive oxygen species, plasma membrane fluidity) were assessed at 0 h and 72 h in AI-semen samples stored at 17 °C. In vivo fertility included only 18 Large White and Landrace boars whose AI-semen was used to inseminated > 100 sows and evaluated both farrowing rate and litter size of 3,167 sows.

RESULTS

The results showed that SP-OXT differed between boars and between ejaculates within boar (P < 0.05) but not between breeds (Duroc, Pietrain, Landrace and Large White). Ejaculates with higher SP-OXT concentration/mL (hierarchically grouped; P < 0.001) had larger volume and came from younger boars (P < 0.05). Ejaculates of boars showing positive farrowing rate deviation exhibited higher (P < 0.05) SP-OXT concentration/mL than those with negative farrowing rate deviation.

CONCLUSION

The SP concentrations of OXT are boar, ejaculate and age dependent, and positively related with ejaculate volume and farrowing rates of liquid-stored semen AI-doses.

Exogenous oxytocin administration improves the testicular blood flow in rams

The current research aimed to examine the effects of single-dose oxytocin administration on testicular blood flow measurements peak systolic velocity (PSV), end-diastolic velocity (EDV), resistive index (RI) and pulsatility index (PI) and plasma steroid (testosterone and oestradiol-17β) concentrations in rams. In the treated group, eight mature Ossimi rams during the breeding season were injected intravenously (iv) with 20 IU oxytocin, while the other eight male rams were administered normal saline (2 ml) iv as a control group. Venous blood samples and testicular blood flow in the left and right testes were examined immediately before (0) and 5, 30, 60 and 120 min after injections. The control group did not show significant changes in the variables examined (p > .05), except for the EDV (p < .05). In the treated group, the administration of oxytocin led to a significant decrease in RI and PI values starting 5 min after oxytocin administration until 60 min after its application (p < .05). The plasma concentrations of testosterone and oestradiol-17β raised from 5 to 30 min after oxytocin injection (p > .05) and then declined significantly until 120 min (p < .05). In conclusion, oxytocin is a potent testicular vasodilator affecting the testicular vascular tone and steroid concentrations in rams.