Molecular characterization of TRIB1 gene and its role in regulation of steroidogenesis in bos grunniens granulosa cells

Differential metabolites screening in yak (Bos grunniens) seminal plasma after cryopreservation and the evaluation of the effect of galactose on post-thaw sperm motility

Sperm survival and activity depend on the provision of energy and nutrients from seminal plasma (SP). This study aimed to investigate the variations of metabolites within SP before and after freezing and subsequently explore the potential regulatory mechanisms affecting yak sperm cryodamage due to changes in metabolites in the SP. Untargeted metabolomics analysis was performed to screen for differential metabolites, followed by KEGG analysis to identify enriched signaling pathways. The combinatorial analysis of metabolomics and sperm proteomics revealed the influence of key SP metabolites on sperm proteins. Subsequently, the relevant differentially expressed proteins were verified by Western blot analysis. Finally, the mechanism underlying the positive effect of galactose on sperm motility was determined by assessing the change in ATP content in sperm before and after freezing and thawing. The data showed that a total of 425 and 269 metabolites were identified in the positive and negative ion modes, respectively. Freezing and thawing resulted in the up-regulation of 70 metabolites and the down-regulation of 29 metabolites in SP. The primary impact of freezing and thawing was observed in carbohydrate metabolism, including pyruvate metabolism, pentose phosphate pathway, galactose metabolism, the TCA cycle, and butanoate metabolism. In the combined analysis and Western blot results, a significant positive correlation was observed between galactose and Aldo-keto reductase family 1 member B1 (AKR1B1) (P < 0.05), which has the ability to convert galactose into galactol. Furthermore, the addition of galactose to thawed semen improved sperm motility by increasing AKR1B1 protein in sperm and was associated with the content of ATP. These data identify differential metabolites between fresh and frozen-thawed SP and suggest that galactose is a valuable additive for cryopreserved sperm, providing a theoretical basis for further exploration of the refrigerant formula for yak sperm cryopreservation.

Dynamic transcriptome analysis of Maiwa yak corpus luteum during the estrous cycle

Maiwa yak is a special breed of animal living on the Qinghai-Tibet Plateau, which has great economic value, but its fertility rate is low. The corpus luteum (CL) is a temporary tissue that plays a crucial role in maintaining the physiological cycle. However, little is known about the transcriptome profile in Maiwa yak CL. In the present study, the transcriptome of Maiwa yak CL at early (EYCL), middle (MYCL) and late-stages (LYCL) was studied employing high-throughput sequencing. A total of 25,922 transcripts were identified, including 22,277 known as well as 3,645 novel ones. Furthermore, 690 and 212 differentially expressed (DE) mRNAs were detected in the EYCL vs. MYCL and MYCL vs. LYCL groups, respectively. KEGG pathway enrichment analysis of DEGs illustrated that the most enriched pathway was PI3K-Akt pathway. Furthermore, twenty-six DEGs were totally found to be associated with different biological processes of CL development. One of these genes, PGRMC1, displayed a dynamical expression trend during the lifespan of yak CL. The knockdown of PGRMC1 in luteinized yak granulosa cells resulted in defective steroidogenesis. In conclusion, this study analyzed the transcriptome profiles in yak CL of different stages, and provided a novel database for analyzing the gene network in yak CL.HIGHLIGHTSThe manuscript analyzed the transcriptome profiles in yak CL during the estrous cycle.Twenty-six DEGs were found to be associated with the development or function of CL.One of the DEGs, PGRMC1, was found to be responsible for steroidogenesis in luteinized yak granulosa cells.

The molecular characteristic analysis of TRIB2 gene and its expressional patterns in Bos grunniens tissue and granulosa cells

Tribbles homolog 2 (TRIB2) plays an important role in the follicular development of female mammals. However, its expression and function in the yak (Bos grunniens) are still unclear. In this study, we predicted the molecular characteristics of TRIB2, and revealed its expression pattern in yak (Bos grunniens) tissues and ovarian granulosa cells. We cloned the full length of the yak TRIB2 gene obtained by RT-PCR was 1368 bp and the coding sequence (CDS) was 624 bp, encoding 207 amino acids (AA). Homology analysis showed that the yak TRIB2 is highly conserved among species. TRIB2 was detected to be extensively expressed in seven tissues of the yak liver, spleen, lung, kidney, ovary, oviduct and uterus by qPCR. The expression of TRIB2 mRNA in the ovary during gestation was significantly lower than that in the non-pregnant (p < 0.05). At each stage of follicle development, the TRIB2 mRNA in granulosa cells showed a significant upward trend with the development of follicles. The expression of TRIB2 gradually decreased with the increase of the culture time of the granulosa cells in vitro. In conclusion, these results suggest that TRIB2 may play an important role in the follicular development of yaks.

Molecular cloning and characterization of STC1 gene and its functional analyses in yak (Bos grunniens) cumulus granulosa cells

Cumulus granulosa cells (CGCs), an important type of ovarian somatic cells, carries out various functions related to oogenesis, follicular development, and steroidogenesis. Studying the biological mechanisms involved in the development and function of CGCs makes a great contribution to understanding the reproductive regulation in female animals. Stanniocalcin-1 (STC1) is an important Ca2+-regulated glycoprotein hormone that exhibits high expression levels in ovaries. In this study, we cloned the coding sequence of the yak STC1, predicted the structure of STC1 protein, detected the expression and localization of STC1 in yak ovaries, and analyzed the functions of STC1 in yak CGCs. The CDS (coding sequence) region of yak STC1 gene was found to be 744 bp and encoded 247 amino acids. Homology comparison revealed that STC1 protein was highly conserved among mammals. The STC1 mRNA displayed dynamic expression profiles in different stages of yak ovaries, and the highest expression was found in the follicular phase. Regarding localization, STC1 protein was widely distributed in various kinds of yak ovarian cells, including oocytes, mural granulosa cells, CGCs, and thecal cells. Repressing the expression of STC1 resulted in defective proliferation and survival of yak CGCs. In addition, knockdown the expression of STC1 repressed the secretion of progesterone and promoted the secretion of estrogen. Overexpression of STC1 partially rescued the proliferation of CGCs and resulted in opposite effects on the secretion of progesterone and estrogen. Several apoptosis and steroidogenesis-related genes, including BAX, BCL2, HSD3B1, HSD17B1, CYP11A1 and CYP17A1 showed altered expressions after repressing or increasing the expression of STC1 in yak CGCs. To the best of our knowledge, this study is the first to focus on the role of STC1 in yak CGCs, and the outcomes offer fresh insights into the mechanism governing yak reproduction.

Effects of vascular endothelial growth factor (VEGF) on the viability, apoptosis and steroidogenesis of yak (Bos grunniens) granulosa cells

Vascular endothelial growth factor (VEGF) is crucial for follicle development through the regulation of granulosa cell (GC) function in some mammals, but its mechanism is unclear in yak (Bos grunniens). Therefore, the objectives of this study were to investigate the effects of VEGF on the viability, apoptosis and steroidogenesis of yak GCs. First, we investigated the localization of VEGF and its receptor (VEGFR2) in yak ovaries by immunohistochemistry analysis and evaluated the effect of culture medium containing different VEGF concentrations and culture times on the viability of yak GCs by Cell Counting Kit-8. Then, optimal treatment with 20 ng/mL VEGF for 24 h was selected to analyze the effects of this compound on intracellular reactive oxygen species levels by DCFH-DA kit, cell cycle and apoptosis by flow cytometry, steroidogenesis by ELISA kit and the expression of the related genes by RT‒qPCR. The results showed that VEGF and VEGFR2 were highly coexpressed in GCs and theca cells. GCs cultured in medium containing 20 ng/mL VEGF for 24 h significantly improved cell viability, decreased ROS production, promoted the transition from G1 phase to S phase (P < 0.05), increased the expression of the CCND1 (P < 0.05), CCNE1, CDK2, CDK4, and PCNA genes (P < 0.01) and decreased the expression of the P53 gene (P < 0.05). This treatment significantly reduced GC apoptosis (P < 0.05) by promoting the expression of BCL2 and GDF9 (P < 0.01) and inhibiting the expression of BAX and CASPASE3 (P < 0.05). VEGF promoted progesterone secretion (P < 0.05) accompanied by increased expression of HSD3B, StAR and CYP11A1 (P < 0.05). Taken together, our findings highlight the beneficial influence exerted by VEGF in improving GC viability and reducing ROS production and the apoptosis rate through the modulation of related gene expression.

TMT-based quantitative proteomics analysis reveals the differential proteins between fresh and frozen-thawed sperm of yak (Bos grunniens)

Sperm cryopreservation is one of the most effective methods for the conservation of germplasm resources and used of superior sires widely. However, the motility of yak (Bos grunniens) sperm was low after thawing and the proteomics changes in sperm cryopreservation remain unknown. Therefore, the aim of this study was to explore the differences between fresh sperm and frozen sperm of yak through the proteomic analysis and thus improve the understanding of sperm cryodamage. The Tandem Mass Tags (TMT) technology was used to screen differentially expressed proteins (DEPs) before and after freezing. Then, GO and KEGG analysis were conducted to analyze the DEPs enriched signaling pathways. Finally, the DEPs, including superoxide dismutase 1 (SOD1) and NADH ubiquinone oxidoreductase core subunit S8 (NDUFS8) were verified by the immunofluorescence technique. The results showed that there were 229 DEPs between fresh and frozen-thawed yak sperm. Compared with the fresh sperm, 120 proteins were up-regulated and 109 proteins were down-regulated in frozen-thawed sperm. The GO annotation showed that the up-regulated proteins enriched in metabolic and cytoskeleton-related processes, including lipoprotein metabolic process, lipid transport, extracellular region and intermediate filament cytoskeleton organization. In contrast, the down-regulated proteins enriched in biological processes including single fertilization, sperm capacitation and response to unfolded protein. KEGG pathway analysis indicated that freezing and thawing affected the oxidative phosphorylation pathway, the fructose and mannose metabolic pathway and the glycerolipid metabolic pathway of yak sperm. Immunofluorescence results showed that the protein expression level of SOD1 protein in the frozen group was significantly lower than that in the fresh group (P < 0.01), and the protein expression level of NDUFS8 protein was significantly higher in frozen group (P < 0.01). This study revealed the DEPs between fresh and frozen-thawed sperm and provides a theoretical basis to further explore the exertion of normal biological functions of yak sperm after freezing and thawing.

Regulation of proliferation, apoptosis, hormone secretion and gene expression by acetyl-L-carnitine in yak (Bos grunniens) granulosa cells

Supplementation with acetyl-l-carnitine (ALC) during in vitro maturation significantly improves the rates of oocyte cleavage and morula and blastocyst formation in sheep and buffalo; however, the mode of action of ALC in improving oocyte competence is not completely understood. Therefore, the aim of this study was to investigate the effects of ALC on proliferation, antioxidant properties, lipid droplet accumulation and steroid hormone secretion in yak (Bos grunniens) granulosa cells (GCs). Yak GCs were identified using FSHR immunofluorescence. The cells were treated with different concentrations of ALC, cell proliferation was detected by cell counting kit-8, and the optimal concentration and treatment time were determined for subsequent experiments. Then, reactive oxygen species (ROS) were detected by a DCFH-DA probe, and lipid droplet accumulation was observed by oil red O staining. Estradiol (E2) and progesterone (P4) in the medium were detected by ELISA, and the expression of genes related to cell proliferation, apoptosis, the cell cycle, antioxidants and steroid synthesis was determined by RT‒qPCR. The results showed that 1 mM ALC treatment for 48 h was the optimum treatment. It significantly increased cell viability (P < 0.05), significantly decreased the amount of ROS and lipid droplet content, and promoted P4 and E2 secretion (P < 0.05) of yak GCs. RT‒qPCR results verified that GCs treated with 1 mM ALC for 48 h significantly increased the expression of genes related to anti-apoptosis and the cell cycle (BCL-2, PCNA, CCND1 and CCNB1), antioxidants (CAT, SOD2 and GPX1), and E2 and P4 secretion (StAR, CYP19A1 and HSD3B1) (P < 0.05), but it significantly decreased the expression of apoptosis genes (BAX and P53) (P < 0.05). In conclusion, ALC increased the viability of yak GCs, reduced the amount of ROS and lipid droplets, increased P4 and E2 synthesis and affected the expression of related genes in yak GCs.

The Biological Characteristics and Differential Expression Patterns of TSSK1B Gene in Yak and Its Infertile Hybrid Offspring

This study aimed to investigate the spatially and temporally expressed patterns and biological characteristics of TSSK1B in male yaks and explore the potential correlation between TSSK1B and male sterility of the yak hybrid offspring (termed cattle-yak). First, the coding sequence (CDS) of TSSK1B was cloned by RT-PCR, and bioinformatics analysis was conducted with relevant software. Quantitative real-time PCR (RT-qPCR) was employed to detect the expression profile of TSSK1B in various tissues of male adult yaks, the spatiotemporal expression of TSSK1B in different stages of yak testes, and the differential expression of TSSK1B between yak and cattle-yak testes. The cellular localization of TSSK1B was determined by immunohistochemistry (IHC). Furthermore, the methylation status of the TSSK1B promoter region was analyzed by bisulfite-sequencing PCR (BSP). The results showed that TSSK1B was 1235 bp long, including 1104 bp of the CDS region, which encoded 367 amino acids. It was a conserved gene sharing the highest homology with Bos mutus (99.67%). In addition, the bioinformatics analysis revealed that TSSK1B was an unstable hydrophilic protein mainly containing the alpha helix of 34.06% and a random coil of 44.41%, with a transmembrane structure of 29 amino acids long. The RT-qPCR results demonstrated that TSSK1B was specifically expressed in yak testes compared with that in other tissues and especially highly expressed in adult yak testes. On the contrary, TSSK1B was hardly expressed in the testis of adult cattle-yak. IHC confirmed that TSSK1B protein was more strongly expressed in the testes of adult yaks than in their fetal and juvenile counterparts. Interestingly, nearly no expression was observed in the testes of cattle-yak compared with the corresponding testes of yak. Bisulfite-sequencing PCR (BSP) revealed that the methylated CpG sites in the TSSK1B promoter region of cattle-yak was significantly higher than that in the yak. Taken together, this study revealed that TSSK1B was specifically expressed in yak testes and highly expressed upon sexual maturity. Moreover, the rare expression in cattle-yak may be related to the hypermethylation of the promoter region, thereby providing a basis for further studies on the regulatory mechanism of TSSK1B in male cattle-yak sterility.