Profiles of plasma progesterone before and at the onset of puberty in yak heifers

Characterization of MicroRNA expression profiles in the ovarian tissue of goats during the sexual maturity period

BACKGROUND

The ovary is an important reproductive organ in mammals, and its development directly affects the sexual maturity and reproductive capacity of individuals. MicroRNAs (miRNAs) are recognized as regulators of reproductive physiological processes in various animals and have been shown to regulate ovarian development through typical targeting and translational repression. However, little is known about the regulatory role of miRNAs in ovarian tissue development during sexual maturity in goats. To comprehensively profile the different physiological stages of sexual maturation in goats, we performed small-RNA sequencing of ovarian tissue samples collected at four specific time points (1 day after birth (D1), 2 months old (M2), 4 months old (M4), and 6 months old (M6)). In addition, we used ELISAs to measure serum levels of reproductive hormones to study their temporal changes.

RESULTS

The results showed that serum levels of gonadotropin-releasing hormone, follicle-stimulating hormone, luteinizing hormone, oestradiol, progesterone, oxytocin, and prolactin were lower in goats at the D1 stage than at the other three developmental stages (P < 0.05). The secretion patterns of these seven hormones show a similar trend, with hormone levels reaching their peaks at 4 months of age. A total of 667 miRNAs were detected in 20 libraries, and 254 differentially expressed miRNAs and 3 groups of miRNA clusters that had unique expression patterns were identified (|log2-fold change|> 1, FDR < 0.05) in the 6 comparison groups. RT‒qPCR was employed to confirm that the expression pattern of the 15 selected miRNAs was consistent with the Illumina sequencing results. Gene ontology analyses revealed significant enrichment of GO terms such as cell proliferation regulation, epithelial cell development, and amino acid transport, as well as important signaling pathways including the MAPK signaling pathway, the PI3K-Akt signaling pathway, and the oestrogen signaling pathway. Further miRNA‒mRNA regulation network analysis revealed that 8 differentially expressed miRNAs (chi-miR-1343, chi-miR-328-3p, chi-miR-877-3p, chi-miR-296-3p, chi-miR-128-5p, chi-miR-331-3p, chi-miR-342-5p and chi-miR-34a) have important regulatory roles in ovarian cell proliferation, hormone secretion and metabolism-related biological processes.

CONCLUSIONS

Overall, our study investigated the changes in serum hormone and miRNA levels in the ovaries. These data provide a valuable resource for understanding the molecular regulatory mechanisms of miRNAs in ovarian tissue during the sexual maturity period in goats.

Analysis of serum reproductive hormones and ovarian genes in pubertal female goats

BACKGROUND

Age at puberty is an important factor affecting goat fertility, with endocrine and genetic factors playing a crucial role in the onset of puberty. To better understand the relationship between endocrine and genetic factors and mechanisms underlying puberty onset in goats, reproductive hormone levels were analyzed by ELISA and ultraperformance liquid chromatography-multiple reaction monitoring-multistage/mass spectrometry and RNA sequencing was performed to analyze ovarian genes.

RESULTS

Serum follicle stimulating hormone, luteinizing hormone, estradiol, 11-deoxycortisol, 11-deoxycorticosterone, corticosterone, cortisone, and cortisol levels were found to be higher but progesterone were lower in pubertal goats as compared to those in prepubertal goats (P < 0.05). A total of 18,139 genes were identified in cDNA libraries, and 75 differentially expressed genes (DEGs) were identified (|log₂ fold change|≥ 1, P ≤ 0.05), of which 32 were significantly up- and 43 were down-regulated in pubertal goats. Gene ontology enrichment analyses indicated that DEGs were mainly involved in "metabolic process," "signaling," "reproduction," and "growth." Further, DEGs were significantly enriched in 91 Kyoto Encyclopedia of Genes and Genomes pathways, including estrogen signaling pathway, steroid hormone biosynthesis, and cAMP signaling pathway. Bioinformatics analysis showed that PRLR and THBS1 were highly expressed in pubertal ovaries, and ZP3, ZP4, and ASTL showed low expression, suggesting their involvement in follicular development and lutealization.

CONCLUSIONS

To summarize, serum hormone changes and ovarian DEGs expression were investigated in our study. Further studies are warranted to comprehensively explore the functions of DEGs in goat puberty.

Leukemia inhibitory factor enhances the development and subsequent blastocysts quality of yak oocytes in vitro

Leukemia inhibitory factor (LIF) is a multipotent cytokine of the IL-6 family which plays a critical role in the maturation and development of oocytes. This study evaluated the influence of LIF on the maturation and development ability of yak oocytes, and the quality of subsequent blastocysts under in vitro culture settings. Different concentrations of LIF (0, 25, 50, and 100 ng/mL) were added during the in vitro culture of oocytes to detect the maturation rate of oocytes, levels of mitochondria, reactive oxygen species (ROS), actin, and apoptosis in oocytes, mRNA transcription levels of apoptosis and antioxidant-related genes in oocytes, and total cell number and apoptosis levels in subsequent blastocysts. The findings revealed that 50 ng/mL LIF could significantly increase the maturation rate (p < 0.01), levels of mitochondria (p < 0.01) and actin (p < 0.01), and mRNA transcription levels of anti-apoptotic and antioxidant-related genes in yak oocytes. Also, 50 ng/mL LIF could significantly lower the generation of ROS (p < 0.01) and apoptosis levels of oocytes (p < 0.01). In addition, blastocysts formed from 50 ng/mL LIF-treated oocytes showed significantly larger total cell numbers (p < 0.01) and lower apoptosis rates (p < 0.01) than the control group. In conclusion, the addition of LIF during the in vitro maturation of yak oocytes improved the quality and the competence of maturation and development in oocytes, as well as the quality of subsequent blastocysts. The result of this study provided some insights into the role and function of LIF in vitro yak oocytes maturation, as well as provided fundamental knowledge for assisted reproductive technologies in the yak.

Effect of rapamycin treatment on oocyte in vitro maturation and embryonic development after parthenogenesis in yaks

Autophagy plays an important role in mammalian oocyte maturation and early embryonic development and rapamycin is well known for inducing autophagy. Although previous studies have reported the effects of rapamycin on oocytes in vitro maturation (IVM) in different species, few studies have been reported on the role of rapamycin in yak oocytes IVM and embryonic development. Therefore, the objective of this study was to examine the effect of rapamycin treatment on yak oocytes IVM and early embryonic development. Specifically, immature yak oocytes during IVM or parthenogenetic (PA) embryos were treated with different rapamycin concentrations to select an optimal dose. Then evaluated its effect on maturation rates, cleavage, and blastocyst formation rates, mitochondrial membrane potential, ROS levels. Related genes and proteins expression in matured oocytes and blastocysts were also evaluated. The results show that 10 nM rapamycin treatment during IVM significantly improved oocyte maturation rates of oocytes and blastocyst formation rates. Treatment with 10 nM rapamycin reduced ROS level but increased mitochondrial membrane potential. Correspondingly, mRNA and protein expressions of LC3, Beclin-1, and Bcl-2 up-regulated while Bax down-regulated in matured yak COCs. When parthenogenetic embryos were treated with different rapamycin concentrations, 10 nM rapamycin treatment showed higher 8-cell and blastocyst formation rates. Also, CDX2, POU5F1, SOX2, and Nanog levels in blastocysts were upregulated. In summary, our findings demonstrate that rapamycin treatment improves oocytes maturation probably by increasing mitochondrial membrane potential, reducing ROS levels, and regulating the apoptosis in mature yak oocytes. Rapamycin treatment also improves embryonic developmental competence in the yak.

Ascorbic acid protects the toxic effects of aflatoxin B1 on yak oocyte maturation

High-quality oocytes are a prerequisite for successful fertilization. Mammals feeding on aflatoxin-contaminated feed can cause reproductive toxicity, including follicular atresia, poor oocyte development and maturation, and aberrant epigenetic modifications of oocytes. In addition, the important role of ascorbic acid (AA) in reproductive biology has been confirmed, and AA is widely used as an antioxidant in cell culture. However, the toxic effects of aflatoxin B₁ (AFB₁ ) on yak oocytes and whether AA has protective effects remain unknown. In this study, we found that exposure to AFB₁ impedes meiotic maturation of oocytes, promotes apoptosis by triggering high levels of reactive oxygen species (ROS), and disrupts mitochondrial distribution and actin integrity, resulting in a decrease in the fertilization ability and parthenogenetic development ability of oocytes. In addition, these injuries changed the DNA methylation transferase transcription level of mature oocytes. After adding 50 μg/ml AA, the indices recovered to levels close to those of the control group. The results showed that AA could protect yak oocytes from the toxic effects of AFB₁ and improve the quality of oocytes.

Low oxygen concentration improves yak oocyte maturation and inhibits apoptosis through HIF-1 and VEGF

The gas-phase environment of in vitro culture system plays an important role in the development of oocytes, and oxygen concentration is one of the important factors. In the present study, we aimed to explore the effect of different oxygen concentrations (20%, 10%, 5% or 1% O₂ ) in yak oocyte maturation and to detect the expression of HIF-1α, VEGF and cell apoptosis in yak COCs. First, the maturation rate of oocytes, cleavage rate and blastocysts rate following parthenogenetic activation in the group with 5% oxygen concentration were significantly higher (p < 0.05) than the other groups. Then, TUNEL analysis showed that the 5% oxygen concentration group significantly inhibited apoptosis of cumulus-oocyte complexes (COCs) compared to the other group, and the transcription and protein levels of pro-apoptotic factor Bax, HIF-1α and VEGF in yak COCs significantly reduced, while anti-apoptotic factor Bcl-2 significantly increased. Furthermore, immunohistochemical staining results indicated that HIF-1α protein was mainly located in theca follicle interna, mural follicular stratum granulosum, corona radiata and ovarian stroma in the follicular ovarian tissue; while VEGF protein was mainly located in the granulosa and theca cell layers. In summary, our findings demonstrate that 5% oxygen concentration may promote maturation and inhibit apoptosis of oocytes through HIF-1α-mediated VEGF expression.

Estrogen improves the development of yak (Bos grunniens) oocytes by targeting cumulus expansion and levels of oocyte-secreted factors during in vitro maturation

The estrogen-signalling pathway is critical for normal follicular development; however, little is known about its importance during in vitro maturation (IVM) in large animals, particularly yaks (Bos grunniens). Through the present study, we aimed to determine the mechanisms underlying estrogen involvement in cumulus expansion and the subsequent development of cumulus-oocyte complexes (COCs). COCs were cultured in the maturation medium supplemented with different concentrations (10⁻⁶–10⁻³ mM) of 17β-estradiol (E2) or its receptor antagonist, fulvestrant, and quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and western blot were performed to determine the expression of cumulus-expansion related factors and oocyte-secreted factors (OSFs). The cumulus expansion of COCs was observed using an inverted microscope, and COCs developmental ability were judged by the evaluation of cleavage and blastulation rates per inseminated oocytes by IVF, and the number of cells in the blastocyst. Cumulus expansion increased with 10⁻⁶–10⁻³ mM E2, but decreased with fulvestrant. HAS2, PTGS2, PTX3 and OSFs expression increased in the 10⁻⁶–10⁻³ mM E2 groups. Significantly higher cleavage and blastocyst rates were observed in the 10⁻⁴ mM E2 group than in the fulvestrant and 0 mM E2 groups. Moreover, in the 10⁻⁴ mM group, blastocysts at 7 days had higher cell counts than the other groups. In conclusion, the increase in cumulus expansion and subsequent oocyte development after the addition of E2 to IVM medium may have resulted from increased cumulus-expansion-related factor expression and OSF levels.

Low oxygen concentrations improve yak oocyte maturation and enhance the developmental competence of preimplantation embryos

Mammalian oocyte maturation and early embryo development are highly sensitive to the in vitro culture environment, and oxygen concentration is one of the important factors. In the present study, we aimed to explore the effects of different oxygen concentrations (20%, 10%, 5% or 1% O₂) on yak oocyte maturation, in vitro fertilization (IVF), and embryo development competence, as well as its effects on the oxidative response, metabolism, and apoptosis in cumulus-oocyte complexes (COCs) and the embryo. The results revealed that the maturation rate of oocytes, blastocysts rate and hatched blastocysts rate in the group with 5% oxygen concentration were significantly higher (P < 0.05) than other groups, but the cleavage rate with 5% oxygen concentration was significantly lower (P < 0.05) than the 20% and 10% oxygen concentrations. The maturation rate of oocytes, the cleavage rate, blastocysts rate and hatched blastocysts rate with the 1% oxygen concentration were the lowest. The blastocyst cultured with 5% oxygen concentration had significantly greater (P < 0.05) numbers of total cells, inner cell mass (ICM) cells and trophectoderm (TE) cells compared to the other groups. Analysis of the apoptosis index of oocytes and blastocyst cells by transferase dUTP nick end labeling (TUNEL) showed that the number of apoptotic cells significantly reduced (P < 0.05) with 5% oxygen concentration, but increased significantly (P < 0.05) in the 1% oxygen concentration group. Also, the qRT-PCR and western immunoblotting analysis confirmed that the transcription levels of the metabolism genes, antioxidant response genes, apoptosis genes, oocyte competence genes and embryonic developmental markers showed significant differences (P < 0.05) in the COCs or blastocysts matured in 5% oxygen concentration group compared to the other groups. In summary, our findings demonstrate that 5% oxygen concentration improves oocyte maturation and blastocyst development in the yak, increases blastocyst cell numbers, reduces apoptosis rate in the oocyte and blastocyst as well as reduces embryo cleavage rate.

Transcriptome analysis revealed key signaling networks regulating ovarian activities in the domestic yak

Domestic yaks are the most important livestock species on the Qinghai-Tibetan Plateau. Adult female yaks normally breed in warm season and enter anestrous in cold season. Currently, how the ovarian activity is regulated at the molecular level remains to be determined. This study was conducted to investigate follicular development and gene expression patterns of yak ovarian tissues in the warm and cold seasons. Dynamics of follicular development was evaluated based on histological analyses and global gene expression was examined by using RNA-sequencing (RNA-seq) technology. Firstly, we found that follicle development of yak cows in cold season was different from that in warm season. Interestingly, ovaries collected from yaks in cold season contained a significant higher number of antral follicles and some of these follicles showed signs of polycystic structure, indicating abnormal granulosa cell function. RNA-seq analyses of ovarian tissues from non-pregnant adult yaks in cold and warm season revealed that a list of 320 transcripts were differentially expressed, specifically, 79 were up-regulated and 241 were down-regulated in the ovaries from yaks during the cold season. Further analysis demonstrated that transcripts associated with estrogen secretion and metabolism signaling pathway were altered, including FST, CYP1A1, PIK3R1 and PIK3R2. This study showed histological features of follicle development and revealed candidate genes that may have important roles in regulating ovarian activities in the yak seasonal reproduction.

FGF10 enhances yak oocyte fertilization competence and subsequent blastocyst quality and regulates the levels of CD9, CD81, DNMT1, and DNMT3B

The fusion of sperm and oocytes determines the fertilization competence and subsequent development of embryos, which, in turn, can be affected by various proteins and DNA methylation. However, several factors in this whole regulation process remain unknown, especially in yaks. Here, we report that fibroblast growth factor 10 (FGF10) is an important growth factor that can enhance the maturation rate of yak oocytes and the motility of frozen spermatozoa. Subsequent blastocyst quality was also improved by increasing the total cell number and level of pregnancy-associated protein in blastocysts. These effects were significantly high in the group that received the 5 ng/ml FGF10 treatment, during both in vitro maturation (IVM) and capacitation. Our data show that the effects of FGF10 were dose-dependent at vital steps of embryogenesis in vitro. Furthermore, quantitative polymerase chain reaction, western blot analysis, and immunofluorescence demonstrated that the levels of CD9, CD81, DNMT1, and DNMT3B in both mature cumulus-oocyte complexes and capacitated sperms were regulated by FGF10, which was also highly expressed in the group treated with 5 ng/ml FGF10 during both IVM and capacitation. From our present study, we concluded that FGF10 promotes yak oocyte fertilization competence and subsequent blastocyst quality, and could also regulate CD9, CD81, DNMT1, and DNMT3B to optimize sperm-oocyte interactions and DNA methylation during fertilization.

DNA methylation regulated by ascorbic acids in yak preimplantation embryo helps to improve blastocyst quality

DNA methylation as an important, essential epigenetic modification is critical for the successful development of mammalian embryos. In recent years, the important role of ascorbic acid (AA) as an irreplaceable cofactor for epigenetic regulation has been confirmed. However, the effect of AA on DNA methylation in preimplantation embryo development of plateau yak remains unknown. In this study, we explored whether AA can help regulates DNA methylation in yak preimplantation embryos to improve the blastocyst quality. First, our results indicate that the preimplantation of the yak still follows the classical pattern of DNA demethylation and remethylation, however, remethylation occurs in the blastocyst stage. Second, the unique expression pattern of the ten-eleven translocation enzyme (TET3) in the cytoplasm plays a key role in the demethylation mechanism. Third, in the blastocyst stage, the pluripotency gene CDX2 promoter region was in a hypomethylated state, and the POU5F1, SOX2, and NANOG promoter regions were in moderate methylation states. In addition, treatment with 50 μg/ml AA mainly improved the expression levels of DNMT1, DNMT3a, and TET3, ensured the establishment, maintenance and transition of 5-methylcytosine. After AA treatment, the methylation level of the pluripotency genes NANOG promoter regions was significantly reduced, and the mRNA transcript abundance of the pluripotency genes NANOG, POU5F1, and CDX2 was upregulated. In conclusion, our findings suggest that AA could increase blastocyst cell numbers by regulating DNA methylation of yak preimplantation embryos .

The histological characteristics, age-related thickness change of skin, and expression of the HSPs in the skin during hair cycle in yak (Bos grunniens)

OBJECTIVE

This experiment was conducted to study the histological characteristics, age-related thickness changes, and expression of HSPs in the skin of yak.

METHODS

A total of 20 yaks (10 males and 10 females) were used. Different regions of the normal skin of three different ages (newborn, half-year-old and adult) of yaks were harvested for histological study and thickness measurement. Biopsy samples were taken from the scapula regions of the skin from the same five approximately 1-year-old yaks during the hair cycle (telogen, anagen and catagen). RT-PCR, western blot and immunohistochemistry methods using the mRNA and protein levels were used to detect the expression of HSP27, HSP70 and HSP90. RT-PCR method was used to detect the mRNA expression of CGI-58 and KDF1. The IPP6.0 software was used to analyze the immunohistochemistry and measure the thickness of the skin.

RESULTS

The general histological structure of hairy yak skin was similar to other domestic mammals. The unique features included prominent cutaneous vascular plexuses, underdeveloped sweat glands, a large number of nasolabial glands in the nasolabial plate, and hair follicle groups composed of one primary follicle and several secondary follicles. The skin, epidermis and dermis thickness did vary significantly between different body regions and different ages. The thickness of the skin, epidermis and dermis increased from newborn to adult in yaks. Yak skin thickness decreased from dorsally to ventrally on the trunk. The skin on the lateral surface was thicker than the skin on the medial surface on the limbs. HSP27, HSP70 and HSP90 showed different expression patterns during the hair cycle using RT-PCR, western blot and immunohistochemistry methods. The expression of HSP27 mRNA and protein in the anagen stage was the highest, followed by the catagen stage, and the expression in the telogen stage was the lowest. The expression of HSP70 mRNA and protein in the telogen stage was the highest, followed by the anagen stage, and the expression in the catagen stage was the lowest. The expression of HSP90 mRNA and protein in the anagen stage was the highest, followed by the telogen stage, and the expression in the catagen stage was the lowest. HSPs were mainly expressed in the outer root sheath of hair follicle during the hair cycle, also expressed in epidermis, sebaceous gland and sweat gland in the skin of Yak. The expression of CGI-58 mRNA in the anagen stage was the highest, followed by the catagen stage, and the expression in the telogen stage was the lowest. The expression of KDF1 mRNA in the telogen stage was the highest, followed by the catagen stage, and the expression in the anagen stage was the lowest.

MEANING

In this study, we examined and fully described the histology of normal skin in Yak and measured the skin thickness of different ages and different regions in Yak. These data may be useful to better understand and appreciate the adaptability features of yak skin. Our investigation reports the expression patterns of HSPs in yak skin for the first time. The different expression pattern of HSPs during the hair cycle suggests they may play different roles in yak hair follicle biology.

Colony-stimulating factor 2 enhances the developmental competence of yak (Poephagus grunniens) preimplantation embryos by modulating the expression of heat shock protein 70 kDa 1A

Colony-stimulating factor 2 (CSF₂) is known to promote the development and survival of rodents and ruminants preimplantation embryos; however, the effect of CSF₂ on yak embryos has not been reported. The objective of this study was to investigate the effects of CSF₂ on the developmental competence of yak embryos cultured in vitro in modified synthetic oviduct fluid (mSOF) medium and on the expression pattern of heat shock protein 70 kDa 1A (HSPA1A). In each experiment, cumulus-oocyte complexes (COCs) were matured in vitro and fertilized with frozen-thawed semen. Zygotes were treated with varying concentrations of CSF₂ (0, 10, 50, 100 ng/mL) until day 8 after fertilization. Embryo development was calculated as the percentage of oocytes that formed embryos at the 2-cell, 4-cell, 8-cell, 16-cell, morula and blastocyst stages. The total cell numbers (TCN) per blastocyst and their allocation to the inner cell mass (ICM) and trophectoderm (TE) lineages were determined using differential CDX2 staining. The expression of HSPA1A was examined by quantitative real-time PCR (qRT-PCR) and immunochemistry to determine the mRNA and protein levels. The results showed that treatment with 50 ng/mL CSF₂ significantly (P < 0.05) increased the rate of blastocyst formation (19.01% versus 9.93%) and the TCN per blastocyst (96.94 versus 81.41) compared to the control group. However, no significant differences were observed in the other stages of development. qRT-PCR analysis confirmed that treatment with 50 ng/mL CSF₂ significantly (P < 0.05) inhibited the expression of HSPA1A mRNA in blastocysts cultured in vitro relative to the control group, but there were no significant differences between the other treatment groups. Immunocytochemical analysis confirmed that HSPA1A protein accumulation was gradually reduced in yak blastocysts cultured in 0, 10, 100 or 50 ng/mL CSF₂, however, no significant differences were observed between the 10 and 100 ng/mL treatments (P > 0.05). In conclusion, these findings demonstrate that CSF₂ inhibits the expression of HSPA1A to facilitate yak blastocyst formation and increase cell numbers.

Recombinant Human Bone Morphogenetic Protein 6 Enhances Oocyte Reprogramming Potential and Subsequent Development of the Cloned Yak Embryos

This study investigated the effects of bone morphogenetic protein 6 (BMP6) supplementation in the medium during in vitro maturation (IVM) on the developmental potential of oocytes and in the subsequent development of cloned yak embryos. Cumulus-oocyte complexes (COCs) were aspirated from the antral follicles of yak ovaries and cultured with different concentrations of recombinant human BMP6 in oocyte maturation medium. Following maturation, the metaphase II (MII) oocytes were used for somatic cell nuclear transfer (SCNT), and these were cultured in vitro. The development of blastocysts and cell numbers were detected on day 8. The apoptosis and histone modifications of yak cloned blastocysts were evaluated by detecting the expression of relevant genes and proteins (Bax, Bcl-2, H3K9ac, H3K18ac, and H3K9me3) using relative quantitative RT-PCR or immunofluorescence. The presence of 100 ng/mL BMP6 significantly enhanced the oocyte maturation ratios (66.12 ± 2.04% vs. 73.11 ± 1.38%), cleavage rates (69.40 ± 1.03% vs. 78.16 ± 0.93%), and blastocyst formation rates (20.63 ± 1.32% vs. 28.16 ± 1.67%) of cloned yak embryos. The total blastocysts (85.24 ± 3.12 vs. 103.36 ± 5.28), inner cell mass (ICM) cell numbers (19.59 ± 2.17 vs. 32.20 ± 2.61), and ratio of ICM to trophectoderm (TE) (22.93 ± 1.43% vs. 31.21 ± 1.62%) were also enhanced (p < 0.05). The ratio of the Bax to the Bcl-2 gene was lowest in the SCNT + BMP6 groups (p < 0.05). The H3K9ac and H3K18ac levels were increased in SCNT + BMP6 groups (p < 0.05), whereas the H3K9me3 level was decreased; the differences in blastocysts were not significant (p > 0.05). These study results demonstrate that addition of oocyte maturation medium with recombinant BMP6 enhances yak oocyte developmental potential and the subsequent developmental competence of SCNT embryos, and provides evidence that BMP6 is an important determinant of mammalian oocyte developmental reprogramming.

Developmental competence of mature yak vitrified-warmed oocytes is enhanced by IGF-I via modulation of CIRP during in vitro maturation

The objective of this study was to investigate whether developmental competence of mature vitrified-warmed yak (Bos grunniens) oocytes can be enhanced by supplemented insulin-like growth factor I (IGF-1) during in vitro maturation (IVM), and its relationship with the expression of cold-inducible RNA-binding protein (CIRP). In experiment 1, immature yak oocytes were divided into four groups, and IVM supplemented with 0, 50, 100 and 200 ng/mL IGF-1 was evaluated; the mRNA and protein expression levels of CIRP in mature oocytes in the four groups were evaluated using quantitative real-time PCR and western blotting analyses. In experiment 2, the mature yak oocytes in the four groups were cryopreserved using the Cryotop (CT) method, followed by chemical activation and in vitro culture for two days and eight days to determine cleavage, blastocyst rates, and total cell number in the blastocysts. Mature yak oocytes without vitrification served as a control group. The outcomes were as following: (1) the expression of CIRP in the matured oocytes was up-regulated in the IGF-1 groups and was highest expression was observed in the 100 ng/mL IGF-1 treatment group. (2) In the vitrified-warmed groups, the rates of cleavage and blastocyst were also highest in the 100 ng/mL IGF-1 treatment group (81.04 ± 1.06%% and 32.16 ± 1.01%), which were close to the rates observed in groups without vitrification (83.25 ± 0.85% and 32.54 ± 0.34%). The rates of cleavage and blastocyst in the other vitrified-warmed groups were 70.92 ± 1.32% and 27.33 ± 1.31% (0 ng/mL); 72.73 ± 0.74% and 29.41 ± 0.84% (50 ng/mL); 72.43 ± 0.61% and 27.61 ± 0.59% (200 ng/mL), respectively. There was no significant difference in the total cell number per blastocysts between the vitrified-warmed groups and group without vitrification. Thus, we conclude that the enhancement in developmental competence of mature yak vitrified-warmed oocytes after the addition of IGF-1 during IVM might result from the regulation of CIRP expression in mature yak oocytes prior to vitrification.

Association of heat shock protein 90 with the developmental competence of immature oocytes following Cryotop and solid surface vitrification in yaks (Bos grunniens)

The correlation between the 90 kDa heat-shock protein (HSP90) and the developmental competence of yak (Bos grunniens) oocytes following the process of vitrification has not been studied clearly. In the present study, we compare the efficacies of Cryotop (CT) and solid surface vitrification (SSV) methods for the cryopreservation of immature yak oocytes. Yak cumulus oocyte complexes were randomly allocated into three groups: (1) controls, (2) CT vitrification, and (3) SSV vitrification. Oocytes were vitrified and in vitro maturated and fertilized. The percentages of nuclear maturation and in vitro development were evaluated. The vitrified-warmed oocytes were evaluated for mRNA and protein expression levels of HSP90 using quantitative real-time PCR and western blotting at various stages: matured oocytes, 2-8 cells embryos and blastocysts. No difference was found in the percentages of nuclear maturation, cleavage or blastocyst in the two vitrified groups; however, the rates of maturation were significantly lower than those in the control group. Among the three groups, the maturation rates in CT: 51.14±0.86% and SSV: 50.82±1.34% were less than those of the controls: 69.65±1.13%; the cleavage rates in CT: 39.16±1.01% and SSV: 39.08±0.92%, were less than those of the controls: 58.14±0.76%; but the blastocysts rates and total cell number in the blastocysts were similar: CT: 32.20±0.73% and 104.6±3.72; SSV: 32.35±0.81% and 102.4±1.34; and controls: 34.38±1.32% and 103.8±4.13, respectively. The HSP90 expression level in the matured oocytes and 2-8 cell embryos of the control group was significantly higher than that in the two vitrified groups; there was not significant difference in the blastocysts in the three groups. We thus conclude that CT and SSV perform equally in the vitrification of immature yak oocytes during the process of cryopreservation, and their influence on oocytes mainly occured from the maturation to cleavage stages. The HSP90 levels in the blastocysts of the vitrified groups increased is associated with the developmental competence of the embryo.

Is the yak (Poephagus grunniens L.) really a seasonal breeder?

Yaks are considered to be seasonally polyestrous and breeding occurs from July to November. Here we show that some yaks in peak non-breeding season do exhibit cyclic luteal activity without exhibiting any behavioral signs around expected estrus. A total of eight non-lactating yaks were selected from the Yak Farm belonging to National Research Centre on Yak for various sets of experiments. The animals were maintained as per semi range system of management. They were allowed to graze during daytime and fed concentrate mixture @2 kg/animal/day as per standard farm practices of the center. Blood samples were collected on alternate days for 30 days by jugular venipuncture from the yaks during peak breeding season (July to November) and from the same yaks in non-breeding season (February to March). The plasma samples were analysed for progesterone and estradiol-17beta by RIA and EIA procedures, respectively. During breeding season, the mean plasma progesterone at estrus was basal (<or=0.2 ng/ml) and there after started to increase and reached a peak at days 15-16 of the cycle and then declined rapidly to basal levels at estrus. Mean plasma estradiol-17beta concentrations were high at estrus and then declined to basal level at days 2-3 of the cycle. The mean plasma estradiol-17beta concentrations stayed low for the remaining part of the estrous cycle except for a small elevation, which was exhibited between days 6 and 12 of the cycle. During non-breeding season, in 50% of the animal studied, plasma progesterone and estradiol-17beta levels were at basal level. However, in the remaining animals distinct luteal activity was recorded in terms of plasma progesterone profile. High concentrations of progesterone were maintained in one animal, which suggested existence of cystic corpus luteum. The trend of progesterone and estradiol-17beta profiles in other three animals indicated that they could be cycling although they did not exhibit estrus symptoms. It was concluded from the present study that with improved nutritional support some yaks exhibit estrous cyclicity even during the non-breeding period of the year.

Reproduction in female yaks (Bos grunniens) and opportunities for improvement

This paper reviews seasonal breeding, puberty, postpartum anestrus, embryonic loss and calf survival and their constraints in female yaks. Methods for improving fertility in postpartum yak cows are also considered. Yaks are seasonal breeders with mating and conception restricted in the warm season. Puberty generally occurs in the 2nd to the 4th warm season following birth, i.e. between 13 and 36 months of age. The cows usually have a long postpartum anestrus period; only a small proportion of the cows return to estrus in the 1st breeding season after calving, most come into estrus in the 2nd and 3rd years. Nutritional status is the most important determinant of reproduction in female yaks. Reproductive success is a direct result of the availability of pasture determined by climate, season, and management practices. Milking delays puberty by reducing milk intake (restricted suckling) and growth rate for the calf. Milking interferes with grazing and prolongs the duration of postpartum acyclicity in cows. Calves born early in the season have a longer suckling season than those born later in the season before the onset of winter. Thus, they can have their first cycle in the breeding season of the following year, while those born late in the season may not have their first estrus until 25 or 26 months of age. Cows calving early in the season are more likely to return to estrus in the year of calving because they have a longer period to recover from the demand on body reserves before the onset of winter. Inbreeding in smallholder yak farms is also discussed and minimizing inbreeding by exchanging bulls among different herds is suggested. Reproductive efficiency can be improved by nutritional supplementation during the winter, however, the most cost-effective and practical strategy for this needs to be determined. Early weaning or restricted suckling may shorten the duration of postpartum acyclicity, however, it is impractical due to reduced growth rates and increased winter mortality of early weaned calves. A single treatment with either GnRH, or PGF(2alpha)+GnRH can successfully induce estrus in yak cows that calved in previous years (with or without calf) but did not calve in the current year, however, it has little effect in cows nursing a calf born in the current year. The effects of administration of exogenous progestogens plus GnRH on the fertility of yak cows are worthy of further study.