Germ cell development in Meishan and White Composite gilts

Cellular Processes in Human Ovarian Follicles Are Regulated by Expression Profile of New Gene Markers—Clinical Approach

In the growing ovarian follicle, the maturing oocyte is accompanied by cumulus (CCs) and granulosa (GCs) cells. Currently, there remain many unanswered questions about the epithelial origin of these cells. Global and targeted gene transcript levels were assessed on 1, 7, 15, 30 days of culture for CCs and GCs. Detailed analysis of the genes belonging to epithelial cell-associated ontological groups allowed us to assess a total of 168 genes expressed in CCs (97 genes) and GCs (71 genes) during long-term in vitro culture. Expression changes of the analyzed genes allowed the identification of the group of genes: TGFBR3, PTGS2, PRKX, AHI1, and IL11, whose expression decreased the most and the group of ANXA3, DKK1, CCND1, STC1, CAV1, and SFRP4 genes, whose expression significantly increased. These genes’ expression indicates CCs and GCs epithelialization processes and their epithelial origin. Expression change analysis of genes involved in epithelization processes in GCs and CCs during their in vitro culture made it possible to describe the most significantly altered of the 11 genes. Detailed analysis of gene expression in these two cell populations at different time intervals confirms their ovarian surface epithelial origin. Furthermore, some gene expression profiles appear to have tumorigenic properties, suggesting that granulosa cells may play a role in cancerogenesis.

Association analysis of mitochondrial DNA polymorphisms with oocyte number in pigs

In pigs, correlations between mitochondrial (mt) DNA polymorphisms and economic traits have been widely reported across and within swine breeds. In fecundity studies, the number of oocytes within ovaries was highly correlated with litter size. However, the effect of mitochondrial polymorphisms on porcine oocyte number remained unclear. In this study, 181 porcine ovaries were collected to analyse the relationship between oocyte number and mtDNA polymorphisms. There were considerable differences in oocyte numbers among different ovaries from commercial pig breeds, ranging from 2.7×105 to 1.3×106. Mitochondrial D-loop sequencing discovered 53 polymorphic sites. Association analysis revealed that 13 variations were associated with the number of oocytes (P<0.05). A C323T polymorphism showed the largest value between the C and T carriers, which differed at 105 oocytes (P<0.05). The 53 polymorphic sites generated 45 haplotypes, which clustered into two haplogroups, A and B. Haplogroup A had a higher number of oocytes than Haplogroup B (P<0.05), whereas Haplotype H6 in Haplogroup A had the highest number of oocytes (~7.5×105) of all haplotypes studied (P<0.05). The results of this study highlight a correlation between mtDNA polymorphisms and oocyte number, and suggest the potential application of mtDNA polymorphism analyses in pig selection and breeding practices.

Dynamic DNA methylation of ovaries during pubertal transition in gilts

Background

In female mammals, the initiation of puberty, coupling with the dramatically morphological changes in ovaries, indicates the sexual and follicular maturation. Previous studies have suggested that the disrupted DNA methylation results in the delayed puberty. However, to date, the changes in ovarian methylomes during pubertal transition have not been investigated. In this study, using gilts as a pubertal model, the genome-wide DNA methylation were profiled to explore their dynamics during pubertal transition across Pre-, In- and Post-puberty.

Results

During pubertal transition, the follicles underwent maturation and luteinization, coupled with the significant changes in the mRNA expression of DNMT1 and DNMT3a. DNA methylation levels of In-puberty were higher than that of Pre- and Post-puberty at the locations of genes and CpG islands (CGIs). Analysis of the DNA methylation changes identified 12,313, 20,960 and 17,694 differentially methylated CpGs (DMCs) for the comparisons of Pre- vs. In-, In vs. Post-, and Pre- vs. Post-puberty, respectively. Moreover, the CGIs, upstream and exonic regions showed a significant underrepresentation of DMCs, but the CGI shores, CGI shelves, intronic, downstream and intergenic regions showed a significant overrepresentation of DMCs. Furthermore, biological functions of these methylation changes enriched in PI3K-Akt signaling pathway, GnRH signaling pathway, and Insulin secretion, and the mRNA expressions of several genes of these signaling pathway, including MMP2, ESR1, GSK3B, FGF21, IGF1R, and TAC3, were significantly changed across Pre-, In- and Post-puberty in ovaries.

Conclusions

During pubertal transition in gilts, the DNA methylation changes of ovaries were likely to affect the transcription of genes related to PI3K-Akt signaling pathway, GnRH signaling pathway, and Insulin secretion. These observations can provide new insight into the epigenetic mechanism of follicular and sexual maturation during pubertal transition in mammals.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5884-x) contains supplementary material, which is available to authorized users.

Developmental ability of oocytes retrieved from Meishan neonatal ovarian tissue grafted into nude mice

Ovarian xenografting makes it possible to obtain oocytes with fertilization ability from immature pigs of Western breeds. In this study, we applied these methods to the Meishan, an indigenous Chinese pig breed, and investigated the developmental competence of oocytes grown in their neonatal tissue after grafting into nude mice. First, mice harboring neonatal ovarian tissue were infused with follicle stimulating hormone (FSH) (62.5 U/ml) for 13 days starting at 10, 30, and 60 days after vaginal opening (D10‐, D30‐, and D60‐FSH groups, respectively). Development of antral follicles and their oocytes was most enhanced in the D60‐FSH group. For the next step, we examined the in vitro maturation ability of the oocytes recovered from host mice after infusion with FSH at a dose of 62.5 U/ml or 125 U/ml (FSH‐62.5 or ‐125 group) for 13 days starting at 60 days after vaginal opening. Many more oocytes with maturation ability were obtained from the FSH‐125 group. The FSH‐125 mature oocytes were fertilized in vitro, as shown by formation of male and female pronuclei, but did not reach the blastocyst stage. These results indicate that Meishan neonatal ovaries are able to produce oocytes with fertilization ability after being grafted into nude mice.

Anti-Müllerian hormone and Oestradiol as markers of future reproductive success in juvenile gilts

There is a need for an early marker for reproductive success in gilts as the traditional process for selecting breeding females is inefficient. There is evidence that circulating anti-Müllerian hormone (AMH) is indicative of ovarian reserve, antral follicle populations, gonadotropin responsiveness and fertility in various species other than the pig. Additionally, oestradiol (E2) has been shown to mark antral follicle populations in cattle and pregnancy outcomes in women, after gonadotropin treatment. The aims of this study were to determine whether 1) serum levels of AMH or E2, prior to or after gonadotropin injection at 60, 80 or 100 days of age, and 2) hormonal changes in response to gonadotropin stimulation (i.e. declining, plateauing or increasing hormone levels), are associated with future reproductive success in juvenile gilts. Serum samples were obtained at 0, 2 and 4 days after injection and mating and litter data were collected until parity three. Results showed that, regardless of age group and parity, Day 0 E2 levels were positively associated with the probability of stillbirth (P = 0.035) and E2 levels on Day 0 (P = 0.032), Day 2 (P = 0.045) and Day 4 (P = 0.019) were negatively associated with the number of piglets born alive. Further, both a single measurement of serum AMH levels at Day 2 (P = 0.048) and the AMH response type were associated with gestation length (P = 0.012). These findings suggest that serum AMH and E2 levels can be used to inform the selection of gilts for the breeding herd.

Quantitative proteomic profiling indicates the difference in reproductive efficiency between Meishan and Duroc boar spermatozoa

The reproductive efficiency of Meishan pigs is higher than that of Duroc pigs, but the underlying molecular mechanism for this disparity remains unclear. No systematic quantitative proteomics studies, comparing global proteins in Meishan and Duroc boar spermatozoa have been reported. Therefore, we applied iTRAQ labeling coupled with mass spectrometry, and analyzed the differences in proteins between Meishan and Duroc sperm. In the present study, a total of 1597 proteins were quantified. Of these proteins, 190 showed statistically significant fold changes between Meishan and Duroc spermatozoa. Bioinformatics analysis revealed that these differentially abundant proteins were primarily involved in energy metabolism, sperm motility, capacitation and sperm-oocyte binding. Remarkably, SPAG6, ACR, LDHC, CALM, ACE and ENO1 which are positively related to high litter size, were more abundant in Meishan spermatozoa than in Duroc spermatozoa. Moreover, APOA1, NDUFS2 and RAB2A which are negatively related to farrowing rates, were less abundant in Meishan spermatozoa than in Duroc spermatozoa. Interestingly, essential enzymes in Glycolysis/Gluconeogenesis, such as HK1, ALDH2, LDHA and LDHC, were markedly up-regulated in Meishan spermatozoa compared to Duroc spermatozoa. In addition, we first demonstrated that the levels of protein phosphorylation in Meishan spermatozoa were higher than those in Duroc. Taken together, the physiologically and functionally differential proteins may be one main reason for explaining the high reproductive efficiency of Meishan boar.

Differentiation of Mouse Primordial Germ Cells into Functional Oocytes In Vitro

Various complex molecular events in oogenesis cannot be observed in vivo. As a bioengineering technique for female reproductive tissues, in vitro culture systems for female germ cells have been used to analyze oogenesis and preserve germ cells for over 20 years. Recently, we have established a new methodological approach for the culture of primordial germ cells (PGCs) and successfully obtained offspring. Our PGC culture system will be useful to clarify unresolved mechanisms of fertility and sterility from the beginning of mammalian oogenesis, before meiosis. This review summarizes the history of culture methods for mammalian germ cells, our current in vitro system, and future prospects for the culture of germ cells.

Follicular development and expression of nuclear respiratory factor-1 and peroxisome proliferator-activated receptor γ coactivator-1 alpha in ovaries of fetal and neonatal doelings

In livestock, the ovarian reserve of follicles is established during the fetal stage. However, at least two-thirds of the oocytes present in the reserve die because of apoptosis before birth. Notably, mitochondria have been reported to play a crucial role in the fate (life/death) of oocytes. In this study, mitochondrial regulators nuclear respiratory factor-1 (NRF-1) and PPAR γ coactivator-1 alpha (PGC-1α) were examined during this period of follicle development to investigate their effects on follicular development and apoptosis. Fetal and neonatal Capra haimen were used, ranging in age from 60 d postcoitum (dpc) to 30 d postpartum (dpp). Our data demonstrated that egg nests were the earliest recognizable gamete cells in ovaries of fetal and neonatal doelings. Proportions of egg nests decreased from 92.68 to 25.08% whereas single follicles increased from 7.32 to 74.92% between 60 and 120 dpc. Subsequently, between 90 and 120 dpc, the proportion of primordial follicles increased from 9.98 to 61.56% (P < 0.01). However, it did not change between 1 and 30 dpp (P = 0.12). The proportion of primary follicles increased from 1.23 to 37.93% between 90 dpc to 1 dpp (P = 0.01) but did not change between 1 and 30 dpp (P = 0.11). Meanwhile, proportions of secondary and tertiary follicles increased in an age-dependent manner. In addition, results of this study suggested that NRF-1 and PGC-1α proteins are mainly localized in germ cells of egg nests, cytoplasm of oocytes, and granulosa cells of follicles ranging from primordial to tertiary follicles. The transcript abundance of NRF-1 mRNA was up-regulated in 60-dpc-old ovaries compared with 1-dpp-old ovaries (P < 0.05), but the PGC-1α mRNA expression pattern did not change (P = 0.05). Nevertheless, the number of terminal deoxynucleotidyltransferase UTP nick-end labeling (TUNEL) positive cells and caspase-3 activity in 60-dpc-old ovaries was less than those in 1-dpp-old ovaries (P < 0.01, P = 0.01). In conclusion, our results demonstrate that the key stage of primordial follicle formation is between 90 and 120 dpc in Capra haimen. Also, this study suggests that NRF-1 and PGC-1α might have roles in cell apoptosis during ovarian development of fetal and neonatal Capra haimen. These results improve our understanding of apoptotic mechanisms in oogenesis and folliculogenesis.

Formation of primordial follicles and immunolocalization of PTEN, PKB and FOXO3A proteins in the ovaries of fetal and neonatal pigs

The assembly of primordial follicles and subsequent development and transition of the primordial follicle to the primary follicle are critical processes in ovarian biology. In order to examine follicle formation and development in fetal and neonatal pigs, ovarian samples were obtained from a famous local breed of Chinese pigs, Erhualian pigs, ranging in age from 50 days postcoitum to 1 day postpartum in our current study. Morphological changes in the ovaries of the fetal and neonatal pigs indicated that egg nests were the earliest recognizable gamete cells. The proportion of egg nests decreased from 98.4 to 25.6% and the proportion of single follicles increased from 1.6 to 74.4% between 70 and 90 days postcoitum. The proportions of primordial follicles increased between 70 and 90 days postcoitum but decreased from 90 days postcoitum to 1 day postpartum. Our results suggested that the key stage of primordial follicle formation was between 70 and 90 days postcoitum and that the major stage of transition from primordial follicles into primary follicles was between 90 days postcoitum and 1 day postpartum. Experiments were also conducted to examine the localization of PTEN, PKB and FOXO3A proteins in the porcine ovaries by immunohistochemistry and immunoblotting. The results indicated that PTEN, PKB and FOXO3A were localized in the germ cells of egg nests, cytoplasm of oocytes and granulosa cells of follicles ranging from the primordial to secondary stages and that the staining intensity was weak in granulosa cells but strong in oocytes. The different staining patterns of PTEN, FOXO3A and PKB suggested that these proteins were expressed in a stage- and cell-specific manner during ovarian follicle formation and development in the fetal and neonatal pig.

The correlation of reproduction-related gene expression with germ cell number in DM and PLL gilts

In this study, the ovarian germ cell number was counted in 3-week-old Duroc x Meishan (DM, n=30) and PIC x (Landrace x Large White) (PLL, n=53) gilts, and the mRNA expression levels of four reproduction-related genes were investigated by quantitative RT-PCR. Correlation of germ cell number with the expression level of these genes was analyzed. Results showed that the germ cell number of DM was significantly higher than that of PLL gilts (P<0.01), although there was no significant difference between the ovarian weight of DM and PLL gilts (P=0.269). No significant correlation existed between germ cell number and ovarian weight in the two gilt groups (R=0.335, P=0.07; R=0.119, P=0.398, respectively). A significant correlation was found between the germ cell number and expression level of ESR and IGF1R mRNA in DM gilts (R=0.648, P<0.05; R=0.757, P<0.01, respectively), but the correlation between the germ cell number and expression level of FSHR and INHBA mRNA did not reach statistical significance. Significant correlation was found between the germ cell number and the expression level of ESR, FSHR, and IGF1R mRNA in PLL gilts (R=0.435, P<0.01; R=0.438, P<0.01; R=0.292, P<0.05, respectively), but not with INHBA mRNA in PLL gilts.