Activin A and follistatin during the oestrous cycle and early pregnancy in ewes

The role of the oviduct environment in embryo survival

CONTEXT

Declining fertility is an issue in multiple mammalian species. As the site of fertilisation and early embryo development, the oviduct plays a critical role in embryo survival, yet there is a paucity of information on how the oviduct regulates this process.

AIMS

We hypothesised that differences in steroid hormone signalling and/or immune function would be observed in a model of poor embryo survival, the peripubertal ewe.

METHODS

We examined expression of steroid hormones in systemic circulation, oviductal expression of oestrogen receptorαand genes important in steroid hormone signalling, and immune function in pregnant and cyclic peripubertal and adult ewes on day 3 after oestrus.

KEY RESULTS

Concentrations of progesterone, but not oestradiol, were decreased in the peripubertal ewe compared to the adult ewe. Oestrogen receptorαprotein expression was increased in the peripubertal ewe, but pathway analysis of gene expression revealed downregulation of the oestrogen signalling pathway compared to the adult ewe. Differential expression of several genes involved in immune function between the peripubertal and adult ewe was consistent with an unfavourable oviductal environment in the peripubertal ewe lamb. Oestradiol concentration was positively correlated with the expression of multiple genes involved in the regulation of immune function.

CONCLUSIONS

Differences in the immune environment of the oviduct, potentially linked to differential modulation by steroid hormones, may partially underly the poor fertilisation and early embryo survival observed in the peripubertal ewe.

IMPLICATIONS

A unfavourable oviductal environment may play an important role in limiting reproductive success.

A Novel c.100C > G Mutation in the FST Gene and Its Relation With the Reproductive Traits of Awassi Ewes

Reproductive traits are affected by many factors, including ovarian function, hormones, and genetics. Genetic polymorphisms of candidate genes are associated with reproductive traits. Several candidate genes are associated with economic traits, including the follistatin (FST) gene. Thus, this study aimed to evaluate whether the genetic variations in the FST gene are associated with the reproductive traits in Awassi ewes. The genomic DNA was extracted from 109 twin ewes and 123 single-progeny ewes. Therefore, 4 sequence fragments from the FST gene were amplified using polymerase chain reaction (PCR) (exon 2/240, exon 3/268, exon 4/254, and exon 5/266 bp, respectively). For a 254 bp amplicon, 3 genotypes were identified: CC, CG, and GG. Sequencing revealed a novel mutation in CG genotypes c.100C > G. The statistical analysis of c.100C > G showed an association with reproductive characteristics. Ewes carrying the c.100C > G had significantly (P ⩽ .01) lower litter sizes, twinning rates, lambing rates, and more days to lambing compared with CG and CC genotypes. Logistic regression analysis confirmed that the c.100C > G single-nucleotide polymorphism (SNP) is responsible for decreasing litter size. According to these results, the variant c.100C > G negatively affects the traits of interest and is associated with lower reproductive traits in Awassi sheep. As a result of this study, ewes carrying the c.100C > G SNP have lower litter size and are less prolific.

Follistatin Is a Novel Chemoattractant for Migration and Invasion of Placental Trophoblasts of Mice

Follistatin (FST) as a gonadal protein is central to the establishment and maintenance of pregnancy. Trophoblasts' migration and invasion into the endometrium are critical events in placental development. This study aimed to elucidate the role of FST in the migration and invasion of placental trophoblasts of mice. We found that FST increased the vitality and proliferation of primary cultured trophoblasts of embryonic day 8.5 (E8.5) mice and promoted wound healing of trophoblasts. Moreover, FST significantly induced migration of trophoblasts in a microfluidic device and increased the number of invasive trophoblasts by Matrigel-coated transwell invasion assay. Being treated with FST, the adhesion of trophoblasts was inhibited, but intracellular calcium flux of trophoblasts was increased. Western blotting results showed that FST had no significant effects on the level of p-Smad3 or the ratio of p-Smad3/Smad3 in trophoblasts. Interestingly, FST elevated the level of p-JNK; the ratio of p-JNK/JNK; and expression of migration-related proteins N-cadherin, vimentin, ezrin and MMP2 in trophoblasts. Additionally, the migration of trophoblasts and expression of N-cadherin, vimentin, and MMP2 in trophoblasts induced by FST were attenuated by JNK inhibitor AS601245. These findings suggest that the elevated FST in pregnancy may act as a chemokine to induce trophoblast migration and invasion through the enhanced JNK signaling to maintain trophoblast function and promote placental development.

A single-cell atlas of the cycling murine ovary

The estrous cycle is regulated by rhythmic endocrine interactions of the nervous and reproductive systems, which coordinate the hormonal and ovulatory functions of the ovary. Folliculogenesis and follicle progression require the orchestrated response of a variety of cell types to allow the maturation of the follicle and its sequela, ovulation, corpus luteum formation, and ovulatory wound repair. Little is known about the cell state dynamics of the ovary during the estrous cycle and the paracrine factors that help coordinate this process. Herein, we used single-cell RNA sequencing to evaluate the transcriptome of >34,000 cells of the adult mouse ovary and describe the transcriptional changes that occur across the normal estrous cycle and other reproductive states to build a comprehensive dynamic atlas of murine ovarian cell types and states.

Analysis of the transcriptome of bovine endometrial cells isolated by laser micro-dissection (1): specific signatures of stromal, glandular and luminal epithelial cells

BACKGROUND

A number of studies have examined mRNA expression profiles of bovine endometrium at estrus and around the peri-implantation period of pregnancy. However, to date, these studies have been performed on the whole endometrium which is a complex tissue. Consequently, the knowledge of cell-specific gene expression, when analysis performed with whole endometrium, is still weak and obviously limits the relevance of the results of gene expression studies. Thus, the aim of this study was to characterize specific transcriptome of the three main cell-types of the bovine endometrium at day-15 of the estrus cycle.

RESULTS

In the RNA-Seq analysis, the number of expressed genes detected over 10 transcripts per million was 6622, 7814 and 8242 for LE, GE and ST respectively. ST expressed exclusively 1236 genes while only 551 transcripts were specific to the GE and 330 specific to LE. For ST, over-represented biological processes included many regulation processes and response to stimulus, cell communication and cell adhesion, extracellular matrix organization as well as developmental process. For GE, cilium organization, cilium movement, protein localization to cilium and microtubule-based process were the only four main biological processes enriched. For LE, over-represented biological processes were enzyme linked receptor protein signaling pathway, cell-substrate adhesion and circulatory system process.

CONCLUSION

The data show that each endometrial cell-type has a distinct molecular signature and provide a significantly improved overview on the biological process supported by specific cell-types. The most interesting result is that stromal cells express more genes than the two epithelial types and are associated with a greater number of pathways and ontology terms.

Molecular profiling demonstrates modulation of immune cell function and matrix remodeling during luteal rescue†

The corpus luteum (CL) is essential for maintenance of pregnancy in all mammals and luteal rescue, which occurs around day 16-19 in the cow, is necessary to maintain luteal progesterone production. Transcriptomic and proteomic profiling were performed to compare the day 17 bovine CL of the estrous cycle and pregnancy. Among mRNA and proteins measured, 140 differentially abundant mRNA and 24 differentially abundant proteins were identified. Pathway analysis was performed using four programs. Modulated pathways included T cell receptor signaling, vascular stability, cytokine signaling, and extracellular matrix remodeling. Two mRNA that were less in pregnancy were regulated by prostaglandin F2A in culture, while two mRNA that were greater in pregnancy were regulated by interferon tau. To identify mRNA that could be critical regulators of luteal fate, the mRNA that were differentially abundant during early pregnancy were compared to mRNA that were differentially abundant during luteal regression. Eight mRNA were common to both datasets, including mRNA related to regulation of steroidogenesis and gene transcription. A subset of differentially abundant mRNA and proteins, including those associated with extracellular matrix functions, were predicted targets of differentially abundant microRNA (miRNA). Integration of miRNA and protein data, using miRPath, revealed pathways such as extracellular matrix-receptor interactions, abundance of glutathione, and cellular metabolism and energy balance. Overall, this study has provided a comprehensive profile of molecular changes in the corpus luteum during maternal recognition of pregnancy and has indicated that some of these functions may be miRNA-regulated.

Follistatin-like 3, an activin A binding protein, is involved in early pregnancy loss

BACKGROUND

Early pregnancy loss (EPL), a common and severe complication in pregnancy, has a long-term personal and social impact. It was previously reported that follistatin-like 3(FSTL3), an activin A binding protein, contributes to the invasion and migration of trophoblast. Simultaneously, activin A induces the release of FSTL3 and the elevated activin A is found to be associated with pregnancy loss in women. This study aimed to identify the roles of FSTL3 in the establishment and maintenance of pregnancy, and to determine whether FSTL3 is involved in the pathophysiology of EPL.

METHODS

Endometrial Ishikawa cells and JAR cells were cultured and FSTL3 siRNA was used to silence FSTL3. The trophoblast spheroids mimicking embryos were used in an embryonic adhesion system. The system aimed to investigate the role of FSTL3 silence on embryonic adhesion onto endometrial cell in vitro. The ICR mice model in vivo was used to investigate whether the FSTL3 works in embryonic implantation. The western blotting was used to determine the expression of FSTL3 and activin A.

RESULTS

In the in vitro study, silence of FSTL3 in JAR cells significantly reduced the number of trophoblast spheroids adhered onto Ishikawa cells compared with the scramble siRNA. For the in vivo study, the number of embryos implanted in the uterine horn injected with FATL3 siRNA mixture was significantly less than that in control group. In the case control study, both the expression of FSTL3 and activin A in EPL women were significantly higher than that in controls.

CONCLUSIONS

FSTL3 plays a biological role in the establishment and maintenance of normal pregnancy. Moreover, FSTL3 may be involved in the early pregnancy loss via neutralizing the elevated activin A.

Transforming growth factor-beta family members are regulated during induced luteolysis in cattle

The transforming growth factors beta (TGFβ) are local factors produced by ovarian cells which, after binding to their receptors, regulate follicular deviation and ovulation. However, their regulation and function during corpus luteum (CL) regression has been poorly investigated. The present study evaluated the mRNA regulation of some TGFβ family ligands and their receptors in the bovine CL during induced luteolysis in vivo. On day 10 of the estrous cycle, cows received an injection of prostaglandin F2α (PGF) and luteal samples were obtained from separate groups of cows (n= 4-5 cows per time-point) at 0, 2, 12, 24 or 48 h after treatment. Since TGF beta family comprises more than 30 ligands, we focused in some candidates genes such as activin receptors (ACVR-1A, -1B, -2A, -2B) AMH, AMHR2, BMPs (BMP-1, -2, -3, -4, -6 and -7), BMP receptors (BMPR-1A, -1B and -2), inhibin subunits (INH-A, -BA, -BB) and betaglycan (TGFBR3). The mRNA levels of BMP4, BMP6 and INHBA were higher at 2 h after PGF administration (P<0.05) in comparison to 0 h. The relative mRNA abundance of BMP1, BMP2, BMP3, BMP4, BMP6, ACVR1B, INHBA and INHBB was upregulated up to 12 h post PGF (P<0.05). On the other hand, TGFBR3 mRNA that codes for a reservoir of ligands that bind to TGF-beta receptors, was lower at 48 h. In conclusion, findings from this study demonstrated that genes encoding several TGFβ family members are expressed in a time-specific manner after PGF administration.

Transcriptome analysis of ovine granulosa cells reveals differences between small antral follicles collected during the follicular and luteal phases

Ovarian follicular growth occurs in both the follicular and luteal phases of the estrous cycle but in very different endocrine contexts. In both phases, many small antral follicles with similar morphologic and histologic characteristics are present within the ovaries as a reserve for the terminal folliculogenesis. However, there are several gaps in our molecular knowledge of the gene expression profiles of small antral follicles in the follicular and luteal phases. The aim of the present study was to use RNA sequencing to compare and analyze the global transcriptional profile of ovine granulosa cells collected from small antral follicles (1-3 mm) either during the follicular or the luteal phase of the estrous cycle, with the hypothesis that they should be differential. We identified 663 genes whose mRNA was differentially expressed or accumulated in the granulosa cell layer of small antral follicles in the two phases. A comprehensive interpretation of these data was performed through integrative analyses (Gene Ontology, Ingenuity Pathway Analysis) and the exploitation of already available transcriptomic data on follicular growth and atresia. In particular, we observed that the contrasted endocrine context between follicular and luteal phases may have an impact on estradiol, follicle-stimulating hormone (FSH), and on the activin/inhibin signaling pathways. Furthermore, we reveal the possible initiation of early follicular atresia in small antral follicles during the follicular phase in interaction with the presence of immune cells. This study provides new insights into the gene expression profile in ovine granulosa cells, and we suggest that these molecular changes may have an implication at the time of follicle selection.