The quality of metaphase II oocytes deteriorates rapidly following ovulation as the result of an aging process associated with impaired fertilizing potential, disrupted developmental competence, and increased likelihood of embryonic resorption. Because oxidative stress accelerates the onset of apoptosis in oocytes and influences their capacity for fertilization, this study aimed to characterize the significance of such stress in the postovulatory aging of mouse oocytes in vitro. We investigated the ability of the potent antioxidant melatonin to arrest the aging process when used to supplement oocyte culture medium. This study demonstrated that oxidative stress may occur in oocytes after as little as 8 h in culture and coincides with the appearance of early apoptotic markers such as phosphatidylserine externalization, followed 16 h later by caspase activation (P < 0.05) and morphological evidence of oocyte senescence. Importantly, supplementation of oocyte culture medium with 1 mM melatonin was able to significantly relieve the time-dependent appearance of oxidative stress in oocytes (P < 0.05) and, as a result, significantly delay the onset of apoptosis (P < 0.05). Furthermore, melatonin supplementation extended the optimal window for fertilization of oocytes aged for 8 and 16 h in vitro (P < 0.05) and significantly improved the quality of the resulting embryos (P < 0.01). We conclude that melatonin may be a useful tool in a clinical setting to prevent the time-dependent deterioration of oocyte quality following prolonged culture in vitro.
Although 90%-100% of mouse oocytes can be fertilized in vitro with capacitated spermatozoa within 1 h after insemination, oocytes within the oviduct are fertilized one by one over a period of several hours. In vitro experiments showed that both acrosome-intact and acrosome-reacted spermatozoa entered the cumulus oophorus, but that acrosome-reacted spermatozoa reached the surface of oocytes more readily than acrosome-intact spermatozoa. During the period of fertilization within the oviduct, acrosome-reacted spermatozoa were seen throughout the isthmus, but with higher incidence in the upper than in the mid- and lower segments of the isthmus. Very few spermatozoa were present in the ampulla, and almost all were acrosome reacted. Although the cumulus oophorus and zona pellucida are known to be able to induce or facilitate the acrosome reaction of spermatozoa, this picture makes it likely that almost all fertilizing mouse spermatozoa within the oviduct begin to react before ascending from the isthmus to the ampulla. We witnessed a reacted spermatozoon that stayed on the zona pellucida of a fertilized oocyte for a while; it then moved out of the cumulus before reaching the zona pellucida of the nearby unfertilized oocyte. We noted that only a few spermatozoa migrate from the isthmus to the ampulla during the progression of fertilization, and this must be one of the reasons why we do not see many spermatozoa swarming around a single oocyte during in vivo fertilization.
Impaired biogenesis of microRNAs disrupts spermatogenesis and leads to infertility in male mice. Spermatogonial differentiation is a key step in spermatogenesis, yet the mechanisms that control this event remain poorly defined. In this study, we discovered microRNA 146 (Mir146) to be highly regulated during spermatogonial differentiation, a process dependent on retinoic acid (RA) signaling. Mir146 transcript levels were diminished nearly 180-fold in differentiating spermatogonia when compared with undifferentiated spermatogonia. Luciferase assays revealed the direct binding of Mir146 to the 3' untranslated region of the mediator complex subunit 1 (Med1), a coregulator of retinoid receptors (RARs and RXRs). Overexpression of Mir146 in cultured undifferentiated spermatogonia reduced Med1 transcript levels, as well as those of differentiation marker kit oncogene (Kit). MED1 protein was also diminished. Conversely, inhibition of Mir146 increased the levels of Kit. When undifferentiated spermatogonia were exposed to RA, Mir146 was downregulated along with a marker for undifferentiated germ cells, zinc finger and BTB domain containing 16 (Zbtb16; Plzf); Kit was upregulated. Overexpression of Mir146 in RA-treated spermatogonia inhibited the upregulation of Kit, stimulated by retinoic acid gene 8 (Stra8), and spermatogenesis-and oogenesis-specific basic helix-loop-helix 2 (Sohlh2). Inhibition of Mir146 in RA-treated spermatogonia greatly enhanced the upregulation of these genes. We conclude that Mir146 modulates the effects of RA on spermatogonial differentiation.
This study examined the effect of the presence of single or multiple embryos on the transcriptome of the bovine oviduct. In experiment 1, cyclic (nonbred, n = 6) and pregnant (artificially inseminated, n = 11) heifers were slaughtered on Day 3 after estrus, and the ampulla and isthmic regions of the oviduct ipsilateral to the corpus luteum were separately flushed. Oviductal epithelial cells from the isthmus region, in which all oocytes/embryos were located, were snap-frozen for microarray analysis. In experiment 2, heifers were divided into cyclic (nonbred, n = 6) or pregnant (multiple embryo transfer, n = 10) groups. In vitro-produced presumptive zygotes were transferred endoscopically to the ipsilateral oviduct on Day 1.5 postestrus (n = 50 zygotes/heifer). Heifers were slaughtered on Day 3, and oviductal isthmus epithelial cells were recovered for RNA sequencing. Microarray analysis in experiment 1 failed to detect any difference in the transcriptome of the oviductal isthmus induced by the presence of a single embryo. In experiment 2, following multiple embryo transfer, RNA sequencing revealed 278 differentially expressed genes, of which 123 were up-regulated and 155 were down-regulated in pregnant heifers. Most of the down-regulated genes were related to immune function. In conclusion, the presence of multiple embryos in the oviduct resulted in the detection of differentially expressed genes in the oviductal isthmus; failure to detect changes in the oviduct transcriptome in the presence of a single embryo may be due to the effect being local and undetectable under the conditions of this study.
MicroRNAs are important regulators of developmental gene expression, but their contribution to fetal gonad development is not well understood. We have identified the evolutionarily conserved gonadal microRNAs miR-202-5p and miR-202-3p as having a potential role in regulating mouse embryonic gonad differentiation. These microRNAs are expressed in a sexually dimorphic pattern as the primordial XY gonad differentiates into a testis, with strong expression in Sertoli cells. In vivo, ectopic expression of pri-miR-202 in XX gonads did not result in molecular changes to the ovarian determination pathway. Expression of the primary transcript of miR-202-5p/3p remained low in XY gonads in a conditional Sox9-null mouse model, suggesting that pri-miR-202 transcription is downstream of SOX9, a transcription factor that is both necessary and sufficient for male sex determination. We identified the pri-miR-202 promoter that is sufficient to drive expression in XY but not XX fetal gonads ex vivo. Mutation of SOX9 and SF1 binding sites reduced ex vivo transactivation of the pri-miR-202 promoter, demonstrating that pri-miR-202 may be a direct transcriptional target of SOX9/SF1 during testis differentiation. Our findings indicate that expression of the conserved gonad microRNA, miR-202-5p/3p, is downstream of the testis-determining factor SOX9, suggesting an early role in testis development.
Developmental exposure to endocrine-disrupting compounds is hypothesized to adversely affect female reproductive physiology by interfering with the organization of the hypothalamic-pituitary-gonadal axis. Here, we compared the effects of neonatal exposure to two environmentally relevant doses of the plastics component bisphenol-A (BPA; 50 Î¼g/kg and 50 mg/kg) with the ESR1 (formerly known as ERalpha)-selective agonist 4,4â²,4â³-(4-propyl-[ 1 H]pyrazole-1,3,5-triyl)trisphenol (PPT; 1 mg/kg) on the development of the female rat hypothalamus and ovary. An oil vehicle and estradiol benzoate (EB; 25 Î¼g) were used as negative and positive controls. Exposure to EB, PPT, or the low dose of BPA advanced pubertal onset. A total of 67% of females exposed to the high BPA dose were acyclic by 15 wk after vaginal opening compared with 14% of those exposed to the low BPA dose, all of the EB- and PPT-treated females, and none of the control animals. Ovaries from the EB-treated females were undersized and showed no evidence of folliculogenesis, whereas ovaries from the PPT-treated females were characterized by large antral-like follicles, which did not appear to support ovulation. Severity of deficits within the BPA-treated groups increased with dose and included large antral-like follicles and lower numbers of corpora lutea. Sexual receptivity, examined after ovariectomy and hormone replacement, was normal in all groups except those neonatally exposed to EB. FOS induction in hypothalamic gonadotropic (GnRH) neurons after hormone priming was impaired in the EB- and PPT-treated groups but neither of the BPA-treated groups. Our data suggest that BPA disrupts ovarian development but not the ability of GnRH neurons to respond to steroid-positive feedback.
Using transgenic mice with spermatozoa expressing enhanced green fluorescent protein in their acrosome and red fluorescent protein in their midpiece mitochondria, we followed the behavior of spermatozoa within the female genital tract after natural mating. When examined 15 min after coitus, many spermatozoa were around the opening of the uterotubal junction. Spermatozoa that entered the uterotubal junction were seemingly not moving, yet they steadily migrated toward the isthmus at a speed only time-lapse video recording could demonstrate. Many spermatozoa reaching the lower isthmus were motile. The site where spermatozoa attached and detached from the isthmus epithelium shifted from the lower to the upper segment of the isthmus with time. Virtually all the live spermatozoa within the lower isthmus were acrosome intact, whereas many of the actively motile spermatozoa in the upper isthmus were acrosome reacted. As far as we could observe, all the spermatozoa we found within the lumen of the ampulla and the cumulus oophorus were acrosome reacted. Even though we saw only a very few spermatozoa within the ampulla during fertilization, all were associated with, or were already within, oocytes, indicating that mouse fertilization in vivo is extremely efficient.
Oxidative stress has been implicated in various aspects of aging, but the role of oxidative stress in ovarian aging remains unclear. Our previous studies have shown that the initiation of apoptotic cell death in ovarian follicles and granulosa cells by various stimuli is initiated by increased reactive oxygen species. Herein, we tested the hypothesis that ovarian antioxidant defenses decrease and oxidative damage increases with age in mice. Healthy, wild-type C57BL/6 female mice aged 2, 6, 9, or 12 mo from the National Institute on Aging Aged Rodent Colony were killed on the morning of metestrus. Quantitative real-time RT-PCR was used to measure ovarian mRNA levels of antioxidant genes. Immunostaining using antibodies directed against 4-hydroxynonenal (4-HNE), nitrotyrosine (NTY), and 8-hydroxy-20-deoxyguanosine (8-OHdG) was used to localize oxidative lipid, protein, and DNA damage, respectively, within the ovaries. TUNEL was used to localize apoptosis. Ovarian expression of glutathione peroxidase 1 (Gpx1) increased and expression of glutaredoxin 1 (Glrx1), glutathione S-transferase mu 2 (Gstm2), peroxiredoxin 3 (Prdx3), and thioredoxin 2 (Txn2) decreased in a statistically significant manner with age. Statistically significant increases in 4-HNE, NTY, and 8-OHdG immunostaining in ovarian interstitial cells and follicles were observed with increasing age. Our data suggest that the decrease in mRNA expression of mitochondrial antioxidants Prdx3 and Txn2 as well as cytosolic antioxidants Glrx1 and Gstm2 may be involved in age-related ovarian oxidative damage to lipid, protein, DNA, and other cellular components vital for maintaining ovarian function and fertility.
Methods to predict numbers of healthy oocytes in the ovaries of young adults could have important diagnostic relevance in family planning and animal agriculture. We have observed that peak antral follicle count (AFC) determined by serial ovarian ultrasonography during follicular waves is very highly reproducible within individual young adult cattle, despite 7-fold variation among animals. Herein, we tested the hypothesis that AFC is positively associated with the number of morphologically healthy oocytes and follicles in ovaries and with serum concentrations of anti-MÃ¼llerian hormone (AMH), an indirect marker for number of healthy follicles and oocytes in ovaries. In the present study, age-matched young adult cattle (12â18 mo old) were subjected to serial ultrasonography to identify animals with a consistently high (â¥25 follicles that were â¥3 mm in diameter) or low (â¤15 follicles) AFC during follicular waves. Differences in serum AMH concentrations, ovary weight, and number of morphologically healthy and atretic follicles and oocytes were determined. The phenotypic classifications of cattle based on AFC during follicular waves or AMH concentrations both predict reliably the relative number of morphologically healthy follicles and oocytes in ovaries of age-matched young adult cattle.
Spermatogenesis is a complex process that originates in a small population of spermatogonial stem cells. Here we report the in vitro culture of spermatogonial stem cells that proliferate for long periods of time. In the presence of glial cell line-derived neurotrophic factor, epidermal growth factor, basic fibroblast growth factor, and leukemia inhibitory factor, gonocytes isolated from neonatal mouse testis proliferated over a 5-month period (>10 14 -fold) and restored fertility to congenitally infertile recipient mice following transplantation into seminiferous tubules. Long-term spermatogonial stem cell culture will be useful for studying spermatogenesis mechanism and has important implications for developing new technology in transgenesis or medicine.
The KISS1 gene encodes the kisspeptin neuropeptide, which activates the KISS1 receptor (KISS1R; G protein-coupled receptor 54; GPR54) and participates in neuroendocrine regulation of GnRH secretion. To study the physiological function(s) and evolutionary conservation of KISS1, we cloned opossum, Xenopus , and zebrafish kiss1 cDNAs. Processing zebrafish, Xenopus , or opossum KISS proteins would liberate a carboxy-terminal amidated peptide with 52, 54, or 53 amino acid residues, respectively. Phylogenetic analysis of all known vertebrate KISS1 peptides showed clear clustering of the sequences according to canonical vertebrate classes. The zebrafish kiss1 gene consists of two exons and one intron. Real-time PCR analysis of two kiss1R cloned from zebrafish brain found expression of kiss1 , kiss1ra , and kiss1rb , with kiss1ra âmore similar to other piscine Kiss1 receptorsâhighly expressed in the gonads and kiss1rb in other nonbrain tissues. In females kiss1 mRNA levels gradually increased during the first few weeks of life to peak in fish with ovaries containing mature oocytes, while in males kiss1 mRNA levels peaked after 6 wk postfertilization when the testes exhibited initial stages of spermatogenesis and decreased after puberty. Zebrafish kiss1ra and kiss1rb were expressed differentially with similar patterns in both genders. These results indicate that the Kiss1/Kiss1r system may participate in puberty initiation in fish as well. Like human KISS1R, Kiss1ra transduces its activity via the PKC pathway, whereas Kiss1rb does so via both PKC and PKA pathways. The human KISS1R was highly activated by both huKISS10amide and zfKISS10amide, whereas both zebrafish Kiss1 receptor types were less sensitive to amidation.
Increasing evidence indicates that microRNAs (miRNAs) may be critical players in spermatogenesis. The miRNA expression profiles of THY1(+)-enriched undifferentiated spermatogonia were characterized, and members of Mir-17-92 (Mirc1) and its paralog Mir-106b-25 (Mirc3) clusters are significantly downregulated during retinoic acid-induced spermatogonial differentiation, both in vitro and in vivo. The repression of microRNA clusters Mir-17-92 (Mirc1) and Mir-106b-25 (Mirc3) by retinoic acid in turn potentially upregulates the expression of Bim, Kit, Socs3, and Stat3. The male germ cell-specific Mir-17-92 (Mirc1) knockout mice exhibit small testes, a lower number of epididymal sperm, and mild defect in spermatogenesis. Absence of Mir-17-92 (Mirc1) in male germ cells dramatically increases expression of Mir-106b-25 (Mirc3) cluster miRNAs in the germ cells. These results suggest that Mir-17-92 (Mirc1) cluster and Mir-106b-25 (Mirc3) cluster miRNAs possibly functionally cooperate in regulating spermatogonial development.
Belclare and Cambridge are prolific sheep breeds, the origins of which involved selecting ewes with exceptionally high litter size records from commercial flocks. The variation in ovulation rate in both breeds is consistent with segregation of a gene (or genes) with a large effect on this trait. Sterile ewes, due to a failure of normal ovarian follicle development, occur in both breeds. New naturally occurring mutations in genes for the oocyte-derived growth factors growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are described. These mutations are associated with increased ovulation rate in heterozygous carriers and sterility in homozygous carriers in both breeds. This is the first time that a mutation in the gene for GDF9 has been found that causes increased ovulation rate and infertility in a manner similar to inactivating mutations in BMP15, and shows that GDF9 is essential for normal folliculogenesis in sheep. Furthermore, it is shown, for the first time in any species, that individuals with mutations in both GDF9 and BMP15 have a greater ovulation rate than sheep with either of the mutations separately.
MicroRNAs (miRNAs) mediate posttranscriptional gene regulation by binding to the 3â² untranslated region of messenger RNAs to either inhibit or enhance translation. The extent and hormonal regulation of miRNA expression by ovarian granulosa cells and their role in ovulation and luteinization is unknown. In the present study, miRNA array analysis was used to identify 212 mature miRNAs as expressed and 13 as differentially expressed in periovulatory granulosa cells collected before and after an ovulatory dose of hCG. Two miRNAs, Mirn132 and Mirn212 (also known as miR-132 and miR-212), were found to be highly upregulated following LH/hCG induction and were further analyzed. In vivo and in vitro temporal expression analysis by quantitative RT-PCR confirmed that LH/hCG and cAMP, respectively, increased transcription of the precursor transcript as well as the mature miRNAs. Locked nucleic acid oligonucleotides complementary to Mirn132 and Mirn212 were shown to block cAMP-mediated mature miRNA expression and function. Computational analyses indicated that 77 putative mRNA targets of Mirn132 and Mirn212 were expressed in ovarian granulosa cells. Furthermore, upon knockdown of Mirn132 and Mirn212 , a known target of Mirn132 , C-terminal binding protein 1, showed decreased protein levels but no change in mRNA levels. The following studies are the first to describe the extent of miRNA expression within ovarian granulosa cells and the first to demonstrate that LH/hCG regulates the expression of select miRNAs, which affect posttranscriptional gene regulation within these cells.
MicroRNAs (miRNAs) are small noncoding RNAs that posttranscriptionally regulate gene expression. Hundreds of miRNAs are expressed in mammals; however, their functions are just starting to be uncovered. MicroRNAs are processed from a long hairpin mRNA transcript, down to a â¼23-nucleotide duplex. The enzyme Dicer1 is required for miRNA processing, and mouse knockouts of Dicer1 are embryonic lethal before 7.5 days postcoitus. To examine the function of miRNAs specifically in the germline, we used a mouse model that expresses Cre recombinase from the TNAP locus and a floxed Dicer1 conditional allele. Removal of Dicer1 from germ cells resulted in male infertility. Germ cells were present in adult testes, but few tubules contained elongating spermatids. Germ cells that did differentiate to elongating spermatids exhibited abnormal morphology and motility. Rarely, sperm lacking Dicer1 could fertilize wild-type eggs to generate viable offspring. These results show that Dicer1 and miRNAs are essential for proper differentiation of the male germline.
Cells release diverse types of membrane-bound vesicles of endosomal and plasma membrane origin, termed exosomes and microvesicles, respectively. Extracellular vesicles (EVs) represent an important mode of intercellular communication by transferring select RNAs, proteins, and lipids between cells. The present studies tested the hypothesis that the elongating ovine conceptus and uterus produces EVs that mediate conceptus-maternal interactions during early pregnancy. In Study 1, EVs were purified from uterine luminal fluid of Day 14 cyclic sheep. The EVs were fluorescently labeled with PKH67 dye and infused into the uterine lumen of pregnant sheep for 6 days using an osmotic pump. On Day 14, labeled EVs were observed in the conceptus trophectoderm and uterine epithelia, but not in the uterine stroma or myometrium. In Study 2, Day 14 conceptuses were cultured ex vivo for 24 h and found to release EVs into the culture medium. Proteomics analysis of the Day 14 conceptus-derived EVs identified 231 proteins that were enriched for extracellular space and several protein classes, including proteases, protease inhibitors, chaperones and chaperonins. RNA sequencing of Day 14 conceptus-derived EVs detected expression of 512 mRNAs. The top-expressed genes were overrepresented in ribosomal functions and components. Isolated EVs from conceptuses were fluorescently labeled with PKH67 and infused into the uterine lumen of cyclic sheep for 6 days using an osmotic pump. On Day 14, labeled EVs were observed in the uterine epithelia, but not in the uterine stroma or myometrium. Labeled EVs were not observed in the ovary or in other maternal tissues. These studies support the ideas that EVs emanate from both the conceptus trophectoderm and uterine epithelia, and are involved in intercellular communication between those cells during the establishment of pregnancy in sheep.
Endometriosis is an estrogen-dependent, progesterone-resistant disorder largely derived from retrograde transplantation of menstrual tissue/cells into the pelvis, eliciting an inflammatory response, pelvic pain, and infertility. Eutopic endometrium (within the uterus), giving rise to pelvic disease, displays cycle-dependent transcriptomic, proteomic, and signaling abnormalities, and although its DNA methylation profiles dynamically change across the cycle in healthy women, studies in endometriosis are limited. Herein, we investigated the DNA methylome and associated gene expression in three phases of the cycle in eutopic endometrium of women with severe endometriosis versus controls, matched for ethnicity, medications, smoking, and no recent contraceptive steroid use. Genome-wide DNA methylation and gene expression were coassessed in each sample. Cycle phase was determined by histology, serum hormone levels, and unsupervised principal component and hierarchical cluster analyses of microarray data. Altered endometrial DNA methylation in endometriosis was most prominent in the midsecretory phase (peak progesterone), with disruption of the normal pattern of cycle-dependent DNA methylation changes, including a bias toward methylation of CpG islands, suggesting wide-range abnormalities of the chromatin remodeling machinery in endometriosis. DNA methylation changes were associated with altered gene expression relevant to endometrial function/dysfunction, including cell proliferation, inflammation/immune response, angiogenesis, and steroid hormone response. The data provide insight into epigenetic reprogramming and steroid hormone actions in endometrium contributing to the pathogenesis and pathophysiology of endometriosis.
Oxygen is a powerful regulator of preimplantation embryo development, affecting gene expression, the proteome, and energy metabolism. Even a transient exposure to atmospheric oxygen can have a negative impact on embryo development, which is greatest prior to compaction, and subsequent post-compaction culture at low oxygen cannot alleviate this damage. In spite of this evidence, the majority of human in vitro fertilization is still performed at atmospheric oxygen. One of the physiological parameters shown to be affected by the relative oxygen concentration, carbohydrate metabolism, is linked to the ability of the mammalian embryo to develop in culture and remain viable after transfer. The aim of this study was, therefore, to determine the effect of oxygen concentration on the ability of mouse embryos to utilize both amino acids and carbohydrates both before and after compaction. Metabolomic and fluorometric analysis of embryo culture media revealed that when embryos were exposed to atmospheric oxygen during the cleavage stages, they exhibited significantly greater amino acid utilization and pyruvate uptake than when cultured under 5% oxygen. In contrast, postcompaction embryos cultured in atmospheric oxygen showed significantly lower mean amino acid utilization and glucose uptake. These metabolic changes correlated with developmental compromise because embryos grown in atmospheric oxygen at all stages showed significantly lower blastocyst formation and proliferation. These findings confirm the need to consider both embryo development and metabolism in establishing optimal human embryo growth conditions and prognostic markers of viability, and further highlight the impact of oxygen on such vital parameters.
Polycystic ovary syndrome (PCOS) pathophysiology is poorly understood, due partly to lack of PCOS animal models fully recapitulating this complex disorder. Recently, a PCOS rat model using letrozole (LET), a nonsteroidal aromatase inhibitor, mimicked multiple PCOS phenotypes, including metabolic features absent in other models. Given the advantages of using genetic and transgenic mouse models, we investigated whether LET produces a similar PCOS phenotype in mice. Pubertal female C57BL/6N mice were treated for 5 wk with LET, which resulted in increased serum testosterone and normal diestrus levels of estradiol, similar to the hyperandrogenemia and follicular phase estrogen levels of PCOS women. As in PCOS, ovaries from LET mice were larger, polycystic, and lacked corpora lutea versus controls. Most LET females were acyclic, and all were infertile. LET females displayed elevated serum LH levels and higher Lhb mRNA in the pituitary. In contrast, serum FSH and Fshb were significantly reduced in LET females, demonstrating differential effects on gonadotropins, as in PCOS. Within the ovary, LET females had higher Cyp17, Cyp19, and Fsh receptor mRNA expression. In the hypothalamus, LET females had higher kisspeptin receptor mRNA expression but lower progesterone receptor mRNA levels. LET females also gained more weight than controls, had increased abdominal adiposity and adipocyte size, elevated adipose inflammatory mRNA levels, and impaired glucose tolerance, mirroring the metabolic phenotype in PCOS women. This is the first report of a LET paradigm in mice that recapitulates both reproductive and metabolic PCOS phenotypes and will be useful to genetically probe the PCOS condition.