Mechanism of follicle deviation in monovular farm species

Differential age-related transcriptomic analysis of ovarian granulosa cells in Kazakh horses

Introduction

The Kazakh horse, renowned for its excellence as a breed, exhibits distinctive reproductive traits characterized by early maturity and seasonal estrus. While normal reproductive function is crucial for ensuring the breeding and expansion of the Kazakh horse population, a noteworthy decline in reproductive capabilities is observed after reaching 14 years of age.

Methods

In this study, ovarian granulosa cells (GCs) were meticulously collected from Kazakh horses aged 1, 2, 7, and above 15 years old (excluding 15 years old) for whole transcriptome sequencing.

Results

The analysis identified and selected differentially expressed mRNAs, lncRNAs, miRNAs, and circRNAs for each age group, followed by a thorough examination through GO enrichment analysis. The study uncovered significant variations in the expression profiles of mRNAs, lncRNAs, miRNAs, and circRNAs within GCs at different stages of maturity. Notably, eca-miR-486-3p and miR-486-y exhibited the highest degree of connectivity. Subsequent GO, KEGG, PPI, and ceRNA network analyses elucidated that the differentially expressed target genes actively participate in signaling pathways associated with cell proliferation, apoptosis, and hormonal regulation. These pathways include but are not limited to the MAPK signaling pathway, Hippo signaling pathway, Wnt signaling pathway, Calcium signaling pathway, Aldosterone synthesis and secretion, Cellular senescence, and NF-kappa B signaling pathway-essentially encompassing signal transduction pathways crucial to reproductive processes.

Discussion

This research significantly contributes to unraveling the molecular mechanisms governing follicular development in Kazakh horses. It establishes and preliminarily validates a differential regulatory network involving lncRNA-miRNA-mRNA, intricately associated with processes such as cell proliferation, differentiation, and apoptosis and integral to the developmental intricacies of stromal follicles. The findings of this study provide a solid theoretical foundation for delving deeper into the realm of reproductive aging in Kazakh mares, presenting itself as a pivotal regulatory pathway in the context of horse ovarian development.

[Sonographic studies on the significance of follicle size and corpus luteum morphology in dairy cows after insemination]

OBJECTIVE

In dairy cattle, numerous factors determine the success of an insemination. The aim of the present study was to generate findings concerning the association between the preovulatory follicles, the corpora lutea with or without cavities and pregnancy in dairy cows under field conditions.

MATERIAL AND METHODS

Data was obtained from 176 dairy cows scheduled for artificial insemination. The cows were gynecologically examined using sonography at the time of insemination, 24 hours later, on day 9, on day 34 and after day 42 after insemination. Additionally, blood samples were collected from the coccygeal vein at the time of insemination and on day 9 in order to determine blood progesterone level.

RESULTS

Depending on the result of the pregnancy test, no difference was detected between the dimensions of the follicles, corpora lutea as well as their cavities and progesterone levels 9 days after insemination in the dairy cows with spontaneous ovulations. In contrast to the corpus luteum without cavity, the surface area of the corpus luteum with cavity remained constant during the study period, while at the same time the cavity decreased in size to a significant degree. In addition, breed differences in corpus luteum sizes were detected on day 34.

CONCLUSION

No cause was detected for the formation of cavities in corpora lutea and there was no link to the follicle from which the corpus luteum developed.

CLINICAL RELEVANCE

Both the changes in corpus luteum sizes over time and their breed-related differences could have an impact on insemination outcome.

A Mathematical Model of Estradiol Production from Ultrasound Data for Bovine Ovarian Follicles

In this paper, we present a new way to assess the concentration of estradiol (E2) and Insulin Growth Factor-1 (IGF) based on the results from ultrasound scans combined with mathematical models. The IGF1 model is based on the progesterone (P4) concentration, which can be estimated with models calculating P4 level based on the size/volume of corpus luteum (CL) measured during ultrasound scans. At this moment little is known about the underlying reasons for double ovulation and silent heat occurrences. Both of these are linked to the level of IGF1: double ovulations are linked to higher IGF1 levels and and silent heat is linked to lower E2 to P4 ratio. These models can help to improve understanding of the related concentrations of E2 and IGF1. Currently, it is known that diet and genetic factors have an impact on ovulation rates and silent heat. In this study, we also examine the decline of the production of E2 in vivo by atretic follicles throughout the process of atresia. This is the first recorded quantitative description of this decline.

Ovarian Follicular Dynamics and Its Functional Significance in Relation with Follicle Deviation, Vaginal Cytology, and Hormone Profiles in Llamas (Lama glama)

The reproductive physiology in camelid species has its particularities. The present study aimed to characterize the ovarian follicular dynamics and its functional significance in relation to follicular deviation, vaginal cytological characteristics, and sexual hormone profiles in llamas as the first report in South American camelids. Non-pregnant, multiparous llamas (Lama glama; n = 10; age: 48−72 mo.; BCS: 2.5−3.0) were enrolled in the study. The ultrasonographic assessment was carried out transvaginally and follicular ablation was performed (day 0) when follicles were larger than 7 mm. The follicle number and diameter were scored daily throughout the process for a proper evaluation of the deviated follicles and to monitor the presence of new follicle pools (1.5 to 2.5 mm diameter). Vaginal cytological evaluation (parabasal, intermediate, and superficial cells) was performed every other day until day 6. Endocrine profiles (17β estradiol, anti-Mullerian hormone, testosterone, and progesterone) during pre- and post-follicular deviation were determined by using the ELISA assay. Differential follicular dynamics both in the presence of a single dominant follicle (DF) and in codominance during the follicular deviation process were detected in llamas (p < 0.05). The percentage of superficial cells was the most related to the follicular wave phase. However, the percentage of parabasal, intermediate, and superficial cells was not related to the phases of follicular growth, dominance, and regression (p > 0.05). Differential patterns among the different hormone concentration levels regarding the 17β estradiol, anti-Mullerian hormone, progesterone, and testosterone during follicular deviation were observed, with the latter being significantly different along the deviation process (p < 0.05). In conclusion, the use of vaginal cytology assessment would not be sufficient to determine the follicular phases in llamas. Therefore, complementary analyses, such as ultrasonography and endocrine assessment, are strongly recommended to determine follicular dynamics during the follicular deviation.

Effect of day of estrus cycle at time of transvaginal follicle aspiration for oocyte recovery on rates of in vitro maturation and blastocyst production after intracytoplasmic sperm injection

OBJECTIVE

To determine the effect of stage of estrus cycle (day after ovulation) at the time of transvaginal ultrasound-guided follicle aspiration (TVA) on parameters related to the success of in vitro equine embryo production.

ANIMALS

14 healthy mares were used; 11 completed the study and were included for analysis.

PROCEDURES

Mares underwent TVA of all follicles ≥ 5 mm diameter at each of 3 timepoints: 7 days after ovulation, 14 days after ovulation, and S-DSF (subordinate to a dominant stimulated follicle), during estrus at 24 hours after gonadotropin administration. The 3 treatments were assigned to each mare in random order; mares underwent follicle growth and ovulation between treatments. Recovered oocytes were matured in vitro, subjected to intracytoplasmic sperm injection (ICSI), and cultured to the blastocyst stage in vitro.

RESULTS

Total follicle numbers differed significantly between individual mares but did not differ between treatments. The number of follicles of different sizes significantly (P < 0.05) differed between treatments, with mares in the Day 7 treatment having more follicles 5 to 9 mm in diameter and fewer follicles 20 to 24 mm in diameter than mares in the other 2 treatments. After in vitro maturation culture, there were significantly more mature oocytes in the S-DSF treatment than in the other 2 treatments. There were no differences in blastocyst rate after ICSI among treatment groups.

CLINICAL RELEVANCE

Timing of TVA for aspiration of S-DSFs may increase the number of mature oocytes available for ICSI. Understanding of the effects of timing of TVA will help veterinarians to maximize the efficiency of this procedure.

Follicular-fluid proteomics during equine follicle development

The complex composition of the follicular fluid (FF), the intimate proximity to the oocyte, and the continual changes in their composition have a major effect on folliculogenesis and oogenesis. To date, the profiling of FF proteomes during follicle selection, development, and ovulation has not been comprehensively investigated. Therefore, a shotgun proteomics approach and bioinformatics analyses were used to profile the proteomes of equine FF harvested in vivo from follicles at the following development stages: predeviation (18-20 mm), deviation (22-25 mm), postdeviation (26-29 mm), preovulatory (30-35 mm), and impending ovulation. A total of 294 proteins were detected in FF (FDR <1%), corresponding to 65 common proteins and 124, 142, 167, 132, and 142 proteins in the predeviation, deviation, postdeviation, preovulatory, and impending ovulation groups, respectively. The higher expression of properdin and several other proteins belonging to the complement system during the deviation time and ovulation suggested their contribution in the selection of the future dominant follicle and ovulation. Apolipoprotein A-1 and antithrombin-III appeared to be important throughout folliculogenesis. The "complement and coagulation cascades" was the major KEGG pathway across all stages of follicle development. The significant expression of several proteins belonging to the serine-type endopeptidase indicated their likely contribution to follicle and oocyte development. Our data provide an extensive description and functional analyses of the equine FF proteome during follicle selection, development, and ovulation. This information will help improve understanding of the ovarian function and ovulatory dysfunctions and might serve as a reference for future biomarker discovery for oocyte quality assessment.

The ovarian and uterine responses of Baixadeiro mares to prostaglandin synchronization during the dry and rainy seasons

This study aimed to evaluate the effect of synchronization with prostaglandin F2α in Baixadeiro mares during the rainy and dry seasons. Fourteen mares were synchronized by administering two doses of 1 mL prostaglandin PGF 2α and monitored by rectal palpation and ultrasound for the assessment of follicular development and uterine echotexture. Of this total, nine mares allowed the collection of blood, in which the blood was collected by venipuncture of the jugular vein to determine progesterone (P4) by ELISA. Mares showed no differences (P > 0.05) in weight, body score condition (BSC), tone, uterine edema, frequency of ovulation, synchronization interval, estrus, and the total number of follicles between periods. However, there was a difference in large increased follicle diameter (P < 0.05) during the dry season. The average concentrations of P4 in mares differed (P < 0.05) between the pre- and post-ovulatory phases for both seasons and after ovulation, with higher concentrations in the rainy season. Furthermore, statistical differences in daily light (P < 0.05) were observed between the dry and rainy periods. Thus, we conclude that mares from the genetic grouping Baixadeiro showed no reproductive seasonality, though there was a difference in luminosity between the rainy and dry seasons. The treatment with two doses of PGF 2α was effective in synchronizing the mares, promoting the return of estrus in the dry and rainy periods. The mares remaining cyclically active throughout the year provided there were appropriate forage availability and quality levels to allow for normal values of body weight and condition.

The two-step process of ovarian follicular growth and maturation in mammals can be compared to a fruit ripening where quality depends on the second step

In human IVF, the main uncertainty factor impacting on success is oocyte quality, which largely depends on the follicular status at the time of collection. Decades of debate ensued to find the perfect stimulation protocol demonstrated the complexity of the ovarian response to exogenous gonadotropins and the dynamic nature of late folliculogenesis. Although several follicular markers, proteins, RNA from granulosa cells or microRNA and follicular fluid metabolites have been associated with outcome, the possibility to influence them during stimulation remains elusive. The heterogeneity of the follicle's maturity following control ovarian stimulation is also an important factor to explain average poor oocyte quality still observed today. In this review, the analogy between the apple ripening on the tree and follicular development is presented to focus the attention on a biphasic process: growth and differentiation. The molecular analysis of the progressive follicular differentiation indicates 2 competing phenomena: growth and differentiation where a delicate balance must operate from one to the other to ensure proper maturity at ovulation. As long as FSH stimulates growth, follicles remain green, and it is only when FSH is replaced by LH that the ripening process begins, and "apples" become red. Both fruits, follicles and apples, depend on a perfect timing of events to generate offspring.

Hemodynamic, endocrine, and gene expression mechanisms regulating equine ovarian follicular and cellular development

Ovulatory follicle development and associated oocyte maturation involve complex coordinated molecular and cellular mechanisms not yet fully understood. This study addresses the relationships among follicle diameter, follicle wall blood flow, follicular-fluid factors, and gene expression for follicle growth, steroidogenesis, angiogenesis, and apoptosis in granulosa/cumulus cells and oocytes during different stages from the beginning of largest/ovulatory follicle to impending ovulation in mares. The most remarkable findings were (i) a positive association between follicle development, follicle blood flow, intrafollicular follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol, progesterone, and messenger RNA (mRNA) expression for FSHR and LHCGR in granulosa cells of the largest/ovulatory follicle; (ii) a plateau or decrease in follicle diameter and blood flow and granulosa cell mRNA for FSHR, LHCGR, IGF1R, VEGFR2, CYP19A1, and CASP3 at the preovulatory stage; (iii) higher StAR and BCL2 and lower CASP3 mRNA in granulosa cells at the time of impending ovulation; (iv) greater IGF1R mRNA for granulosa cells at the predeviation stage; and (v) lower FSHR, LHCGR, IGF1R, and VEGFR2 mRNA in cumulus cells and greater LHCGR and IGF1R mRNA in oocytes at the ovulatory stage. This study is a critical advance in the understanding of molecular mechanisms of follicle development and oocyte maturation and is expected to be vital for future studies targeting potential markers.

Expression of kisspeptin and its receptor in different functional classes of ovarian follicle in the buffalo (Bubalus bubalis)

Recently, we reported the differential expression of kisspeptinergic system in the bubaline hypothalamus and corpus luteum. Here, we document the expression of kisspeptin (Kp) and its receptor (Kiss1r) in the ovarian follicles of the buffalo with respect to the functional status. Follicles of ≥10 to ≤13 mm diameter (n = 45) were retrospectively categorized into active (n = 18), intermediate (n = 16) and atretic (n = 11) follicles based on the concentrations of intrafollicular progesterone (P₄) and estradiol (E₂). The P₄:E₂ ratio was significantly lower in the active follicle (0.43 ± 0.08) than that of the intermediate (3.46 ± 0.53) and atretic (28.4 ± 10.6) follicles (P < 0.05). Relative fold change in the transcripts of kisspeptin (Kiss1), Kiss1r, gonadotrophin receptors, steroid acute regulatory protein (StAR), cytochrome P450 family 11 subfamily A member 1 (CYP11A1), cytochrome P450 Family 19 subfamily A member 1 (CYP19A1), insulin like growth factor -1 (IGF-1), apoptotic factors (caspase 3 and B-cell lymphoma 2, BCL2) was calculated using qPCR in the follicular wall of the three categories of follicle (n = 8/group). In another experiment, histological sections of the ovary (n = 41) were used to group the follicles as described above and immunostaining of Kp, Kiss1r and aromatase was done. A significant upregulation of StAR, CYP11A1 and CYP19A1 in the active follicles supported the endocrine basis of follicular classification. The transcripts of Kiss1 and Kiss1r were upregulated by 19.45 fold and 4.25 fold, respectively in the active follicle as compared to other groups. Immunolocalization studies revealed that Kp and Kiss1r were localized to the basal and antral granulosa cells (GC) of the active and intermediate follicles; however, the staining intensity was stronger in the former group. Strong expression of CYP19A1 in the GC layer of active follicle supported the histological basis of defining the functional status of the follicle. It is concluded that the follicular compartment of the bubaline ovary expressed the constituents of kisspeptinergic system. The expression of Kp and Kiss1r was influenced by the functional status of the follicle with intense localization in the GC layer of the active follicles.

Reproductive patterns and follicular waves in postpartum lactating versus non-postpartum cycling mares

This comparative study between postpartum lactating (PP Lactating) and non-postpartum cycling (N-PP Cycling) mares aimed to characterize reproductive patterns, types and frequencies of follicular waves, corpus luteum and endometrial echotexture dynamics, and the influence of season and body condition. Mares from each group were paired considering the day of parturition of a PP Lactating mare. The partum-ovulation interval (POI) and the postpartum interovulatory interval (PPIOI) were evaluated for PP Lactating mares, and 2 IOIs were evaluated for N-PP Cycling mares. The following observations were made: (i) PP Lactating mares have several different reproductive patterns, such as continuous reproductive activity (i.e., short or long POIs followed by a PPIOI), ovarian inactivity after the first postpartum ovulation, or continuous ovarian inactivity (postpartum anestrous phase); (ii) a greater total number of minor waves was seen in PP Lactating mares; (iii) major primary follicular waves (i.e., ovulatory) emerge around the day of parturition in mares with short POIs; (iv) the season of parturition (spring season), decrease in body condition score, and body-weight loss can have an associated detrimental effect in PP Lactating mares by increasing the total number of minor follicular waves and, consequently, the POI length; (v) endometrial echotexture scores are higher during the POI and can be influenced by the season of parturition; and (vi) corpus luteum development and demise are similar between PP Lactating and N-PP Cycling mares. This study provides, for the first time, detailed information about reproductive physiological aspects during the postpartum period and may facilitate the interpretation of gynecological practices during the foal heat and subsequent IOI in mares.

Global analysis of FSH-regulated gene expression and histone modification in mouse granulosa cells

Follicle-stimulating hormone (FSH) regulates ovarian follicular development through a specific gene expression program. We analyzed FSH-regulated transcriptome and histone modification in granulosa cells during follicular development. We used super-stimulated immature mice and collected granulosa cells before and 48 h after stimulation with equine chorionic gonadotropin (eCG). We profiled the transcriptome using RNA-sequencing (N = 3/time-point) and genome-wide trimethylation of lysine 4 of histone H3 (H3K4me3; an active transcription marker) using chromatin immunoprecipitation and sequencing (ChIP-Seq; N = 2/time-point). Across the mouse genome, 14,583 genes had an associated H3K4me3 peak and 63-66% of these peaks were observed within ≤1 kb promoter region. There were 72 genes with differential H3K4me3 modification at 48 h eCG (absolute log fold change > 1; false discovery rate [FDR] < 0.05) relative to 0 h eCG. Transcriptome data analysis showed 1463 differentially expressed genes at 48 h eCG (absolute log fold change > 1; FDR < 0.05). Among the 20 genes with differential expression and altered H3K4me3 modification, Lhcgr had higher H3K4me3 abundance and expression, while Nrip2 had lower H3K4me3 abundance and expression. Using ChIP-qPCR, we showed that FSH-regulated expression of Lhcgr, Cyp19a1, Nppc, and Nrip2 through regulation of H3K4me3 at their respective promoters. Transcript isoform analysis using Kallisto-Sleuth tool revealed 875 differentially expressed transcripts at 48 h eCG (b > 1; FDR < 0.05). Pathway analysis of RNA-seq data demonstrated that TGF-β signaling and steroidogenic pathways were regulated at 48 h eCG. Thus, FSH regulates gene expression in granulosa cells through multiple mechanisms namely altered H3K4me3 modification and inducing specific transcripts. These data form the basis for further studies investigating how these specific mechanisms regulate granulosa cell functions.

Follicular wave synchronization prior to ovum pick-up

Among the reproductive biotechnologies, in vitro embryo production (IVEP) is an important tool for multiplying genetic material of superior merit. Recently, the number of embryos produced and transferred in vitro became significantly higher than that produced in vivo worldwide. In this context, the enhancement was attributable to ovum pick-up (OPU). With the advent of genomic technology, shortened breeding intervals, and increased selection accuracy, IVEP has attracted increasing attention for commercial use. The IVEP technique is well-established, but the embryo production rate has reached a plateau at 30-40%. Despite constant advances, the OPU/IVEP programs face some challenges that hinder the efficient application of the technique. Previous studies have shown that the quantity and quality of aspirated oocytes are essential factors for successful IVEP. This paper presents a brief overview of alternatives that can be employed to improve the process-seeking methods that assist in the recovery of better-quality oocytes and higher competence in OPU to improve embryo production. These strategies include using follicular wave synchronization prior to OPU, employing the influence of antral follicle populations, using the pre-OPU gonadotrophic stimulus and applying non-hormonal methods for selecting female donors.

Intrafollicular and systemic serotonin, oestradiol and progesterone concentrations in cycling mares

The hypothesis that a local serotonergic network might also exist in the follicle of mares remains poorly documented, with exception for humans and laboratory species. For this reason, the aim of the present study was to clarify this possibility, investigating intrafollicular serotonin concentrations of the cycling mare at ovulation time. Sixty ovaries collected from 30 clinically healthy mares of slaughterhouse meat production with clinically normal reproductive tracts after slaughtering were evaluated. Blood samples were taken prior to sacrifice. Follicles were classified in three categories in relation to size, as small (20-30 mm), medium (31-40 mm) and large (>41 mm), and the follicular fluid samples were extracted from each follicle. Intrafollicular and systemic serotonin (5-HT), oestradiol-17β (E₂ ) and progesterone (P₄ ) were determined by means of enzyme-linked immunosorbent assay and RIA, respectively. Intrafollicular 5-HT, E₂ and P₄ concentrations were higher than systemic ones (p < .05). 5-HT concentrations increased in larger compared to medium follicles, without differences compared to small size follicles (p < .05). 5-HT and E₂ (r = .79) and 5-HT and P₄ (r = .79; p < .05) were positively correlated. 5-HT and P₄ concentrations in follicular fluid increased progressively with the increase in follicular size (p < .05). Follicle diameter and E₂ (r = .85) and P₄ (r = .68) were correlated (p < .05). Since serotonin interacts with steroids, its role on steroidogenesis during growth of the dominant follicle may be suggested.

Differential expression of LHCGR and its isoforms is associated to the variability in superovulation responses of Gir cattle

The aim of this study was to evaluate the pattern of expression of LHCGR isoforms in Gir heifers characterized as good (10.3 ± 1.2 ova/embryos per flush, n = 5) or poor responders (1.1 ± 0.3 ova/embryos per flush, n = 5) to superovulation protocols. In both groups, an adapted ultrasound-guided follicular aspiration system was used to collect granulosa cells from 8 mm follicles formed either during a synchronized, non-stimulated follicular wave (no stimulation control, NS) or on the fourth day of a superovulation protocol (SOV) induced with 200 IU of pFSH. The recovered follicular fluid was centrifuged and granulosa cells were washed with NaCl 0.9% and kept in RNAlater^®. RNA extraction was performed using a commercial RNeasy Micro Kit and eluted samples were quantified and reverse transcribed using the commercial Superscript III kit. cDNA samples were amplified by real-time PCR using a primer to target LH/hCG receptor gene - not selective for LHCGR isoforms (total LHCGR) - and four sets of isoforms selective primers (S1, S10, S10 + 11, and S11). Analyses were performed using the REST software and expression levels are shown as mean ± SEM. Under physiological conditions (NS), poor responders had a higher expression of total LHCGR (4.9 ± 1.7 fold-change, P < 0.01) as well as isoforms S10, S11 and S10 + 11, compared to good responders. In both phenotypes, superovulation down-regulated total LHCGR expression (-0.5 ± 0.2 and -0.9 ± 0.0 for good and poor responders, respectively; P < 0.05). However, in poor responders the exogenous FSH treatment up-regulated the S10 (2.4 ± 2.0; P < 0.05), S10 + 11 (3.8 ± 3.2; P < 0.01), and S1 isoforms (1.8 ± 1.3; P < 0.05), compared to good responders We conclude that down-regulation of total LHCGR, associated to up-regulation of their inactive isoforms, may have compromised follicle development and thus contributed to the low efficiency of superovulation in heifers with a poor responder phenotype.

Novel insights into the genetic basis of buffalo reproductive performance

Background

Fertility is a complex trait that has a major impact on the development of the buffalo industry. Genome-wide association study (GWAS) has increased the ability to detect genes influencing complex traits, and many important genes related to reproductive traits have been identified in ruminants. However, reproductive traits are influenced by many factors. The development of the follicle is one of the most important internal processes affecting fertility. Genes found by GWAS to be associated with follicular development may directly affect fertility. The present study combined GWAS and RNA-seq of follicular granulosa cells to identify important genes which may affect fertility in the buffalo.

Results

The 90 K Affymetrix Axiom Buffalo SNP Array was used to identify the SNPs, genomic regions, and genes that were associated with reproductive traits. A total of 40 suggestive loci (related to 28 genes) were identified to be associated with six reproductive traits (first, second and third calving age, calving interval, the number of services per conception and open days). Interestingly, the mRNA expressions of 25 of these genes were also observed in buffalo follicular granulosa cells. The IGFBP7 gene showed high level of expression during whole antral follicle growth. The knockdown of IGFBP7 in buffalo granulosa cells promoted cell apoptosis and hindered cell proliferation, and increased the production of progesterone and estradiol. Furthermore, a notable signal was detected at 2.3–2.7 Mb on the equivalent of bovine chromosome 5 associated with age at second calving, calving interval, and open days.

Conclusions

The genes associated with buffalo reproductive traits in this study may have effect on fertility by regulating of follicular growth. These results may have important implications for improving buffalo breeding programs through application of genomic information.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5208-6) contains supplementary material, which is available to authorized users.

Treated and untreated anovulation associated with ovarian and uterine blood flow in Arabian mares (a case study)

To investigate the development of treated and untreated hormonal anovulatory follicles (AnOV) associated with uterine and ovarian vascularization, rectal Doppler ultrasound of seven Arabian mares was performed before and after the development of an AnOV. In addition to measuring the diameter, area and volume of the follicle, daily colour and power Doppler scans were analysed in order to measure red, blue and power blood flow areas in pixels. Serum levels of estradiol (E2), progesterone (P4), leptin, insulin-like growth factor-I (IGF-1) and nitric oxide (NO) were measured as well. The diameter (cm), area (cm2), volume (cm3), area in pixels, antral area in pixels, circumference, and percentage change in circulation of the AnOV progressively increased (P<0.0001) after the disappearance of uterine oedema compared to the values obtained during oedema. The blue, total colour and power areas of the AnOV increased after the disappearance of uterine oedema (P<0.0001). When the antral area was excluded, the percentage of the granulosa layer in the colour and power Doppler decreased after the disappearance of uterine oedema. The ipsilateral uterine horn and uterine body had significantly (P<0.0001) high blue and red blood flow vascularization areas in the presence of uterine oedema. The AnOV was associated with low P4, IGF-1 (P<0.001), and leptin (P<0.05). Treatment of the AnOV follicle with GnRH resulted in its luteinization and induced ovulation 9 and 30 days later. It can be concluded that an abrupt increase in blood flow due to decreased progesterone and E2 and increased IGF-1 causes anovulation. The absence of oestrous behaviour and high uterine-oedema-associated follicular and ipsilateral uterine horn vascularization are predictors of ovulation failure.

Impact of Equine and Bovine Oocyte Maturation in Follicular Fluid From Young and Old Mares on Embryo Production in Vitro

Equine follicular fluid (FF) provides autocrine and paracrine factors from theca, granulosa, and cumulus cells, both reflecting and impacting oocyte and follicle maturation. We hypothesized that maturation of oocytes in FF from old versus young mares has a deleterious effect on oocyte maturation and their subsequent developmental potential. Follicular fluid was collected from the large, dominant follicle from young mares (4-13 years) or old mares (21-26 years) and classified as: (1) Noninduced follicular fluid (NFF), FF from noninduced follicle 33 ± 3 mm, or (2) Induced follicular fluid (IFF), FF collected ∼24 hours after administration of ovulation-inducing drugs when a follicle 33 ± 3 mm was observed. In experiment 1, immature equine oocytes were collected, matured in vitro for 30 ± 2 hours in 100% IFF, collected from young or old mares, with the addition of follicle stimulating hormone (5 mU/mL), then fertilized by intracytoplasmic sperm injection. In experiment 2, immature bovine oocytes were collected, matured in 100% IFF or NFF, collected from young mares or old mares, then fertilized via in vitro fertilization. In experiment 1, more blastocysts tended (P = .08) to be produced from equine oocytes that were matured in old versus young mare FF. In experiment 2, when IFF and NFF groups were combined, cleavage rates were higher (P = .001) when bovine oocytes were matured in FF from young than old mares. In contrast to our hypothesis, we observed no conclusive evidence that FF from old mares has a deleterious impact on oocytes and their early developmental potential.

Hormonal stimulation in 4 to 7 months old Nelore (Bos taurus indicus) females improved ovarian follicular responses but not the in vitro embryo production

The inclusion of pre-pubertal bovine females in reproductive management could allow in vitro embryo production and reduce generation interval, thereby causing faster genetic gain of the herd. However, oocytes of pre-pubertal females have lower competence, blastocyst production, and pregnancy rates than those collected from pubertal animals. This study aimed to evaluate the effect of an induced hormonal stimulation on the serum concentrations of Anti-Mullerian hormone (AMH) and FSH, ovarian responses, ovum pick up (OPU), and in vitro produced embryos (IVP) from oocytes obtained from four-to seven-months old Nelore female cattle. In a crossover design, these females were randomly allocated into: 1) Treated Group (TG, n = 9): the animals were subjected to a hormonal protocol (implanted progesterone device, estradiol benzoate, LH, and FSH) from Day 0 (the start of the treatment) to Day 7 (OPU day), and 2) Control Group (CG, n = 9): the females did not receive any hormonal stimulation, but they had ablation of their largest follicles on Day 2 of experiment. Blood collection for serum FSH measurements was done on Days 5, 6, 7, and 8, and collection for serum AMH measurements was done on Days 5 and 8. As hypothesized, TG had higher serum FSH concentrations (p < 0.05) on Day 5 (1.16 ± 0.31 ng/mL), Day 6 (1.21 ± 0.45 ng/mL), and Day 7 (0.95 ± 0.26 ng/mL) than CG (0.56 ± 0.17 ng/mL on Day 5, 0.60 ± 0.25 ng/mL on Day 6, and 0.60 ± 0.14 ng/mL on Day 7). However, serum AMH concentrations were neither significantly different (p > 0.05) between CG and TG, nor between the collection days. Hormonal stimulation also increased (p < 0.05) total follicular population (20.0 ± 4.95 CG vs 26.66 ± 4.24 TG), ovarian diameter (13.08 ± 1.0 mm CG vs 14.81 ± 1.38 mm TG) and number of follicles ≥2.5 mm (6.88 ± 2.14 CG vs 11.55 ± 4.09 TG). In TG, grades I and II oocytes predominated, whereas, in CG grades III and IV oocytes were more abundant (p < 0.05). No significant increases (p > 0.05) in the cleavage (49.33% CG vs 51.42% TG), cleavage > 4 cells (9.33% CG vs 16.19% TG), and blastocysts rates (1.33% CG vs 8.57% TG) were seen in TG. This hormonal protocol increased serum FSH concentrations that possibly contributed to increases in the observed follicle, as well as improving oocyte quality. This exogenous hormonal stimulation increased available oocytes numbers for IVP, despite no increase in the in vitro embryo production efficiency.

Molecular and endocrine factors involved in future dominant follicle dynamics during the induction of luteolysis in Bos indicus cows

The growth profiles of the future dominant follicle (DF) and subordinate follicle (SF) and the gene expression of the granulosa cells during luteolysis induction in Bos indicus cows were evaluated. Forty cows were synchronized with a progesterone and estradiol based protocol. After synchronization, cows with a corpus luteum (CL) were evaluated by ultrasonography every 12 h, beginning at eight days post ovulation. Cows identified with a follicle of at least 6.0 mm in diameter in the second wave were split into two groups (BD-before follicular deviation and AD-after follicular deviation. In the BD group cows received 500 μg of cloprostenol (a synthetic analogue of prostaglandin F2α) when the DF reached a mean diameter of 7.0 mm (6.5-7.5 mm). In the AD group, cows received 500 μg of cloprostenol when the DF reached a mean diameter of 8.0 mm (7.5-8.5 mm). Cows in both groups were submitted to aspiration of the DF at 96 and 72 h after prostaglandin was given. Follicular aspirations were performed to quantify IGF1R, LHR and PAPPA transcripts in the granulosa cells. The diameter of the DF at the moment of prostaglandin administration (P = 0.001) and the growth rate of the SF (P = 0.05) were greater in the AD group. There was greater abundance of LHR transcripts in BD cows (P = 0.04). The remaining variables tested were similar between the experimental groups (P > 0.05). In conclusion, the induction of luteolysis before follicular deviation does not interfere with dominant follicle dynamics. However, it causes granulosa cell LHR down regulation.

Sarcoptes scabiei alters follicular dynamics in female Iberian ibex through a reduction in body weight

Normal development of the ovarian cycle is a key factor in ensuring female reproductive success. Sarcoptes scabiei has been shown to induce changes in host physiology, although the effects of this mite on the female reproductive cycle are still unknown. In an attempt to clarify this issue, the number of ovarian structures (primary follicles, secondary follicles, Graaf follicles, corpus luteum and corpus albicans) in female Iberian ibex (Capra pyrenaica) affected by sarcoptic mange was explored by histological analysis of samples taken from 102 females selectively harvested in the Sierra Nevada Natural Space, southern Spain. The effect of mange status, body weight (corrected for age), age and year of sampling on the number of ovarian structures was assessed using generalized linear models. Our results provide evidence that sarcoptic mange alters follicular dynamics through a reduction in host body weight, whose main consequences are noted in follicular maturation and ovulatory capacity.

Systemic and intrafollicular components of follicle selection in mares

Mares are superb models for study of follicle selection owing to similarities between mares and women in relative follicle diameters at specific events during the follicular wave and follicle accessibility for experimental sampling and manipulation. Usually, only 1 major follicular wave with a dominant follicle (DF) greater than 30 mm develops during the 22 to 24 d of the equine estrous cycle and is termed the primary or ovulatory wave. A major secondary wave occasionally (25%) develops early in the cycle. Follicles of the primary wave emerge at 6 mm on day 10 or 11 (day 0 = ovulation). The 2 largest follicles begin to deviate in diameter on day 16 when the future DF and largest subordinate follicle (SF) are 23 mm and 20 mm, respectively. The deviation process begins the day before diameter deviation as indicated in the future DF but not in the future SF by (1) increase in prominence of an anechoic layer and vascular perfusion of the wall and (2) increase in follicular-fluid concentrations of IGF1, vascular endothelial growth factor, estradiol, and inhibin-A. A systemic component of the deviation process is represented by suppression of circulating FSH from secretion of inhibin and estradiol from the developing DF. Production of inhibin is stimulated by IGF1 and LH, and estradiol is stimulated by LH and not by IGF1 in mares. A local intrafollicular component involves the production of IGF1, which apparently increases the responsiveness of the future DF to FSH. The roles of the IGF system have been well studied in mares, but the effect of IGF1 on increasing the sensitivity of the follicle cells to FSH is based primarily on studies in other species. The greater response of the future DF than the SF to the low concentrations of FSH is the essence of selection. During the common growth phase that precedes deviation, diameter of the 2 largest follicles increases in parallel on average when normalized to emergence or retrospectively to deviation. Study of individual waves indicates that (1) the 2 follicles change ranks (relative diameters) during the common growth phase in about 30% of primary waves and (2) after ablation of 1, 2, or 3 of the largest follicles at the expected beginning of deviation, the next largest retained follicle becomes the DF indicating that several follicles have the capacity for dominance; therefore, it is proposed that the deviation process represents the entire mechanism of follicle selection in mares.

Intrafollicular oestradiol production, expression of the LH receptor (LHR) gene and its isoforms, and early follicular deviation in Bos indicus

The aim of the present study was to characterise the roles of intrafollicular oestradiol production and granulosa cell (GC) expression of the LH receptor (LHR) gene and its isoforms during follicular deviation in Bos indicus. Follicular wave emergence was synchronised in heifers from a Bos taurus dairy (Holstein; n = 10) and a B. indicus dairy breed (Gir; n = 10). Follicles were aspirated individually at sizes corresponding to the periods of predeviation, deviation and postdeviation. Intrafollicular oestradiol (IF-E2) and progesterone (IF-P4) concentrations were determined in the follicular fluid (FF) by radioimmunoassay, and relative expression of P450 aromatase (CYP19A1) and LHR forms was evaluated in GC using real-time quantitative–polymerase chain reaction. Despite differences in the size of the dominant follicle at deviation, changes in CYP19A1 expression and IF-E2 concentrations were similar in follicles of the same diameter in both breeds. A peak in total LHR expression occurred after follicular deviation in association with low expression of LHR isoforms. The results suggest that regulation of LHR function by sequential changes in the expression pattern of LHR isoforms may play a role in the early deviation of the dominant follicle, as observed in B. indicus breeds.

Changes in brain ribonuclease (BRB) messenger RNA in granulosa cells (GCs) of dominant vs subordinate ovarian follicles of cattle and the regulation of BRB gene expression in bovine GCs

Brain ribonuclease (BRB) is a member of the ribonuclease A superfamily that is constitutively expressed in a range of tissues and is the functional homolog of human ribonuclease 1. This study was designed to characterize BRB gene expression in granulosa cells (GCs) during development of bovine dominant ovarian follicles and to determine the hormonal regulation of BRB in GCs. Estrous cycles of Holstein cows (n = 18) were synchronized, and cows were ovariectomized on either day 3 to 4 or day 5 to 6 after ovulation during dominant follicle growth and selection. Ovaries were collected, follicular fluid (FFL) was aspirated, and GCs were collected for RNA isolation and quantitative polymerase chain reaction. Follicles were categorized as small (1-5 mm; pooled per ovary), medium (5-8 mm; individually collected), or large (8.1-17 mm; individually collected) based on surface diameter. Estradiol (E2) and progesterone (P4) levels were measured by radioimmunoassay (RIA) in FFL. Abundance of BRB messenger RNA (mRNA) in GCs was 8.6- to 11.8-fold greater (P < 0.05) in small (n = 31), medium (n = 66), and large (n = 33) subordinate E2-inactive (FFL E2 < P4) follicles than in large (n = 16) dominant E2-active (FFL E2 > P4) follicles. In the largest 4 follicles, GCs BRB mRNA abundance was negatively correlated (P < 0.01) with FFL E2 (r = -0.65) and E2:P4 ratio (r = -0.46). In experiment 2, GCs from large (8-22 mm diameter) and small (1-5 mm diameter) follicles were treated with insulin-like growth factor 1 (IGF1; 0 or 30 ng/mL) and/or tumor necrosis factor alpha (0 or 30 ng/mL); IGF1 increased (P < 0.05) BRB mRNA abundance, and tumor necrosis factor alpha decreased (P < 0.001) the IGF1-induced BRB mRNA abundance in large-follicle GCs. In experiment 3 to 6, E2, follicle-stimulating hormone, fibroblast growth factor 9, cortisol, wingless 3A, or sonic hedgehog did not affect (P > 0.10) abundance of BRB mRNA in GCs; thyroxine and luteinizing hormone increased (P < 0.05), whereas prostaglandin E2 (PGE2) decreased (P < 0.05) BRB mRNA abundance in small-follicle GCs. Treatment of small-follicle GCs with recombinant human RNase1 increased (P < 0.05) GCs numbers and E2 production. In conclusion, BRB is a hormonally and developmentally regulated gene in bovine GCs and may regulate E2 production during follicular growth in cattle.

MicroRNA indicators of follicular steroidogenesis

MicroRNAs (miRNAs) can provide useful biomarkers of tissue function. The aim of the present study was to determine, in bovine follicles (n = 66; diameter 4-22 mm), the relationship among several indices of steroidogenesis and levels of 15 miRNAs previously identified to be associated with follicle development. Oestradiol levels, the oestradiol : progesterone (E : P) ratio and cytochrome P450 family 19 subfamily A member 1 (CYP19A1) expression were strongly correlated with each other (ρ > 0.8) and with LH/choriogonadotropin receptor (LHCGR) expression (ρ ≥ 0.6; P < 0.01). Levels of nine different miRNAs in the follicular wall were correlated (P < 0.01) with oestradiol, the E : P ratio and CYP19A1, with miR-873 showing the strongest correlation in each case (ρ > 0.7). Analyses of follicular fluid miRNAs identified miR-202 as correlated with oestradiol, the E : P ratio and CYP19A1 (ρ > 0.5; P < 0.01). When considering all follicle end-points together, we found that using a cut-off value of E : P = 1 overestimated the number of oestrogen-inactive follicles, whereas using CYP19A1 as a classifier provided a clearer separation of follicle samples based on oestrogen activity, in agreement with the E : P ratio, LHCGR expression and levels of miR-873 and miR-202. In conclusion, we identified miR-873 and miR-202 as miRNAs whose levels in follicular tissues can be used as indicators of steroidogenic capacity in bovine. We showed that these or other gene expression parameters, in addition or alternatively to the E : P ratio, should be used to accurately classify follicles based on steroidogenic capacity.

Involvement of miRNAs and Cell-Secreted Vesicles in Mammalian Ovarian Antral Follicle Development

Ovarian follicular development is a controlled series of events culminating with an ovulatory or atretic follicle. MicroRNAs (miRNAs) are small noncoding RNAs involved in translational regulation of genes in different developmental processes. Deletion of Dicer in mice ovaries demonstrated the importance of miRNAs in reproduction, which led to infertility. The miRNAs were thought to act only within host cells; however, these molecules are also present in cell-secreted vesicles. These vesicles are present in body fluids such as milk, serum, and ovarian follicular fluid. Vesicles are secreted in extracellular fluids and travel from donor to target cells, mediating transfer of bioactive material. Herein we discuss the role of hormonal-regulated miRNAs within different ovarian follicular cells as well as cell-secreted vesicles participation in mammalian ovarian follicular fluid. Furthermore, we discuss the possibility of miRNAs transference mediated by cell-secreted vesicles present in ovarian follicular fluid, increasing the versatility of miRNA functions during antral follicle development.

Expression and immunolocalisation of follicle-stimulating hormone receptors in gonads of newborn and adult female horses

In mares, FSH and its receptor (FSHR) are essential for ovarian function. The objective of the present study was to analyse FSHR gene expression at the mRNA and protein levels in ovarian tissue from newborn and adult horses. Expression of mRNA was analysed by reverse transcription polymerase chain reaction, whereas FSHR protein was visualised by immunohistochemistry (IHC), immunofluorescence labelling (IF) and western blot. FSHR mRNA was detected in ovarian follicles and luteal tissue from adult mares, as well as in the ovaries of neonates. Follicular growth up to 4mm in diameter was already present in neonates. Using IHC and IF, FSHR protein was detected in granulosa cells, cumulus cells and inconsistently in oocytes, independent of the animal's age or the stage of folliculogenesis. A lower FSHR expression was observed in theca cells in comparison to granulosa cells. FSHR was abundant in the ovarian stroma cells of neonates but not of adults. Luteal cells stained positive for FSHR independent of the stage of corpus luteum development. The presence of FSHR protein in various cell populations of the ovary was confirmed by western blot. In conclusion, FSHR is present in horse ovaries consistently from birth onwards and expression remains constant during the oestrous cycle.

The interrelationship between anti-Müllerian hormone, ovarian follicular populations and age in mares

REASONS FOR PERFORMING STUDY

Anti-Müllerian hormone (AMH) is a granulosa-cell-derived glycoprotein, which plays an important inhibitory role during folliculogenesis. Concentrations of AMH are highly correlated with antral follicle counts (AFCs) in other species, which in turn are related to follicular reserve. Relatively little is known about AMH and AFC in the mare.

OBJECTIVES

To determine plasma AMH concentrations and AFCs in mares of different ages, to measure the repeatability of AMH concentrations and AFCs within and across oestrous cycles and to assess the relationship between plasma AMH concentrations and AFCs with regard to mare age and follicle size.

STUDY DESIGN

An observational study examining the relationship between AMH, AFC and age in 45 mares.

METHODS

Young (3-8 years), middle-aged (9-18 years) and old mares (19-27 years) were examined by transrectal ultrasonography over 2 or 3 oestrous cycles. Plasma AMH concentrations and AFCs were determined, and antral follicles were classified by size into different groups.

RESULTS

Plasma AMH concentrations varied widely between mares within similar age groups. Antral follicle counts were significantly lower in old mares than in young and middle-aged mares, and AMH concentrations were significantly lower in old than in middle-aged mares. A positive relationship was detected between AFC and AMH, and this relationship varied by mare age with a strong correlation in older mares (ρ = 0.86; P<0.0001), a moderate correlation in middle-aged mares (ρ = 0.60; P = 0.01) and no correlation in young mares (ρ = 0.40, P<0.4). The AMH concentrations were significantly related to the number of antral follicles between 6 and 20 mm in diameter, and the repeatability of AFCs and AMH concentrations was high within and between oestrous cycles.

CONCLUSIONS

Our findings indicate that the relationship between AMH and AFC varies across age groups, and concentrations of AMH might be a better reflection of reproductive age than calendar age.

Luteinizing hormone, insulin like growth factor-1, and epidermal growth factor stimulate vascular endothelial growth factor production in cultured bubaline granulosa cells

The objective of this study was to characterize in vitro expression and secretion of vascular endothelial growth factor (VEGF) in bubaline granulosa cells (GC), grown in serum containing media supplemented with luteinizing hormone (LH), insulin like growth factor-1 (IGF-1), and epidermal growth factor (EGF) at three different doses and time durations. GCs were collected from ovarian follicles of varying diameters [Gp-I (small), 4-6 mm; Gp-II (medium), 7-9 mm; Gp-III (large), 10-13 mm; Gp-IV (pre-ovulatory), >13 mm]. In general, each of the three treatments resulted in a dose as well as time dependent increase in the mRNA expression and secretion of VEGF in the cultured GCs of Gp-IV follicles. These results were well supported by our observations on immunocytochemistry in Gp IV granulosa cell culture (GCC). We also looked into the expression dynamics of an anti-apoptotic factor--proliferating cellular antigen (PCNA) and a pro-apoptotic factor--Bcl-2-associated X protein (BAX) in GCs of Gp IV follicles on treatments with LH, IGF-1, and EGF to evaluate their cytoprotective/anti-apoptotic property. Relative expressions of PCNA and BAX showed a mutually opposite trend with the PCNA expression increasing and BAX expression decreasing with increase in dose and time to reach the zenith (P<0.05) and nadir (P<0.05) at the highest dose(s) at the maximum time duration (72 h) for PCNA and BAX respectively on treatment with all the three factors. Thus, it can be concluded that LH, IGF-1, and EGF treatments have a cytoprotective/anti-apoptotic effect and stimulate VEGF production in granulosa cells of bubaline pre-ovulatory follicles.

Development of real-time reverse transcription polymerase chain reaction assays to quantify insulin-like growth factor receptor and insulin receptor expression in equine tissue

The insulin-like growth factor system (insulin-like growth factor 1, insulin-like growth factor 2, insulin-like growth factor 1 receptor, insulin-like growth factor 2 receptor and six insulin-like growth factor-binding proteins) and insulin are essential to muscle metabolism and most aspects of male and female reproduction. Insulin-like growth factor and insulin play important roles in the regulation of cell growth, differentiation and the maintenance of cell differentiation in mammals. In order to better understand the local factors that regulate equine physiology, such as muscle metabolism and reproduction (e.g., germ cell development and fertilisation), real-time reverse transcription polymerase chain reaction assays for quantification of equine insulin-like growth factor 1 receptor and insulin receptor messenger ribonucleic acid were developed. The assays were sensitive: 192 copies/μL and 891 copies/μL for insulin-like growth factor 1 receptor, messenger ribonucleic acid and insulin receptor respectively (95% limit of detection), and efficient: 1.01 for the insulin-like growth factor 1 receptor assay and 0.95 for the insulin receptor assay. The assays had a broad linear range of detection (seven logs for insulin-like growth factor 1 receptor and six logs for insulin receptor). This allowed for analysis of very small amounts of messenger ribonucleic acid. Low concentrations of both insulin-like growth factor 1 receptor and insulin receptor messenger ribonucleic acid were detected in endometrium, lung and spleen samples, whilst high concentrations were detected in heart, muscle and kidney samples, this was most likely due to the high level of glucose metabolism and glucose utilisation by these tissues. The assays developed for insulin-like growth factor 1 receptor and insulin receptor messenger ribonucleic acid expression have been shown to work on equine tissue and will contribute to the understanding of insulin and insulin-like growth factor 1 receptor physiology in the horse.

Regulation of granulosa cell cocaine and amphetamine regulated transcript (CART) binding and effect of CART signaling inhibitor on granulosa cell estradiol production during dominant follicle selection in cattle

We previously established a potential role for cocaine and amphetamine regulated transcript (CARTPT) in dominant follicle selection in cattle. CARTPT expression is elevated in subordinate versus dominant follicles, and treatment with the mature form of the CARTPT peptide (CART) decreases follicle-stimulating hormone (FSH)-stimulated granulosa cell estradiol production in vitro and follicular fluid estradiol and granulosa cell CYP19A1 mRNA in vivo. However, mechanisms that regulate granulosa cell CART responsiveness are not understood. In this study, we investigated hormonal regulation of granulosa cell CART-binding sites in vitro and temporal regulation of granulosa cell CART-binding sites in bovine follicles collected at specific stages of a follicular wave. We also determined the effect of inhibition of CART receptor signaling in vivo on estradiol production in future subordinate follicles. Granulosa cell CART binding in vitro was increased by FSH, and this induction was blocked by estrogen receptor antagonist treatment. In follicles collected in vivo at specific stages of a follicular wave, granulosa cell CART binding in the F2 (second largest), future subordinate follicle increased during dominant follicle selection. Injection into the F2 follicle (at onset of diameter deviation) of an inhibitor of the o/i subclass of G proteins (previously shown to block CART actions in vitro) resulted in increased follicular fluid estradiol concentrations in vivo. Collectively, results demonstrate hormonal regulation of granulosa cell CART binding in vitro and temporal regulation of CART binding in subordinate follicles during dominant follicle selection. Results also suggest that CART signaling may help suppress estradiol-producing capacity of the F2 (subordinate) follicle during this time period.