Insulin-like growth factor binding proteins in granulosa and thecal cells from bovine ovarian follicles at different stages of development1,2

Transcriptome Analysis of Neuroendocrine Regulation of Ovine Hypothalamus-Pituitary-Ovary Axis during Ovine Anestrus and the Breeding Season

Most sheep are seasonal estrus, and they breed in autumn when the days get shorter. Seasonal estrus is an important factor that affects the productivity and fertility of sheep. The key point to solve this problem is to explore the regulation mechanism of estrus in sheep. Therefore, in this study, transcriptomic sequencing technology was used to identify differentially expressed mRNAs in the hypothalamus, pituitary and ovary of Small Tail Han sheep (year-round estrus) and tan sheep (seasonal estrus) among luteal, proestrus and estrus stages. There were 256,923,304,156 mRNAs being identified in the hypothalamus, pituitary and ovary, respectively. Functional analysis showed that the photosensor, leucine and isoleucine biosynthesis pathways were enriched significantly. It is speculated that photoperiod may initiate estrus by stimulating the corresponding pathways in hypothalamus. ODC1, PRLH, CRYBB2, SMAD5, OPN1SW, TPH1 are believed to be key genes involved in the estrogen process. In conclusion, this study expanded the database of indigenous sheep breeds, and also provided new candidate genes for future genetic and molecular studies on the seasonal estrus trait in sheep.

The theory of follicle selection in cattle

Selection of the dominant follicle (DF) during a follicular wave is manifested by diameter deviation or continued growth rate of the largest follicle (F1) and decreased growth rate of the next largest follicle (F2) when F1 reaches about 8.5 mm in cattle. The process of deviation in the future DF begins about 12 h before diameter deviation and involves an F1 increase in granulosa LH receptors and estradiol and maintenance of intrafollicular free insulin-like growth factor 1 (IGF1). Thereby, only F1 is developmentally prepared to use the declining FSH in the wave-stimulating FSH surge and to respond to a transient increase in LH to become the DF. A follicle that emerges first may maintain an F1 ranking and become the DF by being first to reach a critical developmental stage. However, an early size advantage is not a requisite component of the deviation process as indicated by (1) F1 and F2 may switch diameter rankings during a common growth phase that precedes diameter deviation owing to intraovarian factors that affect growth of individual follicles; (2) any follicle that reaches 5 mm regardless of diameter ranking may become a DF unless it is selected against during deviation; (3) a subordinate follicle may become dominant if the DF is ablated; (4) when F1 is ablated at 8.5 mm, the next largest follicle that is greater than 7.0 mm or the first follicle to subsequently reach 7.0 mm becomes the DF; (5) after ablation of F1 at 8.5 mm, IGF1 and estradiol increase in the intrafollicular fluid of F2 beginning at 6 h, and F2 grows to 8.5 mm in 12 h to become the DF. These considerations indicate that selection of a DF or partitioning into a DF and subordinate follicles is not initiated before the end of the common growth phase. That is, the deviation process represents the entire follicle selection mechanism.

Crybb2 deficiency impairs fertility in female mice

Beta-B2-crystallin (CRYBB2), encoded by Crybb2 gene, is a major protein in the mammalian eye lens that plays an important role in maintaining the transparency of the ocular lens. However, CRYBB2 also plays important roles in many extra-lenticular tissues and organs such as the retina, brain and testis. Our previous studies demonstrated that male Crybb2 deficient (Crybb2(-/-)) mice have reduced fertility compared with wild-type (WT) mice, while female Crybb2(-/-) mice exhibited reduced ovary weights and shorter estrous cycle percentages. Here we specifically investigated the role of CRYBB2 in the female reproductive system. Our studies revealed that ovaries from female Crybb2(-/-) mice exhibited significantly reduced numbers of primordial, secondary and pre-ovulatory follicles when compared with WT mice, while the rate of atretic follicles was also increased. Additionally, fewer eggs were collected from the oviduct of Crybb2(-/-) female mice after superovulation. Estrogen levels were higher in the metestrus and diestrus cycles of female Crybb2(-/-) mice, while progesterone levels were lower in diestrus cycles. Furthermore, the expression of survival and cell cycle genes, Bcl-2, Cdk4 and Ccnd2, were significantly decreased in granulosa cells isolated from female Crybb2(-/-) mice, consistent with the predominant expression of CRYBB2 in ovarian granulosa cells. Our results reveal a critical role for CRYBB2 in female fertility and specific effects on the proliferation and survival status of ovarian granulosa cells.

Transcriptome profiling of granulosa cells of bovine ovarian follicles during growth from small to large antral sizes

Background

At later stages of folliculogenesis, the mammalian ovarian follicle contains layers of epithelial granulosa cells surrounding an antral cavity. During follicle development granulosa cells replicate, secrete hormones and support the growth of the oocyte. In cattle, the follicle needs to grow > 10 mm in diameter to allow an oocyte to ovulate, following which the granulosa cells cease dividing and differentiate into the specialised cells of the corpus luteum. To better understand the molecular basis of follicular growth and granulosa cell maturation, we undertook transcriptome profiling of granulosa cells from small (< 5 mm; n = 10) and large (> 10 mm, n = 4) healthy bovine follicles using Affymetrix microarrays (24,128 probe sets).

Results

Principal component analysis for the first two components and hierarchical clustering showed clustering into two groups, small and large, with the former being more heterogeneous. Size-frequency distributions of the coefficient of variation of the signal intensities of each probe set also revealed that small follicles were more heterogeneous than the large. IPA and GO enrichment analyses revealed that processes of axonal guidance, immune signalling and cell rearrangement were most affected in large follicles. The most important networks were associated with: (A) Notch, SLIT/ROBO and PI3K signalling, and (B) ITGB5 and extracellular matrix signalling through extracellular signal related kinases (ERKs). Upstream regulator genes which were predicted to be active in large follicles included STAT and XBP1. By comparison, developmental processes such as those stimulated by KIT, IHH and MEST were most active in small follicles. MGEA5 was identified as an upstream regulator in small follicles. It encodes an enzyme that modifies the activity of many target proteins, including those involved in energy sensing, by removal of N-acetylglucosamine from serine and threonine residues.

Conclusions

Our data suggest that as follicles enlarge more genes and/or pathways are activated than are inactivated, and gene expression becomes more uniform. These findings could be interpreted that either the cells in large follicles are more uniform in their gene expression, or that follicles are more uniform or a combination of both and that additional factors, such as LH, are additionally controlling the granulosa cells.

Effect of dietary crude protein source on hormone and follicle characteristics in beef heifers

Ground, raw soybeans (SB), or dried distillers grain plus solubles (DDGS) were utilized in heifer development diets to determine the effect of dietary fat and protein source on hormone and follicle characteristics and ADG. The experiment was conducted over 2 yr with 100 June-born heifers (199 +/- 2 kg initial BW, n = 50 per yr). The experimental periods were 157 and 207 d in yr 1 and 2, respectively. Heifers were provided a dietary supplement (DM basis) of 1.23 kg of SB and 0.40 kg of corn or 1.65 kg of DDGS between weaning and breeding. Estrus was synchronized with 2 injections of PGF(2alpha) 14 d apart. Dominant follicles were measured and aspirated via transvaginal ultrasonography 60 h after the second PGF(2alpha) injection. Heifers were exposed to bulls beginning 14 d after aspiration for 45 d. Heifer ADG was greater (P = 0.02) for DDGS heifers in yr 1, but was similar (P = 0.47) in yr 2. However, there was no difference (P = 0.35) in final BW in either year. There was no difference (P >or= 0.67) in follicle size, follicle hormone concentrations, or pregnancy rate (88%) between yr 1 and 2. Serum estrogen at 48 or 60 h after PGF(2alpha) injection were similar (P >or= 0.91); however, LH at 60 h in yr 2 tended to be greater (P = 0.07) for DDGS heifers. The percentage of heifers experiencing an LH surge 48 and 60 h after PGF(2alpha) injection was not affected (P >/= 0.40) by treatment. Calf production was not affected (P >or= 0.20) by developmental diet. In summary, DDGS and SB have similar effects on hormone and follicle characteristics at the inclusion rates used in these studies.

Molecular mechanisms regulating bovine ovarian follicular selection

Transcription profiling of ovarian follicles. Understanding the mechanisms by which a single follicle is selected for further ovulation is important to control fertility in mammals. However, development of new treatments is limited by our poor understanding of molecular mechanisms regulating follicular selection. Our hypothesis is that genes involved in the control of cell proliferation and apoptosis are differentially regulated during follicular selection. Our objective was to identify these new genes. Bovine follicles were collected and gene expression levels were measured using microarrays. First, follicles were allocated to three groups, according to the time spent from the initiation of follicular wave to surgery (24 H, 36 H, and 48-60 H). Fifty-seven genes are differentially expressed at a false discovery rate of 5%. These genes are involved in the control of lipid metabolism (P-value = 0.0005), cell proliferation (0.007), cell death (0.003), cell morphology (0.003), and immune response (0.003). Follicles were also grouped into four categories, according to the expected time of deviation (early deviation; 8 mm, mid-deviation; 8.5 mm, late deviation; 9 mm, dominant follicles; >or=10 mm). One hundred and twenty eight genes are differentially expressed between these four groups, including genes involved in cell proliferation (0.00002), cell death (0.0006), cell-to-cell signaling (0.003), cell morphology (0.003), lipid metabolism (0.0004), and immune response (0.00007). The expression levels of 10 genes were confirmed using quantitative real time PCR. As expected, we identified new differentially regulated genes involved in the control of cell growth and apoptosis. We also discovered a potential role for immune cells, and in particular macrophages, in follicular selection.

Large variation in steroid concentrations and insulin-like growth factor binding proteins exists among individual small antral follicles collected from within cows at random stages of the estrous cycle

Variation in the biochemical status of individual small (< or = 5 mm diameter) antral follicles within the ovaries of a cow at any given time likely influences the capacity for undergoing recruitment, selection, and establishing dominance. The objectives of this study were to provide insight into the magnitude of variation in follicular fluid concentrations of steroids and activities of IGFBP that exists among individual small antral follicles within and between cows, and to determine the relationships between follicular fluid IGFBP and steroid concentrations in these follicles. A total of 108 small antral follicles were collected from 6 cows at random stages of the estrous cycle, with 10 to 26 follicles/cow. Concentrations of steroids (ng/mL of follicular fluid) in the overall population of follicles ranged from 0.1 (lowest detectable limit) to 51 for estradiol (E2), 4 to 1,149 for progesterone (P4), and 5 to 504 for androstenedione (A4). Concentrations of E2 and A4 were associated positively (r = 0.2; P < 0.02), but E2 (r = -0.4) and A4 (r = -0.4) were associated negatively, with P4. The proportion of variation in steroid concentrations accounted for by differences among animals (P < 0.05) was small for E2 (12%), moderate for P4 (43%), and greatest for A4 (74%). Least differences between minimum and maximum concentrations of steroids observed in follicles from within a cow were 21-, 5.5-, and 3.5-fold for E2, P4, and A4, respectively, whereas the greatest differences between minimum and maximum concentrations were 505-, 108-, and 26-fold for E2, P4, and A4, respectively. Ranges of IGFBP concentrations (arbitrary densitometer units) detected in fluid from a sub-sample of 43 follicles were 1.18 to 4.50 for IGFBP-3, 0.54 to 4.68 for IGFBP-2, 0.07 to 2.56 for IGFBP-4, and 0.01 to 6.71 for IGFBP-5. Concentrations of E2 were correlated negatively with each IGFBP (r = -0.4 to -0.8; P < 0.05) except IGFBP-3. In contrast, concentrations of A4 were correlated positively with IGFBP-3 (r = 0.4; P < 0.05) but were not correlated with other IGFBP. Concentrations of P4 were correlated positively (r > 0.4; P < 0.05) with IGFBP-4 and -5. The results indicate that steroid concentrations and IGFBP activities vary substantially among small antral follicles collected from within and among individual animals and that increasing production of E2, the hallmark of a developing follicle, was associated with reduced activity of all IGFBP except IGFBP-3, thereby implicating these IGFBP in the regulation of follicular recruitment.

Expression of plexin-B1 in the mouse ovary and its possible role in follicular development

OBJECTIVE

To study the expression of plexin-B1 in the mouse ovary and its possible role in follicular development.

DESIGN

Controlled laboratory study.

SETTING

Research laboratory, Ha'Emek Medical Center.

PATIENT(S)

ICR female mice (n = 36) were studied.

MAIN OUTCOME MEASURE(S)

Plexin-B1 expression by immunohistochemistry, Western blot analysis, and reverse transcriptase-polymerase chain reaction. Microscopic morphometric and morphologic analysis for the evaluation of mouse follicular growth and E2, P, and T secretion from the developed follicles.

RESULT(S)

Plexin-B1 was expressed in the mouse ovary mostly in the granulosa cells. Plexin-B1 gene expression increased significantly by 126.8% +/- 38% in the pregnant mare serum gonadotropin-treated group and increased by 98.7% +/- 15.2 and 262.2% +/- 65.4% in the hCG-treated group 6 h and 24 h after injection, respectively (ANOVA; P < .05). Comparison of the maximum diameters of the control and study groups on day 9 of the culture period revealed a significant difference between the two groups (P < .001). In the control group, the mean maximum diameter was 191 +/- 2.6 microm compared with 136 +/- 5.13 microm in the presence of neutralizing antibodies against plexin-B1. Neutralizing antibody against plexin-B1 decreases E2 and P secretion.

CONCLUSION(S)

This study shows for the first time the expression of plexin-B1 in the mouse ovary. A possible role for plexin-B1 in follicular growth and steroidogenesis, most likely via the granulosa cells, is suggested.

Expression of mRNAs encoding insulin-like growth factor (IGF) ligands, IGF receptors and IGF binding proteins during follicular growth and atresia in the ovine ovary throughout the oestrous cycle

The components of the insulin-like growth factor (IGF) system appear to be involved in the regulation of ovarian follicular growth and atresia in sheep. However, previous studies have only investigated a select few components of the system. The aim of the present study was to investigate the expression of mRNA encoding all of the components of the sheep IGF system among follicles of varying size and health status throughout the oestrous cycle using sheep-specific ribonucleotide probes and in situ hybridisation. For all IGF components, gene expression was unaffected by stage of oestrous cycle. IGF-I mRNA expression in all classes of follicle was generally low throughout the oestrous cycle, while IGFBP-1 mRNA expression could not be demonstrated at all. In contrast, there was relatively intense follicular expression of mRNAs encoding all remaining IGF system components. For IGF-II, both IGF receptors and IGFBP-2, -3, -4, -5, and -6, gene expression decreased as follicles increased in diameter (P < 0.01). IGF-II, type I IGF-R and IGFBP-2, -3, -4, and -6 mRNA expression significantly decreased as follicles progressed from healthy to atretic status (P < 0.01), whereas gene expression for type II IGF-R and IGFBP-5 was greater in atretic follicles (P < 0.01). This study demonstrates the spatial patterns of follicular gene expression for all of the IGF system components in cycling sheep for the first time. These results further highlight the potential functional role of IGF-II, in contrast to IGF-I, in the autocrine and/or paracrine regulation of follicle growth in sheep.

Pregnancy-associated plasma protein-A and insulin-like growth factor binding protein mRNAs in granulosa cells of dominant and subordinate follicles of preovulatory cattle

To determine if (1) levels of pregnancy-associated plasma protein-A (PAPP-A) mRNA and insulin-like growth factor binding protein (IGFBP) (-2, -3, -4 and -5) mRNAs differ between the dominant and subordinate follicles during the follicular phase of an estrous cycle, and (2) these differences are associated with differences in follicular fluid (FFL) concentrations of steroids (estradiol, androstenedione, and progesterone), total and free IGF-I, or IGFBPs, estrous cycles of non-lactating Holstein dairy cows (n = 16) were synchronized with two injections of prostaglandin (PGF2 alpha) 11 days apart. Granulosa cells and FFL were collected either 24 h or 48 h after the second injection of PGF2 alpha. FFL from dominant follicles had lower concentrations of progesterone (P < 0.08) and higher concentrations of estradiol (P < 0.05), androstenedione (P < 0.0001), estradiol:progesterone ratio (P < 0.0001), free IGF-I (P < 0.0001), and calculated percentage free IGF-I (P < 0.01) than large subordinate follicles. Levels of IGFBP-2, -4, and -5 in FFL were 3.0- (P < 0.05), 2.4- (P < 0.06), and 3.4-fold (P < 0.05) greater, respectively, in subordinate than in dominant follicles. IGFBP-3, IGFBP-4 and PAPP-A mRNA expression and IGF-II concentration did not differ (P > 0.10) between dominant or subordinate follicles. Levels of IGFBP-2 and -5 mRNA were severalfold greater (P < 0.05) in subordinate than dominant follicles. IGFBP-5 mRNA in granulosa cells decreased (P < 0.05) 62% to 92%, between 24h and 48 h post-PGF2 alpha. We conclude that decreased levels of IGFBP-2 and -5 mRNA in granulosa cells may contribute to the decrease in FFL IGFBP-2 and -5 protein levels of preovulatory dominant follicles, and that changes in granulosa cell IGFBP-3 and -4 mRNA and PAPP-A mRNA levels do not occur during final preovulatory follicular development in cattle.

Relationship between low-molecular-weight insulin-like growth factor-binding proteins, caspase-3 activity, and oocyte quality

Bovine follicular atresia is associated with the apoptosis of granulosa cells and the subsequent loss of oocyte competence through the reduction of cellular contact (e.g., gap junctions). Several components of the insulin-like growth factor (IGF) system are thought to affect follicular atresia. Whereas the IGF-binding proteins (IGFBPs) are present in varying quantities throughout follicular development, IGFBP-5 appears to be present only during atresia, in parallel with its regulation in other tissue remodeling systems. However, to our knowledge, no connection has yet been made between atresia, low-molecular-weight IGFBP content, and oocyte quality in the bovine ovary. Caspases are actively involved in ovarian follicular atresia, and apoptosis in antral follicles is caspase-3-dependent. Hence, the aim of the present study was to investigate the use of these factors in the assessment of oocyte quality and developmental potential. Oocytes were aspirated, morphologically classified, and individually matured in vitro. The follicular fluid and granulosa cells of these follicles were analyzed for IGFBP profile and caspase-3 activity, respectively. A significant correlation was found between the presence of low-molecular-weight IGFBPs in bovine follicular fluid and caspase-3 activity of granulosa cells isolated from individual follicles. The highest percentage of development to the blastocyst stage was observed in oocytes from slightly atretic follicles. This group of oocytes contained an equal proportion of oocytes at grades 1-3. These data demonstrate that low-molecular-weight IGFBP profile is a more reliable method than the traditional morphological assessment of oocytes and can be used as an effective marker of developmentally competent oocytes. Importantly, these results have implications for the use of noninvasive follicular fluid markers in the selection of competent oocytes to improve outcomes of in vitro fertilization.

Ovarian follicular development in cattle selected for twin ovulations and births12

Comparisons of numbers of antral ovarian follicles and corpora lutea (CL), of blood hormone concentrations, and of follicular fluid steroid concentrations and IGFBP activity were conducted between cows selected (twinner) and unselected (control) for twin births to elucidate genetic differences in the regulation of ovarian follicular development. Ovarian follicular development was synchronized among cows by a single i.m. injection of PGF2alpha on d 18 of the estrous cycle; six cows per population were slaughtered at 0, 24, 48, and 72 h after PGF2alpha. Jugular vein blood was collected from each animal at PGF2alpha injection and at 24-h intervals until slaughter. Ovaries of twinner cows contained more small (< or = 5 mm in diameter, P < 0.05), medium (5.1 to 9.9 mm, P < 0.05), and large (> or = 10.0 mm, P < 0.01) follicles and more (P < 0.01) CL than ovaries of controls. Follicular fluid concentrations of estradiol, androstenedione, testosterone, and progesterone reflected the stage of follicular development and were similar for twinner and control follicles at the same stage. Earlier initiation of follicular development and/or selection of twin-dominant follicles in some twinner cows resulted in greater concentrations of estradiol in plasma at 0, 24, and 48 h and of estradiol, androstenedione, and testosterone in follicular fluid of large follicles at 0 h after PGF2alpha for twinner vs. control cows (follicular status x time x population, P < 0.01). Binding activities of IGFBP-5 and -4 were absent or reduced (P < 0.01) in follicular fluid of developing medium and large estro-gen-active (estradiol:progesterone ratio > 1) follicles but increased with atresia. Only preovulatory Graafian follicles lacked IGFBP-2 binding, suggesting a possible role for IGFBP-2 in selection of the dominant follicle. Concentrations of IGF-I were twofold greater (P < 0.01), but GH (P = 0.10) and cholesterol (P < 0.05) were less in blood of twinners. Three generations of selection of cattle for twin ovulations and births enhanced ovarian follicular development as manifested by increased numbers of follicles within a follicular wave and subsequent selection of twin dominant follicles. Because gonadotropin secretion and ovarian steroidogenesis were similar for control and twinner cattle, enhanced follicular development in twinners may result from decreased inhibition by the dominant follicle(s), increased ovarian sensitivity to gonadotropins, and/or increased intragonadal stimulation, possibly by increased IGF-I.