Role of temperature in regulation of ovarian cycle in bull frog Rana tigerina

Effect of temperature on the ovarian cycle was studied in R. tigerina by exposing them to (1) constant low (22 degrees C) temperature during preparatory (active vitellogenic growth) phase (March-May) when the mean ambient temperature ranged from 26 degrees-28 degrees C and (2) to constant high (30 degrees +/- 1 degrees C) temperature during postbreeding regression phase (August-November) when the mean ambient temperature ranged from 22 degrees-26 degrees C. The ovaries of initial controls (biopsy samples taken prior to the commencement of the experiment) in March contained only first growth phase (FGP) oocytes with a maximum size range of 361-480 microns in diameter. In the frogs exposed to constant low temperature for 2 months, only 7% of FGP oocytes were recruited to second growth phase (SGP) with a mean largest diameter of 631 microns compared to 31% large SGP oocytes with a mean diameter of 1114 microns in the frogs collected from natural fields. The number of atretic follicles (AF) was lower and fat body weights were significantly higher in low temperature exposed frogs. The exposure of the frogs to constant high temperature during postbreeding months caused an increase in the mean diameter and number of large FGP oocytes, numerical increase in AF and decrease in fat body weights over corresponding controls maintained at room temperature. The pituitary gonadotrophs of these frogs showed stimulatory changes such as increase in cell size and appearance of secretory granules in the cytoplasm. The results suggest that in R. tigerina high temperature stimulates oocyte growth while low temperature retards it.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanisms regulating the ovarian cycle in the frog Rana cyanophlyctis: effect of unilateral ovariectomy, season, feeding, human chorionic gonadotrophin, and estradiol-17 beta

Effects of 30-day unilateral ovariectomy (ULO) on compensatory ovarian hypertrophy (COH) was studied in adult frog Rana cyanophlyctis in relation to reproductive phase/season, feeding, and treatment with human chorionic gonadotrophin (HCG) or estradiol-17 beta. Compensatory growth of the remaining ovary was assessed in terms of weight as well as changes in the dynamics of the pool sizes of different oocytes viz., first growth phase (FGP), medium-sized second growth phase (MSGP), large-sized second growth phase (LSGP), and atretic oocytes. The frogs were fed with live guppies 6 days a week. The effect of underfeeding on COH was studied in the frogs fed once a week. The ovaries removed at operation and those of the sham-operated frogs were used for comparison (controls). COH occurred in both pre- and postbreeding phases (February and November, respectively). In both instances follicular atresia was greatly reduced. In February, COH was due to recruitment of both MSGP and LSGP oocytes. The number of these oocytes increased significantly over controls, and the ovarian weight nearly doubled. However, in November COH occurred because of an increase in FGP oocytes and therefore total oocytes, but there were no changes in the ovarian weights. Administration of 20 IU HCG (6 days a week) had no influence on the basic pattern of COH-response exhibited by the remaining ovary in relation to reproductive phase/season, but it increased the recruitment of oocytes, i.e., FGP oocytes in November and SGP oocytes in February. Follicular atresia was drastically reduced with HCG. Underfeeding or treatment with estradiol-17 beta abolished the COH in both February and November.(ABSTRACT TRUNCATED AT 250 WORDS)     

Temporal dynamics of oocyte development, plasma sex steroids and somatic energy reserves during seasonal ovarian maturation in captive Murray cod Maccullochella peelii peelii.

The temporal dynamics of oocyte growth, plasma sex steroids and somatic energy stores were examined during a 12 month ovarian maturation cycle in captive Murray cod Maccullochella peelii peelii under simulated natural photothermal conditions. Ovarian function was found to be relatively uninhibited in captivity, with the exception that post-vitellogenic follicles failed to undergo final maturation, resulting in widespread pre-ovulatory atresia. Seasonal patterns of oocyte growth were characterised by cortical alveoli accumulation in March, deposition of lipids in April, and vitellogenesis between May and September. Two distinct batches of vitellogenic oocytes were found in Murray cod ovaries, indicating a capacity for multiple spawns. Plasma profiles of 17beta-oestradiol and testosterone were both highly variable during the maturation period suggesting that multiple roles exist for these steroids during different stages of oocyte growth. Condition factor, liver size and visceral fat stores were all found to increase prior to, or during the peak phase of vitellogenic growth. Murray cod appear to strategically utilise episodes of high feeding activity to accrue energy reserves early in the reproductive cycle prior to its deployment during periods of rapid ovarian growth.     

Temporal dynamics of oocyte development, plasma sex steroids and somatic energy reserves during seasonal ovarian maturation in captive Murray cod Maccullochella peelii peelii

The temporal dynamics of oocyte growth, plasma sex steroids and somatic energy stores were examined during a 12 month ovarian maturation cycle in captive Murray cod Maccullochella peelii peelii under simulated natural photothermal conditions. Ovarian function was found to be relatively uninhibited in captivity, with the exception that post-vitellogenic follicles failed to undergo final maturation, resulting in widespread pre-ovulatory atresia. Seasonal patterns of oocyte growth were characterised by cortical alveoli accumulation in March, deposition of lipids in April, and vitellogenesis between May and September. Two distinct batches of vitellogenic oocytes were found in Murray cod ovaries, indicating a capacity for multiple spawns. Plasma profiles of 17β-oestradiol and testosterone were both highly variable during the maturation period suggesting that multiple roles exist for these steroids during different stages of oocyte growth. Condition factor, liver size and visceral fat stores were all found to increase prior to, or during the peak phase of vitellogenic growth. Murray cod appear to strategically utilise episodes of high feeding activity to accrue energy reserves early in the reproductive cycle prior to its deployment during periods of rapid ovarian growth.     

Interrelationship between food availability, fat body, and ovarian cycles in the frog, Rana tigrina, with a discussion on the role of fat body in anuran reproduction

Long-term experiments were conducted to study the progression of vitellogenic cycles in Rana tigrina (an annual breeder) having different foraging backgrounds and held under conditions of weekly or daily food supply and in presence or absence of abdominal fat bodies. They were autopsied in June to assess fecundity. In nature an adult R. tigrina produces on an average 4,000 eggs/100 g body mass (b.m.) And spawns in June-July following monsoon rains. Weekly feeding from July to next breeding season, June resulted in a significant decrease in both fecundity (1700 eggs/100 g body b.m.) And mean size of eggs, compared to well-fed or wild-caught frogs. The abdominal fat bodies were barely seen in frogs fed weekly throughout, whereas in frogs fed weekly from July-December but daily from January onwards, the fat bodies became noticeable (1% of b.m.) And number and mean size of eggs increased significantly over those fed weekly throughout. Frogs captured in January possessed enlarged fat bodies (5% of b.m.), depicting a good foraging history. Maintenance of these frogs on a weekly feeding regimen led to an exhaustion of fat stores. They produced less number of eggs (2, 000/100 g b.m.) As compared to wild frogs but of normal size, whereas daily feeding slowed down a depletion of fat body mass and also significantly increased fecundity (3,000/100 g b.m.) Over the weekly fed individuals. Sham operation or fat body ablation in October or February had no significant effect on total fecundity per se (3,000-3,500 eggs/100 g b.m.) Compared to that of wild-caught frogs. However, eggs were significantly smaller due to fat body ablation despite daily feeding. The study shows that food abundance/fat bodies influence egg size and number in R. tigrina and that a direct or indirect functional relationship exists between fat body and ovarian cycles that are characteristically inverse to each other. J. Exp. Zool. 286:487-493, 2000.     

Vitellogenic cycles in laboratory-maintained females of the leopard frog, Rana pipiens

As a part of studies on the reproduction of laboratory maintained frogs, wild-caught Rana pipiens were ovulated and maintained at 22-27 degrees C for up to 18 months. Vitellogenic oocytes were periodically staged and counted, and a "maturity index" was calculated to assess the progress of the vitellogenic cycle. The initial cycle was similar to that of wild frogs except that the first oocytes to reach stage 5 (mature eggs) usually began to degenerate before later starting oocytes became mature. In addition, a second cycle began before the first was completed. After more than 1 year at room temperature, abnormal cycles were common. Ovaries of such animals contained very few mature eggs. Many of their oocytes were in early stages of vitellogenesis or, if pigmented, had begun to degenerate. These deficiencies were partially corrected in females placed in 4 degrees C for 4-6 weeks. The average number of mature eggs increased 15-fold and ovary weights more than doubled. Oviduct weights almost doubled. Although the rates of cooling, photoperiod, and nutritional status could be important influences, the results imply that cold treatment alone increases estrogen secretion. We suggest that low estrogen secretion may account for the reproductive deficiencies seen in R. pipiens cultured at room temperature.     

Dynamics of oogenesis in the tropical anuranRana tigrina (Amphibia: Ranidae) with special reference to vitellogenic cycles in wild-caught and captive flogs

The ovarian cycle ofRana tigrina was analysed by quantifying the developing oocytes (classified into stages on the basis of diameter) and atretic ones at monthly intervals. Stages I to IV represent oocytes in the first growth phase and the remaining ones the vitellogenic or second growth phase. Stages I–III occurred year round but exhibited significant variation in their number. The number of stage II oocytes always dominated the other stages. Recruitment of oocytes to stages IV and V in April marked the initiation of vitellogenic growth in all specimens. Of the 30 to 35% second growth phase oocytes, 25 to 28% reached ovulatory sizes by June. After spawning the ovarian mass declined drastically from 15 to 0.2% of body mass in July. Atresia was maximal (5%) in August. In other months, it was less than 1.5% of the total oocytes. Oogenic episodes occurred in March and July yielding new oocytes. The number of first growth phase oocytes fluctuated from 65 to 95%. The fluctuation was inversely correlated with the second growth phase oocytes indicating a 30 to 35% annual turnover rate of oocytes in the frog. The final egg number/ovarian mass is positively correlated with the snout-vent length as well as body mass of the frogs.R. tigrina produces about 4000 eggs/100g body mass. Further, the mean number of yolky eggs/100 g body mass and the total volume (V) of eggs/frog were highly correlated. Frogs living in captivity produced fewer eggs compared to the wild ones (3594 ± 227 in captivevs 4704 ± 317 in wild frogs). Also, these frogs failed to breed though they showed amplexus with breeding males. Injection of desoxycorticosterone acetate however induced spawning in 4 out of 5 frogs. They released about 3000 eggs each. Captivity seems to mainly impair breeding and to a little extent the vitellogenic growth of oocytes inR. tigrina.     

Relations Between Hibernation and Ovarian Functions in a Temperate Zone Frog,Rana temporaria

Adult female frogs were exposed to artificial hibernation in a refrigerator, at about 1–3°C, 1–2 months earlier than in nature, isolated or together with males. Ovarian functional state at the beginning of hibernation was assessed from ovarian biopsies taken in mid-September. All frogs ovulated during hibernation which was interrupted in mid-May, but in seven out of 19 frogs ovulation was incomplete. The number of non-ovulated oocytes varied from a minor fraction to about two thirds of the complement of vitellogenic oocytes, indicating that the follicle size reached at the time of induced hibernation was at the critical level for successful maturation. This critical size was about half the normal oocyte volume at the onset of natural hibernation. There was no vitellogenic growth during hibernation, which presumably constitutes the period of follicle maturation. In five of the frogs, oogenesis sensu stricto had occurred during the period of hibernation, some oogenic events being completely finished at autopsy in mid-May and others still progressing.     

Radiographic diagnosis of metabolic bone disease in captive bred mountain chicken frogs (Leptodactylus fallax)

Asymptomatic captive bred and wild-caught mountain chicken frogs (Leptodactylus fallax) were radiographed for evidence of metabolic bone disease (MBD). All 22 captive bred frogs had multiple folding fractures of long bones, decreased bone density, and cortical thinning, whereas none of the 11 wild-caught frogs had any radiographic evidence of MBD. These findings suggest that the nutritional requirements of L. fallax need to be examined for captive management purposes.     

Factors affecting follicular population, oocyte yield and quality in camels (Camelus dromedarius) ovary with special reference to maturation time in vitro

Three experiments were conducted to study a series of factors affecting in vitro reproductive parameters in camels. In Experiment 1, the effect of season and presence of a corpus luteum (CL) on ovarian follicular populations, oocyte yield and quality was studied using a total of 252 and 208 ovaries collected during the breeding and non-breeding season, respectively. Small, medium, large and the total number of ovarian follicles, oocyte yield and quality were measured. In Experiment 2, the effect of methods of oocyte retrieval and needle gauge on oocyte yield and quality was evaluated with oocytes recovered using slicing and aspiration with 18-, 19- or 20-gauge needle. Oocytes were evaluated microscopically and classified into three categories. The objective of Experiment 3 was to identify the optimum time for oocyte maturation in the dromedary camel. Oocytes were cultured in CR1aa medium at 38.5 degrees C under 5% CO(2) for 24, 32, 36, 48 and 72h. Maturation was calculated as the percentage of cumulus expansion and oocytes reaching metaphase II (MII). The number of small, medium, large and the total number of ovarian follicles were higher (P<0.01) during the breeding than non-breeding season. The recovery of total number of oocytes and Category I oocytes were also greater (P<0.01) during the breeding season. Ovaries without a CL possessed significantly (P<0.01) more ovarian follicles and more (P<0.05) small and large follicles. The total number of oocytes and Category I oocytes were also greater (P<0.01) in ovaries without CL. Slicing of camel ovaries increased (P<0.01) the yield of oocytes as compared to aspiration. The aspiration of follicles using a 20-gauge needle had greater yields of the total number of oocytes and Category I oocytes than when using 19- (P<0.05) and 18-gauge needle (P<0.01). The culture of camel oocytes for 36h produced higher (P<0.01) percentages of cumulus expansion and oocytes at MII. Increasing culture times up to 48 or 72h increased (P<0.01) the percentage of degenerated oocytes.In conclusion, the growth and development of ovarian follicles in the camel as well as yields of Category I oocyte were greater during the breeding season. Slicing or aspirations using a 20-gauge needle yielded greater numbers of total and Category I oocytes. Finally, maturation of oocytes in CR1aa medium for 36h produced higher percentages of cumulus expansion and oocytes at MII stage.     

The Hormonal Control of the Amphibian Ovary

The ultimate control of amphibian gonadal function rests withenvironmen tal factors mediated through the hypothalamus. Itappears that control of ovarian growth resides in the infundibularregion and ovulation in the preoptic area. For normal temporalrelationships between oocyte growth and ovulation to occur,an intact hypothalamo-pituitary complex is necessary. It isuncertain whether the several types of pituitary basophils considered,histologically as gonadotropin producing cells are in fact producingseparate LH and FSH like hormones. Perhaps the concensus indicatesa single hormone has both vitellogenic and ovulatory functions.This hormone stimulates estrogen synthesis and secretion bythe ovarian follicle cells, and this steroid causes oviductgrowth and the hepatic biosynthesis of vitellogenin, the majoryolk platelet precursor. Uptake of this lipoprotein from thecirculation and its conversion to the components of the plateletis mediated by the gonadotropin, the presence of which resultsin the establishment of a rapid micropinocytotic process atthe level of the oocyte surface and of a mechanism for crystallizationof the yolk. A sudden surge of pituitary hormone, when presentedto fully grown oocytes leads to their maturation and ovulation,and to oviducal jelly release in some species. The active hormoneis progestin in nature, again produced by the follicle cells. In this review the known factors involved in the hypothalamohypophysio ovarian axis are discussed together with some considerationof outstanding problemsand the possible relevance ot ovipantvand ovovivipanty in amphibians to the ovarian control foundin viviparous species.     

Effect of photoperiod and temperature on ovarian cycle of the frogRana tigrina (Daud.)

The effect of varying photoperiod regimes (LD: 20,4; 4,20; 6,18; 18,6 and 12,12) on ovarian follicular development was analysed in the frogRana tigrina maintained at ambient and constant 30° ± l°C for 3 months. The experiments were conducted in early recrudescent and quiescent phases. The frogs were fed guppiesad libitum on alternate day. None of the photoperiod regimes had any effect on the ovaries or the fat bodies, whereas exposure to constant high temperature (regardless of photoperiod) during recrudescent phase induced production of greater number of eggs (∼ 18000 vs 13000 in controls) of ovulatory sizes (> 1400 μm) compared to the corresponding controls maintained at ambient temperature. Hence, ovarian mass also increased in these frogs. In the quiescent phase, high temperature merely enhanced growth of previtellogenic oocytes. In both the phases high temperature caused a reduction in the fat bodies over the respective controls, possibly due to increased metabolic activity. The above findings indicate that temperature plays a key role in the regulation of ovarian cycle ofRana tigrina and that the photoperiodic mechanisms may not govern the annual recrudescence of ovaries in the frog. The study also shows that the frog exhibits the phenomenon of “phenotypic plasticity” in its reproductive behaviour by producing significantly greater number of eggs in response to elevated temperature.     

Ultrasonographic-guided retrieval and in vitro maturation of eland (Taurotragus oryx) and bongo (Tragelaphus eurycerus isaaci) antelope oocytes

The limited availability of gametes is a major factor hindering the development and application of assisted reproductive technologies (ART) in large non-domestic ungulates. This is partly due to the small number of captive animals and handling difficulties associated with procedures for gamete recovery. In the present study, results are reported of multi-year studies on ovarian stimulation and oocyte retrieval by ultrasonographic-guided transvaginal follicular aspiration and subsequent in vitro maturation (IVM) in eland and bongo antelopes. All procedures were conducted on sedated females handled in a hydraulic chute without inducing general anesthesia. Five estrous synchronization/ovarian stimulation protocols were evaluated and data are presented on 73 and 15 procedures in eland and bongo, respectively. Repeating procedures (< or =once/month) on the same female did not affect ovarian response or number oocytes recovered in either species. Eland females, but not the ovarian stimulation treatment, affected ovarian response. Ovarian stimulation treatment affected oocyte recovery rate in eland, but not in bongo. In both species, ovarian hormone stimulation treatment affected the distribution of follicles by size and the status of expansion of the cumulus cell investment of oocytes, but not the frequency of metaphase II oocytes during IVM. The timing of extrusion of the first polar body during IVM was more synchronous in bongo than in eland oocytes. It is concluded that Transvaginal oocyte retrieval (TVOR) can be safely and repeatedly applied in gonadotropin-treated eland and bongo females to recover oocytes that can mature in vitro. The methods described for the present study can be adapted to improve the availability of non-domestic ungulate oocytes for basic and applied studies.     

Progesterone and estrogens in the pregnant and nonpregnant dolphin, Tursiops truncatus, and the effects of induced ovulation

Baseline serum levels of progesterone and total immunoreactive estrogens were determined for intact and ovariectomized captive female Atlantic bottlenose dolphins (Tursiops truncatus), as well as newly captured wild adult females. Stimulation of ovarian follicular growth and ovulation was attempted by intramuscular injection of pregnant mare's serum gonadotropin (PMSG). High doses of PMSG were required to increase serum estrogen levels. When PMSG was followed by an injection of human chorionic gonadotropin (hCG), ovulation was presumed to have occurred as indicated by subsequent high levels of serum progesterone. From these observations, it appears that 1) females with progesterone levels greater than 3000 pg/ml over an extended period are pregnant, 2) Tursiops truncatus is capable of spontaneous ovulation in captivity without gonadotropin therapy, 3) captive female dolphins, although relatively resistant to PMSG, can be induced to ovulate using a combination of high intramuscular-injected doses of PMSG followed by hCG, and 4) spontaneous ovulation is likely to follow an induced ovulation.     

Influence of temperature on ovarian recrudescence in the Indian catfish, Heteropneustes fossilis

Over a 60-day experiment during the preparatory phase of the reproductive cycle, ovarian weights increased with rise in temperature in Heteropneustes fossilis and oocyte diameters suggested an optimum temperature of 22° C for Stage II oocyte formation. The oocytes did not reach Stage II at 10° C. Atresia of Stage III oocytes occurred following 60 days of exposure at 30°C.     

Effect of ovine follicular fluid peptide on ovarian responses and other organ weights in rats, Rattus norvegicus Berkenhout 1769

The present study was aimed to study the effect of an ovine follicular fluid peptide on ovarian follicle and good oocyte numbers and weights of ovary, uterus, liver, pancreas and kidney in rats, R. norvegicus. A 30.1 kDa peptide was isolated from ovine follicular fluid by ammonium sulphate precipitation and then gel filtration. The peptide was tested at various levels in normal (22 and 36 day-old), superovulated (29 day-old) immature and 121-day old mature rats on the ovarian responses and other organ weights. The isolated peptide inhibited the growth of antral follicles in normal and superovulated rats. Ovarian, uterine weight and recovery of good oocytes were reduced when the peptide was administered at 100 microg dose. The peptide had no effect on kidney, liver, pancreas weight and recovery of preantral follicles.     

Formation of lipid reserves in fat body and eggs of the yellow fever mosquito, Aedes aegypti

We examined the accumulation of lipids in adult females of the mosquito, Aedes aegypti. Females emerged with about 100 μg lipid in the fat body. With access to sugar water lipids increased over seven days to 300 μg. After a blood meal on day five, sugar-fed females accumulated 120-140 μg of lipids in their ovaries within 2 days. At the same time the lipid content of the fat body decreased by 100 μg, indicating transfer of lipids from fat body to oocytes. Experiments in which fat body lipids were prelabelled support this conclusion. Label was transferred to oocytes: in mature oocytes the specific radioactivity of lipids was 80% of the specific radioactivity of prelabeled fat body lipids. Components of blood meals are also used to synthesize oocyte lipids. Fat bodies of females starved for four days had only 27 μg of lipids left. When these females were given a blood meal, they matured oocytes, although the number of ooyctes was reduced and ovaries contained only half the amount of lipids found in ovaries of females which had first fed on sugar water. Fat body lipids of these females had only slightly increased to 36 μg. This demonstrates that female Ae. aegypti use sugar to synthesize lipids, but they can also use components of blood for this purpose.     

Phylogenetic significance of the structure of adult ovary and oogenesis in a primitive chilognathan diplopod,Hyleoglomeris japonica Verhoeff (Glomerida,Diplopoda)

Some histological details of the adult ovary of Hyleoglomeris japonica are described for the first time in the glomerid diplopods. The ovary is a single, long sac-like organ extending from the 4th to the 12th body segment along the median body axis, lying between the alimentary canal and the ventral nerve cord. The ovarian wall consists of a layer of thin ovarian epithelium which surrounds a wide ovarian lumen. A pair of longitudinal “germ zones,” including female germ cells, runs in the lateral ovarian wall. Each germ zone consists of two types of oogenetic areas: 1) 8–12 narrow patch-shaped areas for oogonial proliferation, arranged metamerically in a row along each of the dorsal and ventral peripheries, and 2) the remaining wide area for oocyte growth. Oogonial proliferation areas include oogonia, very early previtellogenic oocytes, and young somatic interstitial cells, among the ovarian epithelial cells. The larger early previtellogenic oocytes in the oogonial proliferation areas are located nearer to the oocyte growth area, and migrate to the oocyte growth area. They are surrounded by a layer of follicle cells and are connected with the ovarian epithelium of the oocyte growth area by a portion of their follicles. They grow into the ovarian lumen, but their follicles are still connected with the oocyte growth area. Various sizes of the previtellogenic and vitellogenic oocytes in the ovarian lumen are connected with the oocyte growth area; the smaller oocytes are connected nearer to the dorsal and ventral oogonial proliferation areas, while the larger ones are connected nearer to the longitudinal middle line of the oocyte growth area. Following the completion of vitellogenesis and egg membrane formation in the largest primary oocytes, the germinal vesicles break down. Ripe oocytes are released from their follicles directly into the ovarian lumen to be transported into the oviducts. Ovarian structure and oogenesis of H. japonica are very similar to those of other chilognathan diplopods. At the same time, however, some characteristic features of the ovary of H. japonica are helpful for understanding the structure and evolution of the diplopod ovaries. Some aspects of the phylogenetic significance in the paired germ zones of H. japonica are discussed. J. Morphol 231:277–285, 1997. © 1997 Wiley-Liss, Inc.     

Neonatal genistein treatment alters ovarian differentiation in the mouse: inhibition of oocyte nest breakdown and increased oocyte survival

Early in ovarian differentiation, female mouse germ cells develop in clusters called oocyte nests or germline cysts. After birth, mouse germ cell nests break down into individual oocytes that are surrounded by somatic pregranulosa cells to form primordial follicles. Previously, we have shown that mice treated neonatally with genistein, the primary soy phytoestrogen, have multi-oocyte follicles (MOFs), an effect apparently mediated by estrogen receptor 2 (ESR2, more commonly known as ERbeta). To determine if genistein treatment leads to MOFs by inhibiting breakdown of oocyte nests, mice were treated neonatally with genistein (50 mg/kg per day) on Days 1-5, and the differentiation of the ovary was compared with untreated controls. Mice treated with genistein had fewer single oocytes and a higher percentage of oocytes not enclosed in follicles. Oocytes from genistein-treated mice exhibited intercellular bridges at 4 days of age, long after disappearing in controls by 2 days of age. There was also an increase in the number of oocytes that survived during the nest breakdown period and fewer oocytes undergoing apoptosis on Neonatal Day 3 in genistein-treated mice as determined by poly (ADP-ribose) polymerase (PARP1) and deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end-labeling (TUNEL). These data taken together suggest that genistein exposure during development alters ovarian differentiation by inhibiting oocyte nest breakdown and attenuating oocyte cell death.     

Aspects of follicle and oocyte stage that affect in vitro maturation and development of bovine oocytes

Success of in vitro maturation (IVM) and production of bovine embryos as related to aspects of follicle source and oocyte size were evaluated. First, it was determined that bovine oocytes continue growing in all follicular sizes studied, including >1- to 15-mm follicles. Populations of oocytes were collected from surface visible (peripheral) and cortical follicles from the same ovaries. When the number of oocytes from both peripheral and cortical follicles was combined, the yield of oocytes was approximately double that collected from 1 ovarian site alone. Oocytes from cortical follicles were smaller than those from the surface population, and the smaller cortical oocytes had a lower potential for both meiotic maturation and embryo development Only cortical oocytes with the largest diameters underwent IVM and subsequently developed to blastocysts at rates comparable to oocytes from peripheral follicles. As the diameter of the oocytes recovered from peripheral follicles increased, so did their developmental potential. When the stage of the estrous cycle was observed, it was found to have no effect on developmental potential. Finally, oocytes which extruded polar bodies at an earlier time during maturation were, on average, larger than those which extruded polar bodies later. The results serve a practical purpose in assisting selection of oocytes capable of developing into blastocysts and they give useful correlates of oocyte competencies based on knowledge of follicle source and oocyte stage.