Hormone-controlled culture of secondary follicles of domestic cats

Preservation of female genetic resources in feline species

The development of assisted reproduction techniques (ART) specifically for felids has been propagated for two main reasons: (i) most felids are threatened and faced with extinction in all or part of their native habitats (IUCN Red List of Threatened Species, www.catsg.org), and (ii) the domestic cat (Felis catus) can serve as a research model for the implementation of advanced assisted reproductive techniques (ART) to be applied in exotic cats. Domestic cat ovaries can be freshly obtained from veterinary clinics and are frequently used for research on preservation of genetic resources in feline species. The presented review will summarize recent advances and obstacles in biobanking of female genetic resources and discuss alternative approaches which are under investigation.

Comparison of enzymatic and mechanical methods for the collection of bovine preantral follicles

A comparison was made of various devices to obtain preantral follicles from bovine ovaries. The most productive collection methods in terms of number of follicles obtained were the tissue chopper and the grinder method, with an average number of 122·25 (s.e. 5·06) and 120·45 (s.e. 6·89) preantral follicles, respectively. These were followed by ficoll gradation (119·90, s.e. 7·95), mincer (101·75, s.e. 3·98), cell dissociation sieve (100·50, s.e. 3·42) and homogenizer (95·75, s.e. 6·38). For enzymatic digestion, more time was needed and the method was less productive. Microdissection could supply good quality (80% live when collected), larger sized follicles (120 to 220 µm) but with the lowest yield (10·65, s.e. 0·94) per ovary. The isolated follicles did not show any difference (P > 0·05) in viability until day 7 of in-vitro culture irrespective of method used to harvest follicles. Accordingly the new grinding device can be recommended as a replacement for the existing mechanical devices as it can yield the same percentage (47%) of live preantral follicles but of a wider diameter range (40 to 180 µm) per ovary.

The effects of EGF and IGF-1 on FSH-mediated in vitro maturation of domestic cat oocytes derived from follicular and luteal stages

The objective of this study was to evaluate the influence of epidermal growth factor (EGF) and insulin like growth factor-I (IGF-1) on the in vitro maturation of cat oocytes recovered from follicular and luteal stage ovaries. Oocytes from follicular (n=580) and luteal (n=209) stages were harvested and divided into four groups, which were cultured in FSH-mediated maturation medium supplemented with: (1) EGF alone (25ng/mL); (2) IGF-1 alone (100ng/mL); (3) EGF+IGF-1 (25ng/mL EGF+100ng/mL IGF-I); or (4) no growth factor (control). The proportion of follicular stage oocytes reaching the metaphase II stage was significantly higher than that of oocytes obtained at the luteal stage in both control and study groups (p<0.001). The percentages of oocytes reaching the metaphase II stage during the follicular period were 62.6% in control; 70.9% in EGF; 72.8% in IGF-1, and 78.1% in EGF+IGF-1 groups, whereas the respective values for gametes collected from luteal stage ovaries were 12.5%, 17.5%, 12.5%, and 16.9%. Additionally, the differences between the study and control groups were significant in the case of follicular stage oocytes. Finally, supplementing the maturation medium with EGF and/or IGF-1 significantly enhanced the meiotic maturation of oocytes recovered from follicular stage ovaries. The present study also demonstrated that the combination of EGF and IGF-I provides an additional or synergic effect on meiotic maturation of oocytes recovered from the follicular stage.

In vitro survival of follicles collected from domestic cats' ovaries at different stages of oestrous cycle and cultured with IGF-1

Optimal conditions for in vitro culture of feline ovarian follicles have not yet been defined. Follicular development is regulated by intraovarian growth factors, as insulin-like growth factor (IGF-1), and during the different stages of the oestrous cycle, follicles are exposed to specific hormonal environments. The aim of this study was to investigate the effect of IGF-1 on in vitro growth and granulosa cell (GC) viability of preantral follicles collected from domestic cats at follicular and luteal phases of the oestrous cycle. Oestrus and ovulation were induced in 12 cats. A total of 39 and 32 follicles collected at the follicular and luteal phases, respectively, were individually cultured in vitro for 6 days in minimum essential medium media supplemented with or without IGF-1 (100 ng/ml). Follicles collected during the follicular phase and cultured without IGF-1 displayed a significant increase in size and higher GC viability (46.5 ± 22.1 μm, 66.7%, respectively) than that of follicles collected at the luteal phase and cultured without IGF-1 (26.7 ± 14.4 μm, 50%, respectively; p < 0.05). In contrast, when IGF-1 was added to the culture medium, no differences were observed in size or GC viability between follicles collected at the two phases of the cycle. Nonetheless, follicles collected at the luteal phase and cultured with IGF-1 had a significant increase in their diameter and GC viability (31.9 ± 15.9 μm, 63.6%, respectively) than that cultured without IGF-1 (26.7 ± 14.4 μm, 50%, respectively; p < 0.05). These data suggest that in vitro growth and GC survival of feline preantral follicles are affected by the oestrous cycle phase, and the IGF-1 exerts a positive effect on follicles collected at the luteal phase.

Current achievements and future research directions in ovarian tissue culture, in vitro follicle development and transplantation: implications for fertility preservation

BACKGROUND Female cancer patients are offered 'banking' of gametes before starting fertility-threatening cancer therapy. Transplants of fresh and frozen ovarian tissue between healthy fertile and infertile women have demonstrated the utility of the tissue banked for restoration of endocrine and fertility function. Additional methods, like follicle culture and isolated follicle transplantation, are in development. METHODS Specialist reproductive medicine scientists and clinicians with complementary expertise in ovarian tissue culture and transplantation presented relevant published literature in their field of expertise and also unpublished promising data for discussion. As the major aims were to identify the current gaps prohibiting advancement, to share technical experience and to orient new research, contributors were allowed to provide their opinioned expert views on future research. RESULTS Normal healthy children have been born in cancer survivors after orthotopic transplantation of their cryopreserved ovarian tissue. Longevity of the graft might be optimized by using new vitrification techniques and by promoting rapid revascularization of the graft. For the in vitro culture of follicles, a successive battery of culture methods including the use of defined media, growth factors and three-dimensional extracellular matrix support might overcome growth arrest of the follicles. Molecular methods and immunoassay can evaluate stage of maturation and guide adequate differentiation. Large animals, including non-human primates, are essential working models. CONCLUSIONS Experiments on ovarian tissue from non-human primate models and from consenting fertile and infertile patients benefit from a multidisciplinary approach. The new discipline of oncofertility requires professionalization, multidisciplinarity and mobilization of funding for basic and translational research.

Folliculogenesis and morphometry of oocyte and follicle growth in the feline ovary

This study was designed to describe, both quantitatively (morphometry) and qualitatively (histological differentiation), follicle and oocyte growth in the feline ovary. The ovaries of 43 cats were collected and processed for histology. The diameters of 832 follicle/oocyte pairs were measured, with and without zona pellucida (ZP), and a special emphasis was placed on the study of early folliculogenesis. Primordial, primary, secondary, pre-antral and early antral follicles were measured at 44.3, 86.2, 126.0, 155.6 and 223.8 microm in diameter respectively. A biphasic pattern of follicle and oocyte growth was observed. Before antrum formation, follicle (x) and oocyte (y) size were positively and linearly correlated (y = 0.500x + 20.01, r(2) = 0.89). Antrum formation occurred when the follicle reached 160-200 microm in diameter (when oocyte was at 102 microm). After antrum formation, a decoupling was observed, a minimal increase in oocyte size contrasting with a significant follicle development (y = 0.001x + 114.39, r(2) = 0.01). The pre-ovulatory follicle diameter was approximately 3500 microm and the maximal oocyte diameter was 115 microm. The ZP, absent in primordial and primary follicles, appeared at the secondary stage and reached almost 6 microm at the pre-ovulatory stage. These results suggest that (i) in feline ovary, follicle and oocyte growth pattern is similar to that observed in other mammals; (ii) the antrum forms in 160-200 microm follicles, which represents 5% of the pre-ovulatory diameter and (iii) the oocyte had achieved more than 90% of its maximal growth at the stage of antrum formation.

In vitro growth and maturation of caprine oocytes

This study was conducted to culture in vitro caprine pre-antral follicles for determining the competence of growth and maturation of oocytes and establishing a suitable culture system for oocyte maturation from pre-antral follicles. Two different culture methods (microdrop and agar gel clot) were employed to culture caprine pre-antral follicles. The pre-antral follicles were isolated from prepubertal goat ovaries by treatment with collagenase and DNase. The isolated pre-antral follicles were cultured in basic culture medium for 9 days (for growth). And oocytes were cultured in maturation culture medium for another 2 days for maturation. The result demonstrated that the growth rate of oocytes cultured in microdrops was significantly (p < 0.05) higher than that in agar gel clots, whereas the viability of oocytes in microdrops was considerably (p < 0.05) lower than that in agar gel clots. The oocytes grew over 150 microm in diameter, and two of 151 oocytes cultured in microdrops yielded morphologically abnormal first polar bodies. However, the size of oocytes cultured in agar gel approached to 120 microm in diameter and no polar body was produced.

High-Resolution Ultrasonography of Xenografted Domestic Cat Ovarian Cortex

Transplantation of ovarian tissue has high potential for female gamete conservation. However, optimal timing of oocyte recovery for in vitro maturation and fertilization is still critical. Therefore the aim of the present study was to use high-resolution transcutaneous ultrasonography to monitor follicular development within xenografted ovarian tissue. Ovarian cortex fragments (n=44) from domestic cats were transplanted into athymic nude rats (n=12). Graft development in the animals was assessed weekly by high frequency ultrasound (10-22 MHz) under two different FSH regimes. Blood collection for serum estradiol determination and vaginal smears were performed simultaneously. The xenografts were removed at different time points according to the ultrasound findings. The survival rate of the transplants 4 weeks after surgery was 54.5% and antral follicular growth was observed within 10 grafts from 5 different hosts (8.6 +/- 6.43 follicles per graft). Early follicle antrums could be detected from 0.4 mm onwards. The growth rate of the antral cavity was calculated from weekly measurements (0.56 +/- 0.44 mm per week). Although vaginal cells and estradiol levels followed a cyclic pattern, no correlation was found between follicular diameter, estradiol and keratinized vaginal cells. We recovered 5, 1 and 4 cumulus oocyte complexes from three different individuals during weeks 19, 21, and 23 respectively. Extrusion of a polar body (1 oocyte) and germinal vesicle break down (7 oocytes) indicated progression of maturation after in vitro culture. We conclude that ultrasonography und provided a reliable method to examine xenograft survival and follicular development within the grafts. Furthermore, this technique is suitable for assessment of the efficiency of hormonal treatment and narrowing of the optimal time frame for oocyte retrieval. To our knowledge, this is the first report of the in vivo development of early antral follicles in mammalian species.

Preservation of female germ cells from ovaries of cat species

This review provides an overview on recent knowledge on female germ cell population within cat ovaries; on isolation, culture and cryopreservation of feline preantral follicles and on ovarian tissue preservation.

Effect of growth factors on in vitro development of caprine preantral follicle oocytes

The objective of this work was to examine the effect of various growth factors including epidermal growth factor (EGF) and insulin-like growth factor-I (IGF-I), either individually or in association, in the presence of follicle stimulating hormone (FSH) on the in vitro growth and viability of caprine preantral follicle oocytes. Preantral follicles were disassociated enzymatically and mechanically from prepuberal caprine ovaries after the animals were anesthetically ovariectomized. In experiment, caprine preantral follicles in groups 1-4 were cultured in growth culture medium, growth culture medium+EGF, growth culture medium+IGF-I and growth culture medium+IGF-I+EGF, respectively, for 9 days. The results indicated that EGF (50 mg/l) increased the survival rate of oocytes, but decreased the growth rate of oocytes; IGF-I (100 mg/l) effectively maintained the survival of oocytes and stimulated their growth; IGF-I (100 mg/l) and EGF (50mg/l) in combination produced a higher effect on both of the survival and the growth rate of oocytes than IGF-I or EGF alone. Conclusively, the growth factors can effectively maintain the survival of caprine preantral follicle oocytes and regulated their growth in culture. EGF and IGF-I in association could synergically meliorate the culture system of caprine preantral follicle oocytes.

Regulation of in vitro growth of preantral follicles by growth factors in goats

Goat preantral follicles were cultured to investigate the effects of insulin-like growth factor-I (IGF-I), epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) on the in vitro growth and viability of oocytes. Preantral follicles were isolated mechanically and enzymatically (using collagenase and DNase) from prepuberal goat ovaries. The working medium was composed of Defined Eagle's Minimum Essential Medium (DMEM) supplemented with HEPES (20 mM), 10% fetal calf serum (FCS), hypoxanthine (2 mM), dibutyryl cyclic adenosine 3',5'-monophosphate (dbcAMP) (2 mM), penicillin (75 ng/ml) and streptomycin (50 ng/ml). The culture medium consisted of the working medium with follicle stimulating hormone (FSH) (100 ng/ml) and hydrocortisone (40 ng/ml) added. In the experiment, goat preantral follicles were cultured for 9 days in the culture medium and in the culture medium supplemented with either IGF-I (100 ng/ml), EGF (50 ng/ml), bFGF (50 ng/ml) or IGF-I (100 ng/ml)+EGF (50 ng/ml). The results indicated that IGF-I (100 ng/ml) effectively maintained the survival of oocytes and promoted their growth; EGF (50 ng/ml) enhanced the survival rate of oocytes but had a negative effect on oocyte growth; bFGF (50 ng/ml) stimulated oocyte survival but had no obvious effect on their growth while IGF-I (100 ng/ml) and EGF (50 ng/ml) in combination had a greater effect on both survival and growth rate of oocytes than IGF-I or EGF alone. The supplementation of IGF-1 and EGF to the culture medium is recommended in the culture of goat preantral follicles.

Impact of Growth Factors on In Vitro Development of Caprine Oocytes at Pre-antral Stage

The objective of this study was to examine the effect of various growth factors such as the epidermal growth factor (EGF) and insulin-like growth factor-I (IGF-I) either individually or in association, in the presence of follicle-stimulating hormone (FSH) on the in vitro growth and viability of caprine oocytes at pre-antral stage. Pre-antral follicles were disassociated enzymatically and mechanically from pre-pubertal caprine ovaries after the animals were anaesthetically ovariectomized. Caprine pre-antral follicles in group 1, 2, 3 and 4 were cultured in growth culture medium, growth culture medium + EGF, growth culture medium + IGF-I and growth culture medium + IGF-I + EGF, respectively, for 9 days. The results indicated that EGF (50 mg/l) increased the survival rate of oocytes, but decreased the growth rate of oocytes; IGF-I (100 mg/l) effectively maintained the survival of oocytes and stimulated their growth; IGF-I (100 mg/l) and EGF (50 mg/l) in combination produced a higher effect on both the survival and the growth rate of oocytes than IGF-I or EGF alone. Conclusively, the growth factors can effectively maintain the survival of caprine oocytes from pre-antral follicles and regulate their growth in culture. EGF and IGF-I in association could synergically meliorate the culture system of caprine pre-antral follicles.

The potential for gamete recovery from non-domestic canids and felids

Species are becoming extinct at a rate 100 times the natural background rates. Considering all mammalian orders, 24% of all Carnivora species are threatened. The goal of carnivore conservation is to reverse the decline in populations and to secure remaining populations in ways that will assure enduring public support. In this context, biotechnology is a tool with tremendous potential for assisting the conservation of endangered canid and felid species. As the first step for biotechnology development is the gamete obtainment, this review will discuss the potential of gamete recovery from non-domestic canids and felids, based on learning how to apply these procedures in the domestic carnivores. Thus, electroejaculation and obtaining both epidydimal spermatozoon and spermatogonial germ cells are indicated as techniques for male gametes recovery. In the female gametes retrieval, different methods for oocyte recovery from both antral and preantral follicles, and the possibility for ovarian tissue transplantation are discussed. Furthermore, the study discusses the responsibilities involved in the use of assisted reproduction in endangered species conservation.

From the germinal cells to the newborn animal: the transmission of genes and life through the generations

The technology of reproduction progressed considerably during the last decade, leading to a certain availability of in vitro methods for fertilisation, oocyte maturation and embryo culture. The most spectacular manipulations are cloning and transgenesis. This review focuses on the early appearance of germinal cell precursors and the long-standing fate of gametes in mammals. The evident complexity and long-term programming of events in gametes and early embryos explain part of the difficulties encountered during the development of in vitro and in vivo methods such as multiple ovulation and embryo transfer (MOET), oestrus synchronisation, ovulation induction, superovulation, in vitro maturation and fertilisation, cryopreservation, transgenesis, nuclear transfer and cloning) and the occurrence of unexpected alterations of development, e.g. embryonic or fetal mortality, large-weight newborn syndrome and other dysregulations in imprinting or DNA transmission.

Meiotic response of in vitro matured canine oocytes under different proteins and heterologous hormone supplementation

The impact of TCM-199 supplemented with different proteins and heterologous hormones on the in vitro maturation (IVM) rate of bitch oocytes was evaluated by nuclear staining under fluorescence microscopy. Oocytes were recovered by slicing of ovaries from bitches presented at various stages of oestrous cycle to ovariohysterectomy. The basic culture medium was TCM-199 supplemented with 25 mM Hepes/l, with 10% heat-inactivated oestrous cow serum (ECS), 50 microg/ml gentamicin, 2.2 mg/ml sodium bicarbonate and 22-microg/ml pyruvic acid, 1.0-microg/ml oestradiol (E 8875; Sigma), 0.5-microg/ml follicle-stimulating hormone (FSH) (Folltropin-V; Vetrepharm Inc., Ontario, Canada) and 0.03 IU/ml human gonadotropin (hCG) (Profasi HP; Serono, Aubonne, Switzerland). Oocytes were distributed randomly between basic culture medium (control) and the corresponding experimental treatment. Hormone treatments were: oocytes cultured in; (1) medium without FSH, (2) control medium supplemented with 20 microg/ml oestradiol, or (3) medium supplemented with 1 microg/ml human somatotropin (hST; Humatrope, Lilly, Saint Cloud, France). The second experiment consisted of oocytes cultured in medium supplemented with 0.4% (w/v) bovine serum albumin (BSA, fraction V; Gibco Grand Island, NY, USA) instead of ECS, or oocytes cultured in medium with 10% inactivated oestrous bitch serum (EBS) instead of ECS. Oocytes were cultured in 100 microl droplets (up to 25 oocytes per drop) under mineral oil at 37 degrees C in a 100% humidified atmosphere containing 5% CO2 in air. After 72 h of IVM, the highest rates (p < 0.05) of meiotic resumption were achieved with the 0.4% BSA supplementation. A positive influence on the metaphase II (MII) acquisition rate was observed with hST supplement. Oocytes cultured with 10% EBS supplementation did not develop to the MII stage. The results in this study show that the protein and hormone supplements to TCM-199 culture medium tested did not promote the final steps of IVM of bitch oocytes.

Zebu (Bos indicus) ovarian preantral follicles: morphological characterization and development of an efficient isolation method

Preantral follicles are a major source of oocytes, and their utilization as an important tool to store large number of female gametes for future use in reproductive programs has been investigated. The increasing importance of studies in this subject, together with the important role of Zebu cattle in the economy of tropical and subtropical countries as well as their well-known differences from European cattle, led to this research. The present study aims to determine the best size interval for sectioning ovarian tissue to isolate preantral follicles from Zebu cows using a tissue chopper and to evaluate the follicular quality after isolation. Furthermore, it aims to provide information about the Zebu cow preantral follicle population and use this data (as a control) to evaluate the effectiveness of the tested isolation method. Testing eight different tissue sectioning size intervals, it was possible to conclude that the 125-microm-section interval is shown to be better than the intervals of 25, 50, 175 and 200 microm to isolate preantral follicles from Zebu cow ovaries. The 125-microm interval allowed the recovery of 26,050+/-1611 (mean +/- S.E.M.) preantral follicles per one-half ovary, while the number of preantral follicles in situ estimated by evaluation of histological sections was 35,288+/-2342 per one-half ovary. Thus, the mean (+/-S.E.M.) recovery rate (=[number of preantral follicles isolated/number of preantral follicles in situ in the same ovary] x 100) was 74.3+/-4.3%. The morphometrical analysis showed that Bos indicus preantral follicles are similar to B. taurus preantral follicles based on previous reports. In conclusion, this study showed that a simple, mechanical method can be used effectively to isolate a large number of intact preantral follicles from Zebu cow ovaries, with a high recovery rate.

In vitro culture of bovine preantral follicles

Bovine preantral follicles (40-100 microm diameter at collection) were collected from ovaries of slaughtered cows and cultured in vitro with one of the four treatments: follicle stimulating hormone (FSH; 100 ng/ml) alone; FSH plus epidermal growth factor (EGF; 100 ng/ml); FSH plus insulin-transferrin-selenium (ITS; +1%) or FSH plus hypoxanthine (4 mM) in tissue culture medium (TCM 199) supplemented with 10% fetal calf serum (FCS), 0.1 mg/ml sodium pyruvate, 100 IU/ml of penicillin and 100 microg/ml streptomycin. The control culture medium was TCM 199 with supplements without any treatments. Follicles of each size were cultured separately in groups of one to three in 24-well multidishes each containing 500 microl of the appropriate culture medium. Culture commenced at follicle recovery (day 1) and continued for 10 days (harvested on day 11). In each case, half the medium was removed and replaced by fresh medium every third day. Follicle diameters were recorded on days 1, 5 and 11 of the experiment. At the end of the 10-day culture period, half of the follicles were stained with trypan blue to assess their potential viability and half were stained with bisbenzimide plus propidium iodine to estimate various morphological features of the follicles. Follicles of all initial sizes, on all culture treatments, increased in diameter during in vitro cultures with the greatest increases, both in absolute and proportional size, occurring between days 1 and 5 of culture. All of the culture medium supplements caused greater increases in follicle diameters than control medium at both days 5 and 11 of culture for all initial sizes of follicles (p<0.01). The most effective culture supplements for follicles of 40-, 60- and 80-microm initial diameter were FSH alone and FSH+EGF. The size of these follicles at both days 5 and 11 of culture on both the treatments was significantly larger (p<0.01) than follicles cultured in the presence of the other two supplementary treatments. The growth of follicles of 100-microm initial diameter did not differ between culture medium supplements. None of the culture media caused follicle size to increase to the initial diameters of the next larger size category during the 10 days of culture although follicles of 100-microm diameter achieved a diameter of 120 microm, after 4 days of culture. The overall follicular viability and morphology were better with treatments than the controls in all cases; however, there was no significant difference (p>0.05) among them. From this experiment, FSH and FSH plus EGF may be recommended for in vitro culture of smaller (40, 60 and 80 microm) follicles.

Effect of sectioning on the number of isolated ovine preantral follicles

The aim of the present study was to test the effect of the interval of serial sections in the tissue chopper on the number of isolated ovine preantral follicles. Best results were obtained when the ovarian fragments were cut in the tissue chopper at interval of 87.5µm (1592 preantral follicles per treatment). Histochemical analysis showed that the follicular morphology was preserved after mechanical isolation as demonstrated by the normality of oocytes and granulosa cells as well as by preservation of basement membrane. The percentages of isolated primordial, primary and secondary follicles were 92, 6, and 2%, respectively. The follicular sizes varied from 12.5 to 96.3µm in diameter. In conclusion, a greater number of isolated preantral follicles were obtained when the method of isolation used the tissue chopper adjusted at 87.5µm. Besides, this treatment does not affect the follicular integrity after the isolation procedure.

Quantitative and qualitative analysis of the effectiveness of a mechanical method for the isolation of preantral follicles from ovine ovaries

The preantral follicles are the major source of oocytes and its utilization has been investigated as an important tool to store large numbers of female gametes for further utilization in reproductive programs. The aim of the present study was to perform quantitative and qualitative analyses of the efficacy of a mechanical method for isolating of preantral follicles from the ovaries of fetuses and from nonpregnant and pregnant ewes, using as reference the population of preantral follicles in situ. In the isolation method the ovaries were cut into fragments in the tissue chopper. Then, the suspension was filtered through nylon mesh filters. The number of isolated follicles per ovary was 1655, 4735 and 4770, respectively, for the fetus, nonpregnant ewe and pregnant ewe. The number of in situ preantral follicles per ovary was 32961, 16627 and 17794, respectively, for the fetus, nonpregnant ewe and pregnant ewe. The follicle recovery rate (number of isolated preantral follicles/number of in situ preantral follicles x 100) was higher in adult ewes (26 and 28%, respectively, for nonpregnant and pregnant ewes) than in fetuses (5%). Histological analysis showed that very few preantral follicles (less than 0.26% in situ and 0.46% after the isolation procedure) were degenerated. In conclusion, this study showed that a mechanical method could be used effectively to isolate a large number of intact ovine preantral follicles. In the future, with improvements in culture systems, the isolation of a great number of oocytes enclosed in preantral follicles will make a valuable contribution to the rare breeds and endangered species, agricultural efficiency and basic research in folliculogenesis.

Efficient isolation and long-term viability of bovine small preantral follicles in vitro

A comparison of isolation techniques for small preantral follicles (30-70 microm) from bovine ovaries using a mechanical method with a grating device or collagenase treatment was performed. The mean number (157.0) of intact follicles per ovary isolated by the mechanical method was significantly greater (P < 0.05) than that (26.0) of follicles isolated by the enzymatic method. Isolated morphologically normal follicles (MNF) were cultured for up to 30 d either in control cultures (non-coculture) or in coculture with bovine ovary mesenchymal cells (BOM), fetal bovine skin fibroblasts (FBF), and/or bovine granulosa cells (BGC). In control cultures, most of the follicles degenerated and only a few MNF (1.2%) were present after 30 d in culture. In contrast, the cocultures with BOM, FBF, and BGC resulted in 50.7, 46.6, and 21.4% viable MNF, respectively. Trypan blue and Hoechst 33258 staining were used for a quick and sensitive assessment of oocyte and granulosa cell viability during follicle isolation and culture in vitro. After 30 d, percentages of viable follicles in coculture with BOM (18.6%) and FBF (17.1%) were significantly greater than those of follicles in the control cultures (0%) or in coculture with BGC (10.0%). There was a gradual increase in the average diameter of the MNF during culture. The mean diameter of the follicles increased by 15.4 and 30.0% in coculture with BOM and FBF, respectively, by day 30. In conclusion, small bovine preantral follicles were efficiently isolated using a mechanical method that utilizes a grating device, and could be maintained for up to 30 d in the presence of mesenchymal cell cocultures such as BOM and FBF. This in vitro culture system that supports long-term survival of bovine preantral follicles should be beneficial for studying follicle growth and development.

Study of preantral follicle population in situ and after mechanical isolation from caprine ovaries at different reproductive stages

The purposes of this study were to estimate the population of caprine preantral follicles, and to evaluate quantitatively and qualitatively the efficiency of a specific mechanical method for the isolation of preantral follicles from mixed breed goats at different reproductive stages. On average, 37,646+/-4277 preantral follicles were present in goat ovaries, and 13,631+/-2399 preantral follicles were obtained after isolation. The number of preantral follicles isolated or in situ was not significantly affected by the reproductive stage. The mean recovery rate per ovary ([number of isolated follicles/number of in situ follicles] x 100) of isolated follicles was 36.2%. The distribution of follicles in situ was 67.8% primordial, 25.8% primary and 6.4% secondary; the respective distribution after isolation was 93.8%, 5.2% and 1.0%. In this study, many polyovular follicles were also observed, mainly in prepubertal goat ovaries. Histological analysis showed that few preantral follicles were atretic in situ (4.83%+/-0.35) or after the isolation procedure (4.67%+/-0.65) in the three reproductive stages. The percentage of atretic follicles was not affected either by the mechanical method or by the reproductive stage. It is concluded that a large number of preantral follicles can be successfully isolated mechanically, with a high recovery rate and a low rate of follicular atresia, irrespective of the reproductive stage of the caprine female.

Effect of the interval of serial sections of ovarian tissue in the tissue chopper on the number of isolated caprine preantral follicles

The present work investigated the effect of the interval of serial sections of ovarian tissue on the number of isolated preantral follicles in the goat. Goat ovaries were cut in the tissue chopper at eight different intervals. The quality of isolated follicles were evaluated by histology and transmission electron microscopy. Best results were obtained when the ovaries were cut in the tissue chopper at intervals of 75.0 microm (9664 preantral follicles per ovary). Histochemical and ultrastructural analysis showed that the follicular morphology was preserved after mechanical isolation as demonstrated by the normality of oocytes and granulosa cells as well as by preservation of basement membrane. The percentages of isolated primordial, primary and secondary follicles were 96.3%, 2.5%, and 1.2% and their average diameters were 21.5, 34.7 and 65.3 microm, respectively. It was concluded that the interval of serial sections of ovarian tissue in the tissue chopper affects the number of isolated preantral follicles, and that the follicles remained intact after mechanical isolation in goats.

Role of media, protein and energy supplements on maintenance of morphology and DNA-synthesis of small preantral domestic cat follicles during short-term culture

Small preantral follicles (40 to 90 microns in diameter) from domestic cats were cultured for 10 d using different media (M199 and Dulbecco's MEM) and protein (FCS and BSA) supplements. Culture efficacy was determined by Hoechst 33258 staining and estimation of Brom-desoxyuridine (BrdU)-incorporation into oocytes and granulosa cells. Culture in M199 + FCS and in DMEM + FCS resulted in 21.6% and 38.1%, respectively, of morphologically intact preantral follicles. Adding BSA increased the rate of normal follicles to 51.7% in M199 and to 58.6% in DMEM. Oocytes were found in 40% of the follicles, when DMEM and/or BSA supplementation was used, while M199 with FCS induced acute loss of oocytes in 85% of the follicles. About 10% of the oocytes contained degenerating chromatin. Measurement of BrdU-incorporation during culture allows for quick and effective assessment of follicle viability in vitro. Comparison of M199 and Dulbecco's MEM, both with FCS or BSA and DMEM with or without pyruvate/lactate, indicated that Dulbecco's MEM + BSA without pyruvate and lactate is the best medium for culture of cat follicles. However, further research of suitable medium supplements is needed.

Preservation of oocyte and granulosa cell morphology in bovine preantral follicles cultured in vitro

Described in the present paper is a culture system that preserves oocyte and granulosa cell morphology in bovine preantral follicles during 5 d in vitro. The effects of additional hypoxanthine and energy substrata (i.e., pyruvate and glutamine) on the morphology of cultured preantral follicles were investigated. It was shown that addition of a mixture of pyruvate, glutamine and hypoxantine to the culture medium increased the percentage of follicles with an intact oocyte from 29.4 to 78.6%. Morphological criteria are described to discriminate between normal and degenerated preantral follicles during culture by inverted microscopy. In addition, the importance of histological evaluation to judge the quality of oocyte and granulosa cells is demonstrated.