Isolation and identification of germ cells from fetal bovine ovaries

Gonadal cell suspensions were made from bovine fetuses of 35–55-, 56–80-, and 80–130-day age groups corresponding to the periods predominated by primordial germ cells (PGCs), oogonia, and meiotic cells, respectively. Germ cells identified on morphological criteria prior to their isolation from suspensions were compared histochemically and morphologically with cells in cryosections, impression smears, and semithin sections of similar gonads. Oocytes were distinguished by their chromosomal configurations in cell spreads. In suspensions from 35–55-day fetuses, cells considered to be PGCs stood out by their size, large nucleus, intracytoplasmic vesicles, and occasional blebbing. The somatic cells were smaller and contained little cytoplasm and few vesicles. In bovine gonads, in contrast to murine gonads, alkaline phosphatase (AP) activity was not specific enough to identify germ cells once they had entered the gonad. In ovaries from the 56–80-day age group, cells similar to PGCs, but slightly larger and with more cytoplasmic vesicles, were identified as oogonia. The cytoplasmic vesicles stained positively for lipid. In ovaries of 80–130-day fetuses, oogonia, oocytes, degenerating germ cells, and multinucleate germ cells were recognized. Degenerating germ cells exhibited a variety of morphological characteristics and were consistently positive for acid-phosphatase activity. Binucleate germ cells appeared around day 85 of gestation, while multinucleate germ cells were seen from day 95. It was concluded that bovine mitotic germ cells can be isolated from gonadal cell suspensions and that the best time to recover them is between 50 and 70 days of gestation. © 1994 Wiley-Liss, Inc.     

Meiosis-inducing and meiosis-preventing effects of sex steroid hormones on hamster fetal ovaries in organ culture

Day 11 to day 15 p.c. female gonads were cultured for 6-8 days in chemically-defined media. In day 11 and day 12 p.c. ovaries grown in a non-hormonal medium, the germ cells were unable to enter meiosis; they were retained at a stage of oogonia or more frequently at a preleptotene stage. Ovaries of the same ages cultured in an estradiol-containing medium showed germ cells progressing through meiotic prophase in a way close to that in ovaries of equivalent age in vivo. That was the case of the germ cells in day 13 to day 15 p.c. ovaries maintained in a non-hormonal medium. In a testosterone-containing medium, the germ cells in day 13 and day 14 p.c. ovaries were prevented from entering meiosis; by contrast, those in day 15 p.c. ovaries underwent meiotic prophase normally. These results indicated that each of both hormones was able to exert its corresponding (meiosis-inducing or meiosis-preventing) effect before a definite critical time of ovarian development. The possibility is suggested that the germ cell differentiation in the female and male gonads in vivo would also depend on estrogens or androgens precociously synthesized in the gonads or supplied from other organs via the fetal blood.     

Influence of age and medium on formation of epithelial cords in the rat fetal ovary in vitro

Fetal ovaries of 14.5-day-old rats were cultured for periods of up to 19 days in control medium or in medium conditioned by the preliminary culture of testes from fetal or young rats. In all ovaries, after 12 days of culture in either medium, epithelial cords were noted having an aspect identical to that of seminiferous cords present in fetal testes explanted at 14.5 days and also cultured for 12 days, i.e. the epithelial cords appeared in ovaries when there was no 'male' or testicular influence. The appearance of histological preparations suggested that the disappearance of the germ cells might bring about a reorganization of the follicular cells in epithelial cords during the differentiation period of the first follicles. With ovaries cultured in conditioned medium, degeneration of the germ cells was more marked, follicles were rare and intra-ovarian cords were greater in number than in ovaries cultured in control medium. The ovaries thus transformed produced the anti-Müllerian hormone (AMH) although they lacked the "germinostatic activity" normally developed by testes of fetal or young rats. This germinostatic activity prevents the multiplication of oogonia when the testes and ovaries are co-cultured in vitro. The transformed ovaries therefore do not have all the functional capacities of fetal testes.     

Stem cell factor and c-kit gene expression and protein localization in the sheep ovary during fetal development

The aim of this study was to investigate stem cell factor and c-kit gene expression and protein localization in the mesonephros and ovary of sheep fetuses at different days of gestation, using RNA in situ hybridization and immunohistochemical procedures. At days 24 and 26 of gestation, stem cell factor mRNA and protein were present in cells throughout the developing gonad and mesonephros. From day 28 to day 40 of gestation, stem cell factor mRNA and protein became increasingly localized to the cortical region of the ovary, where most germ cells were present as actively proliferating oogonia. From day 40 to day 90 of gestation, stem cell factor mRNA and protein localization were confined mainly to the ovarian cortex. Moreover, within the cortical region, stem cell factor mRNA was low or absent where follicles were first forming and highest in the outer ovarian cortex, where germ cells were undergoing mitosis or the early stages of meiosis. In contrast, stem cell factor protein was present in newly forming follicles, as well as in mitotic and meiotic germ cells, which is consistent with the presence of both membrane-bound and soluble forms of this ligand. However, by day 90 of gestation, both stem cell factor mRNA and protein were observed in the granulosa cells of most (> 90%) primordial follicles. C-kit mRNA and protein were observed from day 24 of gestation in both germ cells and somatic cells but, with increasing gestational age, preferentially in germ cells (for example, pre-meiotic germ cells and both isolated oocytes and follicle-enclosed oocytes). C-kit protein, but not mRNA, was also observed in germ cells that were undergoing meiosis. The results indicate that the cells containing stem cell factor mRNA within the ovary up to day 90 of gestation originated from the gonadal blastema and from cells that migrated from the mesonephros before day 28 of gestation. Since stem cell factor mRNA was absent in both mesonephric cells migrating after day 28 of gestation and in regions where follicles were first forming, it is suggested that these later migrating mesonephric cells are the progenitors of the granulosa cells in the first forming follicles. In conclusion, during follicle formation, c-kit mRNA is localized to germ cells whereas c-kit, together with stem cell factor protein, is localized to both germ cells and somatic cells, consistent with the hypothesis that the presence of this receptor-ligand pair is essential to prevent apoptosis.     

Fetal thymus and thymuline stimulate the in vitro proliferation of oogonia in the fetal rat ovary]

In rat ovaries explanted on day 13.5 p.c. and cultured in vitro for up to 6 days, the number of germ cells is enhanced in thymulin-supplemented medium and/or after co-culture of the ovarian explants with foetal thymic tissue compared to ovaries cultured in synthetic medium. Corticosterone added to the medium prevents the secretion of thymulin by the foetal thymus and in that condition the thymus does not influence the proliferation of oogonia. These results provide additional evidence that the pituitary-adrenal-thymic axis might be involved in the control of oogonia proliferation in vivo, taking into account our previous experimental finding that the number of germ cells is increased in ovaries of hypophysectomized foetuses.     

Gene expression of the tyrosine kinase receptor c-kit during ovarian development in the brushtail possum (Trichosurus vulpecula).

Ovarian development and function have been extensively studied in eutherian species, with stem cell factor and its receptor, c-kit, having been shown to play key roles at various stages of these processes. In contrast, relatively little is known regarding ovarian development in marsupials. The aims of this study were, first, to establish the timing of key events during germ cell maturation and follicular development and, second, to determine the timing and cellular localization of gene expression for c-kit in the ovaries of a marsupial, the brushtail possum (Trichosurus vulpecula). For this study, ovaries were collected from possums ranging in age from Day 1 after birth to adult. Using stereology, the number of germ cells was found to increase rapidly during the first 60-100 days of life. This was followed by a sharp decline in number, wherein almost 90% of germ cells had disappeared by Day 180. From histological examinations, the time of initiation of meiosis, follicular formation, and follicular growth were determined to occur on Days 35, 50, and 60, respectively. Using in situ hybridization, c-kit gene expression was localized to germ cells and somatic cells during the first 15 days of life; however, after Day 30 and into adult life, c-kit expression was exclusive to germ cells. Results from this study suggest that the pattern of ovarian development is similar in marsupials to eutherians, and that c-kit may play a key role in germ cell development at various stages throughout life.     

A New Model of Development of the Mammalian Ovary and Follicles

Ovarian follicular granulosa cells surround and nurture oocytes, and produce sex steroid hormones. It is believed that during development the ovarian surface epithelial cells penetrate into the ovary and develop into granulosa cells when associating with oogonia to form follicles. Using bovine fetal ovaries (n = 80) we identified a novel cell type, termed GREL for Gonadal Ridge Epithelial-Like. Using 26 markers for GREL and other cells and extracellular matrix we conducted immunohistochemistry and electron microscopy and chronologically tracked all somatic cell types during development. Before 70 days of gestation the gonadal ridge/ovarian primordium is formed by proliferation of GREL cells at the surface epithelium of the mesonephros. Primordial germ cells (PGCs) migrate into the ovarian primordium. After 70 days, stroma from the underlying mesonephros begins to penetrate the primordium, partitioning the developing ovary into irregularly-shaped ovigerous cords composed of GREL cells and PGCs/oogonia. Importantly we identified that the cords are always separated from the stroma by a basal lamina. Around 130 days of gestation the stroma expands laterally below the outermost layers of GREL cells forming a sub-epithelial basal lamina and establishing an epithelial-stromal interface. It is at this stage that a mature surface epithelium develops from the GREL cells on the surface of the ovary primordium. Expansion of the stroma continues to partition the ovigerous cords into smaller groups of cells eventually forming follicles containing an oogonium/oocyte surrounded by GREL cells, which become granulosa cells, all enclosed by a basal lamina. Thus in contrast to the prevailing theory, the ovarian surface epithelial cells do not penetrate into the ovary to form the granulosa cells of follicles, instead ovarian surface epithelial cells and granulosa cells have a common precursor, the GREL cell.     

Morpho-functional changes in the ovaries of the sea urchin Strongylocentrotus intermedius after exposure to cadmium

The ovaries were studied in the sea urchins kept in a sea water added with 1, 50 and 100 micrograms/l cadmium chloride for 5, 15, 40, 72 and 130 days. The gland reaction depended on the drug dose and exposure. A short exposure (5 and 15 days) stimulated the development of a larger, as compared with the control, number of oogonia and raised the activity of acid and alkaline phosphatases. A long exposure decreased the number of germ cells, decelerated their growth, destroyed gametes and accessory cells, inhibited the activity of alkaline phosphatase. The cadmium accumulation in the ovaries was noted only on the 130th day at concentrations of 50 and 100 micrograms/l. The monitoring of morphological and biochemical indices allowed to conclude that cadmium exerted a toxic effect on the sea urchin ovaries.     

Proteomic Analysis of Fetal Ovary Reveals That Ovarian Developmental Potential Is Greater in Meishan Pigs than in Yorkshire Pigs

Time-dependent expression of functional proteins in fetal ovaries is important to understand the developmental process of the ovary. This study was carried out to enhance our understanding of the developmental process of porcine fetal ovaries and to better address the differences in fetal ovary development of local and foreign pigs. The objective of the present study is to test the expression of key proteins that regulate the growth and development of fetal ovaries in Meishan and Yorkshire porcine breeds by using proteomics technology. Six Meishan and 6 Yorkshire pregnant gilts were used in this experiment. Fetal ovaries were obtained from Yorkshire and Meishan gilts on days 55 and 90 of the gestation period. Using 2D-DIGE (two dimensional-difference in gel electrophoresis) analysis, the results showed that there are about 1551 and 1400 proteins in gilt fetal ovaries on days 55 and 90, respectively of the gestation. Using MALDI TOF-TOF MS analysis, 27 differentially expressed proteins were identified in the fetal ovaries of the 2 breeds on day 55 of gestation, and a total of 18 proteins were identified on day 90 of gestation. These differentially expressed proteins were involved in the regulation of biological processes (cell death, stress response, cytoskeletal proteins) and molecular functions (enzyme regulator activity). We also found that alpha-1-antitrypsin, actin, vimentin, and PP2A proteins promote the formation of primordial follicles in the ovaries of Yorkshire pigs on day 55 of gestation while low expression heat shock proteins and high expression alpha-fetoproteins (AFP) may promote Meishan fetal ovarian follicular development on day 90 of gestation. These findings provide a deeper understanding of how reduced expression of heat shock proteins and increased expression of AFP can significantly reduce the risk of reproductive disease in obese Meishan sows. Our study also shows how these proteins can increase the ovulation rate and may be responsible for the low reproductive efficiency reported in other obese breeds. The ovarian developmental potential was found to be greater in Meishan pigs than in Yorkshire pigs.     

Expression of activin subunits and receptors in the developing human ovary: activin A promotes germ cell survival and proliferation before primordial follicle formation

The formation of the essential functional unit of the ovary, the primordial follicle, occurs during fetal life in humans. Factors regulating oogonial proliferation and interaction with somatic cells before primordial follicle formation are largely unknown. We have investigated the expression, localisation and functional effects of activin and its receptors in the human fetal ovary at 14-21 weeks gestation. Expression of mRNA for the activin betaA and betaB subunits and the activin receptors ActRIIA and ActRIIB was demonstrated by RT-PCR. Expression of betaA mRNA increased 2-fold across the gestational range examined. Activin subunits and receptors were localised by immunohistochemistry. The betaA subunit was expressed by oogonia, and the betaB subunit and activin receptors were expressed by both oogonia and somatic cells. BetaA expression was increased in larger oogonia at later gestations, but was low in oocytes within newly formed primordial follicles. Treatment of ovary fragments with activin A in vitro increased both the number of oogonia present and oogonial proliferation, as detected by bromodeoxyuridine (BrdU) incorporation. These data indicate that activin may be involved in the autocrine and paracrine regulation of germ cell proliferation in the human ovary during the crucial period of development leading up to primordial follicle formation.     

Cytochemistry and ultrastructure of the prenatal porcine adrenal medulla

The ultrastructure and cytochemistry of fetal porcine adrenal medullae have been studied at 60, 80, and 100 days of gestation. Adrenal medullae from fetuses at 60 days of pregnancy consisted of norepinephrine cells only. Some cells containing chromaffin granules were seen in the process of mitosis. A few epinephrine cells were present in the outer medullary zone at 80 days at pregnancy, their number increasing by the 100 day of pregnancy. Chromaffin cells containing both norepinephrine and epinephrine storing granules were also present at 80 and 100 days of gestation. Norepinephrine and epinephrine specific granular vesicles in the fetal adrenal medullary cells were smaller than those reported for the adult pig. The general ultrastructural characteristics of the porcine fetal adrenal medulla were similar to those reported for prenatal adrenal medulla of other species.     

Comparison of cleft palate induction by Nicotiana glauca in goats and sheep

The induction of cleft palate by Nicotiana glauca (wild tree tobacco) during the first trimester of pregnancy was compared between Spanish-type goats and crossbred western-type sheep. Cleft palate was induced in 100% of the embryonic/fetal goats when their pregnant mothers were gavaged with N. glauca plant material or with anabasine-rich extracts from the latter, during gestation days 32-41. Seventy-five percent of newborn goats had cleft palate after maternal dosing with N. glauca during gestation days 35-41, while no cleft palates were induced when dosing periods included days 36-40, 37-39, or day 38 only. The induced cleft palates were bilateral, involving the entire secondary palates with complete detachment of the vomer. Eleven percent of the newborn goats from does gavaged during gestation days 32-41 had extracranial abnormalities, most often contractures of the metacarpal joints. Most of these contractures resolved spontaneously by 4-6 weeks postpartum. One newborn kid also had an asymmetric skull due to apparent fetal positioning. No cleft palates were induced in lambs whose mothers were gavaged with N. glauca plant or anabasine-rich extracts during gestation days 34-41, 35-40, 35-41, 36-41, 35-51, or 37-50. Only one of five lambs born to three ewes gavaged with N. glauca plant material during gestation days 34-55 had a cleft palate, but all five of these lambs had moderate to severe contractures in the metacarpal joints. The slight to moderate contracture defects resolved spontaneously by 4-6 weeks postpartum, but the severe contractures resolved only partially. Embryonic/fetal death and resorption (determined by ultrasound) occurred in 25% of pregnant goats fed N. glauca compared to only 4% of pregnant sheep. Nicotiana glauca plant material contained the teratogenic alkaloid anabasine at 0.175% to 0.23%, dry weight, demonstrating that Spanish-type goats are susceptible to cleft palate induction by the natural toxin anabasine, while crossbred western-type sheep are resistant. However, clinical signs of toxicity were equally severe in goats and sheep, even though maternal alkaloid tolerance was generally lower in sheep. We postulate that an alkaloid-induced reduction in fetal movement during the period of normal palate closure is the cause of the cleft palate and multiple flexion contractures. Teratology 61:203-210, 2000. Published 2000 Wiley-Liss, Inc.     

Gonadogenesis in early developmental stages of Acipenser naccarii and influence of estrogen immersion on feminization

Gonad development processes and the effects of a single 8‐hour immersion treatment with 17β‐estradiol (E2, 400 μg L⁻¹) on sex differentation in the Adriatic sturgeon, Acipenser naccarii, were investigated. After migration of germ cells, gonadal ridges appeared in 16‐ to 18‐day old larvae and undifferentiated gonads in 55‐ to 60‐day old larvae. Putative ovaries with notches in the germinal epithelium and presumed testes with smooth germinal epithelium appeared in 180–185‐day old juveniles. Ovaries with proliferating oogonia and early meiotic oocytes clusters were observed in 292‐day old juveniles. Testes did not exhibit germ cell mitosis until 430 days of age. Developmental stages in E₂‐treated animals closely followed those of controls up to 430 days. The treatment significantly increased the percentage of ovaries when administered to embryos about 1.5 day before hatching, while did not significantly altered the normal 1/1 sex ratio when administered to 1.5‐day old pre‐larvae and 10‐day old larvae. It is likely that in A. naccarii exogenous E₂ administration may act through a feedback mechanism of self‐supporting steroid production and that steroids are the physiological inducers of sex differentiation, as in most teleosts. The E₂‐immersion treatment, easier than time‐consuming administration through food, could be a good approach to control sex differentiation and caviar production.     

Development and differentiation of the reproductive system of Tropidurus catalanensis (Squamata: Tropiduridae)

Development and differentiation of the reproductive system in lizards begin in the embryonic period, although the stage and time of their occurrence vary according to populations and species. In this study, the events of the development and differentiation of the reproductive system of males and females of Tropidurus catalanensis were characterized during the embryonic, neonatal, and juvenile periods. Embryos at Stages 27, 34, 37, 40, and 41, neonates and juveniles, from Corrientes, Argentina, were analyzed. At Stage 27, the genital ridge was not observed but primordial germ cells were recorded in the yolk sac as well as the mesenteric mesenchyme, indicating the beginning of germ cell migration. Gonadal differentiation commenced at Stage 34. In males from Stage 37, the testes possessed seminiferous cords with Sertoli cells and spermatogonia, while in hatchlings seminiferous tubules and interstitial tissue with mature Leydig cells were present. Spermatogenesis was observed in a specimen of 51.9 mm snout-vent length, corresponding to the minimum reproductive size. In females, from Stage 37 until hatching, the ovaries had a cavernous medulla and a cortex with somatic cells and abundant oogonia. The onset of meiosis and folliculogenesis occurred in the juvenile period.     

Germ cell development in Meishan and White Composite gilts

This study compared dynamics of the germ cell population in two swine breeds that differ in prolifacy, White Composite (WC) and Meishan (MS), during fetal and neonatal life and in mature sows. Germ cell populations developed in a similar pattern in these two diverse breeds during fetal life. Maximal germ cell number was observed at 90 days postcoitum (dpc) in both WC and MS gilts, and substantial oogonial apoptosis was evident thereafter with approximately 30% of maximal numbers present at 25 days postpartum (dpp). Neither gilt nor sow germ cell number was correlated with maternal ovulation rate. Postnatal MS gilts had larger pools of primordial follicles and consistently greater proportions and numbers of primary and secondary follicles compared to postnatal WC gilts, indicative of enhanced follicular recruitment and primordial follicle activation. Occasional antral follicles were present in MS ovaries by 25 dpp and numerous surface follicles were observed at 56 dpp in MS but not WC ovaries, indicative of more rapid ovarian maturation and early onset of puberty. Total germ cell number is unlikely to influence or to predict subsequent ovulation rate. These observations highlight important developmental events during late fetal and early postnatal life that prepare the ovarian environment for early onset of puberty and subsequent ovulation in MS gilts.     

Development of the ovary and ontongeny of mRNA and protein for P450 aromatase (arom) and estrogen receptors (ER) α and β during early fetal life in cattle

Estradiol-17β is the predominant steroid produced during early stages of ovarian development in ruminants and steroid hormones have been hypothesized to regulate ovigerous cord formation, germ cell meiosis and ovarian vascular development. Therefore, the objective was to determine the presence and localization of mRNA and protein encoding cytochrome P450 aromatase (P450arom), and estrogen receptors α (ERα) and β (ERβ) during ovarian development in fetuses of cattle on days 35, 45, 60, 75, 90 and 105 after breeding (n = 4/age) using in situ hybridization and immunohistochemistry. No ovarian tissue was found in the day 35 fetuses, but was found in all later ages studied. There appeared to be little organization of specific structures in ovaries on days 45 and 60, although germ cells could be identified. Evidence of the beginning of ovigerous cord formation was found on day 60. By day 75 of gestation, the ovigerous cords were more extensive and mesonephric-derived cell streams were detectable. By day 90 (and still present at day 105), both ovigerous cords and cell streams/rete tubules were definitive structures of the developing ovaries. Ovaries appeared to develop in “lobular” segments around the periphery of the ovary. Some lobes appeared to be at slightly different developmental stages, as assessed by the extent or definition of ovigerous cord formation.The localization of mRNAs for P450arom, ERα and ERβ were closely associated with protein content. At days 45 and 60, mRNA and protein of P450arom and ERβ were located throughout ovaries with signal in medulla being denser than in the cortex. P450arom mRNA or protein was punctate, but not evident in germ cells. From day 75, P450arom was increasingly becoming localized to cell streams or clusters of cells (rete tubules) in the medulla, and by days 90 and 105 of gestation, was more definitively localized to cell streams and/or rete tubules. Similar to P450arom, ERβ mRNA and protein were observed in cells in the medulla, and also in germ cells, pre-granulosa cells and some surface epithelial cells. ERα mRNA and protein were predominately in the surface epithelium in ovaries of all ages with fainter signal for ERα protein also being observed in pre-granulosa and stromal cells including the cell streams/rete tubules. ERα protein was also detected in a few germ cells at days 90 and 105 of gestation. Thus, in cattle, estradiol-17β has the potential to regulate, in an autocrine/paracrine manner, a number of different cell types during ovarian development.     

Gametic and pleiotropic defects in mouse fetuses with Hertwig''s macrocytic anemia

Pleiotropic effects on germ cell number, hematologic status, and body size are described in 12- to 15-day WBB6F1 normal (+/-) and defective (an/an) mouse fetuses, with special emphasis on gametogenesis. Differences between genotypes were apparent by Day 12. At 12 days, normal testes contained many germ cells and frequent normal mitoses, and the number of germ cells increased rapidly from Day 12 to Day 15. By contrast, 12-day an/an testes contained fewer germ cells, frequently degenerating, and many abnormal mitoses. Their number of germ cells decreased rapidly, so that almost none persisted to Day 15. Normal ovaries contained many germ cells, with much normal mitosis on Day 12 and 13, followed by meioses, but the smaller an/an ovaries contained few germ cells, with little mitosis, some meiosis, and very much degeneration. The erythrocyte counts of both normal and anemic fetuses increased approximately fourfold between 12 and 15 days, but at comparable ages, total counts were always lower in an/an fetuses than in normal littermates. At all ages, Hertwig's anemic (an/an) fetuses were somewhat smaller than their normal littermates. Although both W/Wv and Sl/Sld mice also show macrocytic anemia and germ cell failure, the great difference in etiology of their germ cell defects indicates that an/an gene action must be qualitatively different from that in either W/Wv or Sl/Sld mice.     

Sexual dimorphism in the regulation of meiotic process in the rabbit

Meiosis, mitosis, and apoptosis during fetal and postnatal periods were investigated in order to explore mechanisms of sexual dimorphism in initiation of germ cell meiosis. Gonads were obtained from Japanese white rabbits from 23 to 51 days postcoitum (dpc). Gonadal thin sections were stained with hematoxylin and eosin. Germ cell alkaline phosphatase and apoptosis were detected with histochemical and immunohistochemical methods, respectively. In the ovary, meiotic germ cells were initially recognized at 29 dpc and arrested after enclosure within follicles. Similarly, meiotic germ cells were recognized outside seminiferous tubules at 29 dpc, but no meiotic figures were identified in intratubular spaces. Apoptotic germ cells were not recognized in the intratubular spaces before 35 dpc, and no apoptotic figures were recognized in the ovary during the period studied. In conclusion, the initiation of meiosis in testicular interstitial tissue at the time comparable to that in the ovary indicates that germ cells of both sexes have the ability to enter meiosis during the same stage of fetal development; and it appears most likely that delayed initiation of meiosis in the intratubular space is attributable to meiosis-inhibiting substance(s) present in seminiferous tubules.     

MAPK和p90rsk在大鼠卵泡发育中的表达与活性

利用免疫组织化学方法研究丝裂原激活蛋白激酶(mitogen-activated protein kinases, MAPK)及其底物之一p90rsk在大鼠卵泡发育过程中的表达与活性.结果表明,非活性形式的MAPK存在于大鼠各生长期卵泡的卵母细胞和颗粒细胞中,但磷酸化活性形式的MAPK只存在于部分具有分裂增殖活性的颗粒细胞中.MAPK的作用底物p90rsk只在各期卵泡的卵母细胞中表达,在颗粒细胞中无着色,说明MAPK信号级联在卵母细胞和颗粒细胞中具有不同的作用方式.另外,胎鼠卵巢的免疫组化染色结果显示,MAPK在卵原细胞增殖过程中具有活性,表明MAPK信号级联在这一过程中起作用.