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Biomedical subjects

A G Byskov

Publications and source records attributed to A G Byskov.

At least 73 records · Page 4Linked to original sources
PubMed1987

Maturation of mouse oocytes in vitro is influenced by alkalization during their isolation.

Dictyate oocytes were isolated from the ovaries of 22-day-old mice and cultured for 24 h. Isolation and classification of the oocytes were done at a stable pH of 7.45, during gradual increase of pH from 7.45 to 8.3, or at pH 8.3. In cumulus-enclosed oocytes alkalization beyond pH 7.45 resulted in an increased rate of degeneration and decreased rates of germinal vesicle breakdown and polar body formation. In the naked oocytes, only the rate of degeneration was affected. The results stress the importance of a stable pH during the period of isolation, and of a careful classification of the oocytes before culture.

Animals↗
PubMed1986

Ultrastructure of germ cells and adjacent somatic cells correlated to initiation of meiosis in the fetal pig.

The ultrastructure of female and male germ cells and associated somatic cells were studied in morphologically sex differentiated fetal pig gonads from day 27 to day 95 post insemination. Before meiosis starts in the ovary, the organelles of germ cells and somatic cells of both sexes are poorly developed. In oocytes in leptotene stage, the endoplasmic reticulum attains close proximity to the plasma membrane forming characteristic contact areas which in addition are only seen in male germ cells of the same age. As meiosis progresses, the organelles of the oocyte increase in number and degree of differentiation. In particular the ER is prominent in the diplotene stage. At midgestation the male germ cells become polarized, the organelles gathering at one side of the nucleus. In the granulosa cells the number and extension of organelles increase concomitantly with the oocytes proceeding through meiosis. The Sertoli cells grow progressively complex in shape, with numerous mitochondria and a prominent ER, whereas the Golgi complex remains poorly developed. Small dense bodies are present both in germ cells and somatic cells. They are electron dense, membrane bounded, rounded or elongated granules often connected with endoplasmic reticulum. No activity of peroxidase, catalase or acid phosphatase could be traced in the granules, making them improbable candidates as peroxisomes or lysosomes. Their number is high in all germ cells and somatic cells on day 27 post insemination and in germ cells in leptotene stage.

Animals↗
PubMed1986

Initiation of oogenesis in the human fetal ovary: ultrastructural and squash preparation study.

Ovaries from 27 human fetuses at less than or equal to 12 weeks' gestational age were examined with electron microscopy and squash preparation studies. The findings demonstrated that meiosis begins in the fetal ovary between 11 and 12 weeks of age. This is several weeks after gonadal sex differentiation, which can be recognized in the testis at 6 weeks. Ovaries at earlier ages included primitive germ cells and oogonia. With advancing fetal age, mitotic activity and germ cell degeneration became increasingly evident. Preleptotene cells were found as early as 9 to 10 weeks, suggesting that meiotic capacity is present soon after gonadal sex differentiation but further progression into meiosis is delayed until some specific inductive influence is exerted.

Female↗
PubMed1986

Ultrastructure of human cumulus-oocyte complexes from healthy and atretic follicles.

Follicular fluids with cumulus-oocyte complexes and granulosa cells were aspirated from antral follicles in healthy women at different stages of the normal menstrual cycle. The cumulus-oocyte complexes were processed for light and electron microscopy and classified as pre-ovulatory, healthy non-pre-ovulatory and atretic by certain light microscopical criteria, i.e. degree of expansion, number of layers and pycnotic nuclei in the cumulus investment, size of the peri-vitelline space and oocyte nuclear morphology. Their follicles were similarly classified by follicular steroid measurements and/or flow cytometric DNA analyses of the aspirated granulosa cells. A high degree of correlation between these classifications was found. Moreover, pre-ovulatory and atretic cumulus-oocyte complexes showed particular fine morphological characteristics, some of which were different while others appeared to be identical. Similarities were increased number of lipid droplets in the cumulus cells, widened peri-vitelline space, peripheral displacement or breakdown of the oocyte nucleus and disconnection of the junctions between cumulus cell projections and the oolemma. In addition to the criteria used for the light microscopical classification, pre-ovulatory complexes were characterized by release of the content of cortical granules while atretic ones displayed cumulus cells with pseudopodia-like projections, cumulus cells in the perivitelline space and lipid droplets in the ooplasm.

Androsterone↗
PubMed1986

Differentiation of mammalian embryonic gonad.

Formation and differentiation of a gonad depend on finely controlled interactions between germ cells and various types of somatic cells. These interactions already begin when the germ cells start migrating toward the gonadal ridge. Reaching the presumptive gonadal area on the mesonephros, the germ cells join with the mesonephric-derived cells. These mesonephric cells are probably the precursors of the steroid-producing cells. A crucial event for gonadal function is the enclosure of germ cells and somatic cells in specific germ cell compartments. Survival and differentiation of the germ cells depend on this separation. Differentiation of the steroid-producing cells depends in turn on remaining outside the cell compartments. The mechanisms directing the gonad to develop into a testis or an ovary are still obscure, but specific gene products from the sex chromosomes probably play a basic role in gonadal sex differentiation.

Animals↗
PubMed1986

Flow cytometry and sorting of meiotic prophase cells of female rabbits.

We present a new, flow cytometric method by which cells in various stages of the meiotic prophase can be quantitated and sorted in partly enriched fractions. Ovarian cells of 3-16-day-old rabbits were mechanically dispersed and fixed in ethanol and aldehydes. The cell suspension was stained with the DNA fluorochrome mithramycin and analysed and sorted in a FACS IV cell sorter according to the fluorescence and forward light scatter distribution. Cells sorted onto slides were stained with haematoxylin and eosin and differentially counted in the microscope. In the diploid fraction, preleptotene cells were more fluorescent than somatic cells. Leptotene cells were found throughout the S fraction and the tetraploid fraction. Zygotene and pachytene cells caused a major peak in the tetraploid region with 10-25% more fluorescence than somatic cells. Cells in diplotene had 5-15% more fluorescence than somatic cells. Mitotic cells were 20-40% more fluorescent than somatic cells and scattered the light more intensely than did meiotic cells with the same fluorescence.

Animals↗
PubMed1985

Meiosis-inducing substances in human preovulatory follicular fluid related to time of follicle aspiration and to the potential of the oocyte to fertilize and cleave in vitro.

Meiosis-inducing substance (MIS) and steroid and gonadotropic hormones were investigated in 41 preovulatory follicular fluids (FFs) aspirated at either 0, 12, or 36 hours after human chorionic gonadotropin (hCG) administration in 25 women with clomiphene citrate-stimulated cycles. Twenty-one oocytes were recovered from these FFs and subjected to in vitro fertilization. MIS activity was present in 25 (61%) of the FFs. The frequency of MIS-active FFs increased from 11% (1 of 9) at 0 hours and 40% (2 of 5) at 12 hours to 81% (22 of 27) at 36 hours after hCG administration (P less than 0.001). The concentration of hormones in MIS-active FFs was not significantly different from that of MIS-inactive FFs. Twelve (86%) of 14 oocytes that fertilized and cleaved in vitro were recovered from MIS-active FFs. By contrast, all seven oocytes that remained unfertilized in vitro were recovered from MIS-inactive FFs. These findings support the notion that resumption of meiosis in the preovulatory oocyte is triggered by MIS in FF and suggest that follicular MIS production may be one of the factors that determines the success of in vitro fertilization and early embryonic development.

Androstenedione↗
PubMed1985

Origin and differentiation of the endocrine cells of the ovary.

A large proportion of the somatic cells of the developing ovaries of mouse, human and rabbit stems from the mesonephric tissue. In the immature mouse ovary and in the 19-day-old fetal rabbit ovary, the first steroid-producing cells differentiate among the mesonephric-derived cells within the ovary. In the fetal human ovary, the first steroid-producing cells arise in the inner part of the cortex and differentiate concomitantly with the formation of small follicles. The origin of the early steroid-producing cells in the human ovary is still uncertain. During early ovarian development, formation and further differentiation of the steroid-producing interstitial cells seem to continue only in areas devoid of free viable germ cells.

Animals↗
PubMed1984

Is resumption of meiosis in the human preovulatory oocyte triggered by a meiosis-inducing substance (MIS) in the follicular fluid?

Aspirates from 31 ovarian follicles and 2 corpora lutea of 26 women at different stages of the menstrual cycle were investigated for activity of meiosis-inducing substance (MIS) and meiosis-preventing substance (MPS). The aspirated follicles were classified as dominant (i.e., preovulatory), healthy, or atretic according to their size, steroid hormone content, and stage of the menstrual cycle. To test for MIS and MPS activity, gonads of sexually undifferentiated fetal mice were cultured in media containing either 15% follicular fluid aspirate (test gonads) or 15% human blood serum (control gonads). MIS activity is present in follicular fluid if the test testes contain more meiotic germ cells than the control testes. MPS activity is present if the test ovaries have less meiotic germ cells than their controls. MIS activity was present only in healthy follicles of the late follicular phase (12 of 15 follicles). No MIS activity was seen in healthy or atretic follicles from other phases of the menstrual cycle. The MIS activity is apparently unrelated to the composition of steroids in the follicular fluid. MPS activity was not found in any of the follicles. It is proposed that the preovulatory resumption of meiosis may be triggered by a MIS in the follicular fluid.

Adolescent↗
PubMed1983

Relationship of meiotic prophase and ornithine decarboxylase in the neonatal rabbit ovary.

Ornithine decarboxylase (ODC) activity was measured in homogenates of neonatal rabbit ovaries from the day of birth to day 22, an interval that corresponds to the progressing stages of the meiotic prophase from oogonia to diplotene and follicle formation. The ODC-activity was high on days 1 and 3 when most germ cells start the phase of pre-meiotic DNA-synthesis. A peak of ODC-activity appeared on day 12, simultaneously with a small increase in mitotic activity of the intraovarian rete cells. It is suggested that ODC and therefore polyamine synthesis may be related to the regulation of the onset of meiosis and the mitotic activity of the intraovarian rete cells.

Animals↗
PubMed1983

Abnormal growth of ovarian antral follicles in breast cancer patients.

Ovarian antral follicles from patients with breast cancer were compared with follicles from healthy women. Steroid levels in the follicular fluid and the health status of the follicles were evaluated. Follicles were judged to be healthy or atretic by flow cytometric determinations of the deoxyribonucleic acid content of aspirated granulosa cell nuclei. Fifteen of the 25 follicles (60%) from the cancer patients contained unmeasurable or abnormally low steriod levels (i.e., less than 100 ng/ml) which were significantly (P less than 0.001) lower than in follicles of the same health status from healthy women (500 to 1000 ng/ml). It is speculated whether substances other than the usual follicular steriods are produced by the cancer patients, which stimulate mitotic activity of the granulosa cells.

Adult↗
PubMed1983

Growth pattern of the sex ducts in foetal mouse hermaphrodites.

In this report the morphology of the gonads and the growth of the Wolffian and Müllerian duct in foetal mouse true hermaphrodites (16 days p.c.) have been studied and compared to that of normal mice. The ducts from the hermaphrodites were placed in one of five groups according to the proportion of male and female characteristic of the gonad. When more than 85% of the gonadal tissue was masculine, the Wolffian ducts showed the same percentage of cells in mitosis (mitotic index, MI) as normal males. The MI of the Wolffian ducts was lower, but constant, if the gonad contained between 0 and 85% of testicular tissue. The number of Leydig cells in the gonads showed a linear relationship with the percentage of testicular tissue. Apparently, the MI of the Wolffian duct does not increase with increasing 'maleness' and with the number of Leydig cells. Four possibilities are put forward to explain the constant level of MI: (1) The Leydig cells of hermaphrodites may be deficient in producing testosterone. (2) The Leydig cells may produce testosterone at a normal rate but the epithelial cells of the Wolffian duct may not respond to increasing levels of testosterone by increasing their mitotic activity. (3) The presence of female gonadal tissue may directly or indirectly inhibit the mitotic activity of the epithelial cells of the Wolffian duct. (4) The epithelial cells of the Wolffian duct may respond to a low threshold level of testosterone, but maximal response is only triggered by a critical higher hormone level present only in group V. In hermaphrodites, the Wolffian duct attached to a gonad without testicular tissue and without Leydig cells, has a MI which is significantly to a gonad without testicular tissue and without Leydig cells, has a MI which is significantly higher than in normal females. It is suggested that circulating testosterone from the contralateral gonad is responsible for this high MI. In the Müllerian duct a mitotic index similar to that of the normal females was only found when the gonad contained from 0 to 15% of testicular tissue. If a gonad contained more than 15% of testicular tissue, the MI of the attached Müllerian duct was much lower equalizing that of normal males. No influence on the growth of the Müllerian duct could be observed from the contralateral gonad.

Animals↗
PubMed1982

Flow cytometric deoxyribonucleic acid analysis of granulosa cells aspirated from human ovarian follicles. A new method to distinguish healthy and atretic ovarian follicles.

Granulosa cell aspirates from human ovarian follicles were analyzed by flow cytometry to determine the fraction of cells in the DNA S-phase of the mitotic cell cycle. The aim of the study was to evaluate if the percentage of granulosa cells in S-phase (the S-fraction) could be used to indicate whether a follicle was healthy or atretic. A highly significant relationship was found between the S-fraction and the concentration of estradiol in the follicular fluid (r = 0.6, P less than 0.001). More than 85% of the follicles having an S-fraction of 16% or greater contained intrafollicular levels of estradiol equal to or greater than 200 ng/ml and had a low androstenedione:estradiol ratio. Conversely, 95% or more of the follicles that had an S-fraction of less than 16% contained low estradiol (less than 200 ng/ml) and had a high androstenedione to estradiol ratio. We conclude that flow cytometric DNA measurements on follicular aspirates provide a reliable and rapid method by which to distinguish healthy and atretic ovarian follicles. Since only a small fraction (less than 5%) of an entire granulosa cell population is required for S-phase analysis, the technique allows the majority of cells to be immediately available or other biochemical studies. Moreover, since excision of ovarian tissue is avoided, the technique may be acceptable for studies on women with normal ovarian function but who are undergoing laparotomy or laparoscopy for some reason.

Adolescent↗
PubMed1982

Influence of mesonephros on foetal and neonatal rabbit gonads. I. Sex-steroid release by the testis in vitro.

The experiments were performed to study the influence of mesonephros on gonadal sex hormone release. Foetal and neonatal rabbit testes were cultured for 5 days, with and without their mesonephric tissue. The culture media were harvested every day and analyzed by RIA for the content of testosterone, progesterone and oestradiol. The development of the tissues were evaluated microscopically after culturing. The results show that between day 20 pc and day 1 pp the mesonephric tissue lowered the amounts of testosterone in co-cultures with testis. This effect disappears when the mesonephric derived cells develop the capacity to synthesize a meiosis inducing substance (MIS). A relationship between decrease of testosterone and secretion of MIS is discussed. It is concluded that the steroid producing cells of the testis, the Leydig cells, originate or are heavily influenced by mesonephros during early testicular organogenesis.

Animals↗
PubMed1981

Feminizing effect of mesonephros on cultured differentiating mouse gonads and ducts.

Gonads were removed from fetal mice at about the time that gonadal sex differentiation occurs. The gonads were cultured in vitro with or without their mesonephric tissue. When gonads and ducts removed from sexually undifferentiated fetuses were cultured together, the gonads of both sexes developed female characteristics, whereas gonads cultured without mesonephros developed according to the sex of the fetus from which they were removed. Gonads of sexually differentiated fetuses developed whether they were cultured with or without the mesonephros.

Animals↗
PubMed1981

Germ cell kinetics in the neonatal rabbit testis.

Germ cells in the developing rabbit testis were found to undergo several distinct changes in the first two weeks after birth. Mitotic activity, which had been high in the late fetal period, reached a peak on the day before birth, then diminished steadily and ceased entirely after five days of age. Extensive germ cell degeneration occurred in the first week after birth resulting in accumulation of pools of degenerating germ cells in the central portions of the cells at various stages of preleptotene could be found in squash preparations. This corresponded to the time when germ cells in the rabbit ovary enter and proceed through meiotic prophase. There was no evidence of entry into leptotene or later stages of meiosis in the neonatal testis. The findings suggest that a similar stimulus for entry into meiosis may exist in both sexes, but a blockage occurs in the male.

Animals↗