Biomedical subjects

A G Byskov

Publications and source records attributed to A G Byskov.

At least 19 recordsLinked to original sources

PubMed2006

Biochemical pregnancy after fertilization of an oocyte aspirated from a heterotopic autotransplant of cryopreserved ovarian tissue: case report.

Autotransplantation of frozen/thawed ovarian tissue in women undergoing cancer therapy has so far led to the birth of two healthy babies. In both cases, it can be discussed whether the fertilized oocyte originated from the transplant or from the native ovary. We now present a biochemical pregnancy achieved after heterotopical autotransplantation of cryopreserved ovarian cortical tissue and hence the unquestionable proof that pregnancy can occur after transplantation of cryopreserved ovarian tissue. A woman diagnosed with Hodgkin's lymphoma had ovarian tissue cryopreserved at the age of 28, before receiving chemotherapy and radiation therapy that rendered her amenorrhoeic. After complete remission, she had autotransplantation of ovarian tissue to the remaining ovary, to the right pelvic wall and to a midline subperitoneal pocket on the lower abdominal wall. The transplanted tissue resumed hormone secretion and follicles developed in all three locations. Three times during 8 months, when follicles could not be visualized in other locations, oocytes were aspirated from the subperitoneal autotransplanted tissue on the lower abdominal wall. Twice, an oocyte was retrieved, fertilized by intracytoplasmatic sperm injection (ICSI) and transferred to the woman's uterus. One of the treatments resulted in a positive pregnancy test 14 days after transfer. Clinical pregnancy, however, was not achieved. In conclusion, heterotopic autotransplantation of cryopreserved ovarian tissue can sustain follicle development. The oocytes of aspirated mature follicles are capable of fertilization after ICSI, and the resulting embryo is competent of producing hCG at detectable levels.

Adult↗

PubMed2005

Cryopreservation of intact testicular tissue from boys with cryptorchidism.

BACKGROUND: Boys with cryptorchidism often face fertility problems in adult life despite having orchiopexy performed at a very young age. During this operation, a biopsy of the testis is normally taken in order to evaluate their infertility potential and the presence of malignant cells. This study evaluated the morphology and functional capacity of cryopreserved testes biopsies and their possible use in fertility preservation. METHODS: Biopsies from 11 testes (eight boys) were obtained. Each biopsy was subdivided into six pieces and two pieces were frozen in each of two different cryoprotectants. One fresh and two cryopreserved pieces were cultured for 2 weeks. All pieces were prepared for histology. Used culture media were analysed for testosterone and inhibin B concentrations. RESULTS: The morphology of the fresh and frozen-thawed samples was similar, with well-preserved seminiferous tubules and interstitial cells. A similar picture appeared after 2 weeks of culture, but a few of the cultured biopsies contained small necrotic areas. The presence of spermatogonia was verified by c-kit-positive immunostaining. Production of testosterone and inhibin B (ng/mm(3) testis tissue) in the frozen-thawed pieces was on average similar to that of the fresh samples. CONCLUSIONS: Intact testicular tissue from young boys with non-descended testes tolerates cryopreservation with surviving spermatogonia and without significant loss of the ability to produce testis-specific hormones in vitro. It may be an option to freeze part of the testis biopsy, which is routinely removed during the operation for cryptorchidism, for fertility preservation in adult life.

Biopsy↗

PubMed2005

Number of germ cells and somatic cells in human fetal ovaries during the first weeks after sex differentiation.

BACKGROUND: This study presents the number of germ cells and somatic cells in human fetal ovaries during week 6 to week 9 post conception, i.e. the first weeks following sex differentiation of the gonads. METHODS: One ovary with attached mesonephros from each of 11 individual legal abortions was used for estimation of cell numbers. After recovery of the fetus, the ovary-mesonephric complexes were immediately isolated, fixed and processed for histology. A stereological method was utilized to estimate the total number of oogonia in all ovaries and somatic cells in seven of them. RESULTS: The number of oogonia per ovary increased from approximately 26,000 in week 6 to approximately 250,000 in week 9 and somatic cells from approximately 240,000 to approximately 1.4 x 10(6). The ratio of oogonia to somatic cells tended to increase throughout the period. The concentration of oogonia was similar in the cranial (mesonephric connected) part and the caudal part of the ovaries. CONCLUSIONS: This is the first stereological estimation of the number of oogonia and somatic cells in human fetal ovaries, and the first estimation of germ cells and somatic cells in ovaries aged <9 weeks. The number of oogonia in week 9 is comparable to the numbers previously published based on non-stereological estimations. We found early stages of meiosis in fetal ovaries from week 9.

Cell Count↗

PubMed2005

Follow-up of ovarian function post-chemotherapy following ovarian cryopreservation and transplantation.

BACKGROUND: The purpose of this study was to assess the ovarian function after treatment of a malignant disease in women who previously had cortical tissue from an entire ovary cryopreserved prior to chemotherapy, and to assess ovarian function after autotransplantation of cryopreserved ovarian tissue. All were treated with chemotherapeutic drugs with an estimated high risk of inducing ovarian failure. METHODS: Twenty-two women with breast cancer (n = 8), Hodgkin's disease (n = 6), non-Hodgkin's (n = 2), leukaemia (n = 5) or brain tumour (n = 1) underwent a clinical examination >18 months after cryopreservation. Three patients with premature ovarian failure had ovarian tissue autotransplanted orthotopically and heterotopically. Ovarian function was assessed by ultrasonography of the remaining ovary and hormone measurements. RESULTS: Nine of 22 women (41%) had sonographic and hormonal signs of ovarian failure with ovarian volumes <1.3 cm3, no antral follicles and high FSH levels (median 57.1 IU/l). Thirteen of the 22 women (59%) still menstruated and 10 had a seemingly normal ovarian function, with a median ovarian volume of 6.8 cm3, a median number of antral follicles of six, FSH <15 IU/l and normal estradiol levels. All three patients with autotransplanted ovarian tissue regained ovarian function as confirmed by return of menses, follicles on ultrasonography and normalized hormone levels. Two embryos were created from the crypreserved tissue after IVF. CONCLUSIONS: Treatment with bone-marrow transplantation and/or high doses of alkylating agents led to ovarian failure in all patients. Autotransplantation of ovarian tissue led to return of ovarian function.

Adolescent↗

PubMed2005

Anti-Müllerian hormone initiates growth of human primordial follicles in vitro.

Survival and growth of follicles in human ovarian tissue is presently only performed with limited success. We evaluated the effect of anti-Müllerian hormone (AMH) and/or testosterone on follicular growth during a 4-week culture period using ovarian cortical tissue from six women in their reproductive years. The cortex of each biopsy was isolated and immediately cryopreserved upon collection and stored in liquid nitrogen. After thawing the tissue was placed in culture. After the culture period all follicles were counted on histological sections and classified for viability and stage of development. Based on evaluation of 6603 follicles it was found that the number of growing follicles significantly increased during the culture period as compared to the uncultured control, irrespective of the composition of the culture medium. Furthermore, significantly more follicles advanced to the primary and secondary stage (p<0.05) in tissue cultured with AMH (54%) as compared to tissue cultured in control medium (41%). The mean diameter of follicles classified as primary follicles was significantly enhanced in tissue cultured in the presence of AMH (p=0.002) and AMH plus testosterone (p<0.001) as compared to that observed in tissue cultured with control medium and medium containing testosterone alone. In contrast the mean diameter of the oocyte and its nucleus remained similar irrespective of culture medium. In conclusion, AMH seems to affect early stages of human follicular development by enhancing recruitment, survival and/or growth during a 4-week culture period.

Adult↗

PubMed2003

Density and distribution of primordial follicles in single pieces of cortex from 21 patients and in individual pieces of cortex from three entire human ovaries.

BACKGROUND: At the time of cryopreservation of ovarian tissue for fertility preservation a small biopsy of ovarian cortex is usually taken for histological evaluation of the follicular reserve. The purpose of this study was to evaluate the distribution and density of primordial follicles in single pieces of cortex from individual patients and in pieces of cortex comprising entire ovaries, all prepared for cryopreservation. METHODS: Cortical biopsies from 21 patients and the whole cortex of one ovary were evaluated histologically prior to cryopreservation. In addition, the cortex of two whole ovaries was cryopreserved before histological evaluation. The volume of each cortical fragment was measured, all follicles counted and the follicular density calculated. RESULTS: In individual pieces of cortex follicular density showed a significant inverse linear correlation with age. The follicular density per cortical fragment prepared from each of the three entire ovaries varied from 1.8 to 166, 0.007 to 140 and 0.04 to 4.48 follicles/mm(3) cortical tissue. CONCLUSION: The density of primordial follicles varied more than two orders of magnitude in cortical fragments from each of the three ovaries. Primordial follicles were very unevenly distributed throughout the cortex of these ovaries, although a significant linear correlation between age and follicular density was found.

Adolescent↗

PubMed2003

Survival of primordial follicles following prolonged transportation of ovarian tissue prior to cryopreservation.

BACKGROUND: Cryopreservation of ovarian tissue for fertility preservation is becoming increasingly common. Treatment of diseases that may deprive the ovaries of follicles is often performed at local hospitals that are without the necessary facilities and expertise to cryopreserve ovarian tissue. The aim of the present study was to evaluate whether primordial follicles of ovarian cortex survive transport for up to 4 h prior to cryopreservation. METHODS: Immediately after recovery of one ovary from each of four patients, the cortex was roughly isolated, placed in IVF culture medium, kept on ice and transported for 3-4 h to the centre where final dissection and cryopreservation took place. Transplantation of pieces of thawed ovarian cortex under the skin of ovariectomized immunodeficient mice for a period of 4 weeks was used to assess the survival of primordial follicles. RESULTS: After transplantation, ovarian tissue from each of the four patients contained surviving follicles. CONCLUSIONS: Transport of roughly isolated ovarian cortex cooled on ice for a period of up to 4 h allows survival of primordial follicles following cryopreservation and transplantation to immunodeficient mice.

Adolescent↗

PubMed2003

Erroneous genetic sex determination of a newborn twin girl due to chimerism caused by foetal blood transfusion. A case report.

OBJECTIVE: We present a case of erroneous sex determination in a newborn twin girl (twin A) due to chimerism. CASE REPORT: Amniocentesis and ultrasound examination had pointed towards male sex of both twins. At birth, twin A presented as a phenotypically normal female with 46,XY karyotype, and 46,XY gonadal dysgenesis was suspected. Twin B was a normal male. RESULTS: In our department, further examinations of twin A included undetectable testosterone and inhibin-B and elevated FSH. Ultrasound suspected an infantile uterus, and sequencing of the SRY gene was normal. After gonadectomy, a 46,XX karyotype was demonstrated in both normal infantile ovaries and in the fibroblasts from a skin biopsy. Analysis of X-linked markers in DNA from blood lymphocytes in both twins was identical, consistent with 46,XY karyotypes. CONCLUSION: Twin A is a 46,XX female with a chimeric 46,XY blood cell line due to intrauterine transfusion from her twin brother.

Blood Cells↗

PubMed2001

Human FATE is a novel X-linked gene expressed in fetal and adult testis.

Previously, we identified a partial cDNA sequence of a novel human transcript, designated fetal and adult testis expressed transcript (FATE). FATE is testis-specific in fetal life and co-expressed with SRY in a 7 weeks old fetal testis, suggesting a function in early testicular differentiation. Herein, full-length cDNA clones of human and porcine FATE were isolated and the gene structure and promoter region of the human FATE gene was characterized. The human FATE gene, which maps to Xq28, consists of five exons spanning approximately 7 kb of genomic DNA. Examination of 1 kb of the FATE promoter region revealed the presence of a putative steroidogenic factor 1 (SF-1) binding site at position -79 to -71 upstream of the transcription start site. We propose that FATE might represent a novel target gene of SF-1 in human testicular differentiation and/or germ cell development.

Adult↗

PubMed2001

[Cryopreservation of human ovarian tissue. Method of freezing and therapeutic use].

The medical treatment of various cancers may, as long-term sequelae, cause infertility in girls and young women. In order to preserve the fertility of such women, techniques to cryopreserve ovarian tissue have gained considerable interest during recent years. The ovarian tissue is cryopreserved before cancer treatment is commenced, and first replaced when the woman has been cured. Based on the successful results from the use of this technique in test animals, where normal live young have been born, cryopreservation of human ovarian tissue has been initiated in a number of fertility clinics worldwide over the last few years. So far, only two women have experienced transplantation of cryopreserved ovarian tissue. Menstrual cycles and oestradiol production were restored in both women, but restoration of fertility have not yet been demonstrated. This review describes the technique and its present possibilities and limitations. The legal aspects in Denmark are presented and some ethical aspects described.

Animals↗

PubMed2001

Content of meiosis activating sterols in equine follicular fluids: correlation to follicular size and dominance.

Meiosis activating sterols (MAS) are pre-cholesterol sterols that can be isolated from follicular fluid (FF-MAS) or testes (T-MAS). Meiosis activating sterols trigger the resumption of meiosis in cultured meiotically competent oocytes. In the present work MAS, cholesterol and progesterone were assayed by HPLC in follicular fluids collected from pony mares at fixed days after the last ovulation. Follicles were divided into two groups according to whether they were aspirated before or after Day 17 after the last ovulation. The latter group was further divided according to whether the follicle diameter was < or = 22 mm or > 27 mm. Both FF-MAS and T-MAS were detected in almost all samples. Overall, the total amount of MAS in the follicular fluids increased with the size of the follicles but was accompanied by a decrease in the amount of free cholesterol. The amounts of MAS and progesterone in > 27 mm follicles aspirated after Day 17 were significantly higher as compared to the other groups. A transversal cohort analysis showed that the largest follicle at the time of aspiration had the highest level of MAS after day 17 of the cycle, which was not always true for follicle samples aspirated before Day 17 of the cycle. The study demonstrates that the content of MAS in equine follicular fluids increased during follicular maturation concomitant with a decrease in the concentration of free cholesterol. Moreover, MAS concentration is higher in dominant follicles than in subordinate follicles. The MAS may therefore play an as yet unknown physiological role during pre-ovulatory maturation.

Animals↗

PubMed2001

Testicular concentration of meiosis-activating sterol is associated with normal testicular descent.

In the cryptorchid stallion, spermatogenesis is arrested at various levels before the completion of meiosis. In men, infantile cryptorchidism is also often associated with oligo- and azoospermia during adulthood. An impairment of spermatogenesis might be reflected in the level of locally produced factors. Formerly, a meiosis-activating sterol (T-MAS) has been isolated in murine and bovine testes. This sterol possesses the potential to trigger resumption of meiosis in cultured mouse oocytes, indicating that it might play an important role in the regulation of the meiotic process in the female gamete. The function of T-MAS in the testis is still unclear, but T-MAS may be associated with spermatogenesis. The objectives of this study were 1) to demonstrate the presence of T-MAS in equine testes, 2) to compare the contents of T-MAS in testicular tissue of stallions with complete and incomplete testicular descent and 3) to compare testicular T-MAS concentration before and after puberty Testes were collected from 16 normal and cryptorchid stallions submitted for castration and stored at -80 degrees C until the content of T-MAS was measured quantitatively with an HPLC-assay. In stallions > or = 2 years of age, the content of T-MAS was higher (P < 0.001) in normal testes (19.3+/-1.1 microg T-MAS/g, n=7) than in inguinally (4.1+/-2.4 microg T-MAS/g, n=4) or abdominally located testes (1.6+/-0.2 microg T-MAS/g, n=2). The contents of T-MAS in normal testes from stallions < 2 years of age (2.8+/-1.5 microg T-MAS/g, n=4) was lower than in normal testes from stallions > or =2 years of age (P < 0.001) From the present study it can be concluded that T-MAS is present in equine testicular tissue. Furthermore, the present study demonstrates that the production of T-MAS in testicular tissue is, concurrently with spermatogenesis, associated with normal testicular descent and is temporarily related to the onset of puberty.

Aging↗

PubMed2001

Glucose and pyruvate metabolism during mouse gonadal sex differentiation.

In the mouse, gonadal sex differentiation starts around E12 and meiosis begins in the ovary shortly after E13. In the search for metabolic changes that might be correlated to gonadal sex differentiation and/or possibly the onset of meiosis, we investigated the metabolism of glucose and pyruvate in the developing mouse ovary before (E11.5-E12.5), during (E14.5-16.5), and after meiosis (E18.5), and in fetal testes without meiosis. Gonads were cultured with 14C-labeled glucose (0.02 and 5.58 mM) and 14C-pyruvate (0.17 mM). The oxidation expressed as 14CO2 production and the organification expressed as retention of 14C in the tissues were measured and correlated to the protein content of the gonads. Using 0.02 mM glucose, a decline in oxidation and organification was found in ovaries as well as in testes, which is probably related to starvation. Using 5.58 mM glucose, a continuous decline in oxidation was seen only in the testis. Organification of 0.17 mM pyruvate increased at E12.5 and E14.5 in the ovary but not in the testis. This was in despite of an exponential increase of protein content in the testes compared to only a moderate increase in the ovary. The CO2 production from 5.58 mM glucose was equal to that from 0.17 mM pyruvate in gonads of both sexes. In conclusion, an increased metabolism of 5.58 mM glucose and 0.17 mM pyruvate in the ovaries as compared to the testes is related to sex differences during gonadal formation and onset of meiosis in the ovaries. J. Exp. Zool. 288:130-138, 2001.

Animals↗

PubMed2001

Characteristics of human ovulation in natural cycles correlated with age and achievement of pregnancy.

BACKGROUND: The aim of this study was to evaluate whether characteristics of human ovulation correlate with age and pregnancy potential. METHODS: Two groups of women with regular menstrual cycles were included (i.e. one fertile and one infertile group), which were divided into four age groups (< or =29, 30-34, 35-39, > or = 40 years). Monitoring included observations of follicular phase length, whether ovulations occurred from the left or right ovary, the pattern of ovulations in succeeding natural cycles and, in a subset of women, early follicular phase FSH concentrations. RESULTS: Ovulation moving from one ovary to the other in two consecutive cycles (i.e. contralateral ovulation) was inversely correlated with age, showing a ratio of contralateral ovulation per contra plus ipsilateral ovulations (C/C+I) of 62% in women <29 years, gradually decreasing to 42% in women >40 years. The ratio of right-sided ovulation per right plus left-sided ovulations (R/R+L) was unrelated to age and remained almost constant at a level of approximately 55%. The follicular phase length was inversely correlated with age, being 16.2 +/- 2.9, 15.4 +/- 2.9, 14.8 +/- 2.8 and 13.7 +/- 1.3 days in women < 29, 30-34, 35-39 and >40 years of age respectively. The follicular phase length was similar when comparing ovulations occurring from the right and left ovary, but comparing two successive cycles, the length of the follicular phase of the second cycle, showing contralateral ovulation, was shorter than ipsilateral ovulation with two consecutive ovulations in the same ovary. The pregnancy rate of the four groups decreased with age, being 14, 12, 5 and 3% respectively. The C/C+I ratio correlates with pregnancy rate and follicular phase length, and inversely correlates with basal FSH, whereas R/R+L is unrelated to age and pregnancy rate. CONCLUSIONS: Human ovulation shows characteristics related to age. The interaction between the two ovaries seems to be most pronounced in the younger years, where ovulations jump from one ovary to the other more frequently than later on in life. The C/C+I ratio shows a clear correlation with age and pregnancy rate.

Adult↗

PubMed2001

The effects of meiosis activating sterol on in-vitro maturation and fertilization of human oocytes from stimulated and unstimulated ovaries.

The object of this study was to assess functional maturation in vitro by obtaining data on the fertilization and embryonic competence of human oocytes with or without exposure to meiosis activating sterol (MAS) during maturation in vitro. Immature oocytes were either collected from unstimulated patients with polycystic ovaries (PCO) during gynaecological surgery, or were donated by patients undergoing a cycle of intracytoplasmic sperm injection (ICSI) treatment including ovarian stimulation with gonadotrophins. PCO oocytes had variable cumulus cover, which was retained during culture while those from ICSI patients were cultured without cumulus. The study included 119 oocytes from PCO patients and 72 from ICSI patients. The oocytes were allowed to mature in vitro for up to 46 h in the presence or absence of MAS. Mature oocytes were inseminated by ICSI with fertile donor spermatozoa and embryo development was monitored in vitro. MAS (30 microg/ml) significantly increased the survival of oocytes from PCO patients (P < 0.01) but did not significantly affect the proportion completing maturation in vitro. For the ICSI patients, >90% of oocytes survived in all culture groups, regardless of MAS addition, however MAS (10 or 30 microg/ml) significantly increased the proportion of oocytes maturing in vitro (P < 0.05). The apparent tendency towards improved subsequent development in vitro will require larger numbers of oocytes for evaluation. Oocytes from ICSI patients matured more rapidly in vitro than those from PCO patients. Our results show positive effects of MAS on human oocytes, confirming previous data in mice. This work may have implications for the future clinical application of IVM.

Adult↗

PubMed2001

Identification of human candidate genes for male infertility by digital differential display.

Evidence for the importance of genetic factors in male fertility is accumulating. In the literature and the Mendelian Cytogenetics Network database, 265 cases of infertile males with balanced reciprocal translocations have been described. The candidacy for infertility of 14 testis-expressed transcripts (TETs) were examined by comparing their chromosomal mapping position to the position of balanced reciprocal translocation breakpoints found in the 265 infertile males. The 14 TETs were selected by using digital differential display (electronic subtraction) to search for apparently testis-specific transcripts in the TIGR database. The testis specificity of the 14 TETs was further examined by reverse transcription-polymerase chain reaction (RT-PCR) on adult and fetal tissues showing that four TETs (TET1 to TET4) were testis-expressed only, six TETs (TET5 to TET10) appeared to be differentially expressed and the remaining four TETs (TET11 to TET14) were ubiquitously expressed. Interestingly, the two tesis expressed-only transcripts, TET1 and TET2, mapped to chromosomal regions where seven and six translocation breakpoints have been reported in infertile males respectively. Furthermore, one ubiquitously, but predominantly testis-expressed, transcript, TET11, mapped to 1p32-33, where 13 translocation breakpoints have been found in infertile males. Interestingly, the mouse mutation, skeletal fusions with sterility, sks, maps to the syntenic region in the mouse genome. Another transcript, TET7, was the human homologue of rat Tpx-1, which functions in the specific interaction of spermatogenic cells with Sertoli cells. TPX-1 maps to 6p21 where three cases of chromosomal breakpoints in infertile males have been reported. Finally, TET8 was a novel transcript which in the fetal stage is testis-specific, but in the adult is expressed in multiple tissues, including testis. We named this novel transcript fetal and adult testis-expressed transcript (FATE).

Chromosome Mapping↗

PubMed2001

Effect of different FSH isoforms on cyclic-AMP production by mouse cumulus-oocyte-complexes: a time course study.

The ability of different isoforms of follicle stimulating hormone (FSH) to induce accumulation of cAMP in cultured mouse cumulus-oocyte-complexes (COC) was evaluated in a time course study. Using isoform fractions representing less acidic (pI 6.43-5.69), mid-acidic (pI 5.62-4.96) and acidic (pI 4.69-3.75) isoforms, the accumulation of cAMP was monitored after an exposure time of 0, 5, 10, 15, 30, 60, 120 and 180 min. In addition, cAMP production was monitored for 0, 5, 10, 15 and 30 min following a 5 min exposure to FSH isoform fractions. Based on FSH measurements using radioimmunoassays, the less and mid-acidic isoforms caused almost twice as much cAMP to be accumulated than the acidic isoform fraction, thereby confirming an enhanced biological activity of FSH isoforms with a isoelectric point (pI) of >5.0. For all isoform fractions, maximal accumulation of cAMP was achieved after 30 min of exposure, after which the production declined to background levels. After a 5 min exposure to isoform fractions, levels of cAMP were significantly higher in the less acidic isoform fractions, but after isoform removal, the decline in cAMP production to background levels followed a similar time course. The results demonstrate that FSH isoforms with a pI of >5.0 induced significant biological responses within a period of 30 min and that prolonged exposure caused attenuated signal transduction. The present results, set in the context of the pulsatile characteristics of FSH release from the pituitary and the reported half-life of less acidic isoforms of approximately 35 min, make it conceivable that isoforms with a pI >5.0 actually possess important physiological functions during the periovulatory period.

Animals↗

PubMed2001

Somatic cell exchange occurs between mouse fetal gonads and mesonephroi during in vitro culture.

Mesonephric cell contribution to the developing mouse gonad has previously been shown to be male-specific in in vitro culture models. This study shows that somatic cell exchange occurs between fetal mouse mesonephroi and gonads during in vitro culture of assembled tissues. Assembling gonads with cell marker-carrying mesonephroi and vice versa identified cell exchange. Two different cell markers were used. One of the markers was the thymidine analogue bromodeoxyuridine (BrdU), which was added to the culture medium during an initial culture period before in vitro culture of assembled tissues in medium without BrdU. The other was bacterial beta-galactosidase, which is expressed ubiquitously in tissues from the transgenic mouse strain ROSA26. The tissues were taken from either 10.5- or 11.5-day-old mouse fetuses, and the assembled tissues were cultured for 36-60 h. Both cell markers demonstrated the occurrence of a cell exchange in both directions between the mesonephros and the gonad. The cell contribution was found to be minor and independent of the initial age of the tissue and hours in culture. Further, mesonephric cell contribution was not male-specific. Cell exchange between the two tissues may be due to growth between the assembled tissues rather than active signal-regulated migration. It is suggested that in vitro culture models may not be applicable for investigating mesonephric cell contribution to the developing mouse gonad.

Animals↗