Ontogenesis of somatic and germ cells in sheep fetal testis

Morphometric study of the testis in sheep embryos using unbiased design-based stereology

Sheep have been used as translational models of human postnatal testicular development. However, the morphometric features of the normal developing testis in sheep embryos have not been previously investigated using stereology. The objective of the present work was to establish normal quantitative parameters for fetal testicular tissue components in sheep, using unbiased design-based stereological methods. Twenty-four sheep embryos were divided into four gestational age groups (9-11, 12-14, 15-17 and 18-20 weeks of gestation) on the basis of the embryos' crown-rump length. Isotropic, systematic uniform random sections of the left testes were obtained by employing the orientator method. Testicular total volume, the absolute and proportional volumes occupied by the seminiferous tubules and interstitial tissue, as well as the seminiferous tubule length, were estimated using the point-counting system and the unbiased counting frame principle. All the parameters, with the exception of the interstitial tissue's fractional volume, gradually increased along with gestational age, with the maximum increase especially seen in the late fetal stages. The proportional volume of the interstitial tissue, on the other hand, showed a decreasing trend along with increasing gestational age. The absolute volume of the testes, of the seminiferous tubules and of the interstitial tissue, and the length of the seminiferous tubules showed a significant (p< 0.05) positive linear correlation with gestational age. Several similarities were observed with human testicular embryogenesis. The stereological data emerging from the present study might prove useful as basic contribution to the fields of andrology and embryology and stimulate further research in these areas.

Reduced Sertoli cell number and altered pituitary responsiveness in male lambs undernourished in utero

The nutritional status of females during pregnancy can have profound effects on the fetus reproductive system development that could affect the reproductive potential as later as in adulthood (fetal programming). The aim of the present study was to examine the effects of maternal nutrient restriction imposed during different periods of gestation on pituitary responsiveness at different ages postnatal and on Sertoli cell number in male offspring. Pregnant ewes were fed to 100% of Metabolizable Energy and Crude Protein requirements throughout pregnancy (Control) or to 50% from 0 to 30 (R1) or from 31 to 100 days of gestation (R2). Male lambs were selected and fed to appetite throughout the study. At 2, 5.5 and 10 months of age a GnRH challenge was conducted. At slaughter (10 months) testes were removed and examined histologically. Maternal undernutrition did not affect the time of the onset of puberty, defined as the first increase in plasma testosterone concentrations > or =1 ng/ml. The LH and FSH response to GnRH challenge did not differ between groups at 2 and 5.5 months but at 10 months of age a higher (P<0.05) FSH response was found in R2 group. Testes weight did not differ between groups at slaughter. Mean Sertoli cell number was significantly lower in animals of R2 group compared with Control (P<0.01). A smaller seminiferous tubules diameter was detected in R2 group (P<0.05), while the diameter of the lumen was similar in all groups. Collectively, these results provide clear evidence for a direct effect of nutrient restriction during pregnancy on Sertoli cell number in adulthood. The lower number of Sertoli cells is the most candidate factor for the higher pituitary activity through a reduction in the suppressive effect of inhibin.

Stereological study of postnatal testicular development in Blackbelly sheep

The objective was to characterize testicular development in Blackbelly sheep, focusing primarily on Sertoli cell number. Lambs (n=43) were allotted into eight groups, and surgically castrated at 0, 3, 6, 9, 12, 15,18 or 21 weeks of age (n=4-6 lambs per group). Testes were fixed and paraffin-embedded, cross-sections (5 microm) were stained and evaluated with quantitative morphometry techniques. Testis weight increased at a greater rate between 9 and 15 weeks of age, which was associated with remarkable changes in testicular histology, including increases in tubular tissue volume, and tubule diameter and length. Spermatogenesis started in a period between 9 and 12 weeks, lumen and elongated spermatids were observed for the first time at 12 weeks (78% of the tubules) and 15 weeks (37% of the tubules), respectively. Total number of Sertoli cells (mean+/-S.E.M.) increased steadily from birth (531+/-76 x 10(6)) to 15 weeks (12,008+/-1722 x 10(6)), with no changes afterwards. Sertoli cell number per gram of testicular tissue decreased as lambs were older, with the most remarkable change occurring between Weeks 9 and 12. An early increase in serum LH was observed at 6 weeks of age, with testosterone (T) increasing at Weeks 12 and 21. In conclusion, Sertoli cells maintained the capacity of proliferating from birth to 15 weeks of age in Blackbelly sheep; furthermore, the period of accelerated testis growth was associated with increased serum T concentration and with important changes in testicular morphology, as a consequence of the beginning and establishment of spermatogenesis and Sertoli cell maturation.

Endocrine and paracrine control of Leydig cell steroidogenesis and proliferation in the wall lizard: an in vitro study

The present in vitro study, for the first time, demonstrates the endocrine as well as paracrine control of Leydig cell steroidogenesis and proliferation in the wall lizard Hemidactylus flaviviridis. Unlike mammals, Leydig cell activity in the wall lizard seems to be directly controlled by ovine follicle-stimulating hormone (FSH)-like molecule, since FSH increased the testosterone production and tritiated thymidine ([(3)H]TdR) incorporation by Leydig cells. In addition, Sertoli cell paracrine factor or factors play important roles in controlling Leydig cell activities as non-activated Sertoli cell-conditioned medium (SCCM) alone stimulated testosterone production by both non-activated and FSH-preactivated Leydig cells. As far as the proliferation was concerned, non-activated SCCM did not influence [(3)H]TdR uptake by non-activated or FSH-preactivated Leydig cells, while FSH-preactivated SCCM was able to stimulate proliferation of activated Leydig cells. It may be concluded that FSH, besides directly controlling, also regulates Leydig cell activities indirectly through stimulating the secretion of Sertoli cell paracrine factors. Moreover, steroidogenic factor is different from mitogenic factor because non-activated Leydig cells were responsive to steroidogenic factor but nonresponsive to mitogenic factor.

Effect of maternal overnutrition during pregnancy on pituitary gonadotrophin gene expression and gonadal morphology in female and male foetal sheep at day 103 of gestation

The aim was to determine whether nutritionally mediated restriction of placental growth alters foetal body growth, pituitary gonadotrophin gene expression and gonadal development at Day 103 of gestation. Embryos recovered from adult ewes inseminated by a single sire were transferred, singly, into the uteri of adolescent recipients. After transfer, adolescent ewes were offered a high (H, n=16) or moderate (M, n=12) level of a complete diet. Ewes were slaughtered at 103+/-0.2 days of gestation and foetal blood, brain, pituitary and gonads were collected. Mean placental weight was lower (P< 0.01) in H than in M groups but foetal weight and reproductive organ weights were similar. Maternal nutrition did not influence LHbeta or FSHbeta mRNA expression in either sex but FSHbeta mRNA expression was higher (P< 0.001) in female (n=11) than in male (n=17) foetal pituitaries. Mean foetal plasma gonadotrophin concentrations were not influenced by dietary intake in either sex. Plasma progesterone concentrations were lower (P=0.001) in foetuses derived from H compared with M intake dams. Compared with M foetuses (n=5), ovaries from H foetuses (n=6) had fewer primordial follicles (P< 0.05) and fewer follicles in total (P< 0.005). In contrast, maternal nutritional status did not influence either seminiferous cord or Sertoli cell numbers in male foetuses (H, n=10; M, n=7). It is concluded that high maternal nutrient intakes restricted placental growth and altered foetal ovarian follicular development prior to the end of the second third of gestation. The latter effect was independent of gonadotrophin secretion.Crown

Testicular development, histology, and hormone profiles in three yearling angus bulls with spermatogenic arrest

This article discusses the interactions between testis criteria and hormone profiles in Angus bulls with spermatogenic arrest. From 2 to 12 months (mo), testis diameter and hormone concentrations (basal and GnRH-stimulated) were evaluated in 27 bulls. At 12 mo, testes were excised. The z statistical test was used to determine whether parameters in three infertile bulls were different (P < 0.05) from those in 24 bulls with normal spermatouenesis. Bull 1 had Sertoli cell-only syndrome and Bull 2 had 90% of the tubules without germ cells and only A1 spermatogonia in the remaining. In Bull 3, germ cells did not advance beyond the primary spermatocyte stage. At 12 mo, testes of Bull 1 (99 g), Bull 2 (105 g) and Bull 3 (32 g) weighed less than those of normal bulls (251.5 +/- 56 g). Sertoli cell numbers/testis in Bull 1 (3.8 x 10(9)) and Bull 2 (4.3 x 10(9)) were not different from those in normal bulls (4.9 +/- 0.3 x 10(9)), but were reduced in Bull 3 (1.6 x 10(9)). The number of Leydig cells per gram of testis parenchyma was higher in Bull 1 (5.4 x 10(7)), Bull 2 (7.3 x 10(7)) and Bull 3 (19 x 10(7)) than in normal bulls (3.6 +/- 0.2 x 10(7)). In Bulls 1 and 2, basal and GnRH-stimulated LH, FSH, testosterone (T), androstenedione (delta4A) and estradiol 17-beta (E2) were within normal ranges at most ages. However, basal FSH and LH were greater in Bull 3 than in normal bulls, probably the causes for higher Leydig cell density. Also in the same animal, GnRH induced lower responses in LH and FSH, consequence of low basal T and E2 at some ages. Basal and GnRH-stimulated delta4A in Bull 3 were greater than in normal bulls after 6 mo, indicating impairment of Leydig cell differentiation. Deficiency in hormone secretion did not appear to be the cause of infertility, which points toward impaired gonadal responses or secretion of intratesticular factors, or genetic defects. Moreover, infertile animals may not always show pronounced changes in hormone secretion, but evaluation of testis growth around puberty can help identify those animals that do not have proper gonadal development.

Apoptosis and mitosis in gonocytes of the rat testis during foetal and neonatal development

This study was undertaken to determine the extent of apoptosis and mitosis in the various testicular cell types throughout rat development from foetal day 14.5 to postnatal days 9-10. Apoptotic activity was studied by detecting DNA fragmentation (TUNEL method) in situ. A TUNEL-positive reaction was detected in gonocytes, while none of the other testicular cells were labelled. The morphology of the TUNEL-positive gonocytes was characteristic of apoptotic cells and was different from that observed in experimentally induced necrosis. The percentage of stained gonocytes peaked on day 15.5-16.5 post-conception (dpc), decreased thereafter and no TUNEL-positive gonocytes were found from foetal day 18.5 onwards. On postnatal day 2, apoptosis resumed and increased to reach a maximum on day 7. Mitosis in the gonocytes, as evaluated by the immunodetection of 5-bromo-2'-deoxyuridine (BrdU) incorporation, was present during the same developmental periods but the ratio of BrdU-positive/TUNEL-positive gonocytes was much greater in the foetal period than in the neonatal period. In an organotypic culture system, the changes in the apoptotic and mitotic activities of the gonocytes in testicular explants from foetuses on days 18.5 and 20.5 or from neonates on day 3, cultured for two days were similar to those observed in vivo. Addition of LH or FSH did not influence either apoptosis or mitosis in the germ cells. These results suggest that both apoptosis and mitosis of gonocytes are independent of gonadotrophins and are mainly controlled by intratesticular factors.

Assessment of nuclear totipotency of fetal bovine diploid germ cells by nuclear transfer

Nuclear transfer was used to study nuclear reprogramming of fetal diploid bovine germ cells collected at two stages of the fetal development. In the first case, germ cells of both sexes were collected during their period of intragonadal mitotic multiplication at 48 days post coïtum (d.p.c.). In the second case, only male germ cells were collected after this period, between 105 and 185 d.p.c. Isolated germ cells were fused with enucleated oocytes. Reconstituted embryos were cultured in vitro and those reaching the compacted morula or blastocyst stage were transferred into synchronous recipient heifers. Of 511 reconstituted embryos with 48 d.p.c. germ cells (309 males and 202 females), 48% (247/511 ) cleaved; 2.7% (14/511 ) reached the compacted morula stage and 8 of them the blastocyst stage (1.6%). No difference was observed between sexes. All 14 compacted morulae/blastocysts were transferred into 6 recipients and one pregnancy was initiated. This recipient was slaughtered at Day 35 and an abnormal conceptus (extended trophectoderm and degenerated embryo) was collected. Its male sex, genetically determined, corresponded to that of donor fetus. Of 380 reconstituted embryos with male 105 to 185 d.p.c. germ cells, 72.1% (274/380 ) cleaved, 2.1% (8 380 ) reached the compact morula stage and 7 of these the blastocyst stage (1.8%). Three blastocysts and one morula were transferred into 4 recipients. Two became pregnant at Day 21 but only one at Day 35 which aborted around Day 40. Our results show that the nucleus of diploid bovine germ cells of both sexes can be reprogrammed. However, in the absence of further development of these reconstituted embryos, nuclear totipotency of bovine diploid germ cells remains to be evidenced.