Stereological evaluation of Sertoli cell ontogeny during fetal and neonatal life in two diverse breeds of swine

Hormone measurements and histomorphological observations in male Bactrian camels

The aim of this study was to investigate the effect of age on the hypothalamic-pituitary-gonadal (HPG) axis hormones and to determine the morphological changes of the testis. The Bactrian camels were divided into two groups based on their ages. The results showed that the testicular weight was significantly heavier in adult male camels than in pubertal male camels (P < 0.05). There were also significant differences between testicular length, testicular width, and testicular volume (P < 0.05). In the testes of both pubertal and adult male camels, Sertoli cells, spermatogonia, spermatocytes, round spermatids, and elongated spermatids were observed. Adult male camels had more Sertoli cells (P < 0.01) and elongated spermatids (P < 0.05). The concentrations of testosterone, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were higher in the plasma and testes of adult camels than in pubertal camels (P < 0.05). E2 concentrations were lower in adult camels than in pubertal camels (P < 0.05). The testosterone levels in testicular tissue were higher than in blood plasma in both adult and pubertal stage (P < 0.05). In conclusion, these findings provide supportive knowledge and show the significant differences in terms of testicular volume, testicular hormone concentrations, and testicular morphology between different developmental stages in Bactrian camels.

Factors affecting the production of quality ejaculates from boars

Production of acceptable quality ejaculates in boars is dependent upon the Sertoli cell population established before puberty and how effectively these cells function after sexual maturity. In general, factors affecting Sertoli cell mitosis tend to have a two-fold greater effect on sperm production compared with those affecting spermatogenesis. Birthweight is a reliable indicator of in utero testicular development and prepubertal growth rates are positively correlated with testis size and sperm production after sexual maturity. Colostrum intake and pre-weaning nutrition account for much of the variation associated with quality and quantity of ejaculates and represent opportunities to further enhance lifetime sperm production. Interactions between young boars and humans, shortly after weaning, have important effects on spermatogenesis after sexual maturity and need to be studied further. The seasonal effect on depression in semen quality is the most significant factor affecting production of acceptable quality ejaculates after puberty. Ambient temperatures, greater than those of the thermoneutral zone, have both acute and chronic effects that compromise all aspects of the male reproductive axis. Identification of genes associated with heat-tolerant phenotypes holds promise for addressing this challenge, especially in light of the current trend in global warming. Supplementation of vitamins, minerals and other compounds have positive effects on sperm production during periods in which other stressors, especially heat stress, are present and is an important mitigation strategy. Recent information on housing conditions and boar usage patterns indicate these cause relatively minor changes in sperm production, overall, but for some males can have significant, long-term effects.

Lycium barbarum Polysaccharide Ameliorates Heat-Stress-Induced Impairment of Primary Sertoli Cells and the Blood-Testis Barrier in Rat via Androgen Receptor and Akt Phosphorylation

Male infertility induced by heat stress has been attracting more and more attention. Heat stress not only causes apoptosis of spermatocytes but also has adverse effects on Sertoli cells, further damaging spermatogenesis. Lycium barbarum polysaccharide (LBP) is the main bioactive component of Lycium barbarum, which has a protective effect on male reproduction, but its mechanism is still unclear. In this study, our results proved that LBP blocked the inhibitory effect on the proliferation activity of Sertoli cells after heat stress, reversed the dedifferentiation of Sertoli cells induced by heat stress, and ameliorated the structural integrity of the blood-testis barrier. In addition, it increased the expression of the androgen receptor and activated Akt signaling pathway to resist heat-stress-induced injury of Sertoli cells.

Hypothyroidism induced by postnatal PTU (6-n-propyl-2-thiouracil) treatment decreases Sertoli cell number and spermatogenic efficiency in sexually mature pigs

Studies with 6-n-propyl-2-thiouracil (PTU) in laboratory rodents have shown that transient neonatal hypothyroidism leads to increased Sertoli cell (SC) number, testis size and sperm production. However, scarce and inconclusive data are available for farm animals. In the present study, Piau pigs received PTU in a gel capsule containing 8 mg/kg of body weight for 14 weeks starting from the first week of age, whereas control animals received only the vehicle. Blood samples were collected during the experimental period for hormonal evaluation in the serum. The animals were orchiectomized at adulthood and had their testes used for histomorphometric analysis. Indicating that the PTU concentration used was effective in promoting hypothyroidism, PTU-treated pigs showed a 30% lower body weight and reduced thyroxine levels (p < 0.05) during the treatment period. At adulthood, the body weight was similar in both groups but, surprisingly, PTU-treated pigs showed 30% lower testis weight (p < 0.05). In general, treated pigs presented increased follicle-stimulating hormone levels, whereas testosterone levels tended to be lower from 9 to 23 weeks of age. No significant differences were observed for estradiol, Leydig cell volume and number, tubular diameter, SC number per gram of testis, SC efficiency and meiotic index. However, seminiferous tubule occupancy, total tubular length, SC number per testis, and daily sperm production per testis and per gram of testis (DSP/g/T) were significantly lower (p < 0.05) in PTU-treated pigs. Therefore, in contrast to laboratory rodents, our results showed that SC proliferation and DSP/g/T (spermatogenic efficiency) in Piau pigs is diminished by postnatal PTU treatment.

Integrated analysis of miRNA and mRNA expression profiles in testes of Duroc and Meishan boars

BACKGROUND

MicroRNAs (miRNAs) are small non-coding RNAs playing vital roles in regulating posttranscriptional gene expression. Elucidating the expression regulation of miRNAs underlying pig testis development will contribute to a better understanding of boar fertility and spermatogenesis.

RESULTS

In this study, miRNA expression profile was investigated in testes of Duroc and Meishan boars at 20, 75, and 270 days of age by high-throughput sequencing. Forty-five differentially expressed miRNAs were identified from testes of Duroc and Meishan boars before and after puberty. Integrated analysis of miRNA and mRNA profiles predicted many miRNA-mRNA pairs. Gene ontology and biological pathway analyses revealed that predicted target genes of ssc-mir-423-5p, ssc-mir-34c, ssc-mir-107, ssc-mir-196b-5p, ssc-mir-92a, ssc-mir-320, ssc-mir-10a-5p, and ssc-mir-181b were involved in sexual reproduction, male gamete generation, and spermatogenesis, and GnRH, Wnt, and MAPK signaling pathway. Four significantly differentially expressed miRNAs and their predicted target genes were validated by quantitative real-time polymerase chain reaction, and phospholipase C beta 1 (PLCβ1) gene was verified to be a target of ssc-mir-423-5p.

CONCLUSIONS

This study provides an insight into the functional roles of miRNAs in testis development and spermatogenesis and offers useful resources for understanding differences in sexual function development caused by the change in miRNAs expression between Duroc and Meishan boars.

The Sertoli cell: what can we learn from different vertebrate models?

Besides having medical applications, comparative studies on reproductive biology are very useful, providing, for instance, essential knowledge for basic, conservation and biotechnological research. In order to maintain the reproductive potential and the survival of all vertebrate species, both sperm and steroid production need to occur inside the testis. From the approximately fifty thousand vertebrate species still alive, very few species are already investigated; however, our knowledge regarding Sertoli cell biology is quite good. In this regard, it is already known that since testis differentiation the Sertoli cells are the somatic cells in charge of supporting and orchestrating germ cells during development and full spermatogenesis in adult animals. In the present review, we highlight key aspects related to Sertoli cell biology in vertebrates and show that this key testis somatic cell presents huge and intrinsic plasticity, particularly when cystic (fish and amphibians) and non-cystic (reptiles, birds and mammals) spermatogenesis is compared. In particular, we briefly discuss the main aspects related to Sertoli cells functions, interactions with germ cells, Sertoli cells proliferation and efficiency, as well as those regarding spermatogonial stem cell niche regulation, which are crucial aspects responsible for the magnitude of sperm production. Most importantly, we show that we could greatly benefit from investigations using different vertebrate experimental models, mainly now that there is a big concern regarding the decline in human sperm counts caused by a multitude of factors.

In utero heat stress causes reduced testicular area at puberty, reduced total sperm production, and increased sperm abnormalities in boars

In utero stress has been shown to negatively affect intact male rats and mice, though very little research has been conducted in boars. The objectives of the present studies were to determine the effects of in utero heat stress (IUHS) on postnatal development and the response to postnatal heat stress of boars. Ten boars were selected at weaning from litters subjected to IUHS or in utero thermoneutral (IUTN) during 30-60 days of gestation. The boars were evaluated for reproductive performance from birth through 57 weeks of age (WOA). Testicular area tended to be smaller for IUHS boars compared to IUTN boars at 24 WOA (P = 0.080). Libido did not differ for IUHS or IUTN (P = 0.818). Total sperm production was reduced in IUHS boars compared to IUTN boars (P ≤ 0.038). Semen volume and semen concentration did not differ (P ≥ 0.469 and P ≥ 0.664, respectively). Total motility and progressive motility did not differ for IUHS and IUTN boars (P ≥ 0.430 and P ≥ 0.652, respectively). In utero heat stressed boars had a greater incidence of sperm with tail abnormalities than IUTN (P ≤ 0.042). In utero heat stressed boars had a lower incidence of sperm with proximal droplets following mild, postnatal heat stress compared with IUTN (P = 0.005). In utero heat stress resulted in significant reductions in sperm production and increased sperm abnormalities in boars. The IUHS boars may be slightly more tolerant to postnatal heat stress, though more research is needed.

Characteristic of factors influencing the proper course of folliculogenesis in mammals

Folliculogenesis is the process of ovarian follicle formation,, taking presence during foetal period. During the follicular development, oogoniums undergo meiosis and oocytes are formed. In the ovaries of new born sows, primary and secondary follicles are present and, 90 days after birth, tertiary follicles appear. During development in the ovarian follicles growth of granulosa cells and differentiation of the thecal cells can be observed. A cavity filled with follicular fluid appears. Granulosa cells are divided into: mural cells and corona radiata, which together with the oocyte form the cumulus oophorus. Corona radiata cells, mural layers and oolemma contact each other by a network of gap junctions. Secreted from the pituitary gland, FSH and LH gonadotropin hormones act on receptors located in granular and follicular cells. In the postnatal life tertiary follicles and Graafian follicles are formed. When the follicle reaches a diameter of 1 mm, further growth depends on the secretion of gonadotropins. Mature ovarian follicles produce: progestins, androgens and oestrogens. The growth, differentiation and steroidogenic activity of ovarian follicles, in addition to FSH and LH, is also affected by prolactin, oxytocin, steroid and protein hormones, numerous proteins from the cytokine and interleukin family, metabolic hormones like insulin, glucocorticoids, leptin, thyroid hormones and growth hormones. Despite numerous studies, many processes related to folliculogenesis have not been discovered Learning the mechanisms regulating reproductive processes would allow to easily distinguish pathological processes and discover more and more genes and mechanisms of their expression in cells that build ovarian follicles.

Histological characteristics of the gonads of pig fetuses and their relationship with fetal anatomical measurements

The objective was to evaluate the histomorphometric characteristics of the testis and ovaries of pig fetuses at different gestational ages, as well as their correlation with some fetus measurements. Forty-four fetuses were separated for gender (male and female) and gestational age (50, 80 and 106days of gestation). After slaughter, fetuses had their body length, head and thoracic perimeters measured and their gonads submitted to histomorphometric analyses. The gonadal characteristics at different gestational ages were statistically compared, correlations with the fetal measurements were performed and equations to predict the gonadal characteristics from the fetal measurements were obtained. The testis weight logarithmically increased along pregnancy, whereas ovary weight increased in a linear manner. The cordonal length and number of Sertoli cells were positively correlated with the fetal measurements, being higher at 106days gestation, while the nuclear volume of these cells were negatively correlated. The total number of follicles was higher at day 80 and 106 of pregnancy. The number of oogonia decreased along the pregnancy, however, their nucleus size was increased. The number of follicles and volume of oogonia were positively correlated with the fetal measurements, while the number of oogonia was negatively correlated. Equations were obtained for the prediction of gonadal characteristics of fetuses. We concluded that in pigs testis cell proliferation, ovary development and histological organization was more pronounced during the final third of pregnancy. Fetal weight and size were strongly related to gonadal development, and can be used to estimate the histological characteristics of gonads.

Neonatal hypothyroidism does not increase Sertoli cell proliferation in iNOS−/− mice

Sertoli cell (SC) proliferation in mice occurs until two weeks after birth and is mainly regulated by FSH and thyroid hormones. Previous studies have shown that transient neonatal hypothyroidism in laboratory rodents is able to extend SC mitotic activity, leading ultimately to higher testis size and daily sperm production (DSP) in adult animals. Moreover, we have shown that due to higher SC proliferation and lower germ cell apoptosis, iNOS deficiency in mice also results in higher testis size and DSP. Although the cell size was smaller, the Leydig cells (LCs) number per testis also significantly increased in iNOS−/−mice. Our aims in the present study were to investigate if the combination of neonatal hypothyroidism and iNOS deficiency promotes additive effects in SC number, testis size and DSP. Hypothyroidism was induced in wild-type (WT) and iNOS−/−mice using 6-propyl-2-thiouracil (PTU) through the mother’s drinking water from 0 to 20 days of age, and were sacrificed at adulthood. Our results showed that, in contrast to the WT mice in which testis size, DSP and SC numbers increased significantly by 20, 40 and 70% respectively, after PTU treatment, no additive effects were observed for these parameters in treated iNOS−/−mice, as well as for LC. No alterations were observed in spermatogenesis in any group evaluated. Although we still do not have an explanation for these intriguing findings, we are currently investigating whether thyroid hormones influence iNOS levels and/or counterbalance physiological effects of iNOS deficiency in testis function and spermatogenesis.

Histological and transcriptome analyses of testes from Duroc and Meishan boars

Meishan boars are known for their early sexual maturity. However, they exhibit a significantly smaller testicular size and a reduced proportion of Sertoli cells and daily sperm production compared with Duroc boars. The testes of Duroc and Meishan boars at 20, 75 and 270 days of age were used for histological and transcriptome analyses. Haematoxylin-eosin staining was conducted to observe histological structure of the testes in Duroc and Meishan boars at different ages. Although spermatogenesis occurred prior to 75 days in Meishan boars, the number of spermatogonia and Sertoli cells in Meishan boars were less than in Duroc boars at adulthood. The diameters of the seminiferous tubules of the testes differed significantly during the initiation of development of the seminiferous tubules between the two breeds. We obtained differentially expressed functional genes and analysed seven pathways involved in male sexual maturity and spermatogenesis using RNA-seq. We also detected four main alternative splicing events and many single nucleotide polymorphisms from testes. Eight functionally important genes were validated by qPCR, and Neurotrophin 3 was subjected to quantification and cellular localization analysis. Our study provides the first transcriptome evidence for the differences in sexual function development between Meishan and Duroc boars.

Effect of gestational antiandrogen treatment on Dicer1 expression in the porcine fetal gonads

Recently, we have demonstrated that flutamide-induced androgen deficiency during fetal life led to changes in gene expression that affected both testicular functions and follicular formation. It is known that microRNA-mediated genes regulation is essential for gonadal development and function. Thus, the aim of the present study was to examine whether prenatal flutamide exposure influences expression of Dicer1, an enzyme involved in microRNA maturation, in gonads of porcine fetuses during mid- and late gestation. Pregnant gilts were injected with flutamide (50mg/day/kg b.w.) or corn oil (controls) between days 43-49, 83-89 or 101-107 of gestation. The fetal gonads were obtained on gestational day 50 (GD50), 90 (GD90) or 108 (GD108). To assess Dicer1 mRNA expression real-time PCR were performed. Furthermore, immunohistochemical Dicer1 localization was conducted. In testes from flutamide treated fetuses, increased Dicer1 mRNA expression was observed in the GD50 and GD108 groups, but decreased in the GD90 group. Dicer1 was immunolocalized in the fetal Leydig cells in both control and flutamide-treated groups. In fetal ovaries, antiandrogen treatment increased Dicer1 mRNA level in the GD50 and GD90 groups. In control and flutamide-exposed groups, Dicer1 was localized in the germ cells within oogonia/oocyte nests as well as in the granulosa cells and oocytes of forming follicles. Concluding, diminished androgen action during gestation induces changes in Dicer1 mRNA expression, which may affect post-transcriptional gene regulation via miRNAs in porcine fetal gonads. However, it seems that androgens exert diverse biological effects depending on the gestational period.

Nutrition affects Sertoli cell function but not Sertoli cell numbers in sexually mature male sheep

We tested whether the reversible effects of nutrition on spermatogenesis in sexually mature sheep were mediated by Sertoli cells. Rams were fed with diets designed to achieve a 10% increase (High), no change (Maintenance) or a 10% decrease (Low) in body mass after 65 days. At the end of treatment, testes were lighter in the Low than the High group (PP<0.05) in the expression of seven Sertoli cell-specific genes. Under-nutrition appeared to reverse cellular differentiation leading to disruption of tight-junction morphology. In conclusion, in sexually mature sheep, reversible reductions in testis mass and spermatogenesis caused by under-nutrition were associated with impairment of basic aspects of Sertoli cell function but not with changes in the number of Sertoli cells.

Reduced endogenous estrogen and hemicastration interact synergistically to increase porcine sertoli cell proliferation

Both reduced endogenous estrogen and hemicastration stimulate proliferation of porcine Sertoli cells. The objective of these experiments was to compare the temporal patterns of response to each stimulus with the response to the combined stimuli as indications of shared or separate mechanisms. Within a replicate, one littermate was treated weekly with canola oil vehicle and remained intact; a second littermate was treated weekly with vehicle, and one testis was removed at Day 8; a third littermate was treated weekly with the aromatase inhibitor letrozole to reduce endogenous estrogens and remained intact; and the fourth littermate was treated weekly with letrozole, and one testis was removed at Day 8. Four replicates were evaluated at 2 wk of age, five replicates evaluated at 6.5 wk of age, and five replicates were evaluated at 11 wk of age, with treatment ceasing at 6 wk of age. Numbers of Sertoli cells were determined following GATA4 labeling using the optical dissector method. Levels of estradiol, estrogen conjugates, follicle-stimulating hormone (FSH), luteinizing hormone (LH), and inhibin were determined by radioimmunoassay. Hemicastration appeared to have a rapid effect on Sertoli cell proliferation, but letrozole treatment had no apparent effect on Sertoli cell numbers at 2 wk of age. Both letrozole treatment and hemicastration had stimulated Sertoli cell proliferation by 6.5 wk of age, although the magnitude of the hemicastration response was much greater. Letrozole appeared to have minimal interaction with hemicastration at this age. Letrozole and hemicastration together increased Sertoli cell numbers at 11 wk of age compared with either treatment alone. Estradiol and estrogen conjugates were dramatically reduced by aromatase inhibition as anticipated; treatment-induced changes in inhibin, LH, or FSH were minimal. Differences in timing of response and positive interaction at 11 wk of age suggest that hemicastration and letrozole stimulate proliferation of Sertoli cells by two initially different pathways.

In utero exposure to the anti-androgen flutamide influences connexin 43 and β-catenin expression in porcine fetal gonads

Recent reports have indicated a role of cell-to-cell interactions during gonadal development and functions. Numerous reports indicate that fetal hormonal disruption induces abnormalities in the developing reproductive system and, therefore, may interfere with reproductive functions later in adult life. Hence, this study investigated the effect of androgen deficiency during late prenatal periods on the gap junction-associated connexin 43 (Cx43) and the adherens junction-associated β-catenin expression in the fetal porcine gonads. Thus, pregnant gilts were injected with anti-androgen flutamide (for 7 d, 50 mg/kg BW per day) or corn oil (control groups) starting at 83 (GD90) or 101 (GD108) gestational day. On GD90 and GD108 the fetuses were excised and fetal gonads were obtained. To assess Cx43 and β-catenin expression real-time PCR and immunohistochemistry were performed. In fetal testes, Cx43 was localized between Leydig cells, whereas β-catenin was observed mainly within the seminiferous tubules. In fetal ovaries, Cx43 was detected between interstitial cells and between granulosa cells of forming follicles, whereas β-catenin was found within egg nests, in oocytes' membrane, and in granulosa cells of forming follicles. Immunohistochemistry showed decreased Cx43 and β-catenin expression in fetal gonads from flutamide-treated pigs compared with respective controls. However, the ovaries from animals treated with flutamide on GD108 showed increased Cx43 expression. The changes of Cx43 and β-catenin expression after prenatal flutamide treatment were confirmed at the mRNA level. These findings suggest that androgen deficiency during late gestation may lead to disturbed intercellular interactions in fetal porcine testes affecting testicular functions, as well as impaired follicular formation in fetal ovaries. Our results further signify the role of androgens in the regulation of cell-to-cell interactions within fetal porcine gonads.

Evaluations of boar gonad development, spermatogenesis with regard to semen characteristics, libido and serum testosterone levels based on large White Duroc x Chinese Erhualian crossbred boars

Chinese Erhualian pigs are known for prolificacy with distinct reproductive traits compared with Western commercial breeds. In this study, a four-generation intercross resource population was constructed using White Duroc boars and Chinese Erhualian sows as founder animals, and a total of 14 male reproductive traits were recorded in 411 F2/F3 boars including the testis and epididymis weights, the seminiferous tubular diameter and spermatogenesis at 60, 90 and 300 days of age, semen characteristics, serum testosterone concentration and libido level at 300 days of age. The White Duroc-Erhualian boars showed remarkable segregations in the traits measured except for the seminiferous tubular diameter and had high ratio (13.9%) of the abnormality of spermatogenesis, providing a good experimental population for detecting quantitative trait loci affecting these male reproductive traits. Furthermore, the correlations among nine male reproductive traits at 300 days of age indicated that the testis weight and the body weight were strongly correlated with the sperm production, supporting the two traits as important parameters for boar selection to increase sperm production and ultimately improve boar fertility. The libido level in the White Duroc-Erhualian boars that was evaluated by a new and easily recorded scoring system showed a significant correlation with serum testosterone concentration. Yet, both libido and serum testosterone concentration were not correlated with the sperm production. Results of this study provided new information on the male reproductive physiology and genetics in Chinese Erhualian and White Duroc boars.

Endocrine status and development of porcine testicular tissues in host mice

Clarification of the endocrine status of host mice provides us with basic knowledge with which we can manipulate the growth and function of xenografted testicular tissues. We investigated the hormonal profiles of castrated mice grafted with porcine immature testicular tissues from 30 to 210 or more days after grafting (day 0=castration and grafting). The serum follicle stimulating hormone (FSH) concentrations of the host mice declined (P<0.05) from day 60 compared with those of the castrated, ungrafted mice. The serum inhibin and testosterone levels were higher (P<0.05) than those in the castrated, ungrafted mice from days 30 and 90 days, respectively. The inhibin levels further increased (P<0.05) from day 90, during which time the levels were higher (P<0.05) than those in the intact male mice. In the grafts, formation of lumens occurred in the seminiferous cords on day 90 and spermatozoa appeared in the lumens from day 120. However, spermatogenesis in the grafts did not reach the qualitatively normal levels observed in adult boars. The intensity of the immune reaction to inhibin alpha subunits in the Sertoli cells of the grafts decreased with differentiation of the seminiferous tubules. The present findings indicate that a feedback loop was established between the mouse hypothalamo-pituitary axis and the grafted porcine tissues from 60 days post-grafting. The results also indicate that the serum inhibin levels in the host mice remained high even after the appearance of lumens in the seminiferous tubules of the grafted tissues; this is strikingly different to the situation in normal male animals, in which the serum inhibin levels decline at around the time of tubular differentiation. The lack of efferent ducts in the tubules of the grafted tissues probably caused the accumulation of inhibin to be released into the lumens, resulting in high concentrations of circulating inhibin. These high levels of inhibin may directly affect spermatogenic activity and suppress FSH secretion.

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.

Aromatase and 11beta-hydroxysteroid dehydrogenase 2 localisation in the testes of pigs from birth to puberty linked to changes of hormone pattern and testicular morphology

Oestrogens and glucocorticoids are important for spermatogenesis and are regulated via aromatase for oestradiol synthesis and 11beta-hydroxysteroid dehydrogenase 2 (11beta-HSD 2) as an inactivator of cortisol. In the present study postnatal changes of these two enzymes were monitored together with testicular development and hormone concentrations. Pigs were assigned to three periods: Weeks 0-5, Weeks 5-11 or Weeks 11-17. In Period 1, groups of four piglets were killed after each week. Blood plasma and testes were sampled immediately post mortem. For Periods 2 and 3, groups of six pigs were fitted with vein catheters for daily blood collection. Testes from all pigs were obtained after killing. Levels of testosterone, oestradiol, LH, FSH and cortisol were determined radioimmunologically. The 11beta-HSD 2- and aromatase-expressing cells were stained immunocytochemically. All hormones were maximal 2 weeks after birth. A rise of LH, testosterone and oestradiol occurred again at Week 17. FSH and cortisol remained basal. Parallel to the first postnatal rise, the presence of aromatase and 11beta-HSD 2 in Leydig cells increased, together with germ and Sertoli cell numbers. Expression was low from 3 to 5 weeks, was resumed after Week 5 and was maximal at Week 17. The amount of 11beta-HSD 2 in germ cells was greatest at birth, decreased thereafter and was absent after Week 3.

Production of inhibin A and inhibin B in boars: changes in testicular and circulating levels of dimeric inhibins and characterization of inhibin forms during testis growth

We investigated the production of inhibin in boars from the infantile to pubertal periods by: (1) measurement of testicular and circulating levels of inhibin, (2) characterization of inhibin forms and (3) localization of inhibin alpha subunits in the testis. Total inhibin levels in the testis increased until 8 weeks of age but then declined to much lower values at 15 weeks. Testicular inhibin A and inhibin B were high until 8 weeks. Circulating levels of total inhibin and inhibin A were also high until 8 weeks, then declined from 10 weeks; inhibin B was not detected, because of low sensitivity of the inhibin B assay. Analyses of inhibin A and inhibin B levels in the eluted fractions obtained from testes after immunoaffinity chromatography and SDS-PAGE showed the presence of a peak of approximately 45 kDa until 10 weeks of age. As the boars aged, the levels of inhibin A and inhibin B increased in the molecular weight region of 29-31 kDa. The fractions corresponding to 29 and 30 kDa suppressed FSH release from rat pituitary cells, but the 45 kDa fraction had no FSH-suppressing activity. Total amounts of inhibin A isolated from the SDS gels were similar to those of inhibin B until 10 weeks of age, but were three times higher than those of inhibin B between 15 and 25 weeks. Further fractionation by reverse phase high-performance liquid chromatography revealed that the 29-31 kDa immunoreactive material was composed of mature forms of inhibin A and inhibin B, in addition to a 26 kDa alpha monomer. Immunohistochemistry indicated that positive immunostaining for the alpha subunits was observed in Sertoli cells from the infantile to pubertal periods. Elongated spermatids also showed positive signals at age 25 weeks. These results clearly indicated that: (1) the boar testis has the ability to produce inhibin A and inhibin B during the infantile period but inhibin A is the predominant form towards puberty and (2) the molecular weight forms of inhibin and the sites of production of inhibin change with testicular development.

Changes of testicular aromatase expression during fetal development in male pigs (sus scrofa)

Male pig fetuses secrete considerable amounts of estrogens, but the location of aromatase activity within the fetal testis is not known. The location of aromatase expression was investigated by immunocytochemistry in fetal testes from week 6 (n = 5), weeks 10, 13, and 15 (each: n = 6) of gestation and additionally in neonates (n = 4). Blood was sampled from the umbilical artery of fetuses and jugular vein of neonates. Histological evaluation of testes involved morphological criteria and counting of Leydig cells, Sertoli cells, and gonocytes. Aromatase activity was localized immunocytochemically and quantified by the percentage of positive stained cells within the same cell type. Aromatase expression was further characterized by quantitative RT-PCR. Concentrations of estrogens, testosterone, FSH, and LH were measured in blood plasma. Total estrogens increased from week 10 to a maximum of 31.03 nmol/l in week 15. Increased testosterone concentrations were only measured at week 6 and were paralleled by slightly elevated estrogens. Thereafter, testosterone dropped and was low throughout. The increase of estrogens was not paralleled by a similar increase of FSH and LH but was related to the increase of the total number of Leydig cells. This increase was also found for mRNA expression. Both Leydig cells and gonocytes were identified as contributors to estrogen formation. Gonocytes were the main source of aromatase at week 10, when gene expression by Leydig cells is low due to the preparation of a wave of Leydig cell mitosis.

Chronic ethanol perturbs testicular folate metabolism and dietary folate deficiency reduces sex hormone levels in the Yucatan micropig

Although alcoholism causes changes in hepatic folate metabolism that are aggravated by folate deficiency, male reproductive effects have never been studied. We evaluated changes in folate metabolism in the male reproductive system following chronic ethanol consumption and folate deficiency. Twenty-four juvenile micropigs received folate-sufficient (FS) or folate-depleted (FD) diets or the same diets containing 40% of energy as ethanol (FSE or FDE) for 14 wk, and the differences between the groups were determined by ANOVA. Chronic ethanol consumption (FSE and FDE compared with FS and FD groups) reduced testis and epididymis weights, testis sperm concentrations, and total sperm counts and circulating FSH levels. Folate deficiency (FD and FDE compared with FS and FSE groups) reduced circulating testosterone, estradiol and LH levels, and also testicular 17,20-lyase and aromatase activities. There was histological evidence of testicular lesions and incomplete progression of spermatogenesis in all treated groups relative to the FS control, with the FDE group being the most affected. Chronic ethanol consumption increased testis folate concentrations and decreased testis methionine synthase activity, whereas folate deficiency reduced total testis folate levels and increased methionine synthase activity. In all pigs combined, testicular methionine synthase activity was negatively associated with circulating estradiol, LH and FSH, and 17,20-lyase activity after controlling for ethanol, folate deficiency, and their interaction. Thus, while chronic ethanol consumption primarily impairs spermatogenesis, folate deficiency reduces sex hormones, and the two treatments have opposite effects on testicular folate metabolism. Furthermore, methionine synthase may influence the hormonal regulation of spermatogenesis.

Successful long term culture of immature porcine sertoli cells in the reconstructed testicular cell cord

The ultimate goal of this study was to establish an in vitro system to produce sperms. To pursue this goal, immature porcine testicular cells were cultured in stereostructural form and cultured testicular cord was investigated morphologically. At 4 weeks of age, the seminiferous tubules of the porcine testes consisted of undifferentiated germ cells (gonocytes and undifferentiated spermatogonia) and immature Sertoli cells. The interstitial tissue was largely occupied by Leydig cells. The testes were enzymatically digested, and the dispersed cells were encapsulated with alginate either immediately or after freeze-thawing. The resulting testicular cell cords were cultured for up to 10 weeks. After 2 weeks of culture, Sertoli cells, which were identified by their inhibin-positive reaction in immunohistochemistry, and Leydig cells, which were identified by their morphological characteristics, were observed in the cords. Neither undifferentiated nor differentiated types of germ cells were detected. The number of cells in the cords progressively decreased during the culture period. In order to discover the fate of the Sertoli cells, the level of inhibin in the spent media was determined. Inhibin in the media was at a detectable level after 2 days of culture. The levels increased and peaked at 2 weeks. When frozen-thawed testicular cells were applied to the culture, the peak level was maintained for over 8 weeks, in contrast to the gradual decrease of inhibin level when fresh cells were cultured. These results indicate that the culture conditions can sustain the survival of Sertoli cells. Further improvement is required for proliferation and differentiation of germ cells.

Effect of divergent selection for testosterone production on testicular morphology and daily sperm production in boars

The objective of this study was to characterize correlated responses in testicular morphology and daily sperm production to divergent selection for testosterone production. Duroc boars from high and low lines (HTL and LTL, respectively) divergently selected over 10 generations for testosterone production in response to a GnRH challenge followed by random selection were used. Testicular tissues were sampled from all available males of generation 20 (HTL, n = 46; and LTL, n = 13). Volume densities for Leydig cells, seminiferous tubules, and Sertoli cells were estimated along with sperm production. The HTL boars had greater volume densities of Leydig cells than did LTL (P < 0.01). Volume density of seminiferous tubules tended to differ between lines (P < 0.07), but Sertoli cell volume densities did not differ (P < 0.27). Sperm production traits, adjusted for age, did not differ significantly between lines. Body, testicular, and epididymal weights were recorded for boars from HTL (n = 82) and LTL (n = 44) from generations 20 and 21. After adjustment for BW, average paired testicular weights for HTL and LTL were 417 and 457 g (P < 0.01), respectively. Epididymal weights, adjusted for BW, were heavier for HTL (P < 0.01) than for LTL. To demonstrate that the selection lines still differed for testosterone production, lines were evaluated in generation 21. Endogenous testosterone production of the HTL (n = 54) and LTL (n = 44) testosterone production line averaged 49.0 ng/mL and 27.8 ng/mL (P < 0.01), respectively. Plasma FSH concentrations did not differ between lines (P < 0.30). Selection for testosterone production in response to a GnRH challenge was an effective method of changing testosterone concentrations, testicular size, epididymal weight, and volume density of Leydig cells. However, daily sperm production per gram of testes was unchanged. Based on the results of this study, selection for testosterone production is not recommended as a method of increasing sperm production in pigs.

A variant of porcine thyroxine-binding globulin has reduced affinity for thyroxine and is associated with testis size

The field of genomics applies the dissection of genetic differences toward an understanding of the biology of complex traits. Quantitative trait loci (QTL) for testis size, plasma FSH in boars, and body composition (backfat) have been identified near the centromere on the X chromosome in a Meishan-White Composite resource population. Since thyroid function affects Sertoli cell development and adult testis size in rodents, and thyroxine-binding globulin (TBG) maps to this region on the porcine X chromosome, TBG was a positional candidate gene for testis size. We discovered a polymorphism in exon 2 of the porcine TBG gene that results in an amino acid change of the consensus histidine to an asparagine. This single nucleotide polymorphism (SNP) resides in the ligand-binding domain of the mature polypeptide, and the Meishan allele is the conserved allele found in human, bovine, sheep, and rodent TBG. Binding studies indicate altered binding characteristics of the allelic variants of TBG with the asparagine (White Composite) isoform having significantly greater affinity for thyroxine than the histidine (Meishan) isoform. Alternate alleles in boars from the resource population are also significantly associated with testis weight. Therefore, this polymorphism in TBG is a candidate for the causative variation affecting testis size in boars.