Beyond Testis Size: Links between Spermatogenesis and Sperm Traits in a Seasonal Breeding Mammal

Spermatogenesis is a costly process that is expected to be under selection to maximise sperm quantity and quality. Testis size is often regarded as a proxy measure of sperm investment, implicitly overlooking the quantitative assessment of spermatogenesis. An enhanced understanding of testicular function, beyond testis size, may reveal further sexual traits involved in sperm quantity and quality. Here, we first estimated the inter-male variation in testicular function and sperm traits in red deer across the breeding and non-breeding seasons. Then, we analysed the relationships between the testis mass, eight parameters of spermatogenic function, and seven parameters of sperm quality. Our findings revealed that the Sertoli cell number and function parameters vary greatly between red deer males, and that spermatogenic activity co-varies with testis mass and sperm quality across the breeding and non-breeding seasons. For the first time in a seasonal breeder, we found that not only is the Sertoli cell number important in determining testis mass (r = 0.619, p = 0.007 and r = 0.248, p = 0.047 for the Sertoli cell number assessed by histology and cytology, respectively), but also sperm function (r = 0.703, p = 0.002 and r = 0.328, p = 0.012 for the Sertoli cell number assessed by histology and cytology, respectively). Testicular histology also revealed that a high Sertoli cell number per tubular cross-section is associated with high sperm production (r = 0.600, p = 0.009). Sperm production and function were also positively correlated (r = 0.384, p = 0.004), suggesting that these traits co-vary to maximise sperm fertilisation ability in red deer. In conclusion, our findings contribute to the understanding of the dynamics of spermatogenesis, and reveal new insights into the role of testicular function and the Sertoli cell number on testis size and sperm quality in red deer.     

Expression of the androgen receptor in the testis of mice with a Sertoli cell specific knock-out of the connexin 43 gene (SCCx43KO−/−)

Gap junctions are intercellular channels that connect the cytoplasm of adjacent cells, allowing the passage of small molecules (<1 kDa) and thereby the regulation of many different processes. In the male gonad, the most abundant protein that builds gap junctions is connexin 43 (Cx43, GJA1). Specific knock-out of Sertoli cells (SCCx43KO^?/?) results in an impaired spermatogenesis up to the Sertoli cell only syndrome. The aim of this study was to compare the testicular expression pattern of the androgen receptor (AR) in wild type (WT) and SCCx43KO^?/? mice. In both WT and SCCx43KO^?/? testes, the AR staining was restricted to the nuclei of Sertoli, Leydig, and peritubular cells. However, the staining intensity varied between control and mutant mice. In the latter, the AR expression depended on the level of the seminiferous tubule impairment. In tubules with qualitatively normal spermatogenesis, the AR protein expression was similar to that observed in the testes of WT mice. Conversely, seminiferous tubules with an arrest of spermatogenesis at the level of spermatogonial or spermatocyte phase expressed the AR at a lower intensity. In Sertoli cell only tubules (no germ cells in the tubules), the AR immunoreaction was mainly weak or undetectable. Moreover, AR staining was lower in Sertoli and Leydig cells (p < 0.001 and p < 0.05, respectively) of SCCx43KO^?/? mice compared to WT mice, as revealed by a semiquantitative analysis. In conclusion, the deletion of Cx43 leads to a partial disruption of the AR signaling pathway, indicating a possible reason for the observed impaired spermatogenesis.     

HST-1/FGF-4 protects male germ cells from apoptosis under heat-stress condition

Apoptosis plays an important role in controlling the number of male germ cells and eliminating defective germ cells during testicular development and spermatogenesis. We show here that fibroblast growth factor-4 (HST-1/FGF-4) may play a critical role as a survival factor for germ cells, protecting them from apoptosis. Testes of adult male mice that received an adenovirus carrying human HST-1/FGF-4 (AxHST-1) or a control adenovirus (AxCAwt) were exposed to mild hyperthermia, which causes germ cell apoptosis. An in situ terminal-deoxynucleotidyl transferase-mediated deoxy-UTP nick end-labeling (TUNEL) assay characterized germ cell apoptosis. The results indicated that HST-1/FGF-4 significantly reduced the apoptotic death of germ cells and prevented testicular weight loss and sperm count reduction. We also found that Hst-1/Fgf-4 present in testes is up-regulated in vivo when the testes are exposed to mild hyperthermia, and that endogenous Hst-1/Fgf-4 mRNA expression in Sertoli cells are also induced when the cells are exposed to mild hyperthermia in vitro. In addition, the MAPK cascade, which could increase an FGF-dependent survival signal, is activated by HST-1/FGF-4 stimuli in germ cells. On the other hand, upon HST-1/FGF-4 stimulation, lactate production from Sertoli cells were induced, which is indispensable nutrient for germ cell survival. These results suggest that HST-1/FGF-4 can act as an important physiological anti-apoptotic factor for male germ cells in stimulating lactate production of Sertoli cells upon heat stress, thereby promoting germ cell survival.     

Ontogenetic testicular development and spermatogenesis in rays: the Cownose Ray,Rhinoptera bonasus,as a model

An understanding of testicular anatomy, development, and seasonality has implications for studies of morphology, behavior, physiology, and bioenergetics of males. Ontogenetic testicular development and spermatogenesis is essentially unknown for chondrichthyans. We examined embryo, juvenile, and adult male Cownose Rays (Rhinoptera bonasus) during development and throughout the annual reproductive cycle. Spermatogonia and Sertoli cells originated from germ cells and somatic cells, respectively, in the embryonic testicular germinal epithelium. In embryos and small juveniles, discrete regions of spermatocyst production appeared within a series of papillae that projected from the dorsal surface of each testis. Because these papillary germinal zones appeared to proliferate through ontogeny, we hypothesize that (1) the germinal zones of juvenile and adult testes are derived from embryonic testicular papillae that form from the germinal epithelium and (2) the papillae become the dorso-central portion of the distinct testicular lobes that form at maturation due to increased spermatocyst production. Our observations indicate that testicular development and the process of spermatogenesis began during embryonic development and increased in scale through ontogeny until maturation, when distinct testicular lobes formed and began enlarging or shrinking based on the annual reproductive cycle. Gonadosomatic indices peaked corresponding to seasonal increased sperm production between January and April, just prior to the April–June mating period. In all life stages, spermatocysts had efferent ducts associated with them from their formation through all stages of development. Year-round presence in the Charlotte Harbor estuarine system, Florida made R. bonasus a good model for beginning to understand ontogenetic gonad development and spermatogenesis in chondrichthyans, especially viviparous rays.     

Reduced testicular steroidogenesis in tumor necrosis factor-alpha knockout mice

We previously demonstrated that the expression of Mullerian inhibiting substance (MIS) in Sertoli cells is downregulated by tumor necrosis factor alpha (TNF-alpha), which is secreted by meiotic germ cells, in mouse testes. Several studies have reported that MIS that is secreted by Sertoli cells inhibits steroidogenesis and, thus, the synthesis of testosterone in testicular Leydig cells. Here, we demonstrate that in TNF-alpha knockout testes, which show high levels of MIS, steroidogenesis is decreased compared to that in wild-type testes. The levels of testosterone and the mRNA levels of steroidogenesis-related genes were significantly lower after puberty in TNF-alpha knockout testes than in wild-type testes. Furthermore, the number of sperm was reduced in TNF-alpha knockout mice. Histological analysis revealed that spermatogenesis is also delayed in TNF-alpha knockout testes. In conclusion, TNF-alpha knockout mice show reduced testicular steroidogenesis, which is likely due to the high level of testicular MIS compared to that seen in wild-type mice.     

Testicular fine needle aspiration cytology for the diagnosis of azoospermia and oligospermia

OBJECTIVE: To evaluate qualitative and quantitative cytologic features on testicular fine needle aspiration biopsy in the diagnosis of azoospermia and oligospermia and to correlate cytologic and histologic diagnoses. STUDY DESIGN: In this prospective study, 50 infertile males selected from the infertility clinic of Guru Tegh Bahadur Hospital were studied. Fine needle aspiration cytology (FNAC) smears from both testes of 27 azoospermic and 23 oligospermic patients (sperm count < 10 million per milliliter) were stained with May-Grünwald-Giemsa and Papanicolaou stain. Differential counting of 500 spermatogenic cells was done, and the number of Sertoli cells per 500 germ cells was determined for calculating the spermatic index and Sertoli cell index, respectively. FNAC and testicular biopsy were performed under local anesthesia as a minor surgical procedure. RESULTS: Six groups were identified on FNAC smears from azoospermic patients: I. normal spermatogenesis (8), II. hypospermatogenesis (2), III. maturation arrest (2), IV. Sertoli cells only (6), V. atrophic pattern (7), and VI. Leydig cell predominance (2). In oligospermic patients two groups were identified: I. those with normal spermatogenesis (4), and II. those with subnormal spermatogenesis (19). Correlation with histopathologic examination was seen in 81.5% azoospermic and 65.2% oligospermic patients. CONCLUSION: Qualitative and quantitative evaluation of testicular FNAC provides useful information on both azoospermic and oligospermic patients. FNAC performed under local anesthesia is an acceptable outpatient procedure that consistently yields sufficient diagnostic material in all patients.     

Decreased reproductive performance in xCT-knockout male mice

Sulphoxidation occurs in protamines that are enriched in cysteine and supplies chromatin for packaging. The extracellular fluid contains higher levels of oxidised cysteine (cystine), and some cells utilise system x_c^?, a cystine transporter in which xCT is the main protein component, to fulfil the need for cysteine. We hypothesised that system x_c^? might ensure the supply of cysteine needed for spermatogenesis. The reproductive ability of xCT^?/? male mice at 6- to 18-weeks of age appeared to be lower than xCT^+/+ male mice. The courtship behaviour of the xCT^?/? male mice was undynamic, which appeared to be associated with the low reproductive ability of xCT^?/? male mice. xCT was found to be expressed in mouse testes, notably in Sertoli cells, as well as in the epididymis and the levels were increased at the time of sexual maturation. Despite the normal histological appearance of testicular tissues, the cauda epididymis of xCT^?/? mice contained round, greater numbers of immature spermatogenic cells than that of xCT^+/+ mice. However, there were no significant differences in the numbers of sperm stored in the cauda epididymis or in the concentrations of cysteine or glutathione in the testes. The resulting sperm had normal fertilising ability. Thus, system x_c^? appears to function as a backup system for supplying cysteine to testes and play a pivotal role in supplying cysteine for normal sexual behaviour by a mechanism that is different from that for the supply of cysteine in spermatogenesis.     

Testicular Expression of NGF,TrkA and p75 During Seasonal Spermatogenesis of the Wild Ground Squirrel (Citellus Dauricus Brandt)

The nerve growth factor (NGF) not only has an essential effect on the nervous system, but also plays an important role in a variety of non-neuronal systems, such as the reproductive system. The aim of this study was to compare the quality and quantity in expression of NGF and its receptors (TrkA and p75) in testes of the wild ground squirrel during the breeding and nonbreeding seasons. Immunolocalization for NGF was detected mainly in Leydig cells and Sertoli cells in testes of the breeding and nonbreeding seasons. The immunoreactivity of TrkA was highest in the elongated spermatids, whereas p75 in spermatogonia and spermatocytes in testes of the breeding season. In the nonbreeding season testes, TrkA showed positive immunostainings in Leydig cells, spermatogonia and primary spermatocytes, while p75 showed positive signals in spermatogonia and primary spermatocytes. Consistent with the immunohistochemical results, the mean mRNA and protein level of NGF and TrkA were higher in the testes of the breeding season than in non-breeding season, and then decreased to a relatively low level in the nonbreeding season. In addition, the concentration of plasma gonadotropins and testosterone were assayed by radioimmunoassay (RIA), and the results showed a significant difference between the breeding and nonbreeding seasons with higher concentrations in breeding season. In conclusion, these results of this study provide the first evidence on the potential involvement of NGF and its receptor, TrkA and p75 in the seasonal spermatogenesis and testicular function change of the wild ground squirrel.Key words: NGF, p75, seasonal spermatogenesis, TrkA, wild ground squirrel     

Cultivation of boar spermatogonia on Sertoli cells

We studied the in vitro effect of Sertoli cells on boar spermatogonia isolated from the testes of 60-day-old crossbred boars. In order to enrich the culture with spermatogonia, the cells were purified by density gradient centrifugation with the use of Percoll gradient followed by separation based on adhesive capacities of cells. We found lipid drops stained by Oil Red O in Sertoli cells. The experiments showed that the cultivation of boar spermatogonia in the presence of Sertoli cells (for up to 35 days) provide the same way of differentiation as in testes in natural conditions. After 10 days of cultivation, spermatogenic cells form groups, chains, and suspension clusters. By this time, spermatogenic colonies are formed; we analyzed the expression of Nanog and Plzf genes in these colonies by real-time PCR. The expression rate of Nanog gene in experimental cell clones obtained by the short-term cultivation of spermatogonia cells in the presence of Sertoli cells was 200 times higher than in freshly isolated spermatogonia cells. The product of Plzf gene expression was found both in freshly isolated spermatogenic cells and in cell clones obtained in vitro. After long-term cultivation of spermatogonia on Sertoli cells, we observed in vitro differentiation to the lineage of spermatogenesis and formation of separate motile sperm cells after 30–33 days. At this stage, the cell population was heterogeneous. In the absence of Sertoli cells, the differentiation of boar spermatogonia cells in culture stopped after 7 days of cultivation. The data show that the cultivation of boar spermatogonia cells on Sertoli cells contributes to their in vitro differentiation to the lineage of spermatogenesis and can help to obtain boar sperm cell culture.     

Ankrd7, a novel gene specifically expressed in Sertoli cells and its potential roles in Sertoli cell maturation

The somatic Sertoli cells play an essential role in testis determination and spermatogenesis by providing nutrition and structural support. In the current study, we report on the novel Ankrd7 gene that contains five ankyrin repeat domains. This gene was specifically expressed in Sertoli cells and was regulated in a maturation-dependent manner. Its expression was restricted to testicular tissue, and its mRNA could be detected in testes at as early as 14 dpp (days post partum) using RT-PCR analysis. In both testicular tissue sections and in vitro cultured Sertoli cells, the Ankrd7 protein was localized to the nucleus of the Sertoli cell. Immuno-histochemistry and immunocytochemistry investigations showed that the protein was detectable in testicular tissues at 20 dpp, at which time Sertoli cells were gradually differentiating into their mature cellular form. These results suggest that Ankrd7 is probably involved in the process of Sertoli cell maturation and in spermatogenesis.     

Impaired spermatogenesis associated with changes in spatial arrangement of Sertoli and spermatogonial cells following induced diabetes

The current study was conducted to assess the relationship between testicular cells in spermatogenesis, through which the production of healthy and mature sperm is essential. However, it seems necessary to obtain more information about the three-dimensional pattern of the testis cells arrangement, which is directly related to the function of the testis after induction of diabetes. Twelve adult mice (28-30 g) were assigned into two experimental groups: (1) control and (2) diabetic (40 mg/kg STZ). The epididymal sperm collected from the tail of the epididymis and testes samples were taken for stereology, immunocytochemistry and RNA extraction. Our data showed that diabetes could notably decrease the number of testicular cells, together with a reduction of total sperm count. In addition, the results from the second-order stereology indicated the significant changes in the spatial arrangement of Sertoli cells and spermatogonial cells in the diabetic groups, in comparison with the control (P < .05). Moreover, the immunohistochemistry results showed a significant reduction in Sex-determining Region Y (SRY) box 9 gene (SOX9), vimentin, occludin, and connexin-43 positive cells in the diabetic groups compared with the control (P < .05). Furthermore, our data showed that the expression of steroidogenic acute regulatory protein steroidogenic acute regulatory protein (StAR) and peripheral benzodiazepine receptor peripheral benzodiazepine receptor (PBR) was significantly reduced in the diabetic groups, in comparison with the control (P < .05). These findings suggest that structural and functional changes of testis cells after induction of diabetes cause the alterations in the spatial arrangement of Sertoli and spermatogonial cells, ultimately influencing the normal spermatogenesis in mice.     

Seasonal spermatogenic cycle and morphology of germ cells in the viviparous lizard Mabuya brachypoda (Squamata,Scincidae)

We describe seasonal variations of the histology of the seminiferous tubules and efferent ducts of the tropical, viviparous skink, Mabuya brachypoda, throughout the year. The specimens were collected monthly, in Nacajuca, Tabasco state, Mexico. The results revealed strong annual variations in testicular volume, stages of the germ cells, and diameter and height of the epithelia of seminiferous tubules and efferent ducts. Recrudescence was detected from November to December, when initial mitotic activity of spermatogonia in the seminiferous tubules were observed, coinciding with the decrease of temperature, photoperiod and rainy season. From January to February, early spermatogenesis continued and early primary and secondary spermatocytes were developing within the seminiferous epithelium. From March through April, numerous spermatids in metamorphosis were observed. Spermiogenesis was completed from May through July, which coincided with an increase in temperature, photoperiod, and rainfall. Regression occurred from August through September when testicular volume and spermatogenic activity decreased. During this time, the seminiferous epithelium decreased in thickness, and germ cell recruitment ceased, only Sertoli cells and spermatogonia were present in the epithelium. Throughout testicular regression spermatocytes and spermatids disappeared and the presence of cellular debris, and scattered spermatozoa were observed in the lumen. The regressed testes presented the total suspension of spermatogenesis. During October, the seminiferous tubules contained only spermatogonia and Sertoli cells, and the size of the lumen was reduced, giving the appearance that it was occluded. In concert with testis development, the efferent ducts were packed with spermatozoa from May through August. The epididymis was devoid of spermatozoa by September. M. brachypoda exhibited a prenuptial pattern, in which spermatogenesis preceded the mating season. The seasonal cycle variations of spermatogenesis in M. brachypoda are the result of a single extended spermiation event, which is characteristic of reptilian species. J. Morphol. © 2012 Wiley Periodicals, Inc.     

Peroxisome Proliferator-activated Receptor-D (PPARD) Coordinates Mouse Spermatogenesis by Modulating Extracellular Signal-regulated Kinase (ERK)-dependent Signaling

Ppard^−/− mice exhibit smaller litter size compared with Ppard^+/+ mice. To determine whether peroxisome proliferator-activated receptor-D (PPARD) could possibly influence this phenotype, the role of PPARD in testicular biology was examined. Atrophic testes and testicular degeneration were observed in Ppard^−/− mice compared with Ppard^+/+ mice, indicating that PPARD modulates spermatogenesis. Higher expression of p27 and decreased expression of proliferating cellular nuclear antigen in Sertoli cells were observed in Ppard^+/+ mice as compared with Ppard^−/− mice, and these were associated with decreased Sertoli cell number in Ppard^+/+ mice. Cyclin D1 and cyclin D2 expression was lower in Ppard^+/+ as compared with Ppard^−/− mice. Ligand activation of PPARD inhibited proliferation of a mouse Sertoli cell line, TM4, and an inverse agonist of PPARD (DG172) rescued this effect. Temporal inhibition of extracellular signal-regulated kinase (ERK) activation by PPARD in the testis was observed in Ppard^+/+ mice and was associated with decreased serum follicle-stimulating hormone and higher claudin-11 expression along the blood-testis barrier. PPARD-dependent ERK activation also altered expression of claudin-11, p27, cyclin D1, and cyclin D2 in TM4 cells, causing inhibition of cell proliferation, maturation, and formation of tight junctions in Sertoli cells, thus confirming a requirement for PPARD in accurate Sertoli cell function. Combined, these results reveal for the first time that PPARD regulates spermatogenesis by modulating the function of Sertoli cells during early testis development.     

Apoptosis,proliferation and presence of estradiol receptors in the testes and Bidder's organ of the toad Rhinella arenarum (Amphibia,Anura)

The dynamic equilibrium between spermatogonial proliferation and testicular apoptosis determines the progression of spermatogenesis in amphibians. Estrogens and their receptors play a central role in regulating spermatogenesis in vertebrates, and in some species of anurans, estradiol (E₂) is involved in the regulation of spermatogonial proliferation and apoptosis of germ cells. Bidder's organ (BO) is a structure characteristic of Bufonidae that has historically been compared to an undeveloped ovary. In adult Rhinella arenarum males, BO is one of the main sources of plasma E₂. The aim of this study was 1) to describe the seasonal variations in testicular apoptosis, spermatogonial proliferation, and cellular proliferation in BO; and 2) to analyze the presence and localization of estrogen receptor β (ERβ) in the testes and BO of R. arenarum. Testicular fragments and BOs from animals collected during the year were labeled with 5‐bromo‐2′‐deoxyuridine (BrdU) and BrdU incorporation was determined using immunohistochemistry. Apoptosis in testicular sections was detected using the TUNEL method, and ERβ localization was assessed using immunohistochemistry in testes and BOs. The results indicate that spermatogonial proliferation is highest during the reproductive season and that cysts of spermatocytes and spermatids undergo apoptosis during the postreproductive season. Furthermore, the proliferation of follicular cells is highest during the reproductive and postreproductive seasons. ERβ was primarily detected by immunolocalization in Sertoli cells, follicular cells, and oocytes. Taken together, these results suggest that cysts that do not form spermatozoa are removed from testes by apoptosis and that estrogens regulate both spermatogenesis and oogenesis in adult males of R. arenarum. J. Morphol. 277:412–423, 2016. © 2015 Wiley Periodicals, Inc.     

Overexpression of Bcl-W in the testis disrupts spermatogenesis: revelation of a role of BCL-W in male germ cell cycle control

To explore physiological roles of BCL-W, a prosurvival member of the BCL-2 protein family, we generated transgenic (TG) mice overexpressing Bcl-w driven by a chicken beta-actin promoter. Male Bcl-w TG mice developed normally but were infertile. The adult TG testes displayed disrupted spermatogenesis with various severities ranging from thin seminiferous epithelium containing less germ cells to Sertoli cell-only appearance. No overpopulation of any type of germ cells was observed during testicular development. In contrast, the developing TG testes displayed decreased number of spermatogonia, degeneration, and detachment of spermatocytes and Sertoli cell vacuolization. The proliferative activity of germ cells was significantly reduced during testicular development and spermatogenesis, as determined by in vivo and in vitro 5'-bromo-2'deoxyuridine incorporation assays. Sertoli cells were structurally and functionally normal. The degenerating germ cells were TUNEL-negative and no typical apoptotic DNA ladder was detected. Our data suggest that regulated spatial and temporal expression of BCL-W is required for normal testicular development and spermatogenesis, and overexpression of BCL-W inhibits germ cell cycle entry and/or cell cycle progression leading to disrupted spermatogenesis.     

Secreted proteins from rat Sertoli cells.

Sertoli cell cultures were prepared from the testes of 20-day-old rats. The proteins which were secreted by the cells into the culture medium were labeled with [³H]leucine or l-[³H]fucose. The proteins were concentrated by ultrafiltration and analysed by polyacrylamide slab gel electrophoresis (PAGE) in the presence of sodium dodecyl sulfate (SDS). Autofluorography of the gels at ?70 °C showed that the rat Sertoli cells synthesized and secreted at least 7 major polypeptides. The polypeptides had molecular weights ranging from 16 000 to 140 000 D. Proteins which were secreted from cultures of testicular fibroblasts and myoid cells had electrophoretic properties on SDS-PAGE which were different from Sertoli cell secreted proteins. Addition of FSH and testosterone to the Sertoli cell cultures increased the total synthesis and secretion of [³H]leucine-labeled proteins. No qualitative changes in the proteins as a result of hormone application could be detected. However, the synthesis of a polypeptide of molecular weight 48 000 was increased relative to the other secreted peptides if the cells were maintained in FSH and testosterone. The Sertoli cell secreted proteins were shown to be glycoproteins which can bind to ConA-Sepharose and can be labeled with [³H]fucose. Tunicamycin, a specific inhibitor of N-glycosylation, inhibited the secretion of [³H]proteins by 50% but had little effect on the intracellular protein synthesis.     

Ultrastructure and histochemistry of the testicular efferent duct system and spermiogenesis in Opistognathus whitehurstii (Teleostei, Trachinoidei)

 Testis organization and spermatogenesis, with the emphasis on spermiogenesis, in Opistognathus whitehurstii are described by ultrastructural and histochemical methods. The germinal epithelium is extremely reduced and restricted to the periphery of the testis, while most of the organ is occupied by a highly developed system of testicular efferent ducts. A semicystic type of spermatogenesis is observed and in the germinal epithelium spermatogenesis occurs only until the spermatidal stage. Young spermatids are released into the lumen of the testicular lobules and mature to sperm within the efferent duct system. The epithelial cells of these ducts are involved in protein and glycogen secretion and in phagocytosis of degenerating germ cells and residual bodies cast off by developing spermatids. On the basis of these functions, the testicular efferent duct system cells are considered to be homologous to the Sertoli cells. A correlation between a highly developed testicular efferent duct system and semicystic spermatogenesis is examined and a possible functional meaning of this apparently unusual mode of sperm production is proposed. Accepted: 18 March 1997     

Temporal germ cell development strategy during spermatogenesis within the testis of the Ground Skink, Scincella lateralis (Sauria: Scincidae)

Ground Skink (Scincella lateralis) testes were examined histologically to determine the testicular organization and germ cell development strategy employed during spermatogenesis. Testicular tissues were collected from 19 ground skinks from Aiken County, South Carolina during the months of March-June, August, and October. The testes consisted of seminiferous tubules lined with germinal epithelia in which germ cells matured in close association with Sertoli cells. As germ cells matured, they migrated away from the basal lamina of the epithelia towards the lumina of the seminiferous tubules. The testes were spermatogenically active during the months of March, April, May, June, and October (largest seminiferous tubule diameters and epithelial heights), but entered a quiescent period in August (smallest seminiferous tubule diameter and epithelial height) where only spermatogonia type A and B and early spermatocytes were present in low numbers within the seminiferous epithelium. Although the testicular organization was similar to other amniotes, a temporal germ cell development strategy was employed during spermatogenesis within Ground Skinks, similar to that of anamniotes. Thus, this skink's germ cell development strategy, which also has been recently reported in all other major reptilian clades, may represent an evolutionary intermediate in terms of testicular organization between anamniotes and birds and mammals.     

Expression patterns of gdnf and gfrα1 in rainbow trout testis

In mice, glial cell line-derived neurotrophic factor (GDNF) is essential for normal spermatogenesis and in vitro culture of spermatogonial stem cells. In murine testes, GDNF acts as paracrine factor; Sertoli cells secrete it to a subset of spermatogonial cells expressing its receptor, GDNF family receptor α1 (GFRα1). However, in fish, it is unclear what types of cells express gdnf and gfrα1. In this study, we isolated the rainbow trout orthologues of these genes and analyzed their expression patterns during spermatogenesis. In rainbow trout testes, gdnf and gfrα1 were expressed in almost all type A spermatogonia (ASG). Noticeably, unlike in mice, the expression of gdnf was not observed in Sertoli cells in rainbow trout. During spermatogenesis, the expression levels of these genes changed synchronously; gdnf and gfrα1 showed high expression in ASG and decreased dramatically in subsequent developmental stages. These results suggested that GDNF most likely acts as an autocrine factor in rainbow trout testes.