Ultrastructural changes in testes of the snapping turtle, Chelydra serpentina in relation to plasma testosterone, delta 5-3 beta-hydroxysteroid dehydrogenase, and cholesterol

Male reproductive cycle in a population of the endemic butterfly lizard, Leiolepis ocellata Peters, 1971 (Squamata: Agamidae) from northern Thailand

Background

Fundamental knowledge on the seasonal reproductive microanatomy and endocrinology of reptiles has been collected from several studies of various species. The present study was to determine annual changes in hormonal profiles, and detailed histomorphometric and histochemical characteristics of the entire male reproductive system of the tropical agamid lizard, Leiolepis ocellata.

Results

Male L. ocellata individuals (n = 75) collected from the territory of two provinces (Lampang and Tak) in northern Thailand exhibited annual variation in sex hormonal, histomorphometric, and histochemical characteristics of the male reproductive system. The reproductive cycle was subdivided into eight reproductive periods (early first active, first active, resting, second recrudescent, second active, regressive, quiescent, and first recrudescent), thus displaying a bimodal pattern with two actively reproductive periods. Circulating sex hormones (testosterone, estradiol, and progesterone) peaked in the first active (February) and the second active (June–July) periods. Likewise, gonadosomatic index (GSI) and histomorphometric variables of the testes and of the genital ducts (rete testis, ductuli efferentes, ductus epididymis, and ductus deferens) revealed their highest values in the first active period. Marked increase in protein and carbohydrate production was detectable in the ductuli efferentes during the active periods.

Conclusions

The male reproductive cycle of L. ocellata showed a biannual pattern of the hormonal profile, and detailed histomorphometric and histochemical characteristics of the entire reproductive system. Hence, the present study provides improved basic knowledge on the reptilian reproductive biology with comparative viewpoints to other reptiles.

Year-round plasma steroid hormone profiles and the reproductive ecology of gopher tortoises (Gopherus polyphemus) at the southernmost edge of their range

Populations of wide ranging ectotherms often exhibit variation in traits that are influenced by local environmental conditions. Although the gopher tortoise, Gopherus polyphemus, is well studied in pine flatwoods habitats across their range, little attention has been given to coastal populations existing in the southern extreme portion of the range. We examined the reproductive physiology of a coastal dune population in southwest Florida to determine if reproductive cycles vary across populations. Here we present the first year-round sex hormone profiles for a wild population of gopher tortoises. Male testosterone concentrations varied across the year (F_11,54 = 2.52, P = 0.015) with elevated values from September to December and minimal levels from April to July, with the exception of a secondary peak during the month of June. Female testosterone and estradiol concentrations varied across the sampling period (T: F_11,66 = 8.54, P < 0.001, E: F_11,66 = 4.57, P < 0.001) with highest values from August to February, and lowest levels from May to July. Female progesterone concentrations varied over the year (F_11,64 = 3.29, P = 0.002) and increased in late fall with a peak in March. These data suggest this population has an extended breeding season from fall through spring with mating likely occurring from September through March, and nesting in winter through spring. This pattern is similar to reproductive patterns described for tropical and sub-tropical chelonians but differs from that of gopher tortoise populations in northern portions of the range where hibernation may last for five months and a single clutch of eggs are deposited in late spring.

LIPOPHAGY: a novel form of steroidogenic activity within the LEYDIG cell during the reproductive cycle of turtle

BACKGROUND

Steroidogenesis is an indispensable process that is indirectly associated with spermatogenesis in the Leydig cell (LC) to utilize the lipid droplets (LDs) that are critical to maintaining normal testosterone synthesis. The regulation of LD mobilization, known as lipophagy, in the LC is still largely unknown.

METHOD

In the present study, the LC of the Chinese soft-shelled turtle was investigated to identify the steroidogenic activity and lipophagy during the annual reproductive cycle by light microscopy, immunohistochemistry (IHC), immunofluorescence (IF), and transmission electron microscopy (TEM).

RESULTS

The LC showed a dynamic steroidogenic function with strong activity of 3β-HSD, vimentin and tubular ER during hibernation by IHC and TEM. The tubulo-vesicular ER had a weak immunopositive reaction for 3β-HSD in the LC during reproductive phase, suggesting persistent steroidogenic activity. ORO staining and TEM demonstrated that a larger number of LDs had accumulated in the LC during hibernation than in the reproductive phase. These LDs existed in close association with mitochondria and lysosomes by being dynamically surrounded by intermediate filaments to facilitate LD utilization. Lysosomes were found directly attached to large LDs, forming an autophagic tube and engulfing LDs, suggesting that micro-lipophagy occurs during hibernation. Furthermore, the IHC of ATG7 (Autophagy Related Gene 7) and the IF of the LC3 (Microtubule-associated protein light chain 3), p62 (Sequestosome-1 (SQSTM1) and LAMP1(Lysosomal-associated membrane protein 1) results demonstrated strong expression, and further confirmation by TEM showed the existence of an autophagosome and an autolysosome and their fusion during the hibernation season.

CONCLUSION

In conclusion, the present study provides clear evidence of LD consumption in the LC by lipophagy, lysosome and mitochondria during the hibernation period, which is a key aspect of steroidogenesis in the Chinese soft-shelled turtle.

Claudin 11 inter-sertoli tight junctions in the testis of the korean soft-shelled turtle (Pelodiscus maackii)

Expression of claudin 11 (CLDN11), a tight junction (TJ) protein, was examined in the Korean soft-shelled turtle (Pelodiscus maackii) testis. Spermatogenesis began during the breeding season and peaked at the end of the breeding season. Spermiation started in summer and peaked in autumn. The deduced amino acid sequence of P. maackii CLDN11 was similar to those of avian and mammalian species. During the nonbreeding season when spermatogenesis and testosterone production were active, testicular Cldn11 levels were high. In the seminiferous epithelium, strong, wavy CLDN11 strands parallel to the basement membrane delaminate the spermatogonia, and early spermatocytes are in the open compartment. Otherwise, CLDN11 was found beneath the early spermatocytes and in the Sertoli cell cytoplasm. Punctate zonula occludens 1 (ZO-1) immunoreactivity was found within the CLDN11 strands parallel to the basement membrane or at the outermost periphery of the seminiferous epithelium close to the basal lamina. During the breeding season, when circulating testosterone levels and spermatogenic activity was low, testicular CLDN11 level was lower than those during the nonbreeding season. CLDN11 was found at apicolateral contact sites between adjacent Sertoli cells devoid of the postmeiotic germ cells. At this time, lanthanum tracer diffused to the adluminal compartment of seminiferous epithelium. In cultured testis tissues, testosterone propionate significantly increased the level of Cldn11 mRNA. In P. maackii testis, CLDN11 participates in the development of the blood-testis barrier (BTB), where the CLDN11 expression was coupled with spermatogenic activity and circulating androgen levels, indicating the conserved nature of TJs expressing CLDN11 at the BTB in amniotes.

The reproductive cycle of the male house gecko, Hemidactylus flaviviridis, in relation to plasma steroid concentrations, progesterone receptors, and steroidogenic ultrastructural features, in Oman

The annual testicular cycle of the house gecko Hemidactylus flaviviridis in Oman was studied. Plasma testosterone (T), estradiol (E2) and progesterone (P) concentrations were measured using a sensitive HPLC-MS/MS detection technique. The ultrastructural steroidogenic features in Sertoli and Leydig cells, which were the major source of steriodogenesis, were examined, using transmission electron microscopy (TEM). In addition, progesterone receptors (PR) were examined throughout the testicular cycle, using an immunohistochemical technique. The steroidogenic ultrastructural features were characterized by the presence of smooth endoplasmic reticulum (SER) in the form of cisternal whorls and tubular cisternae, presence of swollen vesiculated mitochondria, and association between SER, mitochondria and lipid droplets. The rise in plasma steroid concentrations was closely associated with the development of the ultrastructural features and PR expression in Leydig and Sertoli cells. During the active phase (November-May), there was a significant rise in plasma steroid concentrations (P<0.05) related to well developed steroidogenic features and strongly expressed PR. During the quiescent phase (June-August) there was a significant decline in plasma steroid concentrations, undeveloped steroiodogenic features and weakly expressed PR. The Renal Sexual Segment (RSS) was fully developed during the active phase. The data provides strong evidence that these ultrastructural steroidogenic features were related to the plasma sex steroid concentrations during the testicular cycle.

Dual functions of TAF7L in adipocyte differentiation

The diverse transcriptional mechanisms governing cellular differentiation and development of mammalian tissue remains poorly understood. Here we report that TAF7L, a paralogue of TFIID subunit TAF7, is enriched in adipocytes and white fat tissue (WAT) in mouse. Depletion of TAF7L reduced adipocyte-specific gene expression, compromised adipocyte differentiation, and WAT development as well. Ectopic expression of TAF7L in myoblasts reprograms these muscle precursors into adipocytes upon induction. Genome-wide mRNA-seq expression profiling and ChIP-seq binding studies confirmed that TAF7L is required for activating adipocyte-specific genes via a dual mechanism wherein it interacts with PPARγ at enhancers and TBP/Pol II at core promoters. In vitro binding studies confirmed that TAF7L forms complexes with both TBP and PPARγ. These findings suggest that TAF7L plays an integral role in adipocyte gene expression by targeting enhancers as a cofactor for PPARγ and promoters as a component of the core transcriptional machinery.

DOI:http://dx.doi.org/10.7554/eLife.00170.001

The development of a single fertilized egg into a highly complex animal is determined by its genome, with a process called differential gene regulation exerting exquisite control over gene expression to ensure that various specialized cells are generated and that many types of tissue are produced. However, the mechanisms responsible for controlling gene expression and, therefore mammalian development, are poorly understood.

Researchers have developed a number of in vitro cell culture models to elucidate the details of differential gene regulation, and this approach has been used to characterize adipocytes—cells that store energy in the form of fat—for close to two decades. The formation of adipocytes, a process known as adipogenesis, has been extensively studied, but there remain major gaps in our knowledge: for example, the identities of many of the transcriptional regulators that are responsible for the differentiation of mesenchymal stem cells into adipocytes remain a mystery. This task is complicated by the fact that some of these regulators are involved in the differentiation of multiple cell lines, and that some of them also have multiple roles in the generation of a single cell type. In addition to being of fundamental interest, improving our knowledge of the properties and behavior of adipocytes is essential for tackling the increasing prevalence of obesity in the developed world.

Zhou et al. now report that TAF7L—a gene that was previously thought to be involved only in the production of sperm cells—has two roles in the differentiation of stem cells to form adipocytes. Using a combination of cellular, biochemical, genetic and genomic techniques, they show that TAF7L interacts with PPARγ, an important adipocyte transcriptional regulator at enhancer sites on the genome to increase the transcription of genes that are involved in adipogenesis. They also show that TAF7L interacts with a general transcription factor called TBP (short for TATA-binding protein) at promoter sequences, again to increase the expression of genes involved in adipogenesis. Moreover, they show that the expression of TAF7L in myoblasts—precursor cells that usually become muscle cells—can induce the formation of fat cells rather than muscle cells. Furthermore, mice lacking TAF7L are lean compared to their normal littermates. A clearer understanding of the underlying causes of fat cell formation could lead to the development of new approaches for the treatment of obesity and associated diseases.

DOI:http://dx.doi.org/10.7554/eLife.00170.002

Seasonal variations in plasma vitellogenin and sex steroids in male and female Eastern Box Turtles, Terrapene carolina carolina

The Eastern Box Turtle (Terrapene carolina carolina) is a widespread species that has recently experienced precipitous declines throughout its range. Although many studies have documented aspects of reproduction in box turtles, reproductive physiology of free-ranging animals is unknown and can be crucial in this species' recovery. Over a two-year period, we measured reproductive parameters, (vitellogenin [Vtg], estradiol-17β [E2], and total testosterone [TT]), in plasma of 116 free-ranging Eastern Box Turtles across their active season. We found similar seasonal variations of Vtg and E2 within females. Mid-season, females showed a sharp peak in E2 that correlates with the putative beginning of the ovarian cycle. Individual females lacking these expected peaks of both Vtg and E2 suggest that some female T. c. carolina may not reproduce annually. Females typically expressed undetectable levels of TT, yet there was a small peak in TT early in the active season. Male Eastern Box Turtles exhibited a dual peak in TT. Elevated TT in males was significantly associated with observed sexual behaviors and smaller home ranges. Body condition had no effect on the concentration of TT or E2 in either sex. This is the first study to (1) document Vtg and sex steroid hormones in free-ranging animals of this genus, and (2) relate those metrics to individuals, the population, the purported annual cycle, and to other chelonian species.

Asynchronic steroid activity of Leydig and Sertoli cells related to spermatogenic and testosterone cycle in Phymaturus antofagastensis

The severe environments where Phymaturus lizards inhabit in the Andes highlands and in Patagonia, Argentina, impose restrictions on their reproduction, offering a framework for the development of life history strategies to overcome hard weather conditions. Among them, prolonged female cycles, asynchrony between sexes in receptivity, and sperm storage in males, were described. Asynchrony in the reproductive timing between males and females is a consequence of different energy requirements for gametogenesis, and often imply the existence of cellular mechanisms to enhance fertilization, such as the asynchronic steroid synthesis between testicular compartments, allowing gametogenesis independently of mating. In the present study ultrastructural and hormone assays were combined for the first time in liolaemids. Specifically, morphological features of steroid activity in Leydig and Sertoli cells, and serum testosterone concentrations have been studied in the lizard Phymaturus antofagastensis. Leydig and Sertoli cells presented morphological features characteristic of steroid synthesis during the spermatogenesis, and evident asynchronic steroid production between testicular compartments. Active Sertoli cells and inactive Leydig cells were observed in spring and autumn, while in mid-summer their steroid activity was synchronic in coincidence with maximal abundance of spermatozoa in epididymis. Serum testosterone concentration was at its maximum in mid-summer (126-230 ng ml(-1)), and minimum in late spring (4-24 ng ml(-1)) and early autumn (2-17 ng ml(-1)). In view of these results, P. antofagastensis males show an original approach to adjust their reproductive activity to physiological and environmental constraints at high latitudes and altitudes in the Andean highlands of Argentina.

The reproductive pattern of male dusky salamanders (genus Desmognathus) is neither associated nor dissociated

Many seasonally breeding vertebrate species have an associated reproductive pattern: mating behavior, gonadal activity, and peak circulating androgen levels occur simultaneously. In these species, androgens influence the expression of male mating behavior. Other species have a dissociated reproductive pattern: mating behavior occurs at a different time than peak gonadal activity. In such species, it is hypothesized that mating behavior is not dependent on androgen levels [Crews, D., 1984. Gamete production, sex hormone secretion, and mating behavior uncoupled. Horm. Behav. 18, 22-28]. The salamander Desmognathus ochrophaeus mates in the spring and fall while spermatogenesis occurs during the summer, suggesting that it has a dissociated reproductive pattern and that androgens do not mediate mating behavior. To assess whether mating behavior is regulated by gonadal androgens, we castrated males to reduce endogenous androgens and implanted testosterone propionate (TP) to restore androgen levels. Castrated males mated significantly less than did control males. Castrated males given TP mated as much as control males. Compared to controls, circulating androgen levels (both testosterone (T) and dihydrotestosterone (DHT)) were reduced in castrated males and elevated in castrated males given TP implants. We also found that plasma corticosterone (CORT) levels were strongly and positively correlated with T levels. Together, these data indicate that, although spermatogenesis is dissociated in time from mating behavior, androgens are associated with the expression of mating. Thus, the associated-dissociated dichotomy does not adequately describe the reproductive pattern of D. ochrophaeus. We discuss the limitations of the associated-dissociated framework in clarifying hormone-behavior relationships in reptiles and amphibians.

Oviductal morphology in relation to hormonal levels in the snapping turtle, Chelydra serpentina

Microscopic and in situ visual observations were used to relate circulating hormone levels to morphological changes in the oviduct of the snapping turtle Chelydra serpentina throughout the ovarian cycle. Increase in levels of progesterone (P), estradiol (E2) and testosterone (T) levels coincide with an increase in number and growth of endometrial glands, luminal epithelial cells and secretory droplets throughout the oviduct. Testosterone and estradiol levels rose significantly (P < 0.05) after the May-June period and remained high throughout the rest of the summer. Progesterone levels remained stable throughout the summer, with a brief decline in July due to luteolysis. Hormonal values declined significantly (P < 0.001) at the end of the ovarian cycle in the fall. In situ visual observation of fresh oviducts at different stages of gravidity in recently ovulated turtles revealed that proteinaceous like components from the endometrial glands were released into the lumen to form fibers. The morphological features of the oviduct remained active throughout the summer months even though the snapping turtle is a monoclutch species which deposits all the eggs in late-May to mid-June. The high steroid levels correlate with and may be responsible for the secretory activity present throughout the summer and their decline correlates with change to low secretory activity in the fall. Calcium deposition accompanied by morphological changes in luminal cells are suggestive of secretory activity. In the egg-bearing turtles, uterine Ca2+ concentrations measured by flame atomic absorption spectrophotometry revealed significantly higher Ca2+ concentrations (P < 0.001) in eggs with soft shell than eggs without shell. There was a significant increase in calcium granules and proteinaceous fibers in luminal surface of the uterus during the period of eggshelling. This supports the fact that in the snapping turtle like in other reptiles, eggshelling process occurs in the uterus.

Evolutionary insights into the regulation of courtship behavior in male amphibians and reptiles

Comparative studies of species differences and similarities in the regulation of courtship behavior afford an understanding of evolutionary pressures and constraints shaping reproductive processes and the relative contributions of hormonal, genetic, and ecological factors. Here, we review species differences and similarities in the control of courtship and copulatory behaviors in male amphibians and reptiles, focusing on the role of sex steroid hormones, the neurohormone arginine vasotocin (AVT), and catecholamines. We discuss species differences in the sensory modalities used during courtship and in the neural correlates of these differences, as well as the value of particular model systems for neural evolution studies with regard to reproductive processes. For example, in some genera of amphibians (e.g., Ambystoma) and reptiles (e.g., Cnemidophorus), interspecific hybridizations occur, making it possible to compare the ancestral with the descendant species, and these systems provide a window into the process of behavioral and neural evolution as well as the effect of genome size. Though our understanding of the hormonal and neural correlates of mating behavior in a variety of amphibian and reptilian species has advanced substantially, more studies that manipulate hormone or neurotransmitter systems are required to assess the functions of these systems.

Variation of plasma sex steroid concentrations in wild and captive populations of Hermann's tortoise (Testudo hermanni hermanni) in Southern France

Plasma levels of sex steroids in both males and females of the endangered Hermann's tortoise (Testudo hermanni hermanni) were measured throughout their active period in a wild population in the Massif des Maures, France, and in a nearby captive population at Le Village des Tortues in Gonfaron. Both plasma progesterone and testosterone were elevated in males at emergence from winter dormancy, and plasma progesterone levels were significantly higher in wild than in captive males. Plasma testosterone in males then fell to the lowest levels (10 ng ml(-1)) during the nesting season from April to June followed by an elevated plateau during summer, with levels reaching 80 ng ml(-1), presumably concomitant with spermiogenesis. Plasma testosterone increased in all females during autumn, an indication of follicular growth, and remained high on emergence from hibernation, to peak during April, although levels were lower in the captive population. Plasma progesterone also peaked during April and May, presumably related to ovulation, but, again, these changes were less marked in the captive than in the wild females. Measurements of testosterone, progesterone and 17beta-oestradiol in the captive females during their period of oviposition in spring suggested that some females did ovulate and lay eggs, whereas others did not. Differences in sex steroid levels between captive and wild populations of Hermann's tortoise may indicate a problem with ovulation and/or with stress in a proportion of captive females.

Fine structure of leydig and sertoli cells in the testis of immature and mature spotted ray Torpedo marmorata

An ultrastructural investigation revealed the presence of true Leydig cells in the testis of sexually mature specimens of Torpedo marmorata. They showed the typical organization of steroid-hormone-producing cells, which, however, changed as spermatocysts approached maturity. In fact, they appeared as active cells among spermatocysts engaged in spermatogenesis, while in regions where spermiation occurred, they progressively regressed resuming the fibroblastic organization typically present in the testis of immature specimens. Such observations strongly suggest that these cells might be engaged in steroidogenesis and actively control spermatogenesis. Sertoli cells, too, appeared to play a role in spermatogenesis control, since, like Leydig cells, they showed the typical aspect of steroidogenic cells. In addition, the presence of gap junctions between Sertoli cells suggests that their activity might be coordinated. After sperm release, most Sertoli cells were modified and, finally, degenerated, but few of them changed into round cells (cytoplasts) or round cell remnants, which continued their steroidogenic activity within the spermatocyst and the genital duct lumen. From the present observations, it can be reasonably concluded that, in T. marmorata, spermatogenesis depends on both Leydig and Sertoli cells, and, as postulated by Callard (1991), in cartilaginous fish, the function of the Leydig cells as producers of steroids might be more recent and subsequent to that of Sertoli cells. In this regard, it is noteworthy that, in immature males, when Leydig cells showed a fibroblastic organization, Sertoli cells already displayed the typical organization of a steroidogenic cell.

Seasonal variation in reproductive steroids of male and female yellow-blotched map turtles, Graptemys flavimaculata

From April to October of 1996 and 1997, we measured seasonal changes in plasma testosterone (T) in male and plasma T and estradiol-17beta (E(2)) in female yellow-blotched map turtles, Graptemys flavimaculata, from the Pascagoula River, Mississippi. In 1996, plasma from females was analyzed for progesterone. In 1997, ovaries of adult females were ultrasound imaged to determine stages of follicular development. Males exhibited peak T levels in September and October of both years, indicating fall gonadal activity. Males also exhibited a low level spring peak in T during April. Female E(2) levels increased significantly in May and June, the primary period of ovarian development. Females with preovulatory follicles did not have significantly higher E(2) levels than females with medium- or small-sized follicles. When compared to other freshwater turtle species, peak levels of E(2) were low. Testosterone levels did not follow a distinct yearly pattern in females. Progesterone levels were elevated in June when peak nesting was observed. Ultrasound and hormone data indicate that females lack ovarian development in the fall and produce on average only one clutch per year.

Seasonal changes in gonadal activity and the effects of stress on reproductive hormones in the common snapping turtle, Chelydra serpentina

The seasonal gonadal cycle (including gonadal histology, sex steroids, and gonadotropins) was studied in freshly captured common snapping turtles, Chelydra serpentina, from Wisconsin, and the effects of capture stress were evaluated. The ovarian and testicular cycles are shorter than those reported in other freshwater turtles; the cycles commence in mid-May and terminate in early September, immediately after the completion of gonadal growth and maturation. In the female, testosterone (T), 17beta-estradiol (E2), and progesterone (Pro) were highly correlated with follicular growth and vitellogenesis. Ovulation in captivity and under natural conditions occurred after mid-May. In captivity, ovulation was a rapid process (24-48 hr); as the follicles descended into the uterine horns there was a significant increase in E2 and Pro and eggs were retained in the uterine horns for about 2 weeks before oviposition. In the male, T was significantly correlated with testicular growth and spermiation. Follicle-stimulating hormone (FSH) reached significantly higher levels (P < 0.01) in males (8.99 +/- 0.38 ng/ml) than in females (2.66 +/- 0.22 ng/ml), but luteinizing hormone was undetectable in both sexes. FSH was not correlated with the steroids in either sex. Sex steroids and FSH began to rise before spermiation and vitellogenesis and remained elevated until completion of gonadal growth and maturation. Leydig cells, the main source of plasma androgen in this species, became active shortly after emergence from hibernation and remained steroidogenically active for the rest of the cycle. Sertoli cells became active only after spermatogenesis was under way but also stayed active for the rest of the summer. Courtship and mating behaviors were observed in spring, summer, and fall. The snapping turtle is strictly aquatic with no basking behavior and limited behavioral thermoregulation so there is little daily fluctuation in body temperature. Environmental correlates indicate that the snapping turtle is temperature dependent: recrudesence occurs with a slight increase in water temperature during spring and early summer, while a dramatic drop in gonadal activity accompanies a slight decrease in temperature in fall. Changes in temperature may underlie changes in gonadal activity in the face of relatively stable FSH. Male turtles subjected to captivity and periodic blood sampling show a significant decline in T. The hormonal levels continued to decline whether the turtles are exposed to optimum or extreme temperatures. However, there is more rapid decline in T values in animals with regressed testes (June) than in those with well-developed testes (July). Male and female turtles kept in captivity at different phases of the cycle exhibit different patterns and degrees of response to stress, possibly related to the hormonal levels and the condition of the gonads.

Spermatogenesis in nonmammalian vertebrates

Spermatogenesis appears to be a fairly conserved process throughout the vertebrate series. Thus, spermatogonia develop into spermatocytes that undergo meiosis to produce spermatids which enter spermiogenesis where they undergo a morphological transformation into spermatozoa. There is, however, variation amongst the vertebrates in how germ cell development and maturation is accomplished. This difference can be broadly divided into two distinct patterns, one present in anamniotes (fish, amphibia) and the other in amniotes (reptiles, birds, mammals). For anamniotes, spermatogenesis occurs in spermatocysts (cysts) which for most species develop within seminiferous lobules. Cysts are produced when a Sertoli cell becomes associated with a primary spermatogonium. Mitotic divisions of the primary spermatogonium produce a cohort of secondary spermatogonia that are enclosed by the Sertoli cell which forms the wall of the cyst. With spermatogenic progression a clone of isogeneic spermatozoa is produced which are released, by rupture of the cyst, into the lumen of the seminiferous lobule. Following spermiation, the Sertoli cell degenerates. For anamniotes, therefore, there is no permanent germinal epithelium since spermatocysts have to be replaced during successive breeding seasons. By contrast, spermatogenesis in amniotes does not occur in cysts but in seminiferous tubules that possess a permanent population of Sertoli cells and spermatogonia which act as a germ cell reservoir for succeeding bouts of spermatogenic activity. There is, in general, a greater variation in the organization of the testis and pattern of spermatogenesis in the anamniotes compared to amniotes. This is primarily due to the fact there is more reproductive diversity in anamniotes ranging from a relatively unspecialized condition where gametes are simply released into the aqueous environment to highly specialized strategies involving internal fertilization. These differences are obviously reflected in the mode of spermatogenesis and this is particularly true of the stage of spermiogenesis where the morphology of the species-specific spermatozoon is determined. Moreover, unlike amniotes, many anamniotes display a spermatogenic wave manifest, depending upon the species, either at the level of the cyst or seminiferous lobule. This variation in the organization of the testis makes certain anamniotes perfect models for investigating germ cell development and maturation. For instance, the presence of a spermatogenic wave provides an opportunity to manually isolate discrete germ cell stages for analysis of specific Sertoli/germ cell interactions. Furthermore, for many anamniotes, germ cells mature in association with a morphologically poorly developed Sertoli cell. This seeming independence of Sertoli cell regulation allows the in vitro culture of isolated germ cells of some species of anamniotes through several developmental stages. Thus, due either to the anatomical organization of the testis, or structural simplicity of the germinal units, nonmammalian vertebrates can provide excellent experimental animal models for investigating many basic problems of male reproduction.

The comparative cell biology of accessory somatic (or Sertoli) cells in the animal testis

A comparative account is given of recent advances in the cell biology of testicular accessory somatic (or Sertoli) cells in mammals, nonmammalian vertebrates, and invertebrates by comparing and contrasting their structure and function. Their structure is discussed in relation to the nucleus, cytoplasmic organelles, and inclusions (lipids, the cytoskeleton, junctional complexes, and blood-testis barrier, which show great diversity and a variable testicular architecture), and mode of spermatogenesis. A very limited somatic cell-germinal association or its complete absence is observed in some groups of invertebrates. Wherever the somatic accessory cells are present, their comparative functions are discussed in relation to (1) mechanical support and nutrition; (2) translocation of germ cells; (3) paracrine regulation and a combination of male germ cell proliferation and differentiation by secretion of regulatory proteins, including peptide growth factors and hormones; (4) phagocytosis; (5) steroid hormone synthesis and metabolism; and (6) spermiation. Comparative cellular and molecular aspects of Sertoli cell-germ cell and peritubular cell interactions and the regulatory (hormonal) mechanisms involved as well as gaps in our knowledge about the molecular aspects of these interactions are emphasized for a better understanding of diversity in the patterns and regulation of spermatogenesis in animals.

The annual testicular cycle in the turtle, Chrysemys picta: a histochemical and electron microscopic study

This work is a study of testicular function in Chrysemys picta using changes in ultrastructure and steroid histochemistry as indices of Leydig and Sertoli cell activity. The cytological features of these cells are described in reference to four periods of tubular development. Leydig and Sertoli cells show distinct changes in morphological appearance during the seasonal cycle. Leydig cells are hypertrophic with an active 3 beta-hydroxysteroid dehydrogenase (HSD) and abundant smooth endoplasmic reticulum (SER) in early spring when androgen levels are high and animals mate and atropic in mid-summer when spermatogenesis is proceeding. Leydig cell atrophy is associated with a reduction in the volume of cytoplasm and SER. Leydig cells become active again in the fall showing a return toward the spring condition, with an increase in 3 beta-HSD activity. In contrast, although Sertoli cells show variations in abundance of organelles and inclusions during the annual cycle, no obvious degenerative changes could be seen and SER is always present. 3 beta-HSD enzyme activity in Sertoli cells is weak or absent in spring but intense during summer. Taken together, these observations suggest that Sertoli and Leydig cell functions are asynchronous.

Seasonal cycles in gonadal activity and plasma gonadotropin in the musk turtle, Sternotherus odoratus

Plasma gonadotropin cycles were examined in relation to the seasonal gonadal cycle in freshly captured musk turtles, Sternotherus odoratus, from South Carolina. Acute and chronic stress effects of captivity on testicular growth and circulating plasma testosterone (T) and follicle-stimulating hormone (FSH) also were examined. Monthly mean FSH levels in freshly captured males were correlated significantly with plasma T. Both T and FSH were minimal in spring when testes were small, and highest in the fall in males that had begun spermiation and whose testes had begun to regress. Individual plasma T and FSH values were significantly correlated during the fall when both hormones were at elevated levels. In contrast, plasma luteinizing hormone (LH) remained undetectable throughout the year in males. Females had nondetectable levels of both plasma LH and FSH throughout the year. There was a seasonal pattern in plasma 17 beta-estradiol which was correlated with follicular growth. Holding males in captivity (outdoors) reduced plasma T by 35-60% within 24 hr of capture (depending on season) and plasma T remained at these lower levels after 2 weeks. However, FSH was not significantly affected by such short-term "stress." Testicular weight and FSH cycles of captive males were similar to those of males in the field. Monthly plasma T of long-term captives also exhibited a seasonal cycle but at a level significantly lower than in the field and with a delayed peak. Thus, while the data suggest that FSH may be important to both seasonal testicular growth and androgen secretion, fluctuations in FSH alone cannot account for all observed patterns or changes in spermatogenesis or plasma androgen levels.