Number of mast cells in the Harderian gland of the lizard Podarcis sicula sicula (Raf): the annual cycle and its relation to environmental factors and estradiol administration

The Italian Wall Lizard Podarcis siculus as a Biological Model for Research in Male Reproductive Toxicology

Spermatogenesis is a genetically driven differentiation process that occurs in the testis and leads to the formation of spermatozoa. This process is extensively studied in several experimental models, particularly in vertebrates that share the morphological structure and functionality of the mammalian testis. Although reptiles are not generally considered biological models, the lizard Podarcis siculus has represented a suitable organism for the study of spermatogenesis over the years. In this lizard, the process of spermatogenesis is regulated by the interaction between systemic factors such as gonadotropins and local factors, i.e., molecules produced by the somatic and germinal cells of the testis. Many exogenous substances are able to alter the production of these regulative factors, thus altering the course of spermatogenesis, and P. siculus has proven to be an excellent model for studying the effects of various endogenous or exogenous substances on mechanisms underlying spermatogenesis. This review summarizes the available data on the effects of different substances on the control of spermatogenesis, highlighting the induced morphological and molecular alterations. Overall, the data show that sex hormone levels as well as the final stages of spermatogenesis are most affected by an imbalance of endogenous compounds or contamination by environmental pollutants. This is helpful for the male individual, since the damage, not affecting the spermatogonial stem cells, can be considered transient and not irreversible.

The Harderian gland: Endocrine function and hormonal control

The Harderian gland (HG) is an exocrine gland located within the eye socket in a variety of tetrapods. During the 1980s and 1990s the HG elicited great interest in the scientific community due to its morphological and functional complexity, and from a phylogenetic point of view. A comparative approach has contributed to a better understanding of its physiology. Whereas the chemical nature of its secretions (mucous, serous or lipids) varies between different groups of tetrapods, the lipids represent the more common component among different species. Indeed, besides being an accessory to lubricate the nictitating membrane, the lipids may have a pheromonal function. Porphyrins and melatonin secretion is a feature of the rodent HG. The porphyrins, being phototransducers, could modulate HG melatonin production. The melatonin synthesis suggests an involvement of the HG in the retinal-pineal axis. Finally, StAR protein and steroidogenic enzyme activities in the rat HG suggests that the gland contributes to steroid hormone synthesis. Over the past twenty years, much has become known on the hamster (Mesocricetus auratus) HG, unique among rodents in displaying a remarkable sexual dimorphism concerning the contents of porphyrins and melatonin. Mainly for this reason, the hamster HG has been used as a model to compare, under normal conditions, the physiological oxidative stress between females (strong) and males (moderate). Androgens are responsible for the sexual dimorphism in hamster and they are known to control the HG secretory activity in different species. Furthermore, HG is a target of pituitary, pineal and thyroid hormones. This review offers a comparative panorama of the endocrine activity of the HG as well as the hormonal control of its secretory activity, with a particular emphasis on the sex dimorphic aspects of the hamster HG.

Exploring the Role of Estrogens in Lizard Spermatogenesis through the Study of Clomiphene and FSH Effects

Spermatogenesis is a fascinating biological process aiming to generate haploid spermatozoa from diploid spermatogonia through a specific hormonal network between gonadotropins and steroids. Increasing evidence suggests that the primary female sex hormone estrogen plays an active role in this process. This research points out on the role of estrogen during lizard spermatogenesis by using three experimental approaches: (1) exposure to an analogue of nonsteroidal estrogen as Clomiphene citrate that acts both as estrogen agonist and antagonist; (2) exposure to the gonadotropin FSH; and (3) exposures to FSH followed by Clomiphene. Histological and immunohistochemical results demonstrate that in the lizard Podarcis sicula during the mating period, Clomiphene as well as FSH determines the breakdown of spermatogenesis and the epididymal regression, presumably through estrogens input as indirectly demonstrated by the appearance of ERα and vitellogenin in the liver. The ability of Clomiphene to restore the gonadal natural condition after FSH treatment is also demonstrated. Finally, data indicate that lizard testis and epididymis control their morphophysiology regulating the intracellular presence of ERα.

The phylogenetic profile of mast cells

Mast cells (MCs) are tissue-based immune cells that participate to both innate and adaptive immunities as well as to tissue-remodelling processes. Their evolutionary history appears as a fascinating process, whose outline we can only partly reconstruct according to current remnant evidence. MCs have been identified in all vertebrate classes, and a cell population with the overall characteristics of higher vertebrate MCs is identifiable even in the most evolutionarily advanced fish species. In invertebrates, cells related to vertebrate MCs have been recognized in ascidians, a class of urochordates which appeared approximately 500 million years ago. These comprise the granular hemocyte with intermediate characteristics of basophils and MCs and the "test cell" (see below). Both types of cells contain histamine and heparin, and provide defensive functions. The test cell releases tryptase after stimulation with compound 48/80. A leukocyte ancestor operating in the context of a primitive local innate immunity probably represents the MC phylogenetic progenitor. This cell was likely involved in phagocytic and killing activity against pathogens and operated as a general inducer of inflammation. This early type of defensive cell possibly expressed concomitant tissue-reparative functions. With the advent of recombinase activating gene (RAG)-mediated adaptive immunity in the Cambrian era, some 550 million years ago, and the emergence of early vertebrates, MC progenitors differentiated towards a more complex cellular entity. Early MCs probably appeared in the last common ancestor we shared with hagfish, lamprey, and sharks about 450-500 million years ago.

Systemic mastocytosis in an African fat-tail gecko (Hemitheconyx caudicinctus)

A 3-year-old African fat-tail gecko (Hemitheconyx caudicinctus) suddenly became lethargic and died 2 days later. Necropsy examination revealed a submandibular mass and discolouration of the liver, kidneys and skeletal muscles of the tail. Microscopical evaluation revealed neoplastic mast cells in the skin, liver, kidneys, skeletal muscles, bones, spleen, uterus, ovaries and lungs. Exfoliative cytological, histopathological and ultrastructural features were consistent with systemic mastocytosis. Neoplastic proliferative disorders of mast cells are rare in reptiles and this is the first report of mast cell neoplasia in geckos.

Role of estrogen in the regulation of spermatogenesis in the Indian wall lizard Hemidactylus flaviviridis

The role of estrogen in the Indian wall lizard, Hemidactylus flaviviridis during PMSG induced spermatogenesis in the regression phase and during normal spermatogenesis in the active breeding phase was investigated. Blood hormone levels demonstrated a high testosterone to estrogen ratio in the breeding and vice verse during the regressed phase. PMSG treatment (30 IU in 100 μl saline/lizard/alternate day for 30 days) during the regressed phase stimulated spermatogenesis which was associated with a significant (p<0.001) rise in plasma testosterone levels. Complete spermatogenesis with sperms was resolved in many tubular sections. However, co-administration of PMSG plus estrogen in high doses (2 μg of estradiol benzoate/alternate day) for the same period not only curtailed germ cell proliferation significantly but also induced apoptosis in germ cells. There was no significant reduction in testicular weight but sperms were found completely absent in all the tubules. Decline in the plasma testosterone was more pronounced in high compared to low estrogen treated groups. Further, low estrogen administration had little effect either on raising the plasma levels of estrogen or subsequently on spermatogenesis which was identically observed in the breeding phase too. Estrogen intervention (2 μg) in the breeding phase also profoundly suppressed spermatogenesis leading to a severe depletion in germ cells. Simultaneously, there was a significant rise in germ cell apoptosis which was associated with an up-regulation of extrinsic (caspase 8, Fas, FasL) and intrinsic (caspase 9, Bax, Bcl2) markers in these cells. Taken together, the above data indicate that the estrogen plays a key role in regulating spermatogenesis in the wall lizard retarding it during testicular quiescence and eliminating germ cells through apoptosis during the active breeding phase.

The mast cell: an evolutionary perspective

This review article is an attempt to trace the evolution of mast cells (MCs). These immune cells have been identified in all vertebrate classes as single-lobed cells containing variable amounts of membrane-bound secretory granules which store a large series of mediators, namely histamine, proteases, cytokines and growth factors. Other MC features, at least in mammals, are the c-kit receptor for the stem cell factor and the high-affinity receptor, FcepsilonRI, for immunoglobulin E (IgE). The c-kit receptor also has been identified in fish MCs. The FcepsilonRI receptor seems to be a more recent acquisition in MC phylogenesis given that IgE originated in mammalian species. Tryptase and histamine have also been recognized in MCs of teleost fish. Thus, a cell population with the overall characteristics of higher vertebrate MCs is identifiable in the most evolutionarily advanced fish species. Two potential MC progenitors have been identified in ascidians (urochordates which appeared approximately 500 million years ago): the basophil/MC-like granular haemocyte and the test cell. Both contain histamine and heparin, and provide defensive functions. Some granular haemocytes in Arthropoda also closely approximate the ultrastructure of modern MCs. The origin of MCs is probably to be found in a leukocyte ancestor operating in the context of a primitive local innate immunity and involved in phagocytic and killing activity against pathogens. From this type of defensive cell, the MC phylogenetic progenitor evolved into a tissue regulatory and remodelling cell, which was incorporated into the networks of recombinase activating genes (RAG)-mediated adaptive immunity in the Cambrian era, some 550 million years ago. Early MCs probably appeared in the last common ancestor we shared with hagfish, lamprey and sharks about 450-500 million years ago.

Hematopoietic prostaglandin D2 synthase in the chicken Harderian gland

The Harderian gland (HG), a sero-mucous secreting organ in the eye orbit, has long been recognized as immunologically important in chickens. During experimentation to characterize immune components of the gland, proteomics analysis revealed the presence of hematopoietic prostaglandin D synthase (H-PGDS). Extraction of total RNA followed by RT-PCR produced cDNA of 597 base pairs. DNA sequencing revealed nucleic acid and predicted amino acid sequences that were 99% aligned with the one published sequence for chicken H-PGDS of the spleen. Alignment with murine, rat, and human H-PGDS were 69, 69, and 66%, respectively. Ocular vaccination of chickens with a Newcastle Disease/Infectious Bronchitis vaccine (Mass.-Ark. Strain) induced an increase in H-PGDS expression determined by real-time PCR. Furthermore, immunohistochemistry of frozen HG sections showed positive stained cells for both H-PGDS and mast cell tryptase in the sub-epithelial cell layers of the HG ducts. Based on the potent vasoactive role of PGD(2), it appears that the chicken HG is a site of active mucosal immunity partially mediated by PGD(2) synthesized by H-PGDS in the gland.

Effects of 17alpha-ethinylestradiol on immune parameters in the lizard Sceloporus occidentalis

We examined the effect of 17alpha-ethinylestradiol on immunity of the Western fence lizard, Sceloporus occidentalis. Injection of 17alpha-ethinylestradiol resulted in dose-dependent suppression of peripheral blood leukocyte levels as determined by cell counts, whereas total spleen cell levels were decreased only at higher doses of 17alpha-ethinylestradiol. In contrast, spleen cell proliferation was enhanced by 17alpha-ethinylestradiol as measured by reduction of MTT to formazan following a two-way mixed lymphocyte reaction. Antibody responses were unaffected. Effects on peripheral blood leukocyte levels and spleen cell proliferation similar to those observed in response to injection of 17alpha-ethinylestradiol were observed following injection of a single dose of hydrocortisone. However, injection of lizards with 17alpha-ethinylestradiol did not result in a significant increase in serum cortisol. Results of this study suggest that exposure of Western fence lizards to 17alpha-ethinylestradiol leads to decreased numbers of circulating leukocytes and total spleen cell numbers and the enhancement of spleen cell proliferation in a two-way mixed lymphocyte reaction. These effects probably involve mechanisms other than or in addition to the induction of cortisol release.

Morphology of the Harderian gland of the Gecko, Tarentola mauritanica

The Harderian gland of the gecko, Tarentola mauritanica, was studied at the histological, histochemical, and ultrastructural levels. It is a nonlobate compound acinar gland surrounded by a thin capsule of connective tissue. Numerous connective tissue-type mast cells, ultrastructurally similar to those described in other higher vertebrates, were identified in the interstitial tissue between the acini. Pyramidal or columnar-shaped secretory glandular cells were observed in the acini. In the glandular cells, two types of structures could be distinguished on the basis of their high or low electron density. Lipid droplets were found in the cytoplasm of the Harderian gland of both sexes. Histochemical tests showed that the Harderian gland of the gecko is a seromucous gland. The secretion is essentially merocrine, although an apocrine type of secretion is sometimes observed.