The adenohypophysis of Mediterranean yellowtail, Seriola dumerilii (Risso, 1810): an immunocytochemical study

Expression of Tshb and Tshr in the ricefield eel Monopterus albus: Potential paracrine/autocrine roles in gonads

Thyroid stimulating hormone (TSH), a glycoprotein synthesized and secreted from thyrotrophs of the pituitary gland, is composed of a glycoprotein hormone common alpha subunit (CGA) and a specific beta subunit (TSHB). The major biological function of TSH is to stimulate thyroidal follicles to synthesize and secrete thyroid hormones through activating its cognate receptor, the thyroid stimulating hormone receptor (TSHR). In the present study, polyclonal antisera against ricefield eel Tshb and Tshr were generated respectively, and the expression of Tshb and Tshr was examined at mRNA and protein levels. RT-PCR analysis showed that tshb mRNA was expressed mainly in the pituitary as well as in some extrapituitary tissues including the ovary and testis. Tshr mRNA was also expressed in a tissue-specific manner, with transcripts detected in tissues including the kidney, ovary, and testis. The immunoreactive Tshb signals in the pituitary were shown to be localized to the inner areas of adenohypophysis which are close to the neurohypophysis of adult ricefield eels. Tshb-immunoreatvie cells in the pituitary of ricefield eel larvae were firstly observed at hatching. The expression of immunoreactive Tshb and Cga was also detected in ricefield eel ovary and testis together with Tshr. In the ovary, immunoreactive Tshb, Cga, and Tshr were observed in oocytes and granulosa cells. In the testis, immunoreactive Tshb was mainly observed in Sertoli cells while immunoreactive Cga and Tshr were detected in germ cells as well as somatic cells. Results of the present study suggest that Tsh may be synthesized both in the ovary and testis locally, which may play paracrine and/or autocrine roles in gonadal development in ricefield eels.

Functional and developmental heterogeneity of pituitary lactotropes in medaka

In fish, prolactin-producing cells (lactotropes) are located in the anterior part of the pituitary and play an essential role in osmoregulation. However, small satellite lactotrope clusters have been described in other parts of the pituitary in several species. The functional and developmental backgrounds of these satellite clusters are not known. We recently discovered two distinct prolactin-expressing cell types in Japanese medaka (Oryzias latipes), a euryhaline species, using single cell transcriptomics. In the present study, we characterize these two transcriptomically distinct lactotrope cell types and explore the hypothesis that they represent spatially distinct cell clusters, as found in other species. Single cell RNA sequencing shows that one of the two lactotrope cell types exhibits an expression profile similar to that of stem cell-like folliculo-stellate cell populations. Using in situ hybridization, we show that the medaka pituitary often develops additional small satellite lactotrope cell clusters, like in other teleost species. These satellite clusters arise early during development and grow in cell number throughout life regardless of the animal's sex. Surprisingly, our data do not show a correspondence between the stem cell-like lactotropes and these satellite lactotrope clusters. Instead, our data support a scenario in which the stem cell-like lactotropes are an intrinsic stage in the development of every spatially distinct lactotrope cluster. In addition, lactotrope activity in both spatially distinct lactotrope clusters decreases when environmental salinity increases, supporting their role in osmoregulation. However, this decrease appears weaker in the satellite lactotrope cell clusters, suggesting that these lactotropes are regulated differently.

Pituitary multi-hormone cells in mammals and fish: history, origin, and roles

The vertebrate pituitary is a dynamic organ, capable of adapting its hormone secretion to different physiological demands. In this context, endocrinologists have debated for the past 40 years if endocrine cells are mono- or multi-hormonal. Since its establishment, the dominant "one cell, one hormone" model has been continuously challenged. In mammals, the use of advanced multi-staining approaches, sensitive gene expression techniques, and the analysis of tumor tissues have helped to quickly demonstrate the existence of pituitary multi-hormone cells. In fishes however, only recent advances in imaging and transcriptomics have enabled the identification of such cells. In this review, we first describe the history of the discovery of cells producing multiple hormones in mammals and fishes. We discuss the technical limitations that have led to uncertainties and debates. Then, we present the current knowledge and hypotheses regarding their origin and biological role, which provides a comprehensive review of pituitary plasticity.

3D Atlas of the Pituitary Gland of the Model Fish Medaka (Oryzias latipes)

In vertebrates, the anterior pituitary plays a crucial role in regulating several essential physiological processes via the secretion of at least seven peptide hormones by different endocrine cell types. Comparative and comprehensive knowledge of the spatial distribution of those endocrine cell types is required to better understand their physiological functions. Using medaka as a model and several combinations of multi-color fluorescence in situ hybridization, we present the first 3D atlas revealing the gland-wide distribution of seven endocrine cell populations: lactotropes, thyrotropes, Lh and Fsh gonadotropes, somatotropes, and pomca-expressing cells (corticotropes and melanotropes) in the anterior pituitary of a teleost fish. By combining in situ hybridization and immunofluorescence techniques, we deciphered the location of corticotropes and melanotropes within the pomca-expressing cell population. The 3D localization approach reveals sexual dimorphism of tshba-, pomca-, and lhb-expressing cells in the adult medaka pituitary. Finally, we show the existence of bi-hormonal cells co-expressing lhb-fshb, fshb-tshba and lhb-sl using single-cell transcriptomics analysis and in situ hybridization. This study offers a solid basis for future comparative studies of the teleost pituitary and its functional plasticity.

Morphological and immunohistochemical comparison of the pituitary gland between a tropical Paracheirodon axelrodi and a subtropical Aphyocharax anisitsi characids (Characiformes: Characidae)

ABSTRACT Cardinal tetra Paracheirodon axelrodi and bloodfin tetra Aphyocharax anisitsi are two species of characids with high trade value as ornamental fish in South America. Although both species inhabit middle water layers, cardinal neon exhibits a tropical distribution and bloodfin tetra a subtropical one. Generally, these species are difficult to grow, so it becomes essential to know some key components of the neuroendocrine system to achieve their reproduction in captivity. Considering the importance of deepening the knowledge of the reproductive physiology through functional morphology, for the first time in this work we performed an anatomical, morphological and immunohistochemical analysis of the pituitary gland of these two species. In both species, a leptobasic type pituitary is found in the ventral zone of the hypothalamus and it is characterized by a neurohypophysis which has a well-developed pituitary stalk and a globular adenohypophysis. The pituitary components, characterized by histochemistry and immunohistochemistry, shows a distribution pattern of cells types similar to other teleost species, with only slight differences in the distribution of βFSH and βLH for P. axelrodi.

Characterization of gonadotropic cells during continuous and seasonal spermatogenesis of two freshwater fish species: a histochemical and immunohistochemical study

This work describes gonadotropic (GtH) cells and their morphological and immunohistochemical changes during the spermatogenic cycle of Serrasalmus maculatus (continuous spermatogenesis) and Pimelodus maculatus (seasonal spermatogenesis). GtH cells, widely distributed in the proximal pars distalis of the adenohypophysis, were characterized as round-shaped cells with eccentric nucleus, and cytoplasm with basophilic secretory granules and a variable number of vacuoles for both species. Immunohistochemistry against β-follicle-stimulating hormone (Fsh) and β-luteinizing hormone (Lh) in adjacent sections showed two separated GtH-producing cell populations, and a third population where both GtHs are expressed in the same cell for both species. In the seasonal spermatogenesis of P. maculatus, GtH cells seemed to be more abundant during developing and spawning capable phases. In contrast, no cyclic changes were detected in the continuous spermatogenesis of S. maculatus, except for the strong immunoreaction for Fsh and Lh in males with intense spermiogenesis. We conclude that changes reported here might reflect the type of spermatogenic cycle (seasonal or continuous) which are under different regulatory mechanisms (environmental and internal cues) controlling the reproduction in these species.

Immunohistochemical study of pituitary cells in wild and captive Salminus hilarii (Characiformes: Characidae) females during the annual reproductive cycle

Freshwater fish that live exclusively in rivers are at particular risk from fragmentation of the aquatic system, mainly the species that migrate upriver for reproduction. That is the case of Salminus hilarii, an important migratory species currently classified as "almost threatened" in the São Paulo State (Brazil), facing water pollution, dam construction, riparian habitat destruction and environmental changes that are even more serious in this State. Additionally, this species show ovulation dysfunction in captivity. Our studies focused on the identification and distribution of the pituitary cell types in the adenohypophysis of S. hilarii females, including a morphometric analysis that compares pituitary cells from wild and captive broodstocks during the reproductive annual cycle. The morphology of adenohypophysial cells showed differences following the reproductive cycle and the environment. In general, optical density suggested a higher cellular activity during the previtellogenic (growth hormone) and vitellogenic (somatolactin) stages in both environments. Additionally, the nucleus/cell ratio analysis suggested that growth hormone and somatolactin cells were larger in wild than in captive females in most reproductive stages of the annual cycle. In contrast, prolactin hormone showed no variation throughout the reproductive cycle (in both environments). Morphometrical analyses related to reproduction of S. hilarii in different environmental conditions, suggest that somatolactin and growth hormone play an important role in reproduction in teleost and can be responsible for the regulation of associated processes that indirectly affect reproductive status.

Immunocytochemical identification of adenohypophyseal cells in the pirarucu (Arapaima gigas), an Amazonian basal teleost

The adenohypophysis (AH) of juvenile pirarucu (Arapaima gigas), a representative species of the Osteoglossomorpha (bonytongue fishes, one of the oldest living groups of the teleosts), was studied using histochemical and immunocytochemical methods. The AH is comprised of the pars distalis (PD), without a clear distinction between rostral pars distalis (RPD) and proximal pars distalis (PPD), and the pars intermedia (PI). The neurohypophysis (NH) is positioned on top of the PD and penetrates and branches into the PI. In the most rostral dorsal portion of the PD, adrenocorticotropic cells and fusiform gonadotropic cells were found. In the central PD, scarce prolactin-producing cells and growth-hormone-producing cells were located mainly in the dorsal part, whereas round gonadotropic cells were abundant in the ventral portion of this region. Human thyrotropin immunoreactive cells were not found in the entire AH. In the PI, melanotropic, some adrenocorticotropic, and somatolactin-producing cells were located intermingled surrounding the neurohypophyseal branches. Our results showed that the A. gigas pituitary has some basal characteristics between the ancient Actinopterygii and the more derived teleosts.

A systematic immunohistochemical survey of the distribution patterns of GH, prolactin, somatolactin, beta-TSH, beta-FSH, beta-LH, ACTH, and alpha-MSH in the adenohypophysis of Oreochromis niloticus, the Nile tilapia

Fish pituitary plays a central role in the control of growth, development, reproduction and adaptation to the environment. Several types of hormone-secreting adenohypophyseal cells have been characterised and localised in diverse teleost species. The results suggest a similar distribution pattern among the species investigated. However, most studies deal with a single hormone or hormone family. Thus, we studied adjacent sections of the pituitary of Oreochromis niloticus, the tilapia, by conventional staining and immunohistochemistry with specific antisera directed against growth hormone (GH), prolactin (PRL), somatolactin (SL), thyrotropin (beta-TSH), follicle-stimulating hormone (beta-FSH), luteinising hormone (beta-LH), adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (alpha-MSH). The pituitary was characterised by a close interdigitating neighbourhood of neurohypophysis (PN) and adenohypophysis. PRL-immunoreactive and ACTH-immunoreactive cells were detected in the rostral pars distalis. GH-immunoreactive cells were present in the proximal pars distalis (PPD). A small region of the PPD contained beta-TSH-immunoreactive cells, and beta-LH-immunoreactive cells covered approximately the remaining parts. Centrally, beta-FSH-immunoreactive cells were detected in the vicinity of the GH-containing cells. Some of these cells also displayed beta-LH immunoreactivity. The pars intermedia was characterised by branches of the PN surrounded by SL-containing and alpha-MSH-immunoreactive cells. The ACTH and alpha-MSH antisera were observed to cross-react with the respective antigens. This cross-reactivity was abolished by pre-absorption. We present a complete map of the distinct localisation sites for the classical pituitary hormones, thereby providing a solid basis for future research on teleost pituitary.

Production, characterization and applications of mouse anti-grass carp (Ctenopharyngodon idellus) growth hormone monoclonal antibodies

Mouse anti-grass carp growth hormone (gcGH) monoclonal antibody (MAb) secretors were produced by PEG-mediated fusion of NS-1 myeloma cells and splenic B-lymphocytes of gcGH hyper-immunized mice. Positive secretors were screened by direct ELISA and cloned by limiting dilution. Three positive secretors, 21D3, 22G5 and 23B3, were obtained in a single fusion trial. Anti-gcGH MAbs were produced by growing hybridomas in the peritoneal cavity of pristane-primed mouse. The three MAbs were isotyped to be IgG2a, IgG2b and IgM, respectively. IgG MAbs were purified from ascitic fluid by Hitrap protein G column and IgM MAb was purified by gel filtration chromatography. The purified MAbs were highly specific and had moderate binding affinity. The MAbs were successfully used for the purification of native gcGH from mature grass carp pituitary extract by one-step immunoaffinity chromatography, for the quantification of gcGH by competitive sandwich ELISA, and for the probing of somatotropes in grass carp pituitary by immunohistochemistry.

Growth hormone expression in ontogenic development in gilthead sea bream

The pattern of expression of the growth hormone (GH) gene was studied during the early development of gilthead sea bream ( Sparus aurata). The GH transcript was detected from the 2nd day of the larval stage onwards. In the next stages the expression level fluctuated, possibly due to different regulatory factors. The distribution of GH mRNA studied by in situ hybridization (ISH) was found to be pituitary specific. Hybridization signals for GH mRNA were detected for the first time in 4-day-old larvae. Throughout development the cells that express GH mRNA were mainly located in the proximal pars distalis. Mammosomatotroph cells coexpressing GH and PRL were not detected in juveniles or adults. Moreover, the possible involvement of GH in asynchronic growth in cultivation of gilthead sea bream was also examined by ISH. No differences in the distribution of GH cells were observed in the three sizes of juveniles of gilthead sea bream studied. These results suggest that the transcription of GH is involved in the early developmental stages of sea bream and the asynchronous growth-related changes are not due to distinct distribution of GH cells.

Immunocytochemical characterization of adenohypophyseal cells in the greater weever fish (Trachinus draco)

The adenohypophysis of the greater weever fish (Trachinus draco) was studied using histochemical and immunocytochemical methods. The adenohypophysis comprised the rostral pars distalis (RPD), the proximal pars distalis (PPD), and the pars intermedia (PI). Neurohypophysis showed a patent hypophyseal stalk which was divided into several branches intermingled with the adenohypophysis. Salmon prolactin (PRL)-immunoreactive (ir) cells, arranged in follicles, resided in the RPD and the most rostral part of the ventral PPD. Human adrenocorticotropin (ACTH)-ir cells were located in the RPD between PRL-ir cells and the neurohypophyseal processes. Salmon and seabream somatotropin (GH)-ir cells were located in both the dorsal and the ventral PPD. Some GH-ir cells were seen in surrounding and in contact with neurohypophyseal branches, whereas other isolated or clustered GH-ir cells were embedded in adenohypophyseal cells of the PPD. In addition, isolated or clustered GH-ir cells were also detected in the tissue of the PPD covering the most rostral part of PI. Only one class of salmon and carp gonadotropin (GTH)-ir cells was detected. Isolated or clustered GTH-ir cells resided in both the dorsal and the ventral PPD and were seen surrounding the PI and in the tissue of the PPD covering the most rostral part of PI. In addition, a few scattered GTH-ir cells were observed in the ventral RPD. Scattered groups of thyrotropin (TSH)-ir cells were present in the anteroventral PPD. Salmon and seabream somatolactin (SL)-ir and bovine melanotropin (MSH)-ir cells were intermingled surrounding the neurohypophyseal tissue. SL-ir cells were negative to periodic acid-Schiff technique. MSH-ir cells showed a very weak immunoreactivity to anti-human ACTH((1-24)) serum. In addition to the PI location, few isolated or clustered SL- and MSH-ir cells were observed in the dorsal PPD.

Differential expression and cellular localization of somatolactin-1 and -2 during early development in the gilthead sea bream

The patterns of expression of the somatolactin 1 and 2 (SL1 and SL2) transcripts were studied during the early development of the gilthead sea bream (Sparus aurata). Gene expression of SL1 and SL2 were detected in embryos and in larvae, although both transcripts presented different levels of expression. The SL1 transcripts in contrast to the SL2 transcripts presented high expression levels in embryos and younger larvae. Moreover, the SL2 transcripts were slightly present or absence in embryonic stage and the newly hatched larvae, respectively. The differences in the expression levels of SL1 and SL2 in embryos and larvae may be due to the fact that two distinct genes express both isoforms of the protein. Thus, both SLs may play different physiological roles throughout development. Moreover, the hybridization signals for SL1- and SL2-mRNAs were detected in 4-day-old larvae. Both in larvae and adults the somatolactotroph cells co-expressed both transcripts of SL and were located bordering the neurohypophysis in the pars intermedia.

Immunocytochemical applications of specific antisera raised against synthetic fragment peptides of mummichog GtH subunits: examining seasonal variations of gonadotrophs (FSH cells and LH cells) in the mummichog and applications to other acanthopterygian fishes

Two distinct types of gonadotrophs, FSH (GtH I) cells and LH (GtH II) cells, were immunocytochemically identified from mummichog (Fundulus heteroclitus; Cyprinodontiformes, Acanthopterygii) pituitary using antisera raised against synthetic fragment peptides of FSHbeta and LHbeta. Both cell types were abundant during the spawning period (spring and early summer) and decreased in number during the post-spawning immature period. The number of FSH cells increased again during the early phases of gonadal development (cortical alveoli accumulation in the oocytes and basal spermatogenesis) in early winter, whereas the number of LH cells did not. Only FSH cells were abundant during the latter phases of gonadal development (vitellogenesis and active spermatogenesis) in early spring. These observations suggest that both GtHs have important yet different roles for reproduction in this species. Antisera against the conservative region of the FSHbeta and the LHbeta subunits immunostained FSH cells and LH cells, respectively, also in red seabream (Pagrus major; Perciformes, Acanthopterygii) and small mouth bass (Micropterus dolomieu; Perciformes, Acanthopterygii), suggesting the possibility of their use for other acanthopterygian fishes.

Functional changes of the LH-immunoreactive cells in adenohypophysis of the common carp (Cyprinus carpio) from rivers contaminated with estrogenic chemicals

The adverse effect of estrogenic chemicals on luteinizing hormone-immunoreactive (LH-ir) cells in the adenohypophysis of common carp (Cyprinus carpio) was examined using immunocytochemical and morphometric methods. Adult male fish were collected from two contaminated sites (Ishizu and Wada Rivers) and from a control pond at Agriculture, Food and Environmental Sciences, Research Center of Osaka Prefecture. The concentration of nonylphenol, bisphenol A and 17beta-estradiol in the Ishizu River was 3-4 times higher than that in the Wada River. The proportion and size of LH-ir cells were evaluated using the point-counting method by optical microscopy. In control carp, the proportion of LH-ir cells in the breeding season was significantly lower than in the pre- and post-breeding seasons. The same tendency was also found in Ishizu and Wada River carp, but without statistical significance. The proportion of LH-ir cells in Ishizu River carp was significantly lower than that of the control and the Wada River in all seasons. The LH-ir cells in control carp increased in size in the breeding season. LH-ir cells in Ishizu River carp were significantly (p<0.05) smaller than those in control fish, but not different from Wada River carp. A disturbance in the secretory function of LH-ir cells was found in carp from the Ishizu River; granulation and vacuolation were not in synchronization with those of control and Wada River fish. Our data suggest that the estrogenic chemicals in the Ishizu River interfere with functions of LH-ir cells directly or through the testis.

Immunocytochemical studies on the pituitary gland of Anguilla anguilla L., in relation to early growth stages and diet-induced sex differentiation

Mammalian and teleost antisera against pituitary hormones were used to identify and localize pituitary cell types in the European eel (Anguilla anguilla L.). The investigation was conducted on unpigmented glass eels of 5.6-6.2 of total body length (L(T)) caught in river mouths, then on yellow eels reared from the pigmented glass eel (or elver) stage up to 12-14 cm of L(T), in an eel farm in warm freshwater. Treated elvers were fed with commercial paste food supplemented with mature carp ovaries, containing oestradiol, that induced an early ovarian differentiation and a higher growth rate. The antisera detected seven types of immunoreactive (ir) cells, six of which were already found in glass eel adenohypophysis, suggesting differentiation of these cell types during the leptocephalus stage. In 12-14 cm treated yellow eels with small ovaries, a seventh type (ir-GtH) was detected in the proximal pars distalis; in the same animals the ir-TSH cells increased in number and size. From unpigmented glass eels to 12-14 cm yellow eels, the whole pituitary volume of controls increased nearly four times, while that of treated ones increased nearly six times. The larger volume of pituitary in treated eels was mainly due to volume increase of proximal pars distalis and rostral pars distalis. The %GH, that is the potential index of GH production, was significantly higher in treated yellow eels with gonads differentiating into ovaries than in controls; no difference was detected in %PRL between treated and control eels. The above results strongly suggest that in eels the feminizing effects of oestrogen is first exerted on the pituitary, probably through the hypothalamus, and later on the gonads.

Identification and localization of eight distinct hormone-producing cell types in the pituitary of male Atlantic halibut (Hippoglossus hippoglossus L.)

The eight distinct hormone-producing cell types in the adenohypophysis of male Atlantic halibut (Hippoglossus hippoglossus L.) were identified and localized using immunohistochemistry and in situ hybridization. Lactotropes either occupied most of the rostral pars distalis (RPD) or they were arranged in follicular structures located along the periphery of the RPD. Corticotropes were confined to a thin layer of RPD cells bordering the pars nervosa (PN). The somatotropes were arranged in multicellular layers bordering the highly convoluted PN penetrating the proximal pars distalis (PPD), while thyrotropes, scattered in small islets in between the somatotropes, were located in the centro-dorsal part of the PPD. Gonadotropes were found throughout the PPD. Immunoreactivity to glycoprotein-alpha and luteinizing hormone beta-subunit was also observed along the periphery of the pars intermedia (PI), indicating that a thin extension of the PPD surrounded the PI. In situ hybridization showed that follicle-stimulating hormone and luteinizing hormone were produced in distinct cells of the PPD. PI contained somatolactotropes bordering the highly convoluted PN, and melanotropes that showed positive immunostaining against both anti-alpha-melanocyte-stimulating hormone and anti-beta-endorphin. The general cellular organization was similar to that of other teleost fish. These results lay the basis for future investigations on Atlantic halibut pituitary physiology.

Investigation into the duality of gonadotropic cells of Mediterranean yellowtail (Seriola dumerilii, Risso 1810): immunocytochemical and ultrastructural studies

Two antisera against the follicle-stimulating hormone-like gonadotropin (FSH) of Mediterranean (M.) yellowtail, anti-My FSHa and anti-My FSHb, were obtained. Anti-My FSHa serum specifically recognized FSH cells and did not react with any other pituitary cell type, while anti-My FSHb serum recognized the alpha-subunit of the pituitary glycoprotein hormones and immunostained FSH, luteinizing hormone-like gonadotropin (LH), and thyrotropin (TSH) cells. Anti-My FSHa serum, together with a previously obtained anti-My LHbeta serum, were used to further investigate the duality of gonadotropic cells in M. yellowtail by light and electron microscopic immunocytochemistry; three immunologically different gonadotropic cell populations expressing FSH, LH, or both hormones, were revealed. The three cell populations had the same regional distribution in the pituitary gland: the proximal pars distalis, including the thin ring surrounding the pars intermedia. However, while FSH cells were found isolated or forming small clusters, LH cells formed strands or compact groups, and were more numerous than FSH cells. FSH/LH cells were scarce. At the ultrastructural level, vesicular, granular, and intermediate FSH, LH, and FSH/LH cells were found; secretory granules and globules, on the one hand, or conspicuous dilated cisternae of rough endoplasmic reticulum (or both) predominated, respectively, in these cell types. The production of either FSH or LH, or both hormones, was not reflected in the ultrastructural features of gonadotropic cells. Thus, a single morphological cell type of varying ultrastructure depending on the functional stage seemed to encompass all gonadotropic cells in M. yellowtail. All forms of FSH, LH, and FSH/LH cells were found in involution.

Immunocytochemical demonstration of melanotropic and adrenocorticotropic cells from the gilthead sea bream (Sparus aurata L., Teleostei) by light and electron microscopy: an ontogenic study

In the pituitary of gilthead sea bream, Sparus aurata, melanotropic (MSH) and adrenocorticotropic (ACTH) cells were identified at the light and electron microscopic levels using rabbit anti-synthetic alphaMSH (MSH) and anti-human ACTH (1-24) (ACTH) sera. The distribution of these cell types was followed from hatching to 48 months. The techniques used included the peroxidase anti-peroxidase (PAP) method, conventional electron microscopy, and an immunogold technique. Using PAP, MSH (immunoreactive to both anti-MSH and anti-ACTH) and ACTH (immunoreactive to anti-ACTH) cells were detected from hatching onward. These cells were distinguished ultrastructurally in 1-day-old larvae. Immunogold labeling was first detected in MSH cells in 5-day-old larvae, while ACTH cells were only immunogold labeled in adults. In newly hatched larvae, MSH cells were located from the middle to the posterior region of the adenohypophysis, while ACTH cells were found in the dorsoanterior region, next to the hypothalamus. At this age, both cell types were scarce. As the fish developed, these cell types progressively increased in number: MSH cells made up a layer surrounding the neurohypophysis (NH) in the pars intermedia (pi), whereas ACTH cells bordered the developing NH in the rostral pars distalis (rpd). From 82 days onward, a few MSH cells were observed in the proximal pars distalis (ppd) next to the pi and some ACTH cells were seen in the ppd next to the rpd. In adult specimens, both MSH and ACTH cells were adjacent to the stellate cells and showed processes and synaptic-like structures. MSH cells exhibited numerous round secretory granules with a granular content and of varying electron density and compactness. These granules were immunogold labeled with anti-MSH serum. Electron-dense secretory granules near the Golgi complex immunoreacted with anti-MSH, anti-ACTH, or with both antisera. ACTH cells exhibited round secretory granules with a homogeneous, high electron-dense core and a narrow, clear halo. These granules immunoreacted with anti-ACTH serum. The main ultrastructural features that characterize the MSH and ACTH cells of adults appeared early during ontogeny. Involutive MSH and ACTH cells were only observed in adult specimens.

An immunocytochemical study of the pituitary gland of the white seabream (Diplodus sargus)

The adenohypophysis of the white seabream (Diplodus sargus) was studied using histochemical and immunocytochemical techniques. The adenohypophysis was composed of rostral pars distalis, proximal pars distalis and pars intermedia. Prolactin (anti-chum salmon prolactin positive) and adrenocorticotropic (anti-human ACTH positive) cells were found in the rostral pars distalis. Prolactin cells were organized into follicles, while ACTH cells were arranged in cords around neurohypophyseal tissue branches that penetrated the rostral pars distalis. In the proximal pars distalis, somatotropic (anti-chum salmon and anti-gilthead seabream growth hormone positive), gonadotropic (anti-chum salmon beta-gonadotrophin II and anti-carp beta-gonadotrophin II positive, but anti-chum salmon beta-gonadotrophin I negative) and thyrotropic (anti-human beta-thyrotropin positive) cells were observed. Growth hormone cells were restricted to the dorsal and ventral part of the proximal pars distalis. They were clustered or surrounded the neurohypophyseal branches. Only one type of gonadotrophin cell was identified and they were clustered or isolated in the proximal pars distalis. Scattered groups of thyrotropin cells were located throughout the proximal pars distalis. In the pars intermedia somatolactin (anti-chum salmon and anti-gilthead seabream somatolactin positive) and melanotropic (anti-alpha-melanotropic hormone positive) cells were localized. In addition, gonadotrophin cells surrounded the pars intermedia or distributed evenly between somatolactin and melanotropic hormone cells. Somatolactin cells were periodic acid-Schiff negative and surrounded the neurohypophyseal branches intermingled with melanotropic cells. These cells were also immunoreactive to anti-human ACTH antiserum.

Immunocytochemical identification of two distinct gonadotropic cells (GTH I and GTH II) in the pituitary of bluefin tuna, Thunnus thynnus

Immunocytochemical identification of GTH I and GTH II cells in the pituitary of the bluefin tuna (Thunnus thynnus) was performed using antisera specific for the common alpha-subunit and the two distinct beta-subunits of tuna (Thunnus obesus) GTH I and GTH II. Cells of the dorsal part of the proximal pars distalis (PPD), in close association with somatotrophs, displayed immunoreactivity of GTHIbeta. GTH IIbeta immunoreactivity was present in cells of the central part of the PPD and the external border of the pars intermedia. Anti-GTHalpha immunostained both GTH Ibeta- and GTH IIbeta-immunoreactive cells and also thyrotrophs. Both GTH Ibeta- and GTH IIbeta-immunoreactive cells were observed in immature bluefin tuna, although there were greater numbers of GTH IIbeta immunoreactive cells. These results suggest that GTH I and GTH II are synthesized in separate cells in the pituitary of the bluefin tuna. The localization and appearance of the two distinct gonadotropic cells of the tuna are compared with the salmonid arrangement.

Gonadotropic and thyrotropic cells from the Mediterranean yellowtail (Seriola dumerilii; Risso, 1810): immunocytochemical and ultrastructural characterization

BACKGROUND

Gonadotropins GTH I and GTH II from the pituitary of Mediterranean (M.) yellowtail (Seriola dumerilii) were isolated and characterized, and antisera to the whole GTH II molecule (anti-My alpha,betaGTH II) and to its beta-subunit (anti-My betaGTH II) were obtained. At the light microscopic level, anti-My alpha,betaGTH II reacted with My betaGTH II-immunoreactive cells (GTH II cells), thyroid-stimulating hormone (TSH) cells, and a third cell population, which could have been GTH I cells. The aim of this study was the ultrastructural characterization of GTH and TSH cells in M. yellowtail using the immunogold method in order to provide a basis for future research into reproduction of this species.

METHODS

Pituitaries from mature male and female specimens reared in captivity were dissected out and processed for electron microscopy. The immunogold method was carried out by using anti-My alpha,betaGTH II, anti-My alpha,betaGTH II preabsorbed with the alpha subunit of the M. yellowtail GTH (My alphaGTH-subunit), anti-My betaGTH II, anti-human (h) alpha,betaTSH, and anti-h betaTSH sera to reveal gonadotropic and thyrotropic cells.

RESULTS

M. yellowtail gonadotropic cells were very heterogeneous with regard to their size, shape, and ultrastructural features. Cells were found with numerous, round, variably electron-dense, secretory granules and globules; others were found with their cytoplasm occupied mostly by dilated cisternae of rough endoplasmic reticulum (RER) and scarce secretory granules; and other intermediate cell forms were found that showed varying proportions of secretory granules and dilated RER. The secretory granules and globules were immunogold labeled with anti-My alpha,betaGTH II, and the reaction was weaker in the latter. A similar immunogold-labeling pattern was found with anti-My betaGTH II and with anti-My alpha,betaGTH II preabsorbed with the My alphaGTH-subunit, although some cells that showed the same ultrastructural features described above were not immunogold labeled and could have been GTH I cells. Thyrotropic cells had small, round, secretory granules of medium or high electron density that were immunogold labeled with anti-My alpha,betaGTH II, anti-h alpha,betaTSH, and anti-h betaTSH sera, but not with anti-My betaGTH II or anti-My alpha,betaGTH II serum preabsorbed with the My alphaGTH-subunit. All of the cell forms described for gonadotropes and thyrotropes were also found in a state of involution.

CONCLUSIONS

Gonadotropes that are of a single morphological type but that vary in ultrastructure are present in the pituitary of captive M. yellowtail. GTH II- and putative GTH I-producing cells were distinguishable from one another and from TSH cells by their different reactions to anti-My alpha,betaGTH II, anti-My betaGTH II, and anti-My alpha,betaGTH II preabsorbed with the My alphaGTH-subunit.

An immunocytochemical study of pituitary cells of the Senegalese sole, Solea senegalensis (Kaup 1858)

Different antisera directed against mammalian and piscine pituitary hormones, as well as a battery of various conventional histochemical techniques (PAS, Alcian Blue pH 2.5, Bromophenol Blue) and lectins, were used to identify the different hormonal cell types in the pituitary of the Senegalese sole, Solea senegalensis. Prolactin and adrenocorticotrophic cells were located in the rostral pars distalis of the pituitary. Gonadotrophic, thyrotrophic and growth hormone cells were distributed in the proximal pars distalis, but gonadotrophic cells appear also at the border of the pars intermedia. Somatolactin cells, as well as alpha-melanotrophic cells were located in the pars intermedia of the Solea senegalensis pituitary. The PAS reaction was positive in somatolactin cells, which were unreactive with the lead-Haematoxylin technique, whereas melanotrophic cells were positive. Glycoproteins containing mannose and/or glucose, as well as N-acetyl-glucosamine and sialic acid sugar residues, are synthesized and secreted by gonadotrophic, thyrotrophic and somatolactin cells. Adrenocorticotrophic cells and, especially, the amphiphilic somatolactin and acidophilic growth hormone cells were stained with the Bromophenol Blue technique that identifies proteins in general, but adrenocorticotrophic and growth hormone cells were unreactive towards PAS, Alcian Blue pH 2.5 and lectins (Con A and WGA).

Immunocytochemical and ultrastructural characterization of melanotropin and adrenocorticotropin cells from the Mediterranean yellowtail (Seriola dumerilii, Risso 1810)

BACKGROUND

Melanotropin (MSH) and adrenocorticotropin (ACTH) are pituitary hormones derived from a common precursor: the proopiomelanocortin (POMC), which is processed differently in the melanotropic and corticotropic cells of several vertebrates. While ACTH is a major final product in corticotropes, it is further processed into alpha-MSH and corticotropin-like intermediate lobe peptide (CLIP) in melanotropes. Cells which are immunoreactive to ACTH (ACTH cells) and to both alpha-MSH and ACTH (MSH cells) have been described in a number of teleosts, including the Mediterranean yellowtail, by light microscopic immunocytochemistry. However, these cells have been ultrastructurally characterized only in a few species. In this paper, we use electron microscopy to identify and characterize the cells producing MSH and ACTH in M. yellowtail (Seriola dumerilii).

METHODS

Pituitaries from adult specimens were dissected and processed for conventional and immunocytochemical electron microscopy. An immunogold technique was performed using anti-synthetic alpha-MSH and anti-human (h) ACTH (1-24) sera.

RESULTS

MSH cells had round secretory granules with a granular content of varying electron density and compactness, which were immunogold-labeled with anti-alpha-MSH. Homogeneous and electron-dense secretory granules found in the Golgi area of these cells reacted with both anti-alpha-MSH and anti-hACTH (1-24). ACTH cells had round secretory granules with a homogeneous and medium or high electron-dense core and narrow clear halo, which were grouped in the cell area near the neurohypophysis (NH). Some granules showed an osmiophilic semicore in the medium electron-dense content, which has not been described in other teleost pituitary cells. Immunogold-labeling over the secretory granules only was obtained with all the antisera used. Some ACTH cells showed involutive features.

CONCLUSIONS

MSH and ACTH are respective final products of the POMC in two ultrastructurally different cells of the pituitary of M. yellowtail, MSH and ACTH cells. The immature granules in the Golgi area of MSH cells seem to be the site of proteolitic cleavage of ACTH into alpha-MSH and CLIP.

Immunocytochemical and ultrastructural characterization of prolactin, growth hormone, and somatolactin cells from the Mediterranean yellowtail (Seriola dumerilii, Risso 1810)

BACKGROUND

Prolactin (PRL), growth hormone (GH), and somatolactin (SL) are structurally related pituitary hormones that belong to a peptide family. Whereas growth hormone and prolactin are present in the hypophysis of all vertebrates, somatolactin, a recently discovered hormone, has been found only in fish. It has been demonstrated immunocytochemically in a few teleost species; ultrastructurally, cells producing this hormone have been characterized only in one species of salmon. In this paper, we identify and characterize ultrastructurally the cells producing these three hormones in Mediterranean yellowtail (Seriola dumerilii).

METHODS

Pituitaries from adult specimens were dissected out and processed for electron microscopy. The immunogold technique was performed in some ultrathin sections using fish primary antibodies.

RESULTS

PRL cells had round, peripherally distributed, very electron-dense, homogeneous secretory granules of variable size. GH cells had dense, round secretory granules with a conspicuous scalloped membrane, which were grouped in the cell area near the neurohypophysis. SL cells had round, polymorphic, or very irregularly shaped secretory granules, the last seeming to arise from the fusion of various secretory granules. The population of secretory granules varied greatly from one cell to another. In all cases, immunogold labeling was seen exclusively in the secretory granules. Exocytosis was observed in all cell types. Some of the PRL, GH, and SL cells showed involutive features.

CONCLUSIONS

PRL, GH, and SL, although structurally and functionally related, are secreted by ultrastructurally different cells in the pituitary of M. yellowtail.