The fine structural localization of acid phosphatase in the prolactin cell of the teleost pituitary following the stimulation and inhibition of secretory activity

Immunocytochemical and ultrastructural identification of adenohypophyseal cells in Ctenopharyngodon idella (Cypriniformes: Cyprinidae) during gonadal differentiation

The adenohypophysis was studied by immunocytochemical and ultrastructural methods in juvenile grass carp (Ctenopharyngodon idella) from natural reproduction in Northern Italian rivers. The adenohypophysis included the rostral pars distalis (RPD), the proximal pars distalis (PPD) and the pars intermedia (PI), all deeply penetrated by branches of the neurohypophysis (Nh). The prolactin (PRL), adrenocorticotropic (ACTH), somatotropic (GH), thyrotropic (TSH), gonadotropic type I (GtH I) and type II (GtH II), somatolactin (SL), melanotropic (MSH) and endorphin (END) cells were identified with antisera raised against piscine and human pituitary hormones. In juveniles of 51-69 mm of total body length (TL) with undifferentiated gonads, the PRL cells, arranged in thick strands, occupied most of the RPD. The ACTH and GH cells organized in cords bordering Nh were, respectively, confined to RPD and PPD. The TSH cells were scattered among ACTH cells in RPD and among GH cells in PPD. Cells simultaneously immunoreactive to anti-follicle stimulating hormone and to anti-croaker gonadotropin were intermingled among GH and TSH cells, which were mostly in the dorsal PPD. The SL cells were detected in PI layers bordering the Nh. The MSH and END cells were intermingled in PI and, unlike what observed in other teleosts, their respective antisera did not cross-react. In individuals of 78-112 mm TL with gonads at the beginning of differentiation, the GtH II cells were detected in PPD; all other cell types increased in number. These results, supported by ultrastructural investigations, suggest that SL and GtH II cells are directly involved in gonadal differentiation in C. idella.

Studies on secretory activity in the pars intermedia of Xenopus laevis 2: A biochemical and electron cytochemical investigation of acid hydrolase activity following the stimulation of secretory activity in vivo

In the MSH cell at the onset of secretory activity, acid hydrolase activity increases. This increased activity, shown quantitatively by assaying beta-glycerophosphatase and R-glucuronidase within the stimulated gland, has been shown by electron cytochemical methods for beta-glycerophosphatase (acid phosphatase) and aryl sulphatase to be related to the production of large numbers of dense bodies. Cytochemical evidence also supports the view that these lytic bodies arise from GERL-like cisternal elements since it is shown that in addition to the flattened, parallel Golgi cisternae these elements are also R-glycerophosphatase-positive. The similarities between the dense bodies and those of other cell types are described and discussed.

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.

Lysosomes in the cessation of vitellogenin secretion by the mosquito fat body; selective degradation of Golgi complexes and secretory granules

A massive and selective degradation of Golgi complexes, secretory granules, and RER is the mechanism responsible for the rapid termination of Vg secretion by trophocytes of the mosquito fat body. These cells are involved in an intensive synthesis of a glycoprotein, vitellogenin (Vg), which is accumulated by developing oocytes as yolk protein. Previously, assays for lysosomal enzymes have demonstrated that the cessation of Vg synthesis is characterized by a sharp increase in lysosomal activity; and fluorescent microscopy has shown that, during this intense lysosomal activity, Vg concentrates in lysosomes. In this report, electron microscopy combined with cytochemistry for lysosomal enzymes and localization of Vg with colloidal gold immunocytochemistry has shown that this lysosomal activity is directed towards selective degradation of Vg and organelles associated with its synthesis and secretion. Three organelles undergo lysosomal breakdown: the Golgi complex, Vg-containing secretory granules, and RER. The degradation of Golgi complexes occurs in two steps similar to that for RER: first, the organelle is sequestered by double isolation membranes, and the resulting pre-lysosome then fuses with a primary or secondary lysosome. In contrast, mature Vg-containing secretory granules fuse with lysosomes directly. This combination of crino- and autophagy is a specific, highly intense, and precisely timed event.

Cathepsin D coexists with renin in the secretory granules of juxtaglomerular epithelioid cells

Mature juxtaglomerular epithelioid cell secretory granules of the rat exhibit both renin- and cathepsin D-like immunoreactivity. On the basis of the coexistence with renin at a pH which, according to previous experiments, is probably in the range of that in lysosomes, cathepsin D is suggested to be involved in the regulation of the granular renin stores available for secretion.

Are the renin-containing granules of juxtaglomerular epithelioid cells modified lysosomes?

Mature secretory granules of epithelioid cells--the so-called renin granules--exhibit certain properties, which in this particular combination are expressed only by lysosomes: Renin granules have autophagic capabilities; they react to the application of lipidosis-inducing, lysosomotropic substances by the gradual accumulation of polar lipids; all secretory granules of epithelioid cells contain acid phosphatase until maturity; and exogenous tracers reach renin granules without labeling the Golgi complex. Several functional implications can therefore be considered. Hydrolytic enzymes, constitutive elements of the granule matrix, might either cleave inactive prorenin to yield active renin within the granules or, by unspecific hydrolysis of renin, participate in the regulation of the overall quantity of secretory product. Autophagic phenomena, the involvement of renin granules in the traffic of exogenous tracers, and the build-up of polar lipids following experimental interference with lipid catabolism indicate a large turnover of membrane material in renin granules. They also suggest that cytoplasmic and extracellular fluid gains access to the granule content and may thus be involved there in the regulation of biochemical reactions by changing the intragranular milieu or via signal molecules. In addition to the lysosome-like properties of epithelioid cell secretory granules, the secretory product, renin, as a carboxyl protease, is structurally related to other acidic proteases. In the case of cathepsin D, even functional similarities exist.

Secretory activity of Poecilia latipinna (Teleostei) pituitary in vitro: rostral pars distalis and proximal pars distalis

The ultrastructure of each adenohypophysial secretory cell type was examined in pituitaries of adult female mollies (Poecilia latipinna) after various periods in vitro, and with varied medium osmotic pressure (OP), Na+, and Ca2+ concentrations. Prolactin (PRL) cells were markedly activated by 18 hr, and after 7 or 14 days were almost totally degranulated, with massive arrays of Golgi and RER. Reduction in OP, but not Na+ or Ca2+, caused an additional activation of PRL cells after periods of 18 hr or longer. Corticotroph (ACTH) cells became noticeably activated by 4 hr, and were possibly affected by OP, but not Na+ or Ca2+. Growth hormone (GH) cells were activated by 6 hr, and after 18 hr were quite degranulated with extensive arrays of RER. OP had no effect on GH cells before 3 days, when reduced OP appeared to cause an additional activation, with the appearance of large irregular secretory granule (SG)-like inclusions. Na+ and Ca2+ again had no effect. Gonadotrophic (GtH) cells appeared to be little affected by in vitro incubation; however, the very active cells from vitellogenic fish underwent a reduction in dilated RER after prolonged culture. Thyrotrophic (TSH) cells gradually became activated in vitro, but the response again varied with the sexual condition of the fish. Neither GtH nor TSH cells were affected by OP, Na+, or Ca2+. The findings are discussed in relation to hypothalamic control, via releasing/inhibiting factors, of adenohypophysial cell activity.

Acid phosphatase activity and cell death in mouse thymus

The distribution of acid phosphatase activity in the thymus of young (8 week) and old (42 week) mice is presented. In 8 week old mice acid phosphatase positive cells represent 1.27 +/- 0.13% of the total population whereas in 42 week old mice, showing involution of the thymus, acid phosphatase positive cells represent 2.40 +/- 0.17% of the total population. Loci of free acid phosphatase activity have been interpreted as sites of cell lysis and death. This has been confirmed at electron microscope level where free acid phosphatase has been demonstrated in the cytoplasm of lysing thymic lymphocytes. Vacuolar sites of acid phosphatase activity have been demonstrated in macrophages which appear to dispose of the lymphocytes. Extensive autophagic activity occurs in the epithelial reticular cells. The role of acid phosphatase in thymic lymphocyte deletion and in the tissue dynamics of the thymus is discussed.

On the lysosomal function of juxtaglomerular granules

The presence of acid phosphatase, beta-glucuronidase and aryl sulfatase in juxtaglomerular cell granules (JGG) as well as the uptake and concentration of certain low molecular weight dyes by these granules have repeatedly suggested that they are akin to lysosomes. In the present experiments, rats were injected with three substances of widely different molecular weight and physicochemical properties--sucrose, iron sorbitol-citric acid complex (Jectofer) and horseradish peroxidase--that are well known to selectively concentrate in renal tubular cell lysosomes. None of these substances was found to enter the JGG to any significant degree, although both sucrose and Jectofer were evident in juxtaglomerular cells. Contrary to previous reports, thorium dioxide (Thorotrast) particles were not detected in the JGG after parenteral injection. These results indicate that JGG do not possess any significant lysosomal function and raise the question of the role of hydrolytic enzymes in the physiology of these granules.

The effects of starvation on the planarian worm Polycelis tenuis Iijima

Employing a combination of microscopical, biochemical and autoradiographic techniques, the primary effects of starvation on adult polycelis tenuis have been studied. Over a five week period of starvation there is on average a 32% decrease in the size of the organism. This decrease is contributed to by a reduction in mitosis and an increase in cell shrinkage autolysis and death. During starvation (following a sharp rise in RNA synthesis) there is a distinct sequence of events; four peaks of acid phosphatase activity can be resolved. The first is associated with the immediate response of the gastrodermis to feeding; the second (after 6 to 7 days) with increased autophagy and dedifferentiation in the gland cells and with muscle lysis of cells. The third peak (after 14 to 15 days) is contributed to largely by the lysis of cells in the gut and the fourth peak (after 25 to 26 days) is caused by an extensive lysis of the reproductive system. Fine structural changes involving increased intracellular vacuolation, autophagy, crinophagy, atrophy of muscle, increased intercellular space and loss of basement membrane matrix have been related to changes in enzyme pattern. Nerve cells appear unchanged throughout the first five weeks of starvation. Pigment and gland cells loose their characteristic granules, dedifferentiate and become morphologically similar to the undifferentiatied neoblasts. Dedifferentiation and the mechanisms involved in the survival of starvation are discussed.