Reproductive trade-offs in a long-lived bird species: condition-dependent reproductive allocation maintains female survival and offspring quality.

Life history theory is an essential framework to understand the evolution of reproductive allocation. It predicts that individuals of long-lived species favour their own survival over current reproduction, leading individuals to refrain from reproducing under harsh conditions. Here we test this prediction in a long-lived bird species, the Siberian jay Perisoreus infaustus. Long-term data revealed that females rarely refrain from breeding, but lay smaller clutches in unfavourable years. Neither offspring body size, female survival nor offspring survival until the next year was influenced by annual condition, habitat quality, clutch size, female age or female phenotype. Given that many nests failed due to nest predation, the variance in the number of fledglings was higher than the variance in the number of eggs and female survival. An experimental challenge with a novel pathogen before egg laying largely replicated these patterns in two consecutive years with contrasting conditions. Challenged females refrained from breeding only in the unfavourable year, but no downstream effects were found in either year. Taken together, these findings demonstrate that condition-dependent reproductive allocation may serve to maintain female survival and offspring quality, supporting patterns found in long-lived mammals. We discuss avenues to develop life history theory concerning strategies to offset reproductive costs.

Effect of the prolactin-release inhibitor quinagolide on lactating dairy cows.

In most mammals, prolactin (PRL) is essential for maintaining lactation, and yet the short-term suppression of PRL during established lactation by bromocriptine has produced inconsistent effects on milk yield in cows and goats. To assess the effect of the long-term inhibition of PRL release in lactating dairy cows, 5 Holstein cows in early lactation received daily intramuscular injections of 1mg of the PRL-release inhibitor quinagolide for 9 wk. Four control cows received the vehicle (water) only. During the last week of the treatments, one udder half was milked once a day (1×) and the other twice a day (2×). Blood samples were harvested at milking in wk -1, 1, 4, and 8. The daily injections of quinagolide reduced milking-induced PRL release but not the basal PRL concentration. Quinagolide induced a faster decline in milk production, which was about 5.3 kg/d lower in the quinagolide-treated cows during the last 4 wk of treatment. During wk 9, the inhibition of milk production by quinagolide was maintained in the udder half that was milked 2× but not in the half milked 1×. Milk production was significantly correlated with the quantity of PRL released at milking. Quinagolide did not affect the release of oxytocin at milking. Serum concentration of insulin-like growth factor-1 was not affected by treatment or correlated with milk production. Serum concentrations of leptin and the calciotropic hormone stanniocalcin were not affected by the treatment. In conclusion, the chronic administration of the PRL-release inhibitor quinagolide decreases milk production in dairy cows. The effect is likely the result of the reduced release of milking-induced PRL and is modulated at the level of the gland by milking frequency.

Expression and localization of stanniocalcin 1 in swine ovary.

Stanniocalcin 1 (STC 1) is a glycoprotein involved in mineral homeostasis and was first identified in fish. Its mammalian homologue has been implicated in the regulation of various biological processes, including angiogenesis and steroidogenesis both of which are fundamental events in ovarian function. Interestingly, the highest level of STC 1 expression in mammals occurs in ovarian tissue but no information is available on swine species. Therefore, the present study was undertaken to investigate the expression and the immunolocalization of STC 1 in swine ovary. In addition, we evaluated whether swine granulosa cells synthesize STC 1 and its possible modulation by hypoxia, a physiological condition in ovarian follicle growth. Our data show STC 1 for the first time in swine ovary; moreover, we demonstrate STC 1 production by granulosa cells, both in basal condition and in response to oxygen deprivation. The latter is suggestive of a potential modulatory role for STC 1 in hypoxia-driven angiogenesis.

Effect of milking frequency on lactation persistency and mammary gland remodeling in mid-lactation cows.

The objective of this study was to evaluate the effect of milking frequency on milk production and composition, mammary cell proliferation, apoptosis, and gene expression. For this investigation, 10 Holstein cows that were being milked twice a day in mid lactation were selected. To study the effect of differential milking, 2 quarters were milked once daily and the other 2 were milked thrice daily for 8wk. After that period, twice-daily milking was resumed for all quarters, and data were collected for an additional 6wk. Mammary gland biopsies were taken 1wk before differential milking (wk -1) and after 4 and 8wk of differential milking. Milk samples were collected weekly throughout the experiment. Once-daily milking resulted in an immediate reduction in milk yield, whereas thrice-daily milking resulted in an increase in milk yield. During differential milking, the daily milk yield of the quarters milked once daily declined by 0.54kg/wk, on average, but remained constant in the quarters milked thrice daily. Part of the difference in milk yield between the glands pairs persisted after twice-daily milking was reinitiated. In the quarters milked once daily, milk BSA concentration increased, indicating an increase in tight junction leakiness, and zymographic analysis of milk enzymes showed increased activity of several proteases. Reducing the milking frequency also increased mammary cell apoptosis and, surprisingly, mammary cell proliferation. Interestingly, milk concentrations of stanniocalcin-1 and insulin-like growth factor-I and mammary gland expression of several genes were also modulated by milking frequency. For example, expression of insulin-like growth factor I receptor was downregulated during once-daily milking. Last, expression of the short and long isoforms of the prolactin receptor and of CSN2 (beta-casein) were upregulated during thrice-daily milking. Taken together, these data suggest that milking frequency not only affects mammary gland remodeling and the expression of paracrine factors but also modulates hormone sensitivity.

Impact of postpartum milking frequency on the immune system and the blood metabolite concentration of dairy cows.

The transition from pregnancy to lactation is marked by metabolic, hormonal, and immunological changes that have an impact on the incidence of infectious and metabolic diseases. The aim of this study was to evaluate the effect on immune function and blood metabolite concentration of limiting milk production in early lactation to reduce negative energy balance. Twenty-two multiparous Holstein cows were milked either once a day (1x) or twice a day (2x) for the first week postpartum. All cows were milked twice daily for the rest of lactation. Blood concentrations of nonesterified fatty acids (NEFA), beta-hydroxybutyric acid (BHBA), calcium, bilirubin, urea, phosphorus, glucose, leptin, stanniocalcin-1, and 17beta-estradiol were determined in samples collected from 5 wk before scheduled calving to 5 wk after calving. Polymorphonuclear leukocytes (PMNL) were isolated from blood to conduct assays for chemotaxis, phagocytosis, and respiratory burst. Peripheral blood mononuclear cells (PBMC) were isolated to evaluate lymphocyte proliferation and cytokine production (tumor necrosis factor-alpha, IL-4, and interferon-gamma). Cows milked 1x produced 31% less milk than cows milked 2x during the first week of lactation. Over the following 13 wk of lactation, the milk production of cows milked 1x during the first week was 8.1% lower than for cows milked 2x. However, because the percentages of fat and protein were greater in the milk from 1x cows, the yields of milk components and energy-corrected milk were similar. Calving induced an increase in the concentrations of NEFA, BHBA, urea, and bilirubin. The increases in levels of NEFA and BHBA were greater in cows milked 2x than in cows milked 1x. During the same period, the serum glucose concentration decreased but remained greater in cows milked 1x. Serum calcium on d 4 and serum phosphorus on d 4 and 5 were greater in cows milked 1x. The differences between the 2 groups persisted beyond treatment until postpartum d 24 for NEFA and glucose and until postpartum d 14 for BHBA. After calving, the concentrations of leptin and stanniocalcin-1 decreased. During the first week postpartum, the decrease of leptin was less marked in cows milked 1x. The immune functions of PBMC and PMNL isolated from experimental cows and incubated using a standard medium did not show clear-cut peripartum immunosuppression. These variables were not significantly affected by the treatments, with the exception of interferon-gamma secretion, which was greater on d 5 and 14 in cows milked 1x. In conclusion, limiting milk production in early lactation had positive effects on metabolite concentration, but larger studies are necessary to establish if this could reduce disease incidence.

Local control of mammary involution: is stanniocalcin-1 involved?

There is considerable evidence to indicate the existence of local control of mammary gland involution, but the exact nature of this control has yet to be defined. Stanniocalcin-1 (STC-1) is a newly discovered mammalian hormone that seems involved in the lactation process and may be implicated in the control of involution. As a first step in investigating this hypothesis, the change in STC-1 levels in milk and serum was measured during drying off. Nine Holstein cows in late lactation were milked twice daily on half the gland, while the other half was left unmilked for a 14-d period. Milk and blood samples and mammary biopsies were taken on d -7, 1, 2, 7, and 14 relative to the onset of the nonmilking period. The concentrations of STC-1 in serum and milk were determined by RIA. The albumin concentration and proteinase activity of the milk were determined. Apoptosis of the mammary epithelium was quantified by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. Finally, the effects of milk on cellular activity and apoptosis were tested in vitro on mammary epithelial cells by measuring the turnover of tetrazolium salts and by counting the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells. The drying off of 2 quarters increased the milk production of the quarters that were milked by 30%. Milk proteinase activity and BSA and STC-1 concentrations increased in the nonmilked quarters, but remained unchanged in the milked quarters. Moreover, at d 2, the apoptotic rate of the mammary cells was higher in the nonmilked quarters than in the milked quarters (0.22 +/- 0.04 vs. 0.07 +/- 0.04%, respectively). Finally, in vitro experimentation demonstrated that mammary epithelial cells cultured in the presence of milk from involuting quarters had 3-fold more apoptotic cells as compared with those cultured in milk from the milked quarters at d 14. The metabolic rate was reduced by 14.6% for milk from d 7 and 23.6% for milk from d 14. Interestingly, the metabolic rate was negatively correlated with the STC-1 concentration in milk (r = -0.65). This study shows for the first time that STC-1 in milk is increased following milk stasis, although its exact role in the involution process remains to be clarified.

Effect of stage of lactation and parity on mammary gland cell renewal.

Milk production is a function of the number and activity of mammary epithelial cells, regardless of stage of lactation. Milk yield is generally higher in multiparous cows than in primiparous cows, but persistency is usually greater in the latter group. We compared several measures related to metabolic activity, apoptosis, and endocrine control of mammary cell growth in 8 primiparous and 9 multiparous cows throughout lactation. Mammary gland biopsies were taken in early [10 d in milk (DIM)], peak (50 DIM), and late (250 DIM) lactation to evaluate gene expression and determine DNA and fatty acid synthase (FAS) content. Milk samples taken the day before the biopsies were used to detect protease activities and to determine stanniocalcin-1 (STC) concentrations. Blood samples served to measure insulin-like growth factor-1, prolactin, and STC concentrations. Milk yield was higher in multiparous cows than in primiparous cows at the 10 DIM (32.8 +/- 1.3 and 25.2 +/- 0.8 kg/d) and 50 DIM (38.0 +/- 1.2 and 29.8 +/- 1.1 kg/d), but it was the same for both groups at 250 DIM (23.9 +/- 1.5 and 23.8 +/- 1.1 kg/d). Except for stearoyl-coenzyme A desaturase, expression of genes related to milk synthesis was not affected by stage of lactation. However, gene expression of acetyl-coenzyme A carboxylase, beta-casein, and FAS was lower in early lactation in primiparous cows. Expression of both proapoptotic bax and antiapoptotic bcl-2 genes was higher in primiparous cows, whereas the bax-to-bcl-2 ratio was not changed. Mammary DNA concentration was higher in multiparous cows, as was the amount of FAS protein in early lactation. Two bands of protease activity were found in milk samples, and one of the bands had an apparent molecular weight similar to gelatinase A and was dependent on the stage of lactation. Serum insulin-like growth factor-1 increased with day of lactation and was higher in primiparous cows. Serum prolactin decreased in late lactation, but peak values were observed in early lactation for primiparous cows and peak lactation for multiparous cows. Milk STC content increased with advancing lactation. The results are consistent with a lower degree of differentiation and a greater capacity for cell renewal in the mammary gland of primiparous cows.

Human stanniocalcin inhibits renal phosphate excretion in the rat.

Stanniocalcin (STC) is a glycoprotein hormone first identified in bony fishes where it counteracts hypercalcemia by inhibiting gill calcium uptake and stimulating renal inorganic phosphate (Pi) reabsorption. Human STC (hSTC) has recently been cloned and sequenced and is highly homologous to the fish hormone at the amino acid level. The objective of this study was to examine the possible effects of hSTC on electrolyte homeostasis and renal function in the rat. Recombinant hSTC was expressed in bacteria and purified by metal-ion affinity chromatography and reverse-phase high performance liquid chromatography. Anesthetized animals were given bolus infusions of 1, 5, or 10 nmol hSTC per kilogram of body weight. Control animals received solvent alone. The most effective dosage was 5 nmol/kg, which caused significant reductions in both absolute and fractional phosphate excretion in comparison with control rats. The hSTC had no effect on the renal excretion of other ions, the glomerular filtration rate, renal blood flow, blood pressure, or plasma electrolytes (Na+, K+, Ca2+, Pi, Mg/+). The maximum effect of hSTC on phosphate excretion was observed 60-80 minutes postinjection. Lesser effects were obtained with higher and lower dosages of hormone. When renal cortical brush-border membrane vesicles were isolated from control and hormone-treated animals 80 minutes postinjection, the rate of Na+/Pi cotransport was found to be 40% higher in vesicles from hormone-treated animals (p < 0.01; 5 nmol hSTC/kg). Together, the renal clearance and membrane vesicle data indicate that hSTC participates in the renal regulation of Pi homeostasis in mammals.

Development of a primary culture system for rainbow trout corpuscles of stannius and characterization of secreted teleocalcin.

A primary culture system has been established for rainbow trout corpuscles of Stannius (CS). A RIA has also been developed to monitor and characterize the teleocalcin secreted by these cultures. The primary cultured CS cells actively synthesized and secreted teleocalcin for up to 39 days when maintained in amphibian and mammalian culture media. Numerous teleocalcin cells were also evident after immunocytochemical staining of the CS cultures. When the cultures were labeled with L-[35S]methionine, de novo synthesized and secreted teleocalcin was judged to be a glycosylated protein on the basis of Concanavalin-A-Sepharose binding and was similar in size to the intracellular form of the hormone. This culture system may prove to be ideal for identifying those factors that regulate teleocalcin secretion.

Immunological studies on teleocalcin and salmon corpuscles of Stannius.

This report describes the characterization of an antiserum to salmon teleocalcin, a glycoprotein hormone that has recently been isolated from sockeye salmon, Oncorhynchus nerka, corpuscles of Stannius (CS). Immunodiffusion studies showed that teleocalcin was immunologically identical in four species of Pacific salmon. Histological staining of adjacent sections of sockeye salmon CS by periodic acid-Schiff reagent and immunocytochemistry revealed that the teleocalcin-immunoreactive cells were also periodic acid-Schiff positive. In bioassays using rainbow trout (Salmo gairdneri), the biological effects of teleocalcin were completely abolished by pretreatment with the antiserum before injection. The antiserum was ineffective by itself, however, in neutralizing endogenous teleocalcin. Immunoprecipitation studies of in vitro translation products from salmon CS poly(A)+ RNA identified a 26K protein, which corresponds to the size of the teleocalcin monomer as predicted by cDNA sequencing studies. Similar banding patterns were obtained with purified teleocalcin and crude CS extracts by Western blot analysis. However, there was one extra band (32K) in the CS extracts that was not present in the purified hormone preparations. This may represent the pro-form of the hormone in salmon.

Dynamic regulation of mouse ovarian stanniocalcin expression during gestation and lactation.

Stanniocalcin is a glycoprotein hormone that appears to play a paracine/autocrine role in several mammalian tissues. Recently studies have shown that stanniocalcin is highly expressed in the ovaries of mice and humans and we have investigated its expression in the mouse ovary during several physiological states to identify potential functional relationships. During postnatal development the pattern of stanniocalcin (STC) gene expression begins to become thecal-restricted as early as day 5 and achieves the adult pattern of expression by two weeks of age. During postnatal development the primary sites of STC protein localization are the theca and oocytes and after maturation it is also strongly concentrated in the corpora lutea. Over the estrous cycle the pattern of both STC gene expression and protein localization do not show dramatic changes though STC immunoreactivity (STCir) staining appears to be greatest during metestrus I. In the superovulation model, however, we observed a significant increase in STC messenger RNA (mRNA) levels after treatment with hCG implying regulation by LH. During gestation the expression of ovarian STC increases 15-fold and is localized to the theca-interstitial cells with lower expression also being found in the corpora lutea. STC also becomes detectable in the serum for the first time suggesting an endocrine role for STC during gestation. Interestingly, the presence of a nursing litter appears to up-regulate STC gene expression in lactating mice suggesting a role for ovarian STC in lactation. Also striking is the intense STCir staining found in oocytes as they are devoid of STC mRNA, thus implying a role for STC in oocyte maturation. Stanniocalcin, to our knowledge, is unique because no other secreted proteins produced by the ovarian thecal-interstitial compartment are significantly induced during mouse pregnancy. In summary, our data provide evidence for the active regulation of STC expression in the ovary during gestation and lactation and therefore implies that STC is a new regulator of the gestational and nursing state.

Immunocytochemical localization of stanniocalcin cells in the rat kidney.

Stanniocalcin (STC) is a polypeptide hormone that was first discovered in fishes, where it functions as a regulator of calcium and phosphate homoeostasis. Recently, complementary DNAs encoding human STC (hSTC) have been characterized, and recombinant hSTC has been synthesized in a bacterial expression system. In preliminary studies, STC-immunoreactive cells have already been identified in human kidney tubules with antibodies to recombinant hSTC. The purpose of this study was to map the overall spatial distribution of STC cells in mammalian kidney, using the rat as a model system. Immunocytochemistry was performed on fixed sections of rat kidney tissue using hSTC antiserum in conjunction with fluorescein isothiocyanate-conjugated second antibodies. STC-immunoreactive cells were found in cortical thick ascending limb, in macula densa, in distal convoluted tubules, and in the cortical and medullary collecting ducts. All cortical thick ascending limb cells contained immunoreactive STC. Most distal convoluted tubules cells contained STC, and these were identified as principal cells. The distribution of STC cells in cortical and medullary collecting ducts also corresponded closely to the known frequently of principle cells in these segments, suggesting that principal cells are the site of STC storage and/or synthesis in both distal convoluted tubules and collecting ducts. Some collecting duct intercalated cells contained STC as well, and these were tentatively identified as alpha-type intercalated cells. As all tubular segments containing STC are known to be involved in regulated ion transport, renally derived STC may be acting in an autocrine, paracrine and/or endocrine fashion to regulate one or more of these transport processes.

Comparative analysis of mammalian stanniocalcin genes.

The recent discovery of mammalian stanniocalcin (STC) prompted an investigation of its gene structure and expression pattern to study its function and regulation. We show that both the human and mouse genes are composed of four exons spanning about 13 kb, with 85% nucleotide sequence identity in coding regions. Remarkably high sequence conservation between species also exists in the approximately 3-kb 3'-untranslated region. Comparative analysis of the 5'-untranslated region and flanking DNA from the rat and human STC genes showed long stretches of CAG trinucleotide repeats and an additional (CA)25 dinucleotide repeat unique to the rat promoter. An analysis of STC expression in the mouse showed that ovary contained the highest level of messenger RNA, with lower, but detectable, levels in most tissues. In situ hybridization revealed strong, specific hybridization over the thecal-interstitial cells of the ovarian stroma, whereas immunohistochemical analysis indicated that STC was present not only in the stroma, but also in the corpora lutea and oocyte of the developing follicle. Consequently, STC may act as a signaling molecule between the thecal-interstitial cell compartment and the corpus luteum and oocyte, thereby regulating the activity of these structures in some way. These findings suggest that in addition to its role in mineral metabolism, STC has acquired an important function in reproduction during its evolution to mammals.

Possible roles for stanniocalcin during early skeletal patterning and joint formation in the mouse.

Stanniocalcin (STC) is a polypeptide hormone discovered first in fish and more recently in mammals. In mammals, the gene is widely expressed and the hormone is, so far, known to be involved in regulating the transport of calcium or phosphate across renal and gut epithelia, and into neuronal cells. Gene expression is also high during development, and in an earlier study we mapped the temporal and spatial pattern of gene expression in the mouse urogenital system. Our data suggested that STC probably acted as a signaling molecule that was produced in mesenchyme cells and targeted to epithelial cell layers in both kidney and testes. Here we have examined STC mRNA and protein distributions between developmental stages E10.5 and E18.5 in the axial and appendicular skeleton. In the axial skeleton, STC was transiently expressed in a rostral-caudal fashion during vertebral development; protein appeared to be made in intervertebral disc mesenchyme cells and targeted to vertebral hypertrophic and prehypertrophic chondrocytes. By stage E18.5, the STC gene was active only in vertebral perichondrocytes. The pattern of expression in the appendicular skeleton was equally striking. Early in development, STC gene expression defined the initial lengths of bone primordia. The gene was expressed in mesenchyme cells at either ends of precartilaginous condensations defining future long bones and the secreted protein was targeted to the chondroblasts. Later on during joint formation, STC was highly expressed in interzone cells that defined all future joints. After cavitation, STC gene expression was greatest in perichondrocytes lining the joints. Underlying resting, proliferative and prehypertrophic chondrocytes appeared to be the targets of STC both during and after cavitation. Therefore, its pattern of expression was indicative of a role in early skeletal patterning and joint formation. Moreover, as occurs during urogenital development, it appeared that STC is made in undifferentiated mesenchyme cells and sequestered by those destined to differentiate.

The co-localization of stanniocalcin protein, mRNA and kidney cell markers in the rat kidney.

Stanniocalcin (STC) is a glycoprotein hormone that was first discovered in fish and recently identified in mammals. STC immunoreactive (STCir) cells have been identified in rat kidney and there is also evidence that the hormone functions as a regulator of renal phosphate homeostasis. In the present study we have identified STCir cells and tubules in the rat kidney by correlative immunocytochemistry using antibodies to STC and specific antigenic markers (Tamm-Horsfall protein and anion exchanger-1). The cellular sites of STC gene expression were also identified by in situ hybridization. Correlative immunocytochemistry revealed that STCir was present in all proximal straight tubule cells, all cortical thick ascending limb cells, all distal convoluted tubule cells, and both principal and alpha-intercalated cells of the collecting duct system. On the other hand, in situ hybridization revealed that the STC gene was expressed only in cortical and medullary collecting duct cells. This suggests either that STC is being sequestered by segments that do not express the gene (making them putative targets of the hormone), or that STC mRNA levels were simply too low in these other segments to be detected by in situ hybridization.

cAMP signaling can antagonize potent glucocorticoid post-transcriptional inhibition of stanniocalcin gene expression.

Stanniocalcin (STC) is a glycoprotein hormone first discovered in fish as a homeostatic regulator of calcium and phosphate transport; it has recently been discovered in mammals, in which it appears to have a similar role. It has also been implicated in a number of different physiological processes through correlative studies, but the factors regulating its production have not been elucidated. In this report, we show that steady-state STC mRNA levels in the mouse corticotrope tumor line, AtT-20, were exquisitely sensitive to glucocorticoids. Hydrocortisone and dexamethasone (Dex) induced a dramatic reduction in steady-state STC mRNA levels in AtT-20 cells through a post-transcriptional mechanism. Similarly, glucocorticoids down-regulated STC mRNA levels in the human fibrosarcoma cell line, HT1080. The specificity of the glucocorticoid-mediated decrease in STC mRNA abundance was shown using the glucocorticoid receptor antagonist, RU-486. Activation of the cAMP-signaling pathway in glucocorticoid-cultured AtT-20 cells transiently restored STC gene expression. Treatment of AtT-20 cells with the transcriptional inhibitor, actinomycin D, rescued steady-state STC mRNA levels from Dex-induced repression, indicating that the Dex-mediated decrease in STC gene expression requires current gene transcription. Taken together, these results describe a unique model system in which cAMP-stimulated events can reverse post-transcriptional repression of gene expression by glucocorticoids.

Salmon calcitonin inhibits whole body Ca2+ uptake in young rainbow trout.

Gill Ca2+ transport (GCAT) in fish is regulated by a number of different hormones. Stanniocalcin (STC) from the corpuscles of Stannius (CS) is an inhibitor of GCAT, whereas pituitary-derived prolactin and cortisol stimulate GCAT. Other than this, however, little is known about the effects of other hormones on this important transport process. The role of calcitonin (CT) in calcium homeostasis in fish is still controversial. Whereas many studies have shown significant effects of CT on plasma calcium levels, an equal number of studies have failed to find any correlations between plasma calcium and CT levels in fish. Previous in vitro studies have shown that salmon CT has potent inhibitory effects on GCAT in isolated, perfused fish gill preparations, a finding that has never been corroborated in vivo. Therefore, in this report we examined the effects of salmon CT on whole body 45Ca uptake (as a measure of GCAT) in young rainbow trout. In support of the in vitro findings, we found that CT had significant inhibitory effects on GCAT. In parallel studies, we found that CT had no effects on STC secretion and only modest, stimulatory effects on STC mRNA levels in cultured trout CS cells. These finding suggest that both CT and STC function as negative regulators of GCAT in fish.

Novel expression of the stanniocalcin gene in fish.

It is currently accepted that the fish stanniocalcin (STC) gene is expressed exclusively in the corpuscles of Stannius (CS), unique endocrine glands on the kidneys of bony fishes. In this study, we have re-examined the pattern of fish STC gene expression in the light of the recent evidence for widespread expression of the gene in mammals. Surprisingly, we found by Northern blotting that the fish gene was also expressed in the kidneys and gonads, in addition to the CS glands. Moreover, Southern blotting of RT-PCR products revealed STC mRNA transcripts in all tissues assayed, including brain, heart, gill, muscle and intestine. In situ hybridization studies using digoxigenin-labeled riboprobes localized STC mRNA to chondrocytes, and both mature and developing nephritic tubules. Immunocytochemical staining indicated that the STC protein was widespread in cells of the gill, kidney, brain, eye, pseudobranch and skin. We also characterized the salmon STC gene, establishing that it was comprised of five exons as opposed to four in mammals. A single transcription start site was identified by primer extension 99 bp upstream of the start codon. This is the first evidence of STC gene expression in fish tissues other than the CS glands and suggests that, as in mammals, fish STC operates via both local and endocrine pathways.

Effects of dibutyryl cAMP on stanniocalcin and stanniocalcin-related protein mRNA expression in neuroblastoma cells.

Stanniocalcin is a polypeptide hormone that was first reported in fish as a regulator of mineral metabolism. Its recent identification in mammals has opened a new area of investigation in basic and clinical endocrinology. In the present study, regulation of the stanniocalcin (STC) and stanniocalcin related protein (STCrP) genes were investigated in mouse neuroblastoma cells (Neuro-2A) in relation to neuronal cell differentiation. Neuro-2A is an undifferentiated cell line that contains measurable levels of STCrP mRNA, but undetectable levels of STC mRNA. Treatment of the cells with either dbcAMP (1-4 mM) or 50 microM euxanthone (PW1) resulted in extensive differentiation and neurite outgrowth. However, only neurites of dbcAMP-treated cells developed varicosities, a phenotypic marker of axon formation. Furthermore, following differentiation induced by dbcAMP, there was an upregulation of STC and downregulation of STCrP mRNA levels. In the first 24 and 48 h of treatments, there was a maximum twofold induction and 1.5-fold reduction in STC and STCrP mRNAs respectively. Following 96 h of treatment, an additional 14-fold STC induction and 1.2-fold STCrP reduction were observed. The increase in STC mRNA levels was accompanied by a concomitant increase in axon-specific low molecular form microtubule-associated protein (MAP-2c) mRNA and varicosities on the neurites, suggesting a possible role for STC in axonogenesis. There was no induction of STC mRNA levels when PW1 was added into the culture media, whereas ionomycin (1-10 microM) had no observable effects on cell differentiation or STC/STCrP mRNA. Immunocytochemical staining of dbcAMP-treated cells revealed abundant levels of immunoreactive STC, particularly in the varicosities, with only weak staining in control, untreated cells. Antisense oligodeoxynucleotides transfection studies indicated that the expression of STC was a cause of varicosity formation and a consequence of cell differentiation. Our findings lend further support to the notion that STC is involved in the process of neural differentiation.

Calcium regulates stanniocalcin mRNA levels in primary cultured rainbow trout corpuscles of stannius.

Stanniocalcin (STC) is an inhibitor of gill calcium transport produced by the corpuscles of Stannius (CS), endocrine glands in bony fishes. In previous studies we have described how STC secretion is regulated by calcium both in vitro and in vivo, using rainbow trout as a model system. In this report we have examined the effects of calcium on STC mRNA levels in primary cultured trout CS cells. The results show that message levels are positively regulated by extracellular calcium concentrations within the physiological range. The calcium response was also temporally-related as more prolonged exposures tended to have greater effects. Similar concentrations of magnesium had no effect on message levels. This represents another level at which calcium regulates the CS cell, in addition to its established effects on STC synthesis and secretion. The results are discussed in relation to the other known calciotropic hormones, calcitonin and parathyroid hormone.