Browsing by Issue Date, starting with "2003-02"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
- Quantification of prolactin (PRL) and PRL receptor messenger RNA in gilthead Seabream (Spares aurata) after treatment with Estradiol-17 betaPublication . Cavaco, J. E. B.; Santos, C. R. A.; Ingleton, P. M.; Canario, Adelino V. M.; Power, DeborahProlactin (PRL) in fish is considered to be an osmoregulatory hormone, although some studies suggest that it may influence the production of steroid hormones in the gonads. The objective of the present study was to establish if PRL is involved in reproduction of the gilthead seabream—a protandrous hermaphrodite. Adult and juvenile gilthead seabream received implants of estradiol-17b (E2) for 1 wk during the breeding season, and the mRNA expressions of PRL and PRL receptor (sbPRLR) were determined. Northern blot analysis revealed a single pituitary PRL transcript, the expression of which was significantly reduced by E2 treatment in adults but significantly increased in juvenile fish. In adult gonads, four sbPRLR transcripts of 1.1, 1.3, 1.9, and 2.8 kilobases were observed. A competitive reverse transcription-polymerase chain reaction was developed and used to determine how E2 treatment alters expression of the gonadal sbPRLR gene. Seabream PRLR was detectable in all samples analyzed by this assay. Levels of sbPRLR mRNA increased significantly (50-fold) after E2 treatment in adults, but a 24-fold decrease was measured in juveniles. Immunohistochemistry using specific polyclonal antibodies raised against an oligopeptide from the extracellular domain of sbPRLR detected the receptor in spermatogonia and oocytes. Taken together, the preceding results suggest that in the seabream, PRL may act on both testis and ovary via its receptor and that the stage of maturity influences this process. The full characterization and relative importance of the different transcripts of sbPRLR in eliciting the action of PRL in the gonads remain to be elucidated.
- Purification of matrix Gla protein from a marine teleost fish, Argyrosomus regius: Calcified cartilage and not bone as the primary site of MGP accumulation in fishPublication . Simes, D; Williamson, MK; Ortiz-Delgado, JB; S B Viegas, Carla; Price, PA; Leonor Cancela, M.Matrix Gla protein (MGP) belongs to the family of vitamin K-dependent, Gla-containing proteins, and in mammals, birds, and Xenopus, its mRNA was previously detected in extracts of bone, cartilage, and soft tissues (mainly heart and kidney), whereas the protein was found to accumulate mainly in bone. However, at that time, it was not evaluated if this accumulation originated from protein synthesized in cartilage or in bone cells because both coexist in skeletal structures of higher vertebrates and Xenopus. Later reports showed that MGP also accumulated in costal calcified cartilage as well as at sites of heart valves and arterial calcification. Interestingly, MGP was also found to accumulate in vertebra of shark, a cartilaginous fish. However, to date, no information is available on sites of MGP expression or accumulation in teleost fishes, the ancestors of terrestrial vertebrates, who have in their skeleton mineralized structures with both bone and calcified cartilage. To analyze MGP structure and function in bony fish, MGP was acid-extracted from the mineralized matrix of either bone tissue (vertebra) or calcified cartilage (branchial arches) from the bony fish, Argyrosomus regius,(1) separated from the mineral phase by dialysis, and purified by Sephacryl S-100 chromatography. No MGP was recovered from bone tissue, whereas a protein peak corresponding to the MGP position in this type of gel filtration was obtained from an extract of branchial arches, rich in calcified cartilage. MGP was identified by N-terminal amino acid sequence analysis, and the resulting protein sequence was used to design specific oligonucleotides suitable to amplify the corresponding DNA by a mixture of reverse transcription-polymerase chain reaction (RT-PCR) and 5'rapid amplification of cDNA (RACE)-PCR. In parallel, ArBGP (bone Gla protein, osteocalcin) was also identified in the same fish, and its complementary DNA cloned by an identical procedure. Tissue distribution/accumulation was analyzed by Northern blot, in situ hybridization, and immunohistochemistry. In mineralized tissues, the MGP gene was predominantly expressed in cartilage from branchial arches, with no expression detected in the different types of bone analyzed, whereas BGP mRNA was located in bone tissue as expected. Accordingly, the MGP protein was found to accumulate, by immunohistochemical analysis, mainly in the extracellular matrix of calcified cartilage. In soft tissues, MGP mRNA was mainly expressed in heart but in situ hybridization, indicated that cells expressing the MGP gene were located in the bulbus arteriosus and aortic wall, rich in smooth muscle and endothelial cells, whereas no expression was detected in the striated muscle myocardial fibers of the ventricle. These results show that in marine teleost fish, as in mammals, the MGP gene is expressed in cartilage, heart, and kidney tissues, but in contrast with results obtained in Xenopus and higher vertebrates, the protein does not accumulate in vertebra of non-osteocytic teleost fish, but only in calcified cartilage. In addition, our results also indicate that the presence of MGP mRNA in heart tissue is due, at least in fish, to the expression of the MGP gene in only two specific cell types, smooth muscle and endothelial cells, whereas no expression was found in the striated muscle fibers of the ventricle. In light of these results and recent information on expression of MGP gene in these same cell types in mammalian aorta, it is likely that the levels of MGP mRNA previously detected in Xenopus, birds, and mammalian heart tissue may be restricted toregions rich in smoot Our results also emphasize the need to re-evaluate which cell types are involved in MGP gene expression in other soft tissues and bring further evidence that fish are a valuable model system to study MGP gene expression and regulation.
- Partition of fish pheromones between water and aggregates of humic acids. Consequences for sexual signalingPublication . Mesquita, Rute M. R. S.; Canario, Adelino V. M.; Melo, Eduardo P.High-molecular-weight suspended organic matter of soil and aquatic origins competes with water for the dissolution of relatively water insoluble organic substances. The same happens with microalgae and other organisms present in natural waters. Several pheromones, which play a specific role in the reproductive cycle of fish, are secreted to the water and are generally, if not always, molecules with hydrophobic or amphiphilic characteristics. The natural tendency of these pheromones to dissolve in suspended or deposited organic matter may cause their signaling function to be adversely affected. In this work we study the partition constants between water and organic reservoirs in suspension, Kh, of two fish pheromones, 4-pregnene-17 alpha, 20β-diol-3-one (17,20β-P) and prostaglandin F2α (PGF2α), and also of 4-pregnene-11β,21-diol-3,20-dione 21-sulfate (21-P-sulfate), used as a proxy for sulfated steroid pheromones. Two types of organic reservoirs are employed: aggregates of suspended humic substances and negatively charged phospholipid vesicles. We find that the three compounds have high affinities for both types of aggregates. However, 17,20β-P, with pKh = 4.4 ± 0.2, is the only one for which we may predict a significant decrease in availability in consideration of the normal content of dissolved organic matter in natural waters. Also to be considered is the fact that a relatively large amount of pheromones is retained and may be released at an inopportune moment. How significant these phenomena are in nature is not as yet clear, considering the variety of habitats in which fish spawn and the little that is known about the nature and mode of action of pheromones.
- Elliptic flow of colored glass in high energy heavy ion collisionsPublication . Krasnitz, A; Nara, Y; Venugopalan, RWe compute the elliptic flow generated by classical gluon fields in a high energy nuclear collision. The classical gluon fields are described by a typical momentum scale, the saturation scale As, which is, for RHIC energies, of the order of 1-2 GeV. A significant elliptic flow is generated only over time scales on the order of the system size R. The flow is dominated by soft modes P-T similar to Lambda(s)/4 which linearize at very late times tau similar to R much greater than 1/Lambda(s). We discuss the implications of our result for the theoretical interpretation of the RHIC data. (C) 2003 Elsevier Science B.V All rights reserved.