Kidney Of Tilapia Research Articles

A Novel Type of P450c17 Lacking the Lyase Activity Is Responsible for C21-Steroid Biosynthesis in the Fish Ovary and Head Kidney

Cytochrome P450c17 is the single enzyme that mediates the 17 alpha-hydroxylase and 17, 20 lyase activities during the biosynthesis of steroid hormones in the gonads and adrenal gland. However, the mechanism underlying its dual action continues to be a controversy in the field of steroidogenesis in fish. In an attempt to resolve this issue, we identified a novel type of P450c17 (P450c17-II) by an in silico analysis from the genomes of six fish species. We cloned P450c17-II from tilapia and medaka, and comparison with the conventional P450c17-I revealed that they differ in gene structure and enzymatic activity. Enzymatic assays by thin-layer chromatography revealed that P450c17-II possesses only the 17 alpha-hydroxylase activity without any 17, 20 lyase activity, unlike P450c17-I, which has both these activities. In testis, both P450c17-I and -II express in the interstitial cells. Remarkable differences, revealed by in situ hybridization, in the expression patterns of the P450c17-I and -II in the ovary and head kidney of tilapia during various stages of development strongly suggest that P450c17-I is responsible for the synthesis of estradiol-17beta in the ovary, whereas P450c17-II is required for the production of C21 steroids such as cortisol in the head kidney. More interestingly, a temporally controlled switching is observable in the expression of these two genes during the steroidogenic shift from estradiol-17beta to the C21 steroid, 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (maturation-inducing hormone of fish oocytes) in the fish ovary, revealing a role for P450c17-II in the production of hormones that induce oocyte maturation in fish.

Response of catalase activity to Ag +, Cd 2+, Cr 6+, Cu 2+ and Zn 2+ in five tissues of freshwater fish Oreochromis niloticus

Catalase (CAT, EC 1.11.1.6) is an important enzyme in antioxidant defense system protecting animals from oxidative stress. Freshwater fish Oreochromis niloticus were exposed for 96 h to different concentrations of Ag +, Cd 2+, Cr 6+, Cu 2+ and Zn 2+, known to cause oxidative stress, and subsequently CAT activities in liver, kidney, gill, intestine and brain were measured. In vivo, CAT was stimulated by all metals except Ag + in the liver and the highest increase in CAT activity (183%) resulted from 1.0 mg Cd 2+/L exposure, whereas 0.5 mg Ag +/L exposure resulted in a sharp decrease (44%). In tilapia kidney, cadmium and zinc had no significant effects on CAT activity, whereas 0.1 mg Cr 6+/L exposure caused a decrease (44%). Cadmium and zinc did not significantly affect the CAT activity in gill; however, 0.5 mg Ag +/L exposure caused an increase (66%) and 1.5 mg Cr 6+/L exposure caused a decrease (97%) in CAT activity. All metals, except Cu 2+(41% increase), caused significant decreases in CAT activity in the intestine. In brain, 1.0 mg Zn 2+/L resulted in an increase in CAT activity (126%), while 1.5 mg Ag +/L exposure caused a 54% decrease. In vitro, all metals — except Ag + and Cu 2+ in kidney — significantly inhibited the CAT activity in all tissues. Results emphasized that CAT may be considered as a sensitive bioindicator of the antioxidant defense system.

Stress response and energy metabolism in various tissues of Nile tilapia Oreochromis niloticus exposed to hypoxic conditions

: Nile tilapia were exposed to severe hypoxic conditions. The respiratory frequency (RF) of the fish reached a maximum level at approximately 10 mmHg PO2 and decreased gradually thereafter. The fish sank to the bottom and subsequently their respiration began to stop. The hypoxic conditions increased the hematocrit value. As RF decreased, plasma cortisol and glucose levels climbed drastically. Just before respiratory arrest, the ATP and the total adenylate (TA) concentrations were significantly depressed in the liver, kidney and ordinary muscle but not in the heart or gill. As RF decreased, ATP and TA in both the liver and kidney decreased rapidly. Cytochrome oxidase activity increased significantly in the brain, heart, gill and ordinary muscle until respiratory frequency peaked. However, from the peak RF, this activity decreased in the liver and kidney. Lactic acid levels in both ordinary muscle and liver increased markedly when the fish sank. These results indicate that the stress response to hypoxic conditions is induced markedly with the decreased RF. It is also suggested that the decreased energy status in the liver and kidney of tilapia occurs at the same stage as the metabolic depression in the whole body, without increases in the aerobic and anaerobic metabolisms.

Elevated levels of multiple cytochrome P450 forms in tilapia from Billings Reservoir-São Paulo, Brazil

Cytochrome P4501A (CYP1A) levels in tissues of fish inhabiting polluted areas have been used extensively in biomonitoring studies in Europe and North America. However, little information is available about the extent of CYP1A expression in fish from South American waters, nor on the expression of other CYP proteins in fish from polluted sites. The content of total cytochrome P450 and b 5 and of proteins cross-reactive with antibodies to teleost (scup) CYP1A-, CYP2B- and CYP3A-like proteins, as well as rates of alkoxy-resorufin- O-dealkylases (ARODs) with methoxy-, ethoxy-, pentoxy- and benzyloxyresorufin substrates, were analyzed in liver and kidney microsomes from tilapia ( Oreochromis niloticus) from a reference site (Estação de Piscicultura de Pindamonhangaba, São Paulo) and a polluted site (Billings Reservoir, São Paulo, Brazil). Levels of total microsomal P450 and b 5 were elevated 1.8- and 3.3-fold, respectively, in liver and 4.3- and 2.4-fold in kidney of tilapia from Billings Reservoir. Rates of all four ARODs and the levels of CYP1A-, CYP2B- and CYP3A-cross-reactive proteins were elevated in liver and kidney of fish from Billings Reservoir compared to those in reference fish. Hepatic microsomal EROD and MROD were about 20-fold greater and levels of 1A protein more than 400-fold greater in Billings fish. Antibodies to teleost CYP1A and putative CYP3A recognized single bands while Pab to the scup CYP2B-like protein recognized three protein bands in liver and kidney. This suggests that there are multiple CYP2B-like proteins expressed in tilapia. Immunohistochemical analysis also indicated increased expression of CYP1A cross-reactive proteins in cells of liver, gill, kidney and heart. The apparent induction of CYP1A probably reflects the exposure to aryl hydrocarbon receptor agonists present as pollutants in the Billings Reservoir. Elevated levels of the other CYP forms in tissues of tilapia from Billings Reservoir could be related either to the presence of pollutants or to some natural compound present in the diet, since tilapia is known as an herbivorous species.

Different thyroid hormone-deiodinating enzymes in tilapia ( Oreochromis niloticus) liver and kidney

Enzymes catalyzing the outer ring deiodination (ORD) of iodothyronines are important for the regulation of thyroid hormone bioactivity. We have studied ORD of thyroxine (T4) and 3,3',5'-triiodothyronine (rT3) in liver and kidney microsomes offish, i.e. tilapia ( Oreochromis niloticus). Tilapia kidney contains an enzyme which resembles the mammalian selenoenzyme type I iodothyronine deiodinase (ID-I) with respect to substrate preference (rT3 > T4) and high (≈ μM) K m values, but is much less sensitive to selenocysteine (Sec)-targeted inhibitors, including 6-propyl-2-thiouracil (PTU). In contrast, tilapia liver contains an enzyme very similar to mammalian type II deiodinase (ID-II) with respect to substrate preference (T4 > rT3), low (≈ nM) K m values, and lack of sensitivity to Sec inhibitors.

Prolactin-binding sites in tilapia ( Sarotherodon mossambicus) kidney

Highly purified 125I-labeled tilapia ( Sarotherodon mossambicus) prolactin (PRL) binds to microsomal membrane fractions prepared from tilapia kidney but not liver or gill. Specificity studies revealed that up to 35% of the labeled tilapia PRL bound to the kidney membrane preparation could be displaced by 100 ng of unlabeled hormone. Ovine PRL displaced 125I-labeled tilapia PRL from the kidney PRL-binding site. However, 125I-labeled ovine PRL demonstrated negligible specific binding to microsomal membrane fractions of tilapia kidney, liver, gill, or muscle. Tilapia PRL did not inhibit the binding of 125I-labeled ovine PRL to lactating rat liver membranes. The specific binding of 125I-labeled tilapia PRL to tilapia kidney membranes was greater with freshwater-acclimated than with seawater-acclimated fish suggesting that the tilapia kidney PRL-binding site is subject to physiological regulation.

A radioreceptor assay for purified teleost growth hormone

Highly purified 125I-labelled tilapia (Sarotherodon mossambicus) growth hormone (GH) binds to membrane fractions prepared from tilapia liver. Specific (displaceable) binding occurred with the 600, 15,000, and 90,000g fractions with the greatest binding observed with the 90,000g microsomal membrane fraction. Binding was dependent on time and membrane concentration. Specificity studies showed that up to 60% of the 125I-labelled tilapia GH bound to the liver microsomal membrane fraction could be displaced by 500 ng of unlabelled hormone. Scatchard analysis of the binding of 125I-labelled tilapia GH revealed a single class of binding site with a binding capacity of 125 ± 7.7 fmol/mg protein and a binding affinity of 1.5 × 1010 ± 0.4 × 1010 (SEM) l/mol. GH preparations from several vertebrate classes and tilapia prolactin and ovine prolactin at high concentrations displayed competition for the tilapia GH-binding site.125I-Labelled tilapia GH demonstrated specific binding to liver microsomal membrane fractions of the teleosts Gillichthys mirabilis, Salmo gairdneri, and Oncorhynchus tschawytscha but not to those of an amphibian Necturus maculosus or a bird Coturnix japonica. Slight, but significant, specific binding was observed with the microsomal membrane fraction of tilapia kidney and gill and of rat liver. These data suggest that this tilapia GH radioreceptor assay may have an application in the detection of teleost GH-like activity.

<i>Tilapia</i>属における耐鹹性の種間差異および腎組織の比較検討

1. African native cichlid T. mossabica showing 100% survival in the sea water of 75% concentration and a lesser survival in undiluted sea water without acclimation procedure was proved to better excel in salinity tolerance than T. nilotica and T. sparrmani (Fig. 1). 2. The kidney of Tilapia exhibits the structure of typical freshwater fish. The scanty interstitial connetive tissue of kidney is characteristic of the fishes Genus Tilapia. 3. A pomacentrid Abudefduf vaigiensis which is provided with the kidney of typical marine fish (lacking in the distal convoluted segment), shows the approximate half value of the size in each component of the kidney. A South American cichlid Pterophyllum eimekei exhibiting freshwater fish type in terms of kidney-structure is the intermediate values between Tilapia and A. vaigiensis (Table 1 and Fig. 2).