Identification and preliminary characterization of white sturgeon (Acipenser transmontanus) vitellogenin mRNA

Changes of vitellogenin and Lipase in captive Sterlet sturgeon Acipenser ruthenus females during previtellogenesis to early atresia

Plasma chemistry, lipid metabolism and vitellogenin gene expression of captive Sterlet sturgeon Acipenser ruthenus were studied in different maturity stages. A total of 32 fish were sampled, and maturity stages were identified on the basis of histological criteria and direct observation. Females were classified to four groups: previtellogenic, vitellogenic, post-vitellogenic, and atresia. Blood, gonad and liver tissue samples were taken through non-lethal biopsy. Our results showed that plasma levels of glucose, cholesterol, triacylglycerol, high-density lipoprotein, low-density lipoprotein, very low-density lipoprotein, calcium, phosphorus, alkaline phosphatase activity, albumin and total protein increased during ovarian development and were highest at post-vitellogenic stage. The lowest amounts in atresia stage demonstrate that lipid and energy imbalance was related to reabsorption and digestion of the yolk. These results suggested that the VLDL was the main plasma lipoprotein component of Sterlet. We determined that lipoprotein lipase and hepatic lipase activity increased during vitellogenesis process which suggested the role of lipase enzymes in regulating blood lipid metabolism. RT-PCR analysis indicates that Vitellogenin (VTG) mRNA could be detected both in livers and ovaries of female Sterlet. Throughout the study, the expression level of VTG gene showed an increase both in ovaries and in livers reaching its peak at late vitellogenesis stage. This strongly indicated a relation between VTG mRNA and ovarian development.

Importance of environmental endocrinology in fisheries management and aquaculture of sturgeons

Less is known about the reproductive endocrinology of sturgeons compared to modern teleosts. However, tools to assess the reproductive endocrinology and effects of environmental factors on reproduction do exist. This review utilizes case studies to describe the parameters involved in environmental endocrinology and the management and recovery efforts for the phylogenetically ancient sturgeon and paddlefish (Clade Chondrostei). Specifically, we discuss the use of environmental endocrinology to determine sex and stage of maturity and identify oviposition on spawning grounds, the importance of understanding endocrine disruption pathways, the challenges and benefits of assessing stress in wild populations of sturgeon, and three major physiological events in the reproductive development of farmed sturgeon understanding of which appears to be crucial for improving sturgeon aquaculture.

Vitellogenin exists as charge isomers in the Indian freshwater murrel, Channa punctatus (Bloch)

Three charge isomeric forms of vitellogenin are reported in the blood of estrogen-treated murrel, Channa punctatus on the basis of the results of native and SDS-PAGE, isoelectric focusing, and Ferguson plot analysis. Vitellogenin was induced in adult murrels by exogenous administration of estradiol-17beta and labelled with 32P in vivo. Labelled vitellogenin isolated from other plasma proteins on Ultrogel AcA 34 columns resolve into three bands on native-PAGE. Ferguson plot analysis reveals free electrophoretic mobilities of the three bands as 6.0, 4.5, and 3.7, which are very similar to the isoelectric point values of 5.9, 4.6, and 3.8, respectively. The apparent molecular weight of native murrel vitellogenin is 530 kDa. It consists of a single peptide with a molecular weight of 175 kDa. All the three bands on native PAGE resolves into a single peptide on SDS-PAGE. N-terminal amino acid sequence for murrel vitellogenin peptide is MKAVVLALLL. The protein phosphorus:lipid phosphorus ratio for murrel vitellogenin is 0.9. The total lipid content is 32.8%, consisting of 45% neutral lipids and 30% phospholipids. Phosphatidyl choline is the major phospholipid whereas triglycerides are the major neutral lipids. Results of these analytical analyses indicate that murrel native vitellogenin circulates as three charge isomers; poor in phosphorus but rich in lipids content.

Vitellogenin-derived yolk proteins in a hybrid sturgeon, bester (Huso huso x Acipencer ruthenus): identification, characterization and course of proteolysis during embryogenesis

Vitellogenin (Vg) and its corresponding yolk protein (YP) products, YP1, YP2 and YP3, were isolated from serum of estrogen-treated hybrid sturgeon (bester; Huso huso X Acipencer ruthenus) and eggs from untreated fish, respectively. Vitellogenin had an apparent molecular mass of 580 kDa and appeared as two major bands corresponding to 180 kDa and 120 kDa after SDS-PAGE. Apparent molecular weights of YP1, YP2 and YP3 were 370 kDa, 88 kDa and 19 kDa, respectively. After SDS-PAGE, YP1 appeared as a main band of 110 kDa, while YP2 was resolved as a single band of 94 kDa and 29 kDa band under non-reducing and reducing conditions, respectively. Yolk protein 3 appeared as a diffuse band corresponding to 16 kDa and two faint bands below 14.4 kDa after SDS-PAGE. However, the 16 kDa band alone was observed after dephosphorylation with alkaline phosphatase. The course of cleavage of yolk proteins in bester embryos and alevins was observed by SDS-PAGE and Western blotting from fertilization onward. After hatching, the main 110 kDa band of YP1 was degraded into smaller peptides during development, while YP2 hardly showed any such structural changes. The amino acid compositions of purified yolk proteins indicated that YP1, YP2 and YP3 were bester lipovitellin, beta-component, and phosvitin, respectively.

Mosquitofish (Gambusia affinis) vitellogenin: identification, purification, and immunoassay

Vitellogenin is a phospholipoglycoprotein precursor of egg yolk. In mature female fish, vitellogenin is synthesized and secreted by the liver in response to circulating estrogens. Vitellogenin is normally undetectable in the blood of male fish, but can be induced by exposure to compounds possessing estrogenic activity. Thus, the presence of vitellogenin in blood of male fish can serve as a useful biomarker for assessing previous exposure to estrogenic compounds. In the present study, we report identification and purification of vitellogenin in the mosquitofish (Gambusia affinis). Anti-vitellogenin immune serum was generated and used to develop an immunoblot assay for detection of vitellogenin. A combination of immunoblotting and densitometric scanning was used to assess the time- and dose-dependent effects of 17alpha-ethynylestradiol on vitellogenesis in male G. affinis. The results indicate that changes in the level of vitellogenin in mosquitofish blood can be reliably detected by the immunoblot assay, and that the mosquitofish may be a useful bioindicator organism for detecting estrogenic contamination of the aquatic environment.

Contrasting effects of estrogen on transthyretin and vitellogenin expression in males of the marine fish, Sparus aurata

A partial cDNA encoding for the C-terminus of vitellogenin (VTG) was cloned from liver of Sparus aurata male treated with 17beta-estradiol (E(2)). E(2) treatment of S. aurata males resulted in increased synthesis and secretion of VTG protein into the plasma, determined by a specific enzyme-linked immunosorbent assay (ELISA) in a time-dependent manner. While VTG mRNA was induced by E(2) treatment, transthyretin (TTR) mRNA levels were reduced. These data provide the first demonstration that estrogen exhibits contrasting effect on VTG and on TTR gene expression in teleosts.

Hyperglycaemic hormones inhibit protein and mRNA synthesis in in vitro-incubated ovarian fragments of the marine shrimp Penaeus semisulcatus

The present work shows for the first time that peptides belonging to the Crustacean hyperglycaemic hormone family (CHH-family hormones) from Penaeus japonicus affect protein and mRNA synthesis in in vitro-incubated ovarian explant fragments removed from vitellogenic females of Penaeus semisulcatus. Reduced levels of protein synthesis, determined by TCA-precipitable 35S-labeled proteins, were found in the presence of crude sinus gland extracts from both P. semisulcatus and P. japonicus. A similar inhibitory effect compared to controls was found with each of the seven CHH-family peptides. Non-CHH-family peptides did not reduce protein synthesis. Crude sinus gland extracts prepared from P. semisulcatus were at least 20-fold more effective than sinus gland extracts of P. japonicus. The inhibition level was directly related to the concentration of the peptide in the incubation media, but its degree varied among the different tested peptides. The profile of proteins synthesized during in vitro incubation was analyzed using polyacrylamide gel electrophoresis under denatured and reduced conditions (SDS-PAGE), followed by autoradiography. Synthesis of several proteins was reduced, including proteins with electrophoretic mobility similar to that of vitellin. Immunoprecipitation with antiserum prepared against native ovarian vitellin confirmed the inhibitory effect of CHH-family peptides on vitellin synthesis. The crude sinus gland extract and CHH-family peptides also inhibited RNA synthesis, as determined by [3H]uridine incorporation into mRNA of ovarian fragments. It is concluded that in addition to their role in carbohydrate metabolism, CHH-family peptides may also influence ovarian physiology in crustaceans.

Characterization of vitellogenin from white sturgeon, Acipenser transmontanus

Sturgeon are an ancient family (Acipenseridae) of fishes that lie close to the divergence of fish that eventually evolved into terrestrial animals and those that evolved into modern teleost species. Therefore, white sturgeon vitellogenin sequences fill a gap in the current understanding of the functional domains of this protein family. Vitellogenin cDNA was sequenced and used to investigate gene expression in white sturgeon, Acipenser transmontanus. Estrogen-induced vitellogenin mRNA was detected in the livers of both males and females and was also detected in undifferentiated gonads of estrogen-treated fish. Low levels of vitellogenin mRNA were also detected in the testis of both control and estrogen-treated males. The cDNA encoded a 186-kDa protein that was missing only six to seven of the amino-terminal amino acids. Comparisons to silver lamprey, Xenopus, and chicken vitellogenin sequences indicate that the overall structure of the yolk protein domains were highly conserved. There was considerable homology in three regions of the lipovitellin I domain. These conserved sequences are likely to be involved in vitellogenin receptor binding. The phosvitin domain of white sturgeon vitellogenin contained fewer and shorter serine repeats as predicted from yolk protein phosphate content of fish compared to Xenopus and chicken. However, the vitellogenin of white sturgeon had a lower serine content as compared with silver lamprey, indicating that an increased serine content is not strictly a function of evolutionary age.