Characterization of incomplete vitellogenin (VgC) in the Indian freshwater murrel, Channa punctatus (Bloch)

Structural modeling and gene expression analysis of phosvitinless vitellogenin (vgc) in the Indian freshwater murrel, Channa punctatus (Bloch, 1793)

Vitellogenin (Vg) is a female-specific egg-yolk precursor protein, synthesized in the liver of fish in response to estrogens. In the present study, complete gene of phosvitinless vitellogenin (vgc) was sequenced, its 3D structure was predicted and validated by web-based softwares. The complete nucleotide sequence of vgc was 4126 bp which encodes for 1272 amino acids and showed the presence of three conserved domains viz. LPD_N, DUF1943 and DUF1944. The retrieved amino acid sequence of VgC protein was subjected to in silico analysis for understanding the structural and functional properties of protein. mRNA levels of multiple vg genes have also been quantified during annual reproductive cycle employing qPCR. A correlation has been observed between seasonal changes in gonadosomatic index with estradiol levels and hepatic expression of three types of vg genes (vga, vgb, vgc) during ovarian cycle of murrel. During preparatory phase, when photoperiod and temperature are low; low titre of E2 in blood induces expression of vgc gene. A rapid increase in the levels of E2 favours induction of vgb and vga genes in liver of murrel during early pre-spawning phase when photoperiod is long and temperature is high in nature. These results suggest that among three vitellogenin proteins, VgC is synthesized earlier than VgA and VgB during oogenesis.

Role of cathepsins B and D in proteolysis of yolk in the catfish Clarias gariepinus

Yolk processing pathways vary in the oocytes of benthophil and pelagophil teleosts. The present study investigated the yolk processing pattern in the oocytes of the fresh water catfish Clarias gariepinus at vitellogenic, maturation, and ovulated stages. This study concludes that during maturation stage, an electrophoretic shift in the major peptide band on Polyacrylamide gel electrophoresis (PAGE) occurs due to a decrease in the size of the yolk protein. The PMF spectrum of corresponding peptides from vitellogenic and ovulated oocytes revealed a difference in the minor ions. A minor difference in the molecular weight of the corresponding peptides occurs due to a difference in their amino acid composition. Maximal activity of the proteases cathepsin D and cathepsin B was observed in the vitellogenic oocytes, thus confirming their role in the processing of yolk. A significant transient increase in the activity of cathepsin B in the mature oocytes also suggests its role in oocyte maturation.

Acute toxic effects of lead (Pb2+) exposure to rare minnow (Gobiocypris rarus) revealed by histopathological examination and transcriptome analysis

Lead (Pb) is a toxic heavy metal that can cause significant damage to the aquatic ecosystem. In this study, acute toxicity test of lead in rare minnow (Gobiocypris rarus) was conducted. The average LC₅₀ for 96 h of Pb²⁺ is 423.01 μg/L (95 % CI: 338.41-531.92 μg/L). The order of bioaccumulation of Pb²⁺ was gills > kidney > intestine > liver > muscle > brain. A number of cellular and tissue alterations were observed in the gill, liver, kidney and intestine tissues of Pb²⁺-treated rare minnows through the histological examination performed by H&E and TEM analyses. Furthermore, we investigated the Pb²⁺-induced toxicity mechanisms in rare minnow based on transcriptome analyses, and a panel of immune-related genes were identified and evaluated by real-time quantitative PCR. In summary, our work indicates that rare minnow could be a valuable model for studying the mechanisms of lead acute toxicity in fish.

Multiple vitellogenin genes (vtgs) in large yellow croaker (Larimichthys crocea): molecular characterization and expression pattern analysis during ovarian development

The large yellow croaker (Larimichthys crocea) is a marine fish that is economically important to Chinese fisheries, and its reproductive and developmental biology have been extensively investigated. However, the molecular mechanism of oogenesis in L. crocea is not clear. Here, we investigated the multiple vitellogenin (Vtg) system in large yellow croaker. Three different vtg cDNA sequences, including vtgAa, vtgAb and vtgC, were cloned, which indicate the existence of multiple Vtg proteins in large yellow croaker (Lc-Vtgs). Subsequently, the vtg cDNA sequences and predicted Vtg protein structures were analysed, and Vtg protein structures were found to be highly conserved. To research the expression of vtgs during the development of the ovaries, we examined ovarian development and oogenesis by histological analysis. Four stages of ovary development - stages II, III, IV and V - were observed and their boundaries were defined. Soon afterwards, the expression of vtgs in the liver (known as the main site of Vtg synthesis in teleosts) and ovary were analysed. The expression of vtgs was detected in the two tissues. Interestingly, in the early stages of development (stages II and III), there is little or no generation of yolk granules and the expression of vtgs in the liver is low. However, in the late stages (stages IV and V), yolk granules are generated rapidly and the expression of vtgs is significantly increased in the liver. These results support the hypothesis that the Vtgs were synthetized by the liver, and absorbed by the growing oocytes to promote oogenesis in large yellow croaker. We also detected the presence of vtg mRNA in the liver cells and oocytes by in situ hybridization, which indicated that vths were expressed both in the liver and ovaries. Importantly, we found that the distribution of vtgAa and vtgAb mRNA was close to the sites of yolk granule formation in oocytes.