Identifying miRNAs in the modulation of gene regulation associated with ammonia toxicity in catfish, Clarias magur (Linnaeus, 1758).

BACKGROUND: The small non-coding microRNAs play a vital role in post-transcriptional gene regulation associated with different physiological events such as metabolism, stress, etc. The freshwater catfish, Clarias magur, can grow within hyper ammonia containing stagnant water bodies and/or muddy substratum. We intended to identify organ-specific miRNAs associated with ammonia stress management. METHODS AND RESULTS: The miRNA-libraries were generated from QC passed total RNA extracted from liver, muscle, and kidney of ammonia-treated (exposed to 25 mM NH4Cl for 14 days) and untreated catfish. The libraries were validated using High sensitivity D1000 Screen tape. The trimmed quality-filtered reads for control and treated samples of kidney were 19,406,210; 14,904,423; for liver 15,467,727; 18,582,072; and for muscle 25,081,345; 19,782,182 respectively. Total 120 known and 150 novel differentially expressed miRNAs were identified, out of which miR-200, miR-217, miR-122, miR-133, miR-145, miR-221, miR-19, miR-138, miR-34, and miR-184 were predicted to be involved in the metabolism of nitrogen. The key miRNAs targeted several genes associated with urea synthesis like Glutaminase 2, Argininosuccinate lyase, Glutamate dehydrogenase 1, Alanine aminotransferase 2-like, Aspartate aminotransferase, cytoplasmic-like, Glutamate ionotropic receptor NMDA type subunit 2A, etc. CONCLUSIONS: This is the first report of miRNAs, which serve as a vital resource for regulating nitrogen metabolism in freshwater catfish, C. magur. The data will be resourceful for further evaluating the regulatory role of miRNAs in fishes, which grow and reproduce very well in hazardous ammonia-contaminated water bodies.

Genomic organization and hypoxia inducible factor responsive regulation of teleost hsp90ß gene during hypoxia stress.

BACKGROUND: The physiological significance of a large family of heat-shock proteins (HSPs), comprised of the cytosolic HSP90A and the endoplasmic reticulum component of HSPB, is evident in prokaryotes and eukaryotes. The HSP90A is believed to play critical roles in diverse physiological functions of cell viability and chromosomal stability including stress management. Heightened abundance of hsp90ß transcript was documented in Channa striatus, a freshwater fish, which is capable of surviving within an extremely hypoxic environment. METHODS AND RESULTS: To better understand the mechanism of hsp90ß gene expression, we investigated its genomic organization. Eleven exons were identified, including a long upstream intron with a remarkable similarity with human, but not with chicken counterpart. Dual-luciferase assays identified promoter activity in a 1366 bp 5'-flanking segment beyond the transcription initiation site. Examination detected a minimal promoter of 754 bp containing a TATA-box, CAAT-enhancer in addition to providing clues regarding other enhancer and repressor elements. The driving capability of this minimal promoter was further validated by its binding ability with TATA-box binding protein and the generation of GFP expressing transgenic zebrafish (F2). Further, deletion of an inverted HIF (hypoxia inducible factor) motif RCGTG (upstream of the TATA-box) dramatically reduced luciferase expression in a hypoxic environment (CoCl2 treated cultivable cells) and was identified as a cis-acting HIF responsive element, necessary for the hypoxia-induced expression. CONCLUSIONS: The results obtained herein provide an insight regarding how hsp90ß gene expression is controlled by HIF responsive element in teleost both during hypoxia stress management and normal physiological functions, and suggested that the hsp90ß gene promoter could be used as a potential candidate for generating ornamental and food-fish transgenics.