Circular RNAs (circRNAs) are covalently closed, endogenous biomolecules in eukaryotes with tissue-specific and cell-specific expression patterns, whose biogenesis is regulated by specific cis-acting elements and trans-acting factors. Some circRNAs are abundant and evolutionarily conserved, and many circRNAs exert important biological functions by acting as microRNA or protein inhibitors ('sponges'), by regulating protein function or by being translated themselves. Furthermore, circRNAs have been implicated in diseases such as diabetes mellitus, neurological disorders, cardiovascular diseases and cancer. Although the circular nature of these transcripts makes their detection, quantification and functional characterization challenging, recent advances in high-throughput RNA sequencing and circRNA-specific computational tools have driven the development of state-of-the-art approaches for their identification, and novel approaches to functional characterization are emerging.

The biogenesis, biology and characterization of circular RNAs.

Environmentally induced oxidative stress in aquatic animals

Molecular biomarkers of oxidative stress in aquatic organisms in relation to toxic environmental pollutants.

Circular RNAs, a novel class of endogenous noncoding RNAs, are characterized by their covalently closed loop structures without a 5′ cap or a 3′ Poly A tail. Although the mechanisms of circular RNAs’ generation and function are not fully clear, recent research has shown that circular RNAs may function as potential molecular markers for disease diagnosis and treatment and play an important role in the initiation and progression of human diseases, especially in tumours. This review summarizes some information about categories, biogenesis, functions at the molecular level, properties of circular RNAs and the possibility of circular RNAs as biomarkers in cancers.

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CircRNA: functions and properties of a novel potential biomarker for cancer

Oxygen in its molecular state O2, is essential for many metabolic processes that are vital to aerobic life. Aerobic organisms cannot exist without oxygen, which nevertheless is inherently dangerous to their lives. Like all aerobic organisms, fish are also susceptible to the effects of reactive oxygen and have inherent and effective antioxidant defenses that are well described in the literature. This review investigates the influence of different biotic and abiotic factors (age, phylogenetic position, feeding behavior, environmental factors, oxygen, temperature, presence of xenobiotics) on antioxidant defenses in fish. Studies of antioxidant activity in fish open a number of novel research lines providing greater knowledge of fish physiology, which will benefit various aspects of fish farming and artificial production.

Antioxidant Defenses in Fish: Biotic and Abiotic Factors

Biomarkers of oxidative stress: a comparative study of river Yamuna fish Wallago attu (Bl. & Schn.).

Oxidative stress biomarkers of exposure to deltamethrin in freshwater fish, Channa punctatus Bloch

Immunomodulatory effects of fenugreek (Trigonella foenum graecum L.) extract in mice.

Effect of a single exposure of endosulfan (5 ppb) on catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), and reduced glutathione (GSH) of liver, kidney, and gill of a freshwater fish (Channa punctatus Bloch) were evaluated after 24 h of treatment. Endosulfan exposure resulted in a significant induction (p < 0.05-0.001) of GPx, GST activity, and GSH levels in all the organs. However, CAT activity was found to be significantly decreased (p < 0.01-0.001). Lipid peroxidation (LPO) values were also determined in liver, kidney, and gill and a significant increase in LPO values (p < 0.05-0.01) was observed in all the organs. We also investigated whether preexposure to low concentration of copper (10 ppb) for 4 weeks has any protective effect against endosulfan-induced oxidative damage. In copper-acclimatized endosulfan-exposed fish, a significant decrease in GPx (p < 0.001), GST (p < 0.05), GSH (p < 0.001) levels, and LPO (p < 0.01) was observed in the liver, whereas CAT activity was increased significantly (p < 0.001). However, kidney and gill did not show any significant alterations in antioxidant levels. The results of this study demonstrate that endosulfan induces peroxidative damage in liver, kidney, and gill in response to which levels of antioxidant were modulated. However, when fish preacclimatized to copper were exposed to endosulfan, protection against oxidative damage was observed only in the liver. It is proposed that measurement of antioxidants in fish tissues may prove to be useful in biomonitoring of exposure to aquatic pollutants.

Effect of endosulfan on antioxidants of freshwater fish Channa punctatus Bloch: 1. Protection against lipid peroxidation in liver by copper preexposure.

The exciting world of research with RNAs has to its credit some breakthrough findings that led to newer insights on multiple problems including that of human diseases After the advent of siRNA, microRNA, and lncRNA, exciting novel molecules called circular RNAs (circRNAs) have been recently described circRNAs are a class of non-coding RNAs, which are produced by scrambling of exons at the time of splicing They are primarily produced in the brain region and are naturally present inside the cell The best known ones so far include a particular type of circRNA namely "circular RNA sponge for miR-7" (ciRS-7 and CDR1as) which is the inhibitor of miR-7 microRNA-known to regulate various diseases like, cancer, neurodegenerative diseases, diabetes, and atherosclerosis Similarly, another circRNA molecule called circmbl modulates the ratio of linear mRNA by competing with linear muscleblind gene through which it is synthesized Considering the complex association of these molecules with critical microRNAs and gene families, circRNAs might have important roles in the cause and progression of human diseases In particular, the multi-factorial nature of neurodegenerative diseases does warrant studies employing novel approaches towards identifying underlying root causes of these ailments The non-coding RNAs, like circRNAs and microRNAs, could well present a common genetic trigger to multiple factors associated with neurodegenerative diseases A specific fingerprint of a combination of various marker circRNAs could be explored for early diagnostic purpose as well Herein, we review the possibility of exploring the role of circRNAs in the context of the central nervous system (CNS) and age-associated neurodegenerative diseases

Rizwanul Haque

Papers

Biomarkers of oxidative stress: a comparative study of river Yamuna fish Wallago attu (Bl. & Schn.).

Oxidative stress biomarkers of exposure to deltamethrin in freshwater fish, Channa punctatus Bloch

Immunomodulatory effects of fenugreek (Trigonella foenum graecum L.) extract in mice.

Effect of endosulfan on antioxidants of freshwater fish Channa punctatus Bloch: 1. Protection against lipid peroxidation in liver by copper preexposure.

Circular RNAs: the Emerging Class of Non-coding RNAs and Their Potential Role in Human Neurodegenerative Diseases