MicroRNAs As well different approaches have led to identify

MicroRNAs
(miRNAs) are small noncoding endogenous RNA that consists
approximately 19–25 nucleotides in length (Kaeuferle et al. 2014). They play a
significant role by post-transcriptionally regulating the gene expression in
plants and animals (Bartel, 2004; Chekulaeva and Filipowicz, 2009).
Furthermore, miRNA can influence target mRNA by binding to protein-coding
regions, thereby modulating the stability or translation of mRNA(1)

miRNAsP1  affect a variety
of key biological processes such as cell differentiation, proliferation and
apoptosis, development, immunity, metabolism and stem cell maintenance (2). Therefore,
function of miRNAs has provided potential pathways in various areas, such as
therapeutic intervention of miRNA against pathogens has led to conduct studies
related to investigate miRNA based therapy (MicroRNA therapeutics: Discovering
novel targets and developing specific therapy). P2 As well different
approaches have led to identify the effective use of miRNA profiling for
diverse applications in disease diagnosis (MicroRNA profiling: approaches and
considerations).P3 

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It is noted that
aberrant miRNA levels can cause diseases such as cancer, age-related diseases,
neurological disorders and immune function disorders. Consequently, appropriate
regulation of miRNA is essential for disease prevention (3). Moreover, miRNAs
have pivotal roles in eukaryotic defense mechanism of the host against
extracellular, invasive bacterial pathogens and viruses (4). (5). The
importance of miRNA in bacterial infections was initially discovered with the
aid of miR-393, regulates auxin signaling P4 against a extracellular
pathogen Pseudomonas  in Arabidopsis thaliana plant.  According to this discovery of miRNAs host
defence function in plants, latterly miRNAs were implicated in bacterial
infections in mammalians (6,7).

 

However, immune regulations
of miRNAs and characterization of miRNAs has not been studied extensively in
teleost fish when compared with mammals. In  8 teleost species from five orders, 1,250
miRNAs were identified (Table 1). However, some specific miRNA genes are available
only in teleost fish but not in higher vertebrates, such as miRNA-734 and miRNA-7132 P5 (Yang et al.,
2015; Yan et al., 2012; Andreassen et al., 2013). Therefore, studies have
conducted on identifying the miRNAs that are differentially expressed between
controls and challenged groups in teleost fish. According to those reports,  altered expression levels of miRNAs was
observed in viral as well as bacterial infections in several teleost fish. Moreover,
miRNAs contribute as regulators of Toll-like P6 receptors (tl) and
following stimulation of nuclear factor (NF-kB ) signaling in bacterial
infections. It is noted miRNAs responding to infection depends on the target
gene(s) they regulate and many of the targets are genes from the host’s immune
response gene networks (8).Aquaculture fish
industry often suffers with severe infections caused by viruses, bacteria and
parasites. Aeromonas
hydrophila is also such bacterium; gram-negative, motile, rod-shaped which
can cause motile aeromonas septicaemia (MAS) disease in fish that leads to high
mortility (9, Harikrishnan and Balasundarama, 2005). Therefore,
studying the immunity and host defence mechanisms of host by proper regulation
of miRNA will support the control and prevention of infectious aeromonas
septicaemia (MAS) disease in aquaculture industry.  

Zebra fish
is suitable animal model for drug screening and many applications because of
easy handling, fecundity and due to low cost screening (Pardo-Martin et al., 2013; Huiting et al., 2015; MacRae and Peterson, 2015; Ordas et al., 2015). The current study
has been carried out using a control and challenged groups to screen miRNAs in zebrafish (Danio
rerio) gut after an infection
of Aeromonas hydrophila and state
those identified miRNAs directly regulate the anti-bacterial activity of zebra
fish.