Function of Circular RNAs in Fish and Their Potential Application as Biomarkers

Abstract

Circular RNAs (circRNAs) are an emerging class of regulatory RNAs with a covalently closed-loop structure formed during pre-mRNA splicing. Recent advances in high-throughput RNA sequencing and circRNA-specific computational tools have driven the development of novel approaches to their identification and functional characterization. CircRNAs are stable, developmentally regulated, and show tissue- and cell-type-specific expression across different taxonomic groups. They play a crucial role in regulating various biological processes at post-transcriptional and translational levels. However, the involvement of circRNAs in fish immunity has only recently been recognized. There is also broad evidence in mammals that the timely expression of circRNAs in muscle plays an essential role in growth regulation but our understanding of their expression and function in teleosts is still very limited. Here, we discuss the available knowledge about circRNAs and their role in growth and immunity in vertebrates from a comparative perspective, with emphasis on cultured teleost fish. We expect that the interest in teleost circRNAs will increase substantially soon, and we propose that they may be used as biomarkers for selective breeding of farmed fish, thus contributing to the sustainability of the aquaculture sector.

CircRNA Identification and CircRNA–miRNA–mRNA Network in Cynoglossus semilaevis Sexual Size Dimorphism

“…In mammals, birds, and teleosts, it was reported that circRNA plays important roles in muscle growth regulation [ 41 , 68 , 69 , 70 ]. Moreover, there are also studies addressing the involvement of circRNAs in the ovary development and sex determination for birds and teleosts [ 43 , 44 , 71 ].…”

“…CircRNA plays important roles in many biological and pathophysiological processes including immune, metabolism, skeletal muscle and fat tissue growth, follicle development, nerve system development, cell proliferation, and diseases [ 24 , 25 ], by decoying miRNAs, binding to protein, and translating into peptides [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. In teleosts such as the large yellow croaker ( Larimichthys crocea ), the grass carp ( Ctenopharyngodon idellus ), and the Nile tilapia ( Oreochromis niloticus ), circRNAs have been identified to be involved in growth, immunity, and heat stress [ 36 , 37 , 38 , 39 , 40 , 41 ]. In C. semilaevis , circRNA has been reported to regulate sex determination and differentiation [ 42 , 43 , 44 ].…”

Functions and clinical significance of circular RNAs in acute myeloid leukemia

“…CircRNAs was first reported in viroids by Sanger et al, in 1976 ( Sanger et al, 1976 ). With the development of high-throughput sequencing and increased research interest in circRNAs, many bioinformatics tools have been improved to study circRNAs in the past few years ( Wang Y. et al, 2020 ; Rbbani et al, 2021 ; Yang et al, 2021 ). Especially, accumulating evidence demonstrates that circRNA expression is deregulated in AML compared with healthy control and reveals AML subgroup-specific signatures ( Li W. et al, 2017 ; Chen H. L. et al, 2018 ; Lv et al, 2018 ; Lux et al, 2021 ; Wang J. H. et al, 2021 ).…”

The novel circular RNA CircMef2c is positively associated with muscle growth in Nile tilapia

“…These processes require a coordinated expression of many genes and diverse molecular pathways. In recent years, an increasing number of studies have suggested the importance of epigenetic mechanisms, including non-coding RNAs, in fish muscle development [ 5 – 10 ]. In-depth knowledge about regulatory mechanisms involved in fish growth is essential to explore the observed phenotypic variation in aquaculture conditions.…”