SummaryRuditapes philippinarum is an economically important bivalve with remarkable diversity in its shell coloration patterns. In this study, we sequenced the whole genome of the Manila clam and investigated the molecular basis of its adaptation to hypoxia, acidification, and parasite stress with transcriptome sequencing and an RNA sequence analysis of different tissues and developmental stages to clarify these major issues. A number of immune-related gene families are expanded in the R. philippinarum genome, such as TEP, C3, C1qDC, Hsp70, SABL, and lysozyme, which are potentially important for its stress resistance and adaptation to a coastal benthic life. The transcriptome analyses demonstrated the dynamic and orchestrated specific expression of numerous innate immune-related genes in response to experimental challenge with pathogens. These findings suggest that the expansion of immune- and stress-related genes may play vital roles in resistance to adverse environments and has a profound effect on the clam's adaptation to benthic life.

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Circular RNAs (circRNAs) are long noncoding RNAs that play a significant role in various biological processes, including embryonic development and stress responses. These regulatory molecules can modulate microRNA activity and are involved in different molecular pathways as indirect regulators of gene expression. Thousands of circRNAs have been described in diverse taxa due to the recent advances in high throughput sequencing technologies, which led to a huge variety of total RNA sequencing being publicly available. A number of circRNA de novo and host gene prediction tools are available to date, but their ability to accurately predict circRNA host genes is limited in the case of low-quality genome assemblies or annotations. Here, we present CircParser, a simple and fast Unix/Linux pipeline that uses the outputs from the most common circular RNAs in silico prediction tools (CIRI, CIRI2, CircExplorer2, find_circ, and circFinder) to annotate circular RNAs, assigning presumptive host genes from local or public databases such as National Center for Biotechnology Information (NCBI). Also, this pipeline can discriminate circular RNAs based on their structural components (exonic, intronic, exon-intronic or intergenic) using a genome annotation file.

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.