Circular RNA alterations in the Bombyx mori midgut following B. mori nucleopolyhedrovirus infection

Identification and characterization of circular RNAs in the skin of rainbow trout (Oncorhynchus mykiss) infected with infectious hematopoietic necrosis virus

Rainbow trout (Oncorhynchus mykiss) is an economically significant freshwater-farmed fish worldwide, and the frequent outbreaks of infectious hematopoietic necrosis (IHN) in recent years have gravely compromised the healthy growth of the rainbow trout aquaculture industry. Fish skin is an essential immune barrier against the invasion of external pathogens, but it is poorly known about the role of circRNAs in rainbow trout skin. Therefore, we examined the expression profiles of circRNAs in rainbow trout skin following IHNV infection using RNA-seq. A total of 6607 circRNAs were identified, of which 34 circRNAs were differentially expressed (DE) and these DE circRNA source genes were related to immune-related pathways such as Toll-like receptor signaling pathway, NOD-like receptor signaling pathway, Cytokine-cytokine receptor interaction, ubiquitin mediated proteolysis, and ferroptosis. We used qRT-PCR, Sanger sequencing, and subcellular localization to validate the chosen DE circRNAs, confirming their localization and expression patterns in rainbow trout skin. Further, 12 DE circRNAs were selected to construct the circRNA-miRNA-mRNA regulatory network, finding one miRNA could connect one or more circRNAs and mRNAs, and some miRNAs were reported to be associated with antiviral immunity. The functional prediction findings revealed that novel_circ_002779 and novel_circ_004118 may act as sponges for miR-205-z and miR-155-y to regulate the expression of target genes TLR8 and PIK3R1, respectively, and participated in the antiviral immune responses in rainbow trout. These results shed light on the immunological mechanism of circRNAs in rainbow trout skin and offer fundamental information for further research on the innate immune system and breeding rainbow trout resistant to disease.

Advances in the understanding of circRNAs that influence viral replication in host cells

Circular RNAs (circRNAs) are non-coding RNAs discovered in recent years, which are produced by back-splicing involving the 3' and 5' ends of RNA molecules. There is increasing evidence that circRNAs have important roles in cancer, neurological diseases, cardiovascular and cerebrovascular diseases, and other diseases. In addition, host circRNAs and virus-encoded circRNAs participate in the body's immune response, with antiviral roles. This review summarizes the mechanisms by which host and viral circRNAs interact during the host immune response. Comprehensive investigations have revealed that host circRNAs function as miRNA sponges in a particular manner, primarily by inhibiting viral replication. Viral circRNAs have more diverse functions, which generally involve promoting viral replication. In addition, in contrast to circRNAs from RNA viruses, circRNAs from DNA viruses can influence host cell migration, proliferation, and apoptosis, along with their effects on viral replication. In summary, circRNAs have potential as diagnostic and therapeutic targets, offering a foundation for the diagnosis and treatment of viral diseases.

Novel Insights into the circRNA-Modulated Developmental Mechanism of Western Honey Bee Larval Guts

Circular RNAs (circRNAs) are a class of novel non-coding RNAs (ncRNAs) that play essential roles in the development and growth of vertebrates through multiple manners. However, the mechanism by which circRNAs modulate the honey bee gut development is currently poorly understood. Utilizing the transcriptome data we obtained earlier, the highly expressed circRNAs in the Apis mellifera worker 4-, 5-, and 6-day-old larval guts were analyzed, which was followed by an in-depth investigation of the expression pattern of circRNAs during the process of larval guts development and the potential regulatory roles of differentially expressed circRNAs (DEcircRNAs). In total, 1728 expressed circRNAs were detected in the A. mellifera larval guts. Among the most highly expressed 10 circRNAs, seven (novel_circ_000069, novel_circ_000027, novel_circ_000438, etc.) were shared by the 4-, 5-, and 6-day-old larval guts. In addition, 21 (46) up-regulated and 22 (27) down-regulated circRNAs were, respectively, screened in the Am4 vs. Am5 (Am5 vs. Am6) comparison groups. Additionally, nine DEcircRNAs, such as novel_circ_000340, novel_circ_000758 and novel_circ_001116, were shared by these two comparison groups. These DEcircRNAs were predicted to be transcribed from 14 and 29 parental genes; these were respectively annotated to 15 and 22 GO terms such as biological regulation and catalytic activity as well as 16 and 21 KEGG pathways such as dorsoventral axis formation and apoptosis. Moreover, a complicated competing endogenous RNA (ceRNA) network was observed; novel_circ_000838 in the Am4 vs. Am5 comparison group potentially targeted ame-miR-6000a-3p, further targeting 518 mRNAs engaged in several developmental signaling pathways (e.g., TGF-beta, hedgehog, and wnt signaling pathway) and immune pathways (e.g., phagosome, lysosome, and MAPK signaling pathway). The results demonstrated that the novel_circ_000838-ame-miR-6000a-3p axis may plays a critical regulatory part in the larval gut development and immunity. Furthermore, back-splicing sites of six randomly selected DEcircRNAs were amplified and verified by PCR; an RT-qPCR assay of these six DEcircRNAs confirmed the reliability of the used high-throughput sequencing data. Our findings provide a novel insight into the honey bee gut development and pave a way for illustration of the circRNA-modulated developmental mechanisms underlying the A. mellifera worker larval guts.

A review on circular RNAs and bacterial infections

Bacterial infections and related diseases have been a major burden on social public health and economic stability around the world. However, the effective diagnostic methods and therapeutic approaches to treat bacterial infections are still limited. As a group of non-coding RNA, circular RNAs (circRNAs) that were expressed specifically in host cells and played a key regulatory role have the potential to be of diagnostic and therapeutic value. In this review, we systematically summarize the role of circRNAs in common bacterial infections and their potential roles as diagnostic markers and therapeutic targets.

The Potential Biological Roles of Circular RNAs in the Immune Systems of Insects to Pathogen Invasion

Circular RNAs (circRNAs) are a newly discovered class of endogenously expressed non-coding RNAs (ncRNAs). They are highly stable, covalently closed molecules that frequently exhibit tissue-specific expression in eukaryotes. A small number of circRNAs are abundant and have been remarkably conserved throughout evolution. Numerous circRNAs are known to play important biological roles by acting as microRNAs (miRNAs) or protein inhibitors ('sponges'), by regulating the function of proteins, or by being translated themselves. CircRNAs have distinct cellular functions due to structural and production differences from mRNAs. Recent advances highlight the importance of characterizing circRNAs and their targets in a variety of insect species in order to fully understand how they contribute to the immune responses of these insects. Here, we focus on the recent advances in our understanding of the biogenesis of circRNAs, regulation of their abundance, and biological roles, such as serving as templates for translation and in the regulation of signaling pathways. We also discuss the emerging roles of circRNAs in regulating immune responses to various microbial pathogens. Furthermore, we describe the functions of circRNAs encoded by microbial pathogens that play in their hosts.

BmNPV circular RNA-encoded peptide VSP39 promotes viral replication

CircRNAs are covalently closed single-stranded circular RNA molecules, which are not easily degraded by endonucleases and play vital roles in many biological processes. Currently, most studies on circRNAs focus on endogenous circRNAs in cells, and there are few studies on virus-encoded circRNAs. In this study, a viral circRNA (circRNA-000010) derived from the region (-/bp: 114514-115,319) of the complementary strand of Bombyx mori Nucleopolyhedrovirus (BmNPV) genome was identified with the circRNA-sequencing. The authenticity of viral circRNA-000010 was further confirmed by reverse transcription PCR, reverse transcription-rolling circle amplification (TCA), in situ hybridization, immunofluorescent staining, and Northern blotting. The results of overexpression and knockdown experiments showed that circRNA-000010 promoted viral replication. Furthermore, a viral small peptide VSP39 with 39 amino acid residues translated by circRNA-000010 but not its linear molecule was confirmed. Finally, VSP39 was found to promote viral replication. Our findings indicated that a viral circRNA encoded by BmNPV promoted viral replication. These findings will provide new clues for further understanding coding information of the BmNPV genome and open a new insight for investigating host-virus interactions.

The Mechanisms of Silkworm Resistance to the Baculovirus and Antiviral Breeding

Silkworm (Bombyx mori) is not only an economic insect but also a model organism for life science research. Bombyx mori nucleopolyhedrovirus (BmNPV) disease is a major infectious disease in the world's sericulture industry. The cocoon loss caused by this disease accounts for more than 60% of the total loss caused by all silkworm diseases. To date, there has been no effective solution for preventing and treating this disease. The most effective measure is to breed disease-resistant varieties. The quickest way to breed disease-resistant varieties is to apply genetic modification. However, this requires that we obtain disease resistance genes and know the mechanism of disease resistance. Since the discovery of disease-resistant resources in 1989, scholars in the sericulture industry around the world have been inspired to search for resistance genes. In the past two decades, with the help of multi-omics technologies, screening of resistance genes, gene localization, protein modification, virus-host interactions, etc., researchers have found some candidate genes that have been proposed to function at the cellular or individual level. Several disease-resistant varieties have been obtained and used in production through hybrid breeding, RNA interference, and genetic modification. This article summarizes and reviews the discovery of and research advances related to silkworm resistance to BmNPV. It is anticipated that the review will inspire scientific researchers to continue searching for disease resistance genes, clarify the molecular mechanism of silkworm disease resistance, and promote disease-resistant silkworm breeding.

CircRNA-regulated immune responses of asian honey bee workers to microsporidian infection

Nosema ceranae is a widespread fungal parasite for honey bees, causing bee nosemosis. Based on deep sequencing and bioinformatics, identification of circular RNAs (circRNAs) in Apis cerana workers' midguts and circRNA-regulated immune response of host to N. ceranae invasion were conducted in this current work, followed by molecular verification of back-splicing sites and expression trends of circRNAs. Here, 10185 and 7405 circRNAs were identified in the midguts of workers at 7 days (AcT1) and 10 days (AcT2) post inoculation days post-inoculation with N. ceranae. PCR amplification result verified the back-splicing sites within three specific circRNAs (novel_circ_005123, novel_circ_007177, and novel_circ_015140) expressed in N. ceranae-inoculated midgut. In combination with transcriptome data from corresponding un-inoculated midguts (AcCK1 and AcCK2), 2266 circRNAs were found to be shared by the aforementioned four groups, whereas the numbers of specific ones were 2618, 1917, 5691, and 3723 respectively. Further, 83 52) differentially expressed circRNAs (DEcircRNAs) were identified in AcCK1 vs. AcT1 (AcCK2 vs. AcT2) comparison group. Source genes of DEcircRNAs in workers' midgut at seven dpi were involved in two cellular immune-related pathways such as endocytosis and ubiquitin mediated proteolysis. Additionally, competing endogenous RNA (ceRNA) network analysis showed that 23 13) DEcircRNAs in AcCK1 vs. AcT1 (AcCK2 vs. AcT2) comparison group could target 18 14) miRNAs and further link to 1111 (1093) mRNAs. These target mRNAs were annotated to six cellular immunity pathways including endocytosis, lysosome, phagosome, ubiquitin mediated proteolysis, metabolism of xenobiotics by cytochrome P450, and insect hormone biosynthesis. Moreover, 284 164) internal ribosome entry site and 54 26) ORFs were identified from DEcircRNAs in AcCK1 vs. AcT1 (AcCK2 vs. AcT2) comparison group; additionally, ORFs in DEcircRNAs in midgut at seven dpi with N. ceranae were associated with several cellular immune pathways including endocytosis and ubiquitin-mediated proteolysis. Ultimately, RT-qPCR results showed that the expression trends of six DEcircRNAs were consistent with those in transcriptome data. These results demonstrated that N. ceranae altered the expression pattern of circRNAs in A. c. cerana workers' midguts, and DEcircRNAs were likely to regulate host cellular and humoral immune response to microsporidian infection. Our findings lay a foundation for clarifying the mechanism underlying host immune response to N. ceranae infection and provide a new insight into interaction between Asian honey bee and microsporidian.

Deciphering the CircRNA-Regulated Response of Western Honey Bee (Apis mellifera) Workers to Microsporidian Invasion

Vairimorpha ceranae is a widespread fungal parasite of adult honey bees that leads to a serious disease called nosemosis. Circular RNAs (circRNAs) are newly discovered non-coding RNAs (ncRNAs) that regulate biological processes such as immune defense and development. Here, 8199 and 8711 circRNAs were predicted from the midguts of Apis mellifera ligustica workers at 7 d (Am7T) and 10 d (Am10T) after inoculation (dpi) with V. ceranae spores. In combination with transcriptome data from corresponding uninoculated midguts (Am7CK and Am10CK), 4464 circRNAs were found to be shared by these four groups. Additionally, 16 circRNAs were highly conserved among A. m. ligustica, Apis cerana cerana, and Homo sapiens. In the Am7CK vs. Am7T (Am10CK vs. Am10T) comparison group, 168 (306) differentially expressed circRNAs (DEcircRNAs) were identified. RT-qPCR results showed that the expression trend of eight DEcircRNAs was consistent with that in the transcriptome datasets. The source genes of DEcircRNAs in Am7CK vs. Am7T (Am10CK vs. Am10T) were engaged in 27 (35) GO functional terms, including 1 (1) immunity-associated terms. Moreover, the aforementioned source genes were involved in three cellular immune-related pathways. Moreover, 86 (178) DEcircRNAs in workers' midguts at 7 (10) dpi could interact with 75 (103) miRNAs, further targeting 215 (305) mRNAs. These targets were associated with cellular renewal, cellular structure, carbohydrate and energy metabolism, and cellular and humoral immunity. Findings in the present study unraveled the mechanism underlying circRNA-mediated immune responses of western honey bee workers to V. ceranae invasion, but also provided new insights into host-microsporidian interaction during nosemosis.

Viral Circular RNAs and Their Possible Roles in Virus-Host Interaction

Circular RNAs (circRNAs) as novel regulatory molecules have been recognized in diverse species, including viruses. The virus-derived circRNAs play various roles in the host biological process and the life cycle of the viruses. This review summarized the circRNAs from the DNA and RNA viruses and discussed the biogenesis of viral and host circRNAs, the potential roles of viral circRNAs, and their future perspective. This review will elaborate on new insights gained on viruses encoded circRNAs during virus infection.

Micropeptide vsp21 translated by Reovirus circular RNA 000048 attenuates viral replication

To date, some DNA viruses and single-stranded RNA viruses have been found to generate circRNAs. However, the reports on circRNAs produced by double-stranded RNA viruses are very limited. In this study, Bombyx mori cypovirus (BmCPV), a typical double-stranded RNA virus belonging to the Reoviridae, was demonstrated to generate viral circRNAs (vcircRNAs) and a vcircRNA_000048 whose sequence corresponds with the region 164-1245 nt on the BmCPV genomic dsRNA S5 segment (GQ294468.1) was validated by PCR, Sanger sequencing, reverse transcription-rolling circle amplification, and Northern blotting. Furthermore, we verified that vcircRNA_000048 translates a micropeptide vsp21 with 21 amino acid residues in an IRES-dependent manner, and vsp21 attenuates the viral replication. These findings provided a novel clue to understanding the regulation of viral multiplication and interaction of reovirus with the host.

Identification of Silkworm Hemocyte Subsets and Analysis of Their Response to Baculovirus Infection Based on Single-Cell RNA Sequencing

A wide range of hemocyte types exist in insects but a full definition of the different subclasses is not yet established. The current knowledge of the classification of silkworm hemocytes mainly comes from morphology rather than specific markers, so our understanding of the detailed classification, hemocyte lineage and functions of silkworm hemocytes is very incomplete. Bombyx mori nucleopolyhedrovirus (BmNPV) is a representative member of the baculoviruses and a major pathogen that specifically infects silkworms (Bombyx mori) and causes serious losses in sericulture industry. Here, we performed single-cell RNA sequencing (scRNA-seq) of hemocytes in BmNPV and mock-infected larvae to comprehensively identify silkworm hemocyte subsets and determined specific molecular and cellular characteristics in each hemocyte subset before and after viral infectmadion. A total of 20 cell clusters and their potential marker genes were identified in silkworm hemocytes. All of the hemocyte clusters were infected by BmNPV at 3 days after inoculation. Interestingly, BmNPV infection can cause great changes in the distribution of hemocyte types. The cells appearing in the infection group mainly belong to prohemocytes (PR), while plasmatocytes (PL) and granulocytes (GR) are very much reduced. Furthermore, we found that BmNPV infection suppresses the RNA interference (RNAi) and immune response in the major hemocyte types. In summary, our results revealed the diversity of silkworm hemocytes and provided a rich resource of gene expression profiles for a systems-level understanding of their functions in the uninfected condition and as a response to BmNPV.

Integrative analysis of circRNA/miRNA/mRNA regulatory network reveals the potential immune function of circRNAs in the Bombyx mori fat body

Bombyx mori nucleopolyhedrosis virus (BmNPV) is one of the greatest threats to sustainable development of the sericulture industry. Circular RNA (circRNA), a type of non-coding RNA, has been shown to play important roles in gene expression regulation, immune response, and diseases. The fat body is a tissue with both metabolic and immune functions. To explore the potential immune function of circRNAs, we analyzed differentially expressed (DE)circRNAs, microRNAs(miRNAs), and mRNAs in the B. mori fat body in response to BmNPV infection using high-throughput RNA sequencing. A total of 77 DEcircRNAs, 32 DEmiRNAs, and 730 DEmRNAs that are associated with BmNPV infection were identified. We constructed a DEcircRNA/DEmiRNA/DEmRNA and DEcircRNA/DEmiRNA/BmNPV gene regulatory network and validated the differential expression of circ_0001432 and its corresponding miRNA (miR-2774c and miR-3406-5p) and mRNA (778467 and 101745232) in the network. Tissue-specific expression of circ_0001432 and its expression at different time points were also examined. KEGG pathway analysis of DEmRNAs, target genes of DEmiRNAs, and host genes of DEcircRNAs in the network showed that these genes were enriched in several metabolic pathways and signaling pathways, which could play important roles in insect immune responses. Our results suggest that circRNA could be involved in immune responses of the B. mori fat body and help in understanding the molecular mechanisms underlying silkworm-pathogen interactions.

Expression profile analysis of circular RNAs in BmN cells (Bombyx mori) upon BmNPV infection

The disease caused by Bombyx mori nucleopolyhedrovirus (BmNPV) has always been difficult to control, resulting in tremendous economic losses in the sericulture industry. Although much has been learned about the impact of noncoding RNAs on pathogenesis, the role of circular RNA (circRNA) in insect immunity remains unclear. To explore circRNA regulation involved in BmNPV infection, we used transcriptome analysis of BmN cells with or without BmNPV infection to generate circRNA data set. A total of 444 novel circRNAs were identified in BmN cells, with 198 pervasively distributed both in the control group and BmNPV-infection group. The host genes were enriched inMAPK signaling pathway, dorso-ventral axis formation, and ECM-receptor interaction, which were required for the normal larval growth. A total of 75 circRNAs were differentially expressed (DE) on BmNPV infection. Six downregulated circRNAs were validated by Sanger sequencing and qRT-PCR. DEcircRNA-miRNA-DEmRNA network was constructed based on the six validated circRNAs. Pathway analysis indicated that the predicted target genes were mainly enriched in the metabolic pathway and immune-related signaling pathway. Our results may provide a basis for further studies on circRNA function in BmN cells challenged by BmNPV infection and offer an insight into the molecular mechanism on silkworm-virus interaction.

The role of circular RNAs in viral infection and related diseases

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CircRNAs are formed by pre-mRNA through “back-splicing”.

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CircRNAs regulate host immune response and virus replication.

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CircRNAs have potential as diagnostic markers or treatment targets for viral infection.

Circular RNAs (circRNAs) are a class of non-coding RNAs with a special covalently closed circular structure, which is formed by precursor mRNA (pre-mRNA) through “back-splicing”. CircRNAs are more stable than linear RNAs because they are resistant to exoribonucleases. Viral infections often cause abnormal expression of circRNAs, which could serve as novel biomarkers for the diagnosis of viral infections by detecting specific circRNAs in cells, body fluids, or tissues. CircRNAs also play a critical role in regulating host immune response and virus replication. Here, we reviewed the production and function of circRNAs, mainly focusing on their regulation on virus infection, to provide novel insights into the potential role of circRNAs as diagnostic marker or treatment targets for viral infection.

[Continuous expression and functional prediction of circular RNA in mouse lung development]

OBJECTIVE

To study the continuous expression and potential function of circular RNA (circRNA), circ4:150439343|150477468 and circ15:73330849|73343359, in mouse lung development.

METHODS

According to the stage of lung development, lung tissue samples were collected from mice on embryonic day 16.5 (E16.5), embryonic day 18.5 (E18.5), and postnatal day 2 (P2). Hematoxylin and eosin staining was performed to observe the morphology of lung tissue. Quantitative real-time PCR (qRT-PCR) was used to measure the mRNA expression of circ4:150439343|150477468 and circ15:73330849|73343359 during late lung development; miRanda and TargetScan were used to predict the target miRNAs of circRNAs, and then GO and KEGG analysis was performed for the target genes to predict the potential function of circRNAs.

RESULTS

Type II alveolar epithelial cells were observed in the lung slices of E16.5 mice, with a gradual increase in number. On P2, the pulmonary alveoli expanded rapidly, the pulmonary interstitium became thinner, and the alveolar structure gradually became mature. The results of qRT-PCR showed that the relative expression of circ4:150439343|150477468 was continuously upregulated over time and the relative expression of circ15:73330849|73343359 was first downregulated and then upregulated (P<0.05). The KEGG and GO analysis showed that circRNAs were involved in the Notch, PI3K-Akt, and NF-κB signaling pathways.

CONCLUSIONS

Circ4:150439343|150477468 and circ15:73330849|73343359 can participate in lung development through the Notch signaling pathway.

circEgg regulates histone H3K9me3 by sponging bmo-miR-3391-5p and encoding circEgg-P122 protein in the silkworm, Bombyx mori

A large number of circular RNAs (circRNAs) have been found in different organisms; however, their function in the regulation of histone modification remains unknown. In this study, we found that the circRNA circEgg, cyclized by the 9th-13th exon of Bombyx mori histone-lysine N-methyltransferase eggless (BmEgg) gene, mainly distributes in the cytoplasm, its expression levels changed with silkworm developmental stages, and the linear transcript level of the BmEgg gene was decreased when circEgg was overexpressed. Moreover, circEgg was found to repress histone H3 lysine 9 methylation (H3K9me3), promote histone H3 lysine 9 acetylation (H3K9ac), and positively regulate histone deacetylase (HDAC) Rpd3 (BmHDAC Rpd3) gene expression by sponging the microRNA bmo-miR-3391-5p. Furthermore, circEgg encodes a circEgg-P122 protein which appears to inhibit H3K9me3. These results suggest that circEgg regulates histone modification by sponging bmo-miR-3391-5p and encoding circEgg-P122 protein. To our knowledge, this is the first report showing that a circRNA produced by BmEgg plays an important role in histone epigenetic modification.

Systematic identification of circular RNAs and corresponding regulatory networks unveil their potential roles in the midguts of eastern honeybee workers

Currently, knowledge of circular RNAs (circRNAs) in insects including honeybee is extremely limited. Here, differential expression profiles and regulatory networks of circRNAs in the midguts of Apis cerana cerana workers were comprehensively investigated using transcriptome sequencing and bioinformatics. In total, 9589 circRNAs (201-800 nt in length) were identified from 8-day-old and 11-day-old workers' midguts (Ac1 and Ac2); among them, 5916 (61.70%) A. cerana cerana circRNAs showed conservation with our previously indentified circRNAs in Apis mellifera ligucstica workers' midguts (Xiong et al., Acta Entomologica Sinica 61:1363-1375, 2018). Five circRNAs were confirmed by RT-PCR and Sanger sequencing. Interestingly, novel_circ_003723, novel_circ_002714, novel_circ_002451, and novel_circ_001980 were highly expressed in both Ac1 and Ac2. In addition, the source genes of circRNAs were involved in 34 GO terms including organelle and cellular process and 141 pathways such as endocytosis and Wnt signaling pathway. Moreover, 55 DEcircRNAs including 34 upregulated and 21 downregulated circRNAs were identified in Ac2 compared with Ac1. circRNA-miRNA regulatory networks indicated that 1060 circRNAs can target 74 miRNAs; additionally, the DEcircRNA-miRNA-mRNA networks suggested that 13 downregulated circRNAs can bind to eight miRNAs and 29 miRNA-targeted mRNAs, while 16 upregulated circRNAs can link to 9 miRNAs and 29 miRNA-targeted mRNAs. These results indicated that DEcircRNAs as ceRNAs may play a comprehensive role in the growth, development, and metabolism of the worker's midgut via regulating source genes and interacting with miRNAs. Notably, eight DEcircRNAs targeting miR-6001-y were likely to be key participants in the midgut development. Our findings not only offer a valuable resource for further studies on A. cerana cerana circRNA and novel insights into understanding the molecular mechanisms underlying the midgut development of eastern honeybee but also provide putative circRNA candidates for functional research in the near future and novel biomarkers for identification of eastern honeybee species including A. cerana cerana and honeybee diseases such as chalkbrood and microsporidiosis.

Identification and characterization of novel type of RNAs, circRNAs in crucian carp Carassius auratus gibelio

Circular RNAs (circRNAs) with regulatory potency activity was identified from varieties of species. Crucian carp (Carassius auratus gibelio) is one of the most freshwater aquaculture species in China. Every year, huge economic damage to the farming was caused by the virus and bacterial infection. Until now, there is any information about circRNA reported from the Crucian carp. In this study, the expression pattern of circRNA in Crucian carp was investigated with transcriptomic analysis. The results showed that only 37 circRNAs were identified from the Crucian carp, and these circRNAs biogenesis was formed with canonical GU-AG splicing mechanism with unevenly distributed on the chromosomes. Wherein, most of the circRNAs were derived from the sense overlapping strategy. Reverse transcript PCR and Sanger sequencing data indicated that these circRNAs were existed authenticity in Crucian carp. The bioinformatics analysis indicated that circRNAs identified from the Crucian carp with potential miRNA sponge regulate the expression level of mRNAs. GO annotation and KEGG pathway analysis of these circRNAs showed that more than 20% circRNAs were related with catalytic activity and binding in the category of molecular function, and these circRNAs were enriched in 9 signaling pathways, such as, Wnt signaling pathway, MAPK signaling pathway, Ubiquitin mediated proteolysis et al. 220 mRNAs would be regulated by the circRNAs via miRNAs mediation. These target mRNAs were further analyzed with functional annotation and KEGG analysis. GO annotation analysis showed that several genes were related with function of nucleotide binding, transcription regulatory activity. KEGG pathway analysis showed that 5 genes were enriched in the pathway of Endocytosis. The circRNA-miRNA-mRNA regulation network indicated that one miRNA can link one or more circRNA and one or more mRNA. Overall, these results will not only help us to further understand the novel RNA transcripts in Crucian carp, but also provide the novel clue to investigate the interaction between host and pathogens from this novel circRNA molecule.