MiR-26 regulates ddx3x expression in medaka (Oryzias latipes) gonads

miR-330 targeting BCO2 is involved in carotenoid metabolism to regulate skin pigmentation in rainbow trout (Oncorhynchus mykiss)

BACKGROUND

MicroRNAs (miRNAs) play a critical role in regulating skin pigmentation. As a key economic trait, skin color directly affects the market value of rainbow trout (Oncorhynchus mykiss), however, the regulatory mechanism of most miRNAs in fish skin color is still unclear.

RESULTS

In this study, the full-length cDNA sequence of β-carotene oxygenase 2 (BCO2, a key regulator of carotenoid metabolism) from the rainbow trout was obtained using rapid-amplification of cDNA ends (RACE) technology, and qRT-PCR was used to investigate the differential expression of miR-330 and BCO2 in 14 developmental stages and 13 tissues between wild-type rainbow trout (WTrt) and yellow mutant rainbow trout (YMrt). Additionally, the function of miR-330 was verified by overexpression and silencing in vitro and in vivo. The results showed that the complete cDNA sequence of BCO2 was 2057 bp with a 1707 bp ORF, encoding a 568 amino acid protein having a molecular weight of 64.07 kD. Sequence alignment revealed that higher conservation of BCO2 protein amongst fishes than amongst other vertebrates, which was further confirmed by phylogenetic analysis. The analysis of spatial and temporal expression patterns suggested that BCO2 and miR-330 were abundantly expressed from fertilized-stage to multi-cell as well as in the dorsal and ventral skin of WTrt and YMrt, and their expression patterns were opposite in most of the same periods and tissues. In vitro, luciferase reporter assay confirmed that BCO2 was a direct target of miR-330, and transfection of miR-330 mimics into rainbow trout liver cells resulted in a decrease in the expression of BCO2; conversely, miR-330 inhibitor had the opposite effect to the miR-330 mimics. In vivo, miR-330 agomir significantly decreased BCO2 expression in dorsal skin, tail fin, and liver. Furthermore, overexpression of miR-330 could suppress cell proliferation and induce apoptosis.

CONCLUSION

Our results showed that miR-330 is involved in the regulation of skin pigmentation in rainbow trout by targeting BCO2 and shows its promise as a potential molecular target to assist the selection of rainbow trout with better skin color patterns.

Distinct patterns of gene expression during regeneration and asexual reproduction in the annelid Pristina leidyi

Regeneration, the ability to replace lost body parts, is a widespread phenomenon in the animal kingdom often connected to asexual reproduction or fission, since the only difference between the two appears to be the stimulus that triggers them. Both developmental processes have largely been characterized; however, the molecular toolkit and genetic mechanisms underlying these events remain poorly unexplored. Annelids, in particular the oligochaete Pristina leidyi, provide a good model system to investigate these processes as they show diverse ways to regenerate, and can reproduce asexually through fission under laboratory conditions. Here, we used a comparative transcriptomics approach based on RNA-sequencing and differential gene expression analyses to understand the molecular mechanisms involved in anterior regeneration and asexual reproduction. We found 291 genes upregulated during anterior regeneration, including several regeneration-related genes previously reported in other annelids such as frizzled, paics, and vdra. On the other hand, during asexual reproduction, 130 genes were found upregulated, and unexpectedly, many of them were related to germline development during sexual reproduction. We also found important differences between anterior regeneration and asexual reproduction, with the latter showing a gene expression profile more similar to that of control individuals. Nevertheless, we identified 35 genes that were upregulated in both conditions, many of them related to cell pluripotency, stem cells, and cell proliferation. Overall, our results shed light on the molecular mechanisms that control anterior regeneration and asexual reproduction in annelids and reveal similarities with other animals, suggesting that the genetic machinery controlling these processes is conserved across metazoans.

Identification and expression analysis of sex biased miRNAs in chinese hook snout carp Opsariichthys bidens

As an economically important fish, Opsariichthys bidens has obvious sexual dimorphism and strong reproductive capacity, but no epigenetics study can well explain its phenotypic variations. In recent years, many microRNAs involved in the regulation of reproductive development have been explored. In this study, the small RNA libraries of O. bidens on the testis and ovary were constructed and sequenced. A total of 295 known miRNAs were obtained and 100 novel miRNAs were predicted. By comparing testis and ovary libraries, 115 differentially expressed (DE) miRNAs were selected, of which 53 were up-regulated and 62 were down-regulated. A total of 64 GO items (padj < 0.01) and 206 KEGG pathways (padj < 0.01) were enriched in the target gene of miRNA. After that, the expression levels of nine DE miRNAs, including let-7a, miR-146b, miR-18c, miR-202-5p, miR-135c, miR-9-5p, miR-34c-3p, miR-460-5p and miR-338 were verified by qRT-PCR. Furthermore, bidirectional prediction of DE miRNAs and sex-related genes was carried out and the targeting correlation between miR-9-5p and nanos1 was verified by Dual-Luciferase reporter assay. Our findings identified the differentially expressed miRNA and paved the way to new possibilities for the follow-up study on the mechanism of miRNA-mRNA interaction in the gonads of O. bidens.

Comparative transcriptome analysis of brain and gonad reveals reproduction-related miRNAs in the giant prawn, Macrobrachium rosenbergii

Macrobrachium rosenbergii (M. rosenbergii), as a species of common prawn, is a delicacy that is consumed all over the world. By interacting with the target gene 3′-untranslated region (3'-UTR), microRNAs (miRNAs) regulate its expression and ultimately participate in the regulation of reproductive development. However, research focusing on miRNA regulation during gonadal development in M. rosenbergii received very little attention. To explore the association between miRNA and reproduction, we performed RNA sequencing (RNA-seq) on brain and gonad organs in male and female M. rosenbergii. A total of 494 miRNAs were obtained in RNA-seq, including 31 and 59 differentially expressed (DE) miRNAs in the brain and gonads, respectively. Furthermore, 9 DE miRNAs were randomly selected from the brain and gonads, and qRT-PCR was conducted to validate the results of RNA-seq. Interestingly, dpu-miR-133 was found to be substantially expressed in the male brain and testis but poorly expressed in the female brain, ovary, and other organs. Analysis of dpu-miR-133 by Targetscan and MiRanda predicted to target 5-HT1. Furthermore, the dual-luciferase reporter assay manifested that dpu-miR-133 can combine with 5-HT1. Overall, our research work provides basic data for further study on the miRNA-mediated regulation of brain, gonad, and reproductive development of study M. rosenbergii.

Small RNA sequencing reveals sex-related miRNAs in Collichthys lucidus

Collichthys lucidus (C. lucidus) is an economically important fish species, exhibiting sexual dimorphism in its growth rate. However, there is a lack of research on its underlying sex-related mechanisms. Therefore, small RNA sequencing was performed to better comprehend these sex-related molecular mechanisms. In total, 171 differentially expressed miRNAs (DE-miRNAs) were identified between the ovaries and testes. Functional enrichment analysis revealed that the target genes of DE-miRNAs were considerably enriched in the p53 signaling, PI3K–Akt signaling, and TGF-beta signaling pathways. In addition, sex-related miRNAs were identified, and the expression of miR-430c-3p and miR-430f-3p was specifically observed in the gonads compared with other organs and their expression was markedly upregulated in the testes relative to the ovaries. Bmp15 was a target of miR-430c-3p and was greatly expressed in the ovaries compared with the testes. Importantly, miR-430c-3p and bmp15 co-expressed in the ovaries and testes. This research provides the first detailed miRNA profiles for C. lucidus concerning sex, likely laying the basis for further studies on sex differentiation in C. lucidus.

Vasa identifies germ cells in embryos and gonads of Oryzias celebensis

Vasa is the most studied germ cell marker that is indispensable for germ cell development in teleost fishes. Here, a vasa full-length cDNA from Oryzias celebensis was isolated. Analysis of gene expression by reversed transcription polymerase chain reaction and in situ hybridization showed the vasa transcript was maternally inherited and specifically expressed in germ cells during embryogenesis and in adult gonads. During embryogenesis, vasa mRNA was widely distributed in the embryos until the somitogenesis stage and then specifically expressed in primordial germ cells (PGCs). In the testis, vasa expression was highest in spermatogonia and gradually decreased during spermatogenesis. In ovary, vasa expression was present predominantly in immature oocytes and persisted throughout oogenesis. Constructs containing green or red fluorescence proteins and vasa 3' UTR or dnd 3' UTR, confirmed stable vasa expression in the PGCs of O. celebensis and co-expression of the two genes. In summary, the conservation of vasa expression in embryonic and adult germ cells of both sexes compared to other vertebrates suggests its function is also widely conserved.

Low-Cost and Rapid Method of DNA Extraction from Scaled Fish Blood and Skin Mucus

PCR-based DNA amplification has been one of the major methods in aquaculture research for decades, although its use outside the modern laboratory environment is limited due to the relatively complex methods and high costs. To this end, we investigated a swabbing and disc protocol for the collection of DNA samples from fish which could extract DNA from fish skin mucus by a non-invasion technique costing only $0.02 (USD) and requiring less than 30 seconds. The disc method that we chose could use the cheap filter paper to extract DNA from above 10⁴ crucian carp blood cells, which is comparable to the commercial kit. By using skin mucus swabbing and the disc method, we can obtain amplification-ready DNA from mucus to distinguish different species from our smallest fish (medaka, ~2.5 cm and crucian carp, ~7 cm) to our biggest fish (tilapia, ~15 cm). Furthermore, the viral pathogen Carassius auratus herpesvirus (CaHV) of crucian carp was detected using our method, which would make performing molecular diagnostic assays achievable in limited-resource settings including aquafarms and aqua stores outside the laboratory environment.

miR-133b targets tagln2 and functions in tilapia oogenesis

microRNAs (miRNAs) are important components of non-coding RNAs that participate in diverse life activities by regulating gene expression at the post transcriptional level through base complementary pairing with 3'UTRs of target mRNAs. miR-133b is a member of the miR-133 family, which play important roles in muscle differentiation and tumorigenesis. Recently, miR-133b was reported to affect estrogen synthesis by targeting foxl2 in mouse, while its role in fish reproduction remains to be elucidated. In the present study, we isolated the complete sequence of miR-133b, which was highly expressed in tilapia ovary at 30 and 90 dah (days after hatching) and subsequently decreased at 120 to 150 dah by qPCR. Interestingly, only a few oogonia were remained in the antagomir-133b treated tilapia ovary, while phase I and II oocytes were observed in the ovaries of the control group. Unexpectedly, the expression of foxl2 and cyp19a1a, as well as estradiol levels in serum were increased in the treated group. Furthermore, tagln2, an important factor for oogenesis, was predicted as the target gene of miR-133b, which was confirmed by dual luciferase reporter vector experiments. miR-133b and tagln2 were co-expressed in tilapia ovaries. Taken together, miR-133b may be involved in the early oogenesis of tilapia by regulating tagln2 expression. This study enriches the understanding of miR-133b function during oogenesis and lays a foundation for further study of the regulatory network during oogenesis.

Transcriptome analysis provides insights into long noncoding RNAs in medaka gonads

Long non-coding RNAs (lncRNAs) are gradually regarded as regulators in sex determination and gonad development of various animals. Medaka (Oryzias latipes) is an excellent reproductive research model with sex-determining genes. However, the regulation of gonadal lncRNAs on medaka reproductive development remains unknown. Here, 5317 lncRNAs were obtained from medaka ovary and testis by Illumina HiSeq4000, among which 177 lncRNAs were up-regulated and 120 lncRNAs were down-regulated in the testis compared to the ovary. In addition, 6904 cis-regulated target genes were predicted from 3099 lncRNAs. GO and KEGG enrichment analysis showed that these target genes were mainly involved in phosphorylation, metabolic, metabolism of xenobiotics by cytochrome P450, insulin secretion, and GnRH signaling pathways. Furthermore, six highly expressed lncRNAs were randomly selected to verify the sequencing data by quantitative real time PCR (qRT-PCR). Next, in situ hybridization revealed that one of the sex-biased lncRNA MSTRG.14827.1 was highly expressed in immature germ cells, indicating MSTRG.14827.1 may play a key role in gametogenesis. Taken together, this study provides emerging lncRNA libraries and opens new avenues for future investigation of lncRNAs in medaka.

CircRNA profiling reveals circ880 functions as miR-375-3p sponge in medaka gonads

Circular RNAs (circRNAs) have been regarded as regulators in the biological processes of various species. However, there is no report about circRNAs in the gonads of model fish medaka (Oryzias latipes). In this study, 1157 and 1570 circRNAs were obtained in the ovary and testis by RNA-sequencing. The characteristics of circRNAs were explored in sequence length, exon composition, and chromosome position. 24 circRNAs were significantly up or down-regulated in the testis compared to the ovary, 9 of which were verified by qRT-PCR. Interestingly, circ452 was highly expressed in the testis while circ880 expression exhibited sexual dimorphism. In situ hybridization (ISH) revealed that circ452 and circ880 were expressed in meiotic germ cells, and circ880 was also abundant in spermatogonia. In addition, dual-luciferase reporter assay manifested that circ880 and Oldnd can combine with miR-375-3p. Overall, these results provide emerging circRNA libraries and open new avenues for future investigation of circRNAs in medaka.