Sexual dimorphism in Odontobutis sinensis brain-pituitary-gonad axis and liver highlighted by histological and transcriptomic approach.

In this study, sexual dimorphism in Chinese dark sleeper (Odontobutis sinensis) brain-pituitary-gonad axis and liver was highlighted by histological and transcriptomic approach. The results showed that there were two significant differences between males and females. Firstly, males grew larger and faster than females. Transcriptomic analysis and qPCR validation indicated that two key growth genes, insulin-like growth factor (igf) and 25-hydroxyvitamin D-1 alpha hydroxylase (cyp27b), were more highly detected in male liver than that in female liver. Secondly, histological analysis displayed that the liver in males showed an obvious ivory fatty phenomenon with more fat vacuoles and lipid droplet aggregation compared to that in females. Transcriptomic analysis indicated that the transcript level of vitellogenin (vtg) in male liver were significantly lower than that in female liver. After 17ß-estradiol (E2) treatment of primary cultured hepatocytes, the vtg mRNA expression was induced significantly, while dihydrotestosterone (DHT) treatment had little effect on it. Generally, this study will provide some ideas for further exploring the mechanism of sexual dimorphism in Odontobutis sinensis.

A Chromosome-Level Genome Assembly of the Dark Sleeper Odontobutis potamophila.

The dark sleeper, Odontobutis potamophila, is a commercially valuable fish that widely distributed in China and Southeast Asia countries. The phenomenon of sexual dimorphism in growth is conspicuous, which the males grow substantially larger and faster than the females. However, the high-quality genome resources for gaining insight into sex-determining mechanisms to develop sex-control breeding are still lacking. Here, a chromosomal-level genome assembly of O. potamophila was generated from a combination of Illumina reads, 10× Genomics sequencing, and Hi-C chromatin interaction sequencing. The assembled genome was 1,134.62 Mb with a contig N50 of 22.25 Mb and a scaffold N50 of 24.85 Mb, representing 94.4% completeness (Benchmarking Universal Single-Copy Orthologs). Using Hi-C data, 96.49% of the total contig bases were anchored to the 22 chromosomes, with a contig N50 of 22.25 Mb and a scaffold N50 of 47.68 Mb. Approximately 54.18% of the genome were identified as repetitive elements, and 23,923 protein-coding genes were annotated in the genome. The assembled genome can be used as a valuable resource for molecular breeding and functional studies of O. potamophila in the future.

Integrated analysis of proteomics and metabolomics reveals the potential sex determination mechanism in Odontobutis potamophila.

Odontobutis potamophila is a valuable species for aquaculture in China, which shows asexually dimorphic growth pattern. In this study, the integrated proteomics and metabolomics were used to analyze the sex determination mechanism. A total of 2781 significantly different regulated proteins were identified by proteomics and 2693 significantly different expressed metabolites were identified by metabolomics. Among them, 2560 proteins and 1701 metabolites were significantly up-regulated in testes, whereas 221 proteins and 992 metabolites were significantly up-regulated in ovaries. Venn diagram analysis showed 513 proteins were differentially regulated at both protein and metabolite levels. Correlation analysis of differentially-regulated proteins and metabolites were identified by Gene Ontology annotation and Kyoto Encyclopedia of Genes and Genomes pathway analysis. The results showed lipid metabolism plays an important role in sex determination. The metabolites decanoyl-CoA, leukotriene, 3-dehydrosphinganine, and arachidonate were the biomarkers in testes, whereas estrone and taurocholate were the biomarkers in ovaries. Interaction networks of the significant differentially co-regulated proteins and metabolites in the process of lipid metabolism showed arachidonic acid metabolism and steroid hormone biosynthesis were the most important pathways in sex determination. The findings of this study provide valuable information for selective breeding of O. potamophila. SIGNIFICANCE OF THE STUDY: The male O. potamophila grows substantially larger and at a quicker rate than the female. Thus, males have greater economic value than females. However, limited research was done to analyze the sex determination mechanism of O. potamophila, which seriously hindered the development of whole-male O. potamophila breeding. In this study, four key proteins (Ctnnb1, Piwil1, Hsd17b1, and Dnali1), six most important biomarkers (decanoyl-CoA, leukotriene, 3-dehydrosphinganine, arachidonate, estrone, and taurocholate) and two key pathways (arachidonic acid metabolism and steroid hormone biosynthesis) in sex determination of O. potamophila were found by integrated application of iTRAQ and LC-MS techniques. The results give valuable information for molecular breeding of O. potamophila in aquaculture.

Evolutionary conservation and divergence of Vasa, Dazl and Nanos1 during embryogenesis and gametogenesis in dark sleeper (Odontobutis potamophila).

Germline-specific genes, Vasa, Dazl and Nanos1, have highly conserved functions in germline development and fertility across animal phyla. In this study, the full-length sequences of Opvasa, Opdazl and Opnanos1 were cloned and characterized from the dark sleeper (Odontobutis potamophila). Gonad-specific expression patterns of Opvasa and Opdazl were confirmed in adult tissues by quantitative real-time PCR (qRT-PCR). Different from Opvasa and Opdazl, the expression of Opnanos1 was ubiquitously detected in all examined tissues except for the liver and spleen. Time-course dynamic expressions during embryogenesis were assessed, and all three genes (Opvasa, Opdazl and Opnanos1) persisted at a high level until gastrulation. qRT-PCR and Western blotting analyses revealed that all three genes were highly expressed throughout gametogenesis. In testis, the expressions of all three genes at the mRNA and protein levels were down-regulated during spermatogenesis. In ovary, different expression patterns were found, and all three genes had a differential role in translational regulation during oogenesis. The expressions of Opvasa, Opdazl and Opnanos1 at the mRNA but not the protein level were high in stage IV. Different expression patterns were found in premeiotic gonads treated by HPG axis hormones (HCG and LHRH-A). Immunolocalization analysis demonstrated that in testis, Opvasa, Opdazl and Opnanos1 were detected in spermatogonia and spermatocytes but absent in the meiotic products, such as spermatids and spermatozoa. In ovary, Opvasa, Opdazl and Opnanos1 persisted at a high level throughout oogenesis. These findings indicated that Opvasa, Opdazl and Opnanos1 played an important role in mitotic and early meiotic phases of oogenesis and spermatogenesis, and they functioned as maternal factors in early embryogenesis. Their proteins could be used as three new markers for germ cells during gametogenesis in O. potamophila gonad. Our data laid a good foundation for improving the breeding efficiency of O. potamophila.