Dy identified two forms of preproinsulin genes (ins, insl) and preproglucagon
Dy identified two forms of preproinsulin genes (ins, insl) and preproglucagon (glp1?, glp2?) genes. All these transcripts were upregulated at 20 dph, with fold change >8 when compared to those at 12 dph. These results suggest that insulin and glucagon or glucagon derivatives may be produced in the ovary of ricefield eel larvae, and play important roles via paracrine and/or autocrine manners in the ovarian development after initiation of meiosis.Conclusions To our knowledge, our present study is the first report of large-scale RNA sequencing of the early gonads ofCai et al. BMC Genomics (2017) 18:Page 14 ofricefiled eel larvae. Results of our present study suggest that high expression of female development-related genes and low expression of male development-related genes in the early gonads of ricefield eel larvae participate in the cascade of sex differentiation leading to the final female phenotype. The peak expression of rdh and aldh genes at 12 dph and continuously low expression of the three cyp26s from 6 dph to 20 dph may ensure peak production of RA around 12 dph, which in turn induces biochemical changes inside germ cells for the initiation of meiosis. Stra6 might be a downstream target of RA in the early gonads of ricefield eel larvae and probably associated with RA metabolism and/or the initiation of meiosis. Data of present study could lay a good foundation for further unraveling the mechanisms underlying the ovarian differentiation in ricefield eels and other teleosts as well.DEG: Differentially expressed gene; dNTP: PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/28914615 Deoxy-ribonucleoside triphosphate; dph: Day post hatching; FPKM: Reads per kilo bases per million mapped reads; Gh: Growth hormone; Ghr2: Growth hormone receptor 2; GO: Gene Ontology; KEGG: Kyoto encyclopedia of genes and genomes database; KO: Kyoto encyclopedia of genes and genomes ortholog database; KOG/ COG: EuKaryotic ortholog groups/clusters of orthologous groups of proteins; LGR4: Leucine rich repeat containing G PD98059 chemical information protein-coupled receptor 4; LGR5: Leucine rich repeat containing G protein-coupled receptor 5; N50: N50 statistic defines assembly quality. Given a set of contigs, each with its own length, the N50 length is defined as the shortest sequence length at 50 of the genome; Nr: Non-redundant protein sequences; Nt: NCBI nucleotide sequences; Pfam: Protein family; PGC: Primordial germ cell; Prl: Prolactin; Prlr: Prolactin receptor; Q20: Percentage of bases with a Phred value of at least 20; Q30: Percentage of bases with a Phred value of at least 30; RA: Retinoic acid; Rdh: Retinol dehydrogenase; RT-PCR: Reverse transcriptasepolymerase chain reaction; RT-qPCR: Real-time quantitative PCR; STRA6: Stimulated by retinoic acid 6; SwissProt: A manually annotated PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/27527552 and reviewed protein sequence database; TGF: Transforming growth factor beta; TGICL: A software system for fast clustering of large EST datasets Acknowledgments We are grateful to Dazhong Breeding Co. Ltd. (Jianyang, Sichuan, China) for providing mature ricefield eels for breeding, and Mr. Tao Yan and Zhiqiang Zheng for their assistance in collecting samples. Funding L.H.Z is funded by the National Natural Science Foundation of China for the mechanisms of ovarian morphogenesis in ricefield eels (No. 31172088 and No. 31572604); W.M.Z is also funded by the National Natural Science Foundation of China for gene expression analysis in gonadal development in ricefield eels (No. 31372513). The funding bodies did not have a role in the design of the study, data.

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