Transcriptome Profile Analysis of Ovarian Tissues from Diploid and Tetraploid Loaches Misgurnus anguillicaudatus.

RNA sequencing and short-read assembly was utilized to produce a transcriptome of ovarian tissues from three-year-old diploid and tetraploid loaches (Misgurnus anguillicaudatus). A total of 28,369 unigenes were obtained, comprising 10,546 unigenes with length longer than 1000 bp. More than 73% of the unigenes were annotated through sequence comparison with databases. The RNA-seq data revealed that 2253 genes were differentially expressed between diploid and tetraploid loaches, including 1263 up-regulated and 990 down-regulated genes in tetraploid loach. Some differentially expressed genes, such as vitellogenin (Vtg), gonadotropin releasing hormone receptor type A (GnRHRA), steroidogenic acute regulatory protein (StAR), mitogen-activated protein kinase 14a (MAPK14a), ATP synthase subunit alpha (atp5a), and synaptonemal complex protein 1 (Scp1), were involved in regulation of cell proliferation, division, gene transcription, ovarian development and energy metabolism, suggesting that these genes were related to egg diameter of the loach. Results of transcriptome profiling here were validated using real time quantitative PCR in ten selected genes. The present study provided insights into the transcriptome profile of ovarian tissues from diploid and tetraploid loaches Misgurnus anguillicaudatus, which was made available to the research community for functional genomics, comparative genomics, polyploidy evolution and molecular breeding of this loach and other related species.

Comparative Transcriptomic Analysis of Regenerated Skins Provides Insights into Cutaneous Air-Breathing Formation in Fish.

Cutaneous air-breathing is one of the air-breathing patterns in bimodal respiration fishes, while little is known about its underlying formation mechanisms. Here, we first investigated the skin regeneration of loach (Misgurnus anguillicaudatus, a cutaneous air-breathing fish) and yellow catfish (Pelteobagrus fulvidraco, a water-breathing fish) through morphological and histological observations. Then, the original skins (OS: MOS, POS) and regenerated skins (RS: MRS, PRS) when their capillaries were the most abundant (the structural foundation of air-breathing in fish) during healing, of the two fish species were collected for high-throughput RNA-seq. A total of 56,054 unigenes and 53,731 unigenes were assembled in loach and yellow catfish, respectively. A total of 640 (460 up- and 180 down-regulated) and 4446 (2340 up- and 2106 down-regulated) differentially expressed genes (DEGs) were respectively observed in RS/OS of loach and yellow catfish. Subsequently, the two DEG datasets were clustered in GO, KOG and KEGG databases, and further analyzed by comparison and screening. Consequently, tens of genes and thirteen key pathways were targeted, indicating that these genes and pathways had strong ties to cutaneous skin air-breathing in loach. This study provides new insights into the formation mechanism of cutaneous air-breathing and also offers a substantial contribution to the gene expression profiles of skin regeneration in fish.

Developmental transcriptome analysis and identification of genes involved in formation of intestinal air-breathing function of Dojo loach, Misgurnus anguillicaudatus.

Dojo loach, Misgurnus anguillicaudatus is a freshwater fish species of the loach family Cobitidae, using its posterior intestine as an accessory air-breathing organ. Little is known about the molecular regulatory mechanisms in the formation of intestinal air-breathing function of M. anguillicaudatus. Here high-throughput sequencing of mRNAs was performed from six developmental stages of posterior intestine of M. anguillicaudatus: 4-Dph (days post hatch) group, 8-Dph group, 12-Dph group, 20-Dph group, 40-Dph group and Oyd (one-year-old) group. These six libraries were assembled into 81300 unigenes. Totally 40757 unigenes were annotated. Subsequently, 35291 differentially expressed genes (DEGs) were scanned among different developmental stages and clustered into 20 gene expression profiles. Finally, 15 key pathways and 25 key genes were mined, providing potential targets for candidate gene selection involved in formation of intestinal air-breathing function in M. anguillicaudatus. This is the first report of developmental transcriptome of posterior intestine in M. anguillicaudatus, offering a substantial contribution to the sequence resources for this species and providing a deep insight into the formation mechanism of its intestinal air-breathing function. This report demonstrates that M. anguillicaudatus is a good model for studies to identify and characterize the molecular basis of accessory air-breathing organ development in fish.