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

Abstract

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.

Figure 1. Histological observations of intestine tissues of M. anguillicaudatus during different developmental stages.

(a) Longitudinal section of intestine from 8-Dph loach. (b) Longitudinal section of intestine from 10-Dph loach. (c) Cross section of posterior intestine from 40-Dph loach. (d) Cross section of anterior intestine from Oyd. (e) Cross section of posterior intestine from Oyd. Abbreviations: air bubble (AB); capillary vessel (CA); simple columnar epithelium (CE); erythrocyte (ER); goblet cell (GC). Bar indicated 20 μm.

Figure 2. GO classifications of all unigenes from posterior intestine of M. anguillicaudatus.

Figure 3. KOG classifications of all unigenes from posterior intestine of M. anguillicaudatus.

Figure 4. Expression profiles and clusters of DEGs obtained from the STEM clustering.

Numbers indicated profiles or gene numbers. Significantly different profiles were represented by different background colors.

Figure 5. Protein-protein interaction network for the 50 important enzymes encoded by key DEGs of key pathways.

Different nodes represented different enzymes. The interactions among these enzymes were represented by different colorful lines.