Transcriptomic analysis of skin immunity genes in the Chinese spiny frog (Quasipaa spinosa) after Proteus mirabilis infection

Recently, populations of Chinese spiny frogs (Quasipaa spinosa), an important amphibian species in China, have decreased, mainly due to a disease caused by the gram-negative bacteria Proteus mirabilis. To elucidate the immune response of the frogs, this study aimed to identify novel candidate genes functionally associated with P. mirabilis infection-induced "rotting skin" disease. Chinese spiny frogs were infected with P. mirabilis, and the skin transcriptome was sequenced using the MGISEQ-2000 platform. A total of 233,965 unigenes were obtained by sequencing, of which 27.23 % were known genes. Screening of differentially expressed genes (DEGs) indicated 210 unigenes differentially expressed after P. mirabilis infection, of which 132 unigenes were up-regulated, and 78 unigenes were down-regulated. Using Kyoto Encyclopedia of Genes and Genomes enrichment analysis, DEGs were identified as enriched in signal pathways, such as oxidative phosphorylation, apoptosis, and the Janus kinase-signal transducer and activator of transcription pathway. Of the DEGs, there was a significant upregulation of the colony stimulating factor 2 receptor beta common subunit, interleukin 2 receptor subunit gamma, cathelicidin antimicrobial peptide, interleukin-17 receptor E, receptor-interacting serine/threonine-protein kinase 3, and pulmonary surfactant-associated protein D immune genes following P. mirabilis infection. Conversely, scavenger receptor cysteine-rich domain-containing group B protein, tumor protein p53 inducible nuclear protein 2, suppressor of cytokine signaling 2, and metalloreductase STEAP3 were significantly downregulated. In conclusion, the first skin transcriptome database of Chinese spiny frogs was established, and several immune genes were identified to elucidate the pathogenic mechanism of "skin rot" in Chinese spiny frogs and other cultured frogs.