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The skin of amphibians is a tissue with biological functions, such as defense, respiration, and excretion. In recent years, researchers have discovered a large number of peptides in the skin secretions of amphibians, including antimicrobial peptides, antioxidant peptides, bradykinins, insulin-releasing peptides, and other peptides. This review focuses on the origin, primary structure, secondary structure, length, and functions of peptides secreted from amphibians’ skin. We hope that this review will provide further information and promote the further study of amphibian skin secretions, in order to provide reference for expanding the research and application of amphibian bioactive peptides.

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Insulin like growth factor 1 receptor (IGF-1R) is a candidate gene for growth and carcass traits in regulating animal growth, metabolism and endocrine. It is widely expressed in liver, muscle, bone tissues where the IGF-1R functions as a factor that promotes cell growth. In this study, the protein expression level of IGF-1R gene in liver and muscle tissues of three periods (birth, weaning and adult) of three pig breeds (BamaXiang pigs (BM), Tibetan pigs (TM) and Junmu No.1 pigs (JM)) were tested by western blot. SNPs within the regulatory region of pig IGF-1R gene were detected using direct sequencing and then the genotypes were identified through AS-PCR approach. Results showed expression profiles of IGF-1R gene between liver and muscle tissues were different and significant differences were also found among pig breeds. In the same time, four SNPs were detected in the regulatory region of IGF-1R gene, among which the genotype frequency of three (g.-1468G > C, g.-1192 C > T and g.330,424 C > T) were significantly different among the pig breeds. BM tended to heterozygous (GC/CT) of the anterior two loci, while TM and JM preferred the other two homozygotes respectively. For the g.330,424 C > T, all pig breeds were tended to be the heterozygous. In conclusion, the SNPs with different genotype distribution among the three pig breeds may explain the gene expression difference between the different pig breeds.

Dexamethasone (Dex) has been widely used as a potent anti-inflammatory, antishock, and immunosuppressive agent. However, high dose or long-term use of Dex is accompanied by side effects including skeletal muscle atrophy, whose underlying mechanisms remain incompletely understood. A number of microRNAs (miRNAs) have been shown to play key roles in skeletal muscle atrophy. Previous studies showed significantly increased miR-322 expression in Dex-treated C2C12 myotubes. In our study, the glucocorticoid receptor (GR) was required for Dex to increase miR-322 expression in C2C12 myotubes. miR-322 mimic or miR-322 inhibitor was used for regulating the expression of miR-322. Insulin-like growth factor 1 receptor (IGF1R) and insulin receptor (INSR) were identified as target genes of miR-322 using luciferase reporter assays and played key roles in Dex-induced muscle atrophy. miR-322 overexpression promoted atrophy in Dex-treated C2C12 myotubes and the gastrocnemius muscles of mice. Conversely, miR-322 inhibition showed the opposite effects. These data suggested that miR-322 contributes to Dex-induced muscle atrophy via targeting of IGF1R and INSR. Furthermore, miR-322 might be a potential target to counter Dex-induced muscle atrophy. miR-322 inhibition might also represent a therapeutic approach for Dex-induced muscle atrophy.

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