During summer days the extreme heat may cause damage to the integrity of animal intestinal barrier. Little information is available concerning morphological changes in the duck intestines in response to high temperature. And the molecular mechanisms underlying the pathogenesis of high temperature-induced intestinal injury remain undefined. MicroRNAs (miRNAs) are known to play key roles in post-transcriptional regulation of gene expression that influences various biological processes. The purpose of this study was to explore the changes in morphology and miRNA expression profiles of the three intestinal segments (duodenum, jejunum and ileum) of ducks in response to high temperature. Sixty female Shaoxing ducks (Anas platyrhynchos), 60 days old, were allocated in two groups, including control ducks kept at 25 °C, and ducks subjected to high ambient temperatures of 30-40 °C for 15 successive days, which mimicked the diurnal temperature variations experienced in hot seasons. Three ducks from each group were executed at the end of feeding experiment, and the samples of three intestinal segments were collected for morphological examination and Illumina deep sequencing analyses. Histopathological examination of the intestinal mucous membrane was performed with HE staining method. The results demonstrated that varying degrees of damage to each intestinal segment were found in heat-treated ducks, and there were more severe injuries in duodenum and jejunum than those in ileum. Illumina high-throughput sequencing and bioinformatic methods were employed in this study to identify the miRNA expression profile of three different intestinal tissues in control and heat-treated ducks. A total of 75,981,636, 88,345,563 and 100,179,422 raw reads were obtained from duodenum, jejunum and ileum, respectively, from which 74,797,633 clean reads in duodenal libraries, 86,406,445 clean reads in jejunal libraries, and 98,518,858 lean reads in ileal libraries were derived after quality control, respectively. And a total of 276 known and 182 novel miRNAs were identified in the three intestinal segments of ducks under control and heat-treated conditions. By comparing the same tissues in different conditions, 16, 18 and 15 miRNAs were found to be significantly differentially expressed between control and heat-treated ducks in duodenum, jejunum and ileum, respectively, of which 1 miRNA was expressed in both the duodenum and jejunum, 2 miRNAs were expressed in both the duodenum and ileum, and 3 miRNAs were found to be expressed in both the jejunum and ileum. In addition, two differentially expressed miRNAs in each comparison were randomly selected and validated by quantitative qRT-PCR. Gene Ontology annotation and Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that the differentially expressed miRNAs may be involved in the high temperature-induced intestinal injury in ducks. Our work provides the comprehensive miRNA expression profiles of small intestines in the normal and heat-treated ducks. These findings suggest the involvement of specific molecular mechanisms of post-transcriptional regulation to explain the high temperature-induced changes in the duck small intestine.
Keywords: Ducks; High temperature response; Histopathology; Small intestine; miRNAs.