The Histological Features Of Alimentary Canal And Expression Profile Of Epigenetic Modification Gene In Aestivating Sea Cucumber Apostichopus Japonicus Selenka

Aestivation is an important physiological habit of the sea cucumberApostichopus japonicus Selenka. In order to clarify the changes of digestive tractstructure and gene expression levels involved in epigenetic modification duringdifferent aestivating stages, histological and molecular biological methods were usedto analyze the thicknesses of alimentary canal layers in different stages of aestivation,to compare the ultrastructure of intestinal epithelial cells in the arousal stage ofaestivation and non-aestivation stage, and to detect the DNA methylation andchromatin remodeling-related gene expression in different stages of aestivation. Themain results are as follows:1. We selected intestinal tissues at three different time points: the initial stage ofaestivation, the deep stage of aestivation, and the arousal stage of aestivation.Meanwhile, we chose non-aestivation stage as control group. As for thesubmucosa thickness, there was no significant difference between control groupand any other stages (P>0.05). As for the intestinal epithelium and the coelarium,the thicknesses of the initial stage of aestivation were significantly smaller thanthose of control group (P<0.05). At the deep stage of aestivation, the thicknessesof intestinal epithelium and muscular layer were significantly smaller than thoseof control group (P<0.05). The diameter of anterior intestine at the deep stage ofaestivation was significantly smaller than that of control group (P<0.05).Calculating the proportion of each layer of the anterior intestine wall thickness,we found that the proportions of intestinal epithelium and coelarium at the initialstage were significantly smaller than that of control group (P<0.05). However, theproportion of submucosa at the initial stage was significantly bigger than that of control group (P<0.05). The proportion of muscular layer at the deep stage ofaestivation was significantly smaller than any other stages (P <0.05).2. Changes in the intestinal epithelial ultrastructure were compared between thearousal stage of aestivation and non-aestivation stage. During the arousal stage ofaestivation, sea cucumber’s intestinal epithelium underwent a series of changes.The quantities of microvillus, mitochondria and ribosomes reduced significantly,and the structures of nucleus and mitochondria and the whole cell were destroyedbadly. For non-aestivation sea cucumbers, intestinal epithelial cells were rich inmicrovillus and mitochondria, the chromatins were well-regulated, and thestructures of other organelles and the whole cell were intact.3. Alimentary canal, respiratory tree, muscle and body wall tissues of sea cucumberwere selected at five different time points including non-aestivation period(control group), the initial stage of aestivation, and deep stage of aestivation, thearousal stage of aestivation and the recovery stage of aestivation. Wequantitatively analyzed the expression profiles of three DNA methylation andchromatin remodeling regulatory genes including DNA(cytosine-5)-methyltransferase1gene (DNMT1), methyl-CpG-binding domainprotein2gene (MBD2), and chromodomain-helicase-DNA-binding protein5gene(CHD5) applying quantitative PCR technology. The results showed that comparedwith non-aestivation stage, the expression levels of these three genes in thealimentary canal and respiratory tree tissues were significantly increased at deepstage of aestivation (P<0.05), the expression level of DNMT1in muscle tissue didnot change significantly, the expression levels of MBD2and CHD5genes at deepstage of aestivation increased significantly (P<0.05). In body wall tissue, theexpression levels of these three genes all increased around the arousal stage ofaestivation (P <0.05).