Abstract: This study aimed to compare the changes in tissue morphology and the expression of coding genes in the rumen tissues of the Bactrian camel between embryonic and adult stages, to discover the key genes and pathways affecting the development of rumen of the Bactrian camel, and to explore the desert adaptive mechanism of the Bactrian camel from the digestive system. Three adult Alxa Bactrian camels aged 10-12 years old with good health and three embryonic Alxa Bactrian camels aged 9-10 months old with good health were selected to make paraffin tissue sections, observe the rumen of adult and embryonic Bactrian camels, and compare the differences in tissue structure. The total RNA was extracted from rumen tissue of adult and embryonic Bactrian camels, RNA-Seq analysis was performed by Illumination Hiseq 2000 platform, the RNA-Seq data were performed quality-controlled, alignment, differential genes screening, GO and KEGG analysis. Six differentially expressed genes were randomly selected for RT-qPCR, the results of RNA-Seq and RT-qPCR was compared. The results showed that epithelial cells and muscle fiber cells were clearly visible and densely distributed in the rumen of Bactrian camel at embryonic stage. In the rumen of Bactrian camel at adult stage, obvious muscle fibers could be observed, the diameter of the muscle fibers was wider and the space between the muscle fibers was larger. The RNA-Seq sequencing results showed that at least 10G data was obtained from each sample, the clean ratio were more than 90%, and Q30 data were more than 88%. The embryonic rumen was set as the control group and the adult rumen as the experimental group, 1 207 differentially expressed genes were screened, contained 456 up-regulated genes and 751 down-regulated genes. The hierarchical clustering analysis of differentially expressed genes showed that the similar expression pattern was detected among adult individuals(M1, M2, M3) and among embryonic individuals (T1, T2, T3). The GO enrichment analysis results showed that the up-regulated differentially expressed genes were significantly enriched in 62 GO terms, down-regulated differentially expressed genes were significantly enriched in 366 GO terms. GO terms were mainly enriched in negative regulation of metabolic process, negative regulation of RNA biosynthetic process, negative regulation of gene expression, etc. The KEGG pathway analysis of differentially expressed genes showed that 73 significant KEGG pathways were enriched in MAPK signaling pathway, PI3K-Akt signaling pathway, AGE-RAGE signaling pathway in diabetic complications, insulin signaling pathway, aldosterone synthesis and secretion, etc. At the same time, MAPK12, MAPK13, FABP5, PPARγ, CaMK1 and other genes related to desert adaptation of Bactrian camel were screened. The expression pattern of 6 differentially expressed genes detected by RT-qRCR was consistent with the results of RNA-Seq analysis. The above results indicate that the rumen of Bactrian camel may be related to adipocyte differentiation. And in a desert environment, the Bactrian camel might reduce the metabolic efficiency of rumen, improve blood glucose tolerance through insulin resistance, and promote the synthesis and secretion of aldosterone to regulate blood pressure balance to better survive in the dry and water-deficient environment of the desert.

Key words: Bactrian camel, rumen, differentially expressed genes, adaptability, RNA-Seq