Study On The Tracheal Mucus-secreting Tissue And Mucin Expression In Sheep

The present study was conducted to investigate the anatomical distribution,morphometry,histochemical characteristics,and mucin expression distribution and structural characteristics of mucus-secreting tissues in sheep trachea to reveal the characteristics of mucus secretion in sheep trachea,to provide basic data to guide the treatment of respiratory-related diseases in sheep in actual production,and to provide researchers with a better understanding of this important respiratory pathological model in sheep.Methods: Descriptive data about mucus secretion in sheep trachea were obtained by basic morphometric measurement,micrometric analysis of HE sections,four special glycohistochemical staining,real-time quantitative PCR detection and immunohistochemical experiments.Results: The basic morphological data of sheep trachea were the same as most mammalian trachea morphological patterns.The morphology of epithelial secretory cells was not all goblet-shaped,and there were also oval secretory cells with narrow upper and lower sections and large differences in size.Both cells were also heterogeneous in glycohistochemical staining.Moreover,the oval secretory cells tend to be more likely to aggregate into clusters,and the middle subsides to form mucus secreting pits,which is a new morphological structure that has not been reported.The height and number of secretory cells on the ventral and dorsal sides of the trachea were also significantly different,while the cranial,middle and caudal segments of the trachea on the same side were more evenly distributed.The submucosal glands were more commonly located above the cartilage ring in the ventral part of the trachea The glands in the dorsal part tend to be outside the muscles.The volume of glands per unit of lumen area varies greatly between the ventral and dorsal sides,and the ventral side is 2-3 times larger than the dorsal side,but the overall difference between the cranial,middle,and caudal segments of the trachea is small.It generally contains neutral glycoconjugates(neutral mucins),and the relative content of serous cells in submucosal glands is the highest,followed by submucosal gland mucinous cells,and epithelial secretory cells are the least.Acidic glycoconjugates(acidic mucins)were also prevalent,with the most cells in the submucosal gland,followed by the oval cells in the epithelial secretory cells,and the lesser goblet cells and submucosal gland serous cells.The sulfated glycoconjugate(sulfomucin)is the dominant component of the acid glycoconjugate;the transcripts of three gel-forming mucin genes were detected in the trachea of sheep,Muc5ac、Muc5b and Muc2,Muc5 ac were expressed The most abundant,followed by Muc5 b,and the lower abundance of Muc2.It indicated that the first two mucins were the main components of tracheal mucus in sheep.In terms of immunohistochemical localization of mucin expression,two mucins were recognized by antibodies,namely Muc5 ac protein localized in secretory cells of mucosal epithelium and Muc2 protein localized in submucosal gland serous cells.Comparison of the conserved domain structures of the mucins revealed that the N-terminal and Cterminal ends of all three mucins are more conserved,rich in cysteine residues required for oligomerization,and specificity exists in the length of the glycosylation binding site sequence in the middle of the protein.