| Chinese mitten crab is a kind of aquaculture product with great economic value in China.It has delicious meat and high nutritional value.It is widely cultured in the Yangtze River Basin,Yellow River and Liaohe River Basin in China.In order to study the histological structure of the main organs of adult Chinese mitten crab,three different staining methods,HE,Masson and AB-Pas,were used to observe the digestive system(esophagus,stomach,midgut,intestinal bulb,hindgut and hepatopancreas),reproductive system(testis,vas deferens,accessory gland and ovary),gill,antennal gland,heart,muscle and other tissues of Chinese mitten crab.The results showed that the stomach in the digestive system of Eriocheir sinensis included cardia stomach and pylorus stomach.In the cardia stomach,it could be observed that the stratum corneum was calcified into horny bones,chitin teeth,ridges,bristles and other structures in different parts of the cardia stomach,which together constituted ’ stomach mill ’ and had the function of grinding food.Pyloric stomach has a special comb structure and rows of bar setae.They are an important part of the gland filter and have the function of filtering and screening food.The digestive tract wall of Eriocheir sinensis consists of four layers : mucosal layer,submucosa layer,muscular layer and outer membrane layer.The surface of the mucosal layer of the esophagus and hindgut has a developed cuticle and rows of setae.There are special mucous glands,esophageal glands and hindgut glands in the submucosa.There is no cuticle on the surface of the midgut mucosa,and there are dense microvilli.The intestinal bulb has the morphological characteristics of midgut to hindgut transition.Hepatopancreas is composed of many hepatic tubules.Four kinds of cells are common in hepatic tubules,including resorptive cells(R cells),blister-like cells(B cells),fibrillar cells(F cells)and embryonic cells(E cells).In the reproductive system of Eriocheir sinensis,it can be observed that the testis is mainly composed of a large number of seminiferous tubules,and the development of germ cells in different seminiferous tubules is not synchronized,and sperm cells with different periods can be observed.The vas deferens is connected to the testis.The vas deferens of Eriocheir sinensis is mainly composed of three parts: anterior vas deferens,posterior vas deferens and seminal vesicle.Spermatophores of different sizes and a large number of secretions can be observed in the vas deferens.Ruptured spermatophores can be observed in the lumen of the accessory gland.In the ovary,we mainly observed two kinds of cells,one is the primary oocyte that has accumulated a large number of yolk granules,and the other is the elongated lamellar follicular cells.The gill of Eriocheir sinensis is composed of gill axis and gill filament.The gill sinus can be observed at the base of the gill.The gill filament is composed of cuticle,epithelial cells,gill cavity and cystites.A large number of blood cells can be observed in the gill cavity.The antennal gland is the main excretory organ of Chinese mitten crab,which is mainly composed of coelomosac,labyrinth and nephridial canal.There are a large number of podocytes in the epithelium of coelomocytes.In the heart,the outer membrane composed of connective tissue can be observed,as well as scattered myocardial fibers and a large number of nuclei in the myocardial layer.The muscle of the Chinese mitten crab can clearly observe the stripes on the muscle fibers.After studying the tissue structure of Eriocheir sinensis,high-throughput sequencing was performed on six tissues of the digestive system,including the esophagus,pyloric stomach,midgut,intestinal bulb,hindgut,and hepatopancreas.A total of 51920 transcripts were obtained.The results of transcriptome data showed that13252,13285,13634,11147,13127,12551 transcripts were expressed in esophagus,pylorus stomach,midgut,intestinal bulb,hindgut and hepatopancreas,and1529,549,1199,624,990,1688 transcripts were specifically expressed.Among the six different tissues of the digestive system,the hepatopancreas expressed the largest number of transcripts and the pyloric stomach expressed the least.According to the results of transcriptome,a total of 25 digestive enzyme genes were isolated.Except for maltase-glucoamylase and phosphatase A2,the expression levels of other digestive enzymes were the highest in hepatopancreas,including trypsin,chymotrypsin,carboxypeptidase B,and ɑ-amylase.Finally,according to the expression levels and differences of digestive enzyme genes in different tissues of the digestive system of Eriocheir sinensis,we speculated that chymotrypsin,trypsin,amylase and carboxypeptidase B played an important role in the process of food digestion,and hepatopancreas was the main synthesis site of most digestive enzymes.The research content provides histological data for the follow-up study of chinese mitten crab,and also provides transcript basis for the later study of digestive enzymes in chinese mitten crab. |
