Histological morphology and gene expression in the digestive system of Procambarus clarkii

To unravel the intricate morphological structure and functional aspects of the digestive system in Procambarus clarkii, this study employed histology and transcriptome sequencing techniques for a comprehensive analysis of its digestive system. The investigation revealed that the digestive system of P. clarkii comprises the esophagus, stomach (including cardiac and pyloric regions), caeca, midgut, hindgut, and hepatopancreas. The esophageal lumen displayed an "X" shape, with clearly visible radial muscle bundles within the connecting tissues. The internal architecture of the stomach and intestines mirrored that of the esophagus. Notably, the pyloric region of the stomach exhibited a comb-like structure, which facilitated food selection and filtration. The caeca showcased a larger lumen within the intestines, while the hindgut displayed smaller folds. The hepatopancreas, representing the digestive glands, demonstrated predominant bilaterally symmetrical features, encompassing the midgut on both sides. It consisted of multi-stage branching hepatic ducts, crucial for digestion and absorption. Transcriptomic analysis of the digestive system revealed significant gene expression in the esophagus, stomach, caeca, midgut, hindgut, and hepatopancreas, with 23,006, 22,208, 23,485, 23,196, 22,781, and 21,375 genes expressed, respectively. Moreover, tissue-specific expression was observed in 161, 459, 374, 547, 337, and 1080 genes. Additionally, a subset of 447, 453, 553, 506, 433, and 711 genes exhibited high expression levels. Further analysis led to the identification of 36 digestive enzyme genes across six distinct digestive tissues, categorized into three groups: carbohydrate metabolism, lipid breakdown, and protein metabolism. In conclusion, this study provides a comprehensive understanding of the morphological structure, gene expression characteristics, and classification of digestive enzyme genes in the digestive system of P. clarkii. These findings lay a solid foundation for future investigations on the digestive physiology and food digestion in P. clarkii.