Effect of high alkalinity on shrimp gills: Histopathological alternations and cell specific responses

Abstract

High alkalinity stress was considered as a major risk factor for aquatic animals surviving in saline-alkaline water. However, few information exists on the effects of alkalinity stress in crustacean species. As the dominant role of gills in osmotic and ionic regulation, the present study firstly evaluated the effect of alkalinity stress in Exopalaemon carinicauda to determine changes in gill microstructure, and then explore the heterogeneity response of gill cells in alkalinity adaptation by single-cell RNA sequencing (scRNA-seq). Hemolymph osmolality and pH were increased remarkably, and gills showed pillar cells with more symmetrical arrangement and longer lateral flanges and nephrocytes with larger vacuoles in high alkalinity. ScRNA-seq results showed that alkalinity stress reduced the proportion of pillar cells and increased the proportion of nephrocytes significantly. The differentially expressed genes (DEGs) related to ion transport, especially acid-base regulation, such as V(H+)-ATPases and carbonic anhydrases, were down-regulated in pillar cells and up-regulated in nephrocytes. Furthermore, pseudotime analysis showed that some nephrocytes transformed to perform ion transport function in alkalinity adaption. Notedly, the positive signals of carbonic anhydrase were obviously observed in the nephrocytes after alkalinity stress. These results indicated that the alkalinity stress inhibited the ion transport function of pillar cells, but induced the active role of nephrocytes in alkalinity adaptation. Collectively, our results provided the new insight into the cellular and molecular mechanism behind the adverse effects of saline-alkaline water and the saline-alkaline adaption mechanism in crustaceans.