Transcriptome-based insights into the calcium transport mechanism of chick chorioallantoic membrane

Chorioallantoic membrane (CAM) is responsible for respiratory gas exchange, eggshell calcium transport, embryonic acid-base equilibrium, allantoic ion, and water reabsorption during avian embryonic development. To further understand the timing of CAM gene expression during chick embryonic development, especially the calcium absorption mechanism, transcriptome quantitative comparative analysis was conducted on chick CAM during the embryonic period (E) of 9, 13, 17, and 20 days. A total of 6378 differentially expressed genes (DEGs) were identified. Functional enrichment analysis of DEGs showed that CAM DEGs were mainly involved in biological processes such as "ion transport regulation", "immune response" and "cell cycle". Time series analysis of the differential genes showed that the functional cells of CAM began to proliferate and differentiate at E9 and the calcium content of egg embryo increased significantly at E13. Simultaneously, the observation of the ultrastructure of the eggshell showed that the interstice of the fiber layer was enlarged at E13, and the mastoid layer was partly exposed. Therefore, it is preliminarily inferred that CAM calcium transport starts at E13, and genes such as TRPV6, S100A10, and RANKL cooperate to regulate calcium release and transport.