Fig. 7

The general model describing clock-controlled miRNA regulates ion transporters during eggshell calcification in the chicken uterus. This figure summarizes the general mechanisms involved in the regulation of the transport, distribution, and transformation of Ca²⁺ from the blood plasma through the uterine tubular gland cell membrane (Ca²⁺ trans-epithelial transport) and then suspended in the uterine fluid in a usable form (CaCO₃) for utilization in eggshell calcification. Clock-controlled miR-449c-5p in the uterus of chickens regulates Ca²⁺ transport by targeting ATP2B4 during eggshell calcification. ATP2B4 was responsible for utilizing the stored energy in the form of ATP to extrude Ca²⁺ from the cell against the electrochemical gradient and it was also involved in the active transport of calcium out of the tubular gland cells into the calcium-rich fluid of the uterine lumen. NPAS2, one of the core clock genes, was predicted to be the target gene of clock-controlled miR-218-5p, and another target gene CA2 was related to the carbonic anhydrase activity of the hen oviduct