ERC/Mesothelin Is Associated with the Formation of Microvilli on the Mesothelium and Has Limited Functional Relevance Under Physiological Conditions

In adults, expressed in renal cancer (ERC)/mesothelin is exclusively expressed in the mesothelial cells lining the pleural, pericardial, and peritoneal cavities, yet its function under physiological conditions is unknown. To explore this, we studied ERC expression in wild-type (WT) mice at different developmental stages by immunohistochemistry and analyzed the ultrastructure of the mesothelium in WT and <i>Erc</i>-knockout (KO) mice via electron microscopy. Additionally, cardiopulmonary function in adult WT and <i>Erc</i>-KO mice was assessed using echocardiography and the forced oscillation technique (FOT). During embryonic development in WT mice, ERC expression was detected in the epicardium as early as embryonic day (E)12.5 but was absent in the pleura until E18.5. The timing of expression appeared to coincide with the active maturation of these organs, which implied a potential role in cardiopulmonary development. Electron microscopy revealed that microvilli on the mesothelium of <i>Erc</i>-KO mice were immature compared to those of WT mice. Based on these findings, we hypothesized that ERC might contribute to cardiopulmonary function; however, echocardiography and FOT did not reveal any functional differences between WT and <i>Erc</i>-KO mice. This suggests that ERC has limited functional relevance under physiological conditions.