2.1. Mice

This study was carried out in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the Ministry of Education, Culture, Sports, Science, and Technology of Japan. The protocol was approved by the Committee on the Ethics of Animal Experiments of Chiba Cancer Center (Permit Number: 13‐18). All efforts were made to minimize suffering. C57BL/6 strain mice were used as recipients for targeted ES cells and as the background strain in this study. The generation of mice carrying the floxed allele of the Cenp‐50/U gene (Cenp‐50/U ^fl/fl) is described elsewhere. ²⁴ Cenp‐50/U ^fl/fl mice were mated to K14‐Cre^ER transgenic mice. ³⁸ K14‐Cre^ER transgenic mice were obtained from the Jackson Laboratory (JaX 005107). To disrupt Cenp‐50/U, K14Cre^ER‐Cenp‐50/U ^fl/fl and Cenp‐50/U ^fl/fl mice at 8 wk old were injected subcutaneously 5 times with 1.0 mg/mL of tamoxifen (Sigma‐Aldrich) that had been prepared following the manufacturer's instructions by completely dissolving tamoxifen into 1 mL of 100% ethanol at 50°C, adding 9 mL of sunflower oil and mixing this thoroughly by vortexing.