We thank the members of Aruga Laboratory for valuable discussions, Naoko Yamada, Yoshie Ito and Ryoko Takei for technical assistance, and Katsuhiko Mikoshiba for continuous encouragement of our Zic biology project. This work was supported by RIKEN BSI Funds and by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan. A part of this study is the result of “Development of biomarker candidates for social behavior” carried out under the Strategic Research Program for Brain Sciences by the Ministry of Education, Culture, Sports, Science and Technology of Japan.