To investigate the cause of male infertility, we observed testes of Cib4+/−7and Cib4–7/−7 adult male mice (Figure 3A) and found that the average testis weight of Cib4–7/−7 mice is smaller than that of Cib4+/−7 mice (Figure 3B). Here, CIB4 is linked to male infertility.