Ontogeny of mouse basolateral efflux transporter mRNA expression in kidneys. Tissues from C57BL/6 mice were obtained at −2, 0, 5, 10, 15, 22, 30, and 45 days. Day −2 represents gestational day 17. Male (♂) mRNA is shown on the left, whereas female (♀) mRNA is shown on the right side of each box. Data are summarized from unpublished observations (C. Klaassen) and previous publications (Maher et al., 2005b; Cheng and Klaassen, 2009).