α-Actin immunoreactivity in human female reproductive tracts at (A) 9, (B) 11, (C) 12, and (D) 18 weeks. Faint α-actin immunoreactivity first appears focally in mesenchyme of the 9-week uterovaginal canal, increasing in intensity by the 11 weeksBy 12 weeks α-actin immunoreactivity is strong in the middle 2/4ths of the developing reproductive tract, and by 18 weeks, is strongly expressed throughout the developing female reproductive tract. From Robboy et al (2017) with permission.