Surface Morphology of Uterine and Vaginal Epithelia in Mice During Normal Postnatal Development

Scanning electron microscopy was used to investigate postnatal development of uterine and vaginal epithelia in the mouse. Animals were killed on postnatal Days 1 or 2, 4, 7, 14 and 21, and luminal surfaces of the Müllerian vaginal canal, vaginal fornix and uterus were examined. Vaginal canal and fornix: On Days 1 and 2 cell apices were round or oval, convex, and devoid of microvilli and cilia. Cytoplasmic protrusions ("blebs") were prevalent. During the first 2 weeks cell apices gradually acquired microvilli, lost blebs, and became relatively flat. On Day 21 cell apices were irregular in size and shape and amorphous, possibly secretory, material was present. These changes are consistent with a gradual differentiation of the Müllerian epithelium lining the neonatal mouse Müllerian vagina into a secretory epithelium. Uterus: On the day of birth the luminal surface showed signs of morphologic differentiation. Two types of cells were detected: cells with small, round, convex apices and those with larger, flatter apices; microvilli were present on both types. During the first postnatal week, the round apices became localized into slightly recessed clusters. On Day 14 two discrete cell types were no longer apparent. The luminal epithelium was then composed of cells with round or oval, moderately convex apices that differed from each other primarily in size. Orifices resembling gland pits were present. On day 21 the luminal surface was similar to that of the adult uterus.