The postnatal development of the ovary in the "nude" mouse.

The postnatal development of the ovary of the heterozygous nude (nu/+) mouse with the genetic background BALB/c is very similar--if not identical-- to that of other mouse strains. As other BALB/c mice, the nu/+ females become sexually mature during the 5th week post partum (p.p.). At this age the ovaries corpora lutea at various stages of differentiation. In the ovaries of newborn and 1 week-old homozygous (nu/nu) mice, the differentiation of oocytes into primary and secondary follicles is delayed. In the third postnatal week, the ovaries of homozygous females contain more atretic follicles than those of their heterozygous littermates. This increased degeneration of follicles may account for the greater mass of secondary interstitial tissue, which is observed in the ovaries of adult nu/nu females. In nine out of the 5 to 7 week-old nu/nu mice studied, the ovaries contained no-/or only very few corpora lutea. Thus in homozygous nude females, the onset of sexual maturity is delayed. This ovarial immaturity may persist throughout life. In other animals development may become normal. In addition to the impaired postnatal development of the ovary, unspecific inflammation of the uterine wall (endo- and/or myometritis) was detected in 47% of nu/nu animals older than five weeks. No direct correlation was, however, found between the delay of sexual maturation and the inflammatory changes in the uterus as many of the animals with an endo- or myometritis possessed mature ovaries. The low fertility of the female homozygous "nude" mouse seems, therefore, to be caused not only by an impaired differentiation of the ovary but also by inflammatory processes in the uterus.