Production of müllerian-inhibiting substance (MIS) and sulfated glycoprotein-2 (SGP-2) associated with testicular differentiation in the XX mouse gonadal graft

Regulation of the phenotype of ovarian somatic cells by estrogen

The pathway of mammalian sex determination, and subsequent differentiation of the gonads is under the control of the sex-determining gene, Sry, on the Y chromosome. The presence of Sry leads to the formation of a testis with its complement of Sertoli and Leydig somatic cells. In the absence of Sry, an ovary develops with granulosa and theca cells. Ovarian development is said to initiate in the XX gonad as a default pathway because the XX cells do not express Sry. This review summarizes evidence supporting the view that the ovary is not entirely a default gonad. Studies of mice with deletions in both estrogen receptor (ERalphabetaKO) or aromatase (ArKO) genes have identified an important role of estrogens in maintaining differentiation and development of somatic cells in the ovary of eutherian mammals. In the absence of estrogen (ArKO) or the capacity to transduce an estrogen signal (ERalphabetaKO), the somatic cells in the ovary exhibited a male phenotype including Sertoli and Leydig cells. When ArKO mice were replaced with estrogen, the male phenotype was diminished and there was evidence of normal folliculogenesis in the ovary. It is concluded that the differentiation of somatic cells in the eutherian ovary is influenced by the sex steroid environment.

Contrasting phenotypes in reproductive tissues of female estrogen receptor null mice

The estrogen receptor (ER) exists in two known forms, ERalpha and ERbeta, and acts as a ligand-inducible transcription factor to fulfill critical roles in reproductive physiology. Although in vitro studies suggest the ERs may play redundant roles, a dissimilar tissue distribution indicates otherwise. Therefore, to gain insight into the role of each ER form, individual lines of mice lacking each respective receptor, as well as mice lacking both ER forms, were generated. alphaERKO and betaERKO female mice possess a normally developed reproductive tract and maintain expression of the opposite ER. The alphaERKO female is infertile and exhibits a hypoplastic uterus that is refractory to estrogens. The ovaries of the alphaERKO female are consistently polycystic and lack indications of spontaneous ovulation. In contrast, the betaERKO female exhibits a hormonally responsive uterus and grossly normal ovaries, but is subfertile in terms of the frequency and size of litters. Immature females of both ERKO lines successfully ovulate viable ova when superovulated with exogenous gonadotropins, yet the average yield of ooctyes is reduced. Mice lacking both known ER forms (alphabetaERKO) are infertile, possess the expected reproductive tract structures, but exhibit a remarkably distinct ovarian phenotype characterized by postnatal loss of oocytes and redifferentiation of the remaining somatic cells to Sertoli-like cells. This "sex-reversal" in the alphabetaERKO ovary is accompanied by the ectopic expression of testis-specific genes, for example, Sox9 and sulfatedglycoprotein-2.

Wnts and the female reproductive system

Wnts are intercellular growth and differentiation factors that regulate several key developmental steps, such as gastrulation, neurulation, and organogenesis, including the development of the midbrain, central nervous system, kidney, and limbs. Wnts are also needed for a normal development of the reproductive system. Deficiency of Wnt-4, -5a, and -7a, for example, results in sex reversal, infertility, and/or malformation of the internal and external genitals. Here we focus on the importance of Wnts in the female reproductive system.

Postnatal sex reversal of the ovaries in mice lacking estrogen receptors alpha and beta

Mice lacking estrogen receptors alpha and beta were generated to clarify the roles of each receptor in the physiology of estrogen target tissues. Both sexes of alphabeta estrogen receptor knockout (alphabetaERKO) mutants exhibit normal reproductive tract development but are infertile. Ovaries of adult alphabetaERKO females exhibit follicle transdifferentiation to structures resembling seminiferous tubules of the testis, including Sertoli-like cells and expression of Müllerian inhibiting substance, sulfated glycoprotein-2, and Sox9. Therefore, loss of both receptors leads to an ovarian phenotype that is distinct from that of the individual ERKO mutants, which indicates that both receptors are required for the maintenance of germ and somatic cells in the postnatal ovary.

XX germ cells: the difference between an ovary and a testis

In mammals, gonadal sex is determined by the action of the testis-determining gene, SRY. In the absence of SRY, the indifferent gonad follows an alternative pathway and develops as an ovary. Both mitotic and meiotic germ cells appear to play an essential role in ensuring ovarian development. Ovaries depleted of germ cells before or after ovarian differentiation has commenced can develop seminiferous cords, suggesting that XX germ cells may inhibit testicular differentiation in the ovary.

Gonadal sex reversal of the developing marsupial ovary in vivo and in vitro

Undifferentiated tammar wallaby ovaries were transplanted under the skin of male pouch young during the period of mitotic division of the XX germ cells. After 25 days, all the germ cells had disappeared and the ovaries contained seminiferous-like cords. Similarly, undifferentiated ovaries cultured for 4 days with recombinant human Mullerian-inhibiting substance (rhMIS) also contained well-differentiated seminiferous-like cords and few or no surviving germ cells. The majority of controls cultured without rhMIS developed as normal ovaries. However, in a few control ovaries seminiferous-like cords developed in those regions of the ovaries that were partially necrotic and contained few germ cells. These results strongly suggest that sex-reversal of the tammar ovary is the direct result of loss of mitotic germ cells, rather than an effect of MIS on female somatic cells. MIS is apparently toxic to these female germ cells in mitosis, but not to male germ cells in mitosis. Thus, in normal development in the tammar, the presence of XX germ cells in the ovary inhibits the formation of seminiferous cords so that the gonad develops as an ovary.