BMP signaling in the human fetal ovary is developmentally regulated and promotes primordial germ cell apoptosis.

Primordial germ cells (PGCs) are the embryonic precursors of gametes in the adult organism, and their development, differentiation, and survival are regulated by a combination of growth factors collectively known as the germ cell niche. Although many candidate niche components have been identified through studies on mouse PGCs, the growth factor composition of the human PGC niche has not been studied extensively. Here we report a detailed analysis of the expression of components of the bone morphogenetic protein (BMP) signaling apparatus in the human fetal ovary, from postmigratory PGC proliferation to the onset of primordial follicle formation. We find developmentally regulated and reciprocal patterns of expression of BMP2 and BMP4 and identify germ cells to be the exclusive targets of ovarian BMP signaling. By establishing long-term cultures of human fetal ovaries in which PGCs are retained within their physiological niche, we find that BMP4 negatively regulates postmigratory PGC numbers in the human fetal ovary by promoting PGC apoptosis. Finally, we report expression of both muscle segment homeobox (MSX)1 and MSX2 in the human fetal ovary and reveal a selective upregulation of MSX2 expression in human fetal ovary in response to BMP4, suggesting this gene may act as a downstream effector of BMP-induced apoptosis in the ovary, as in other systems. These data reveal for the first time growth factor regulation of human PGC development in a physiologically relevant context and have significant implications for the development of cultures systems for the in vitro maturation of germ cells, and their derivation from pluripotent stem cells.

Differential expression and regulation by activin of the neurotrophins BDNF and NT4 during human and mouse ovarian development.

The tropomyosin-related kinase (Trk) B neurotrophin receptor is essential for ovarian germ cell survival and primordial follicle formation, but the contributions of its ligands, brain-derived neurotrophic factor (BDNF) and neurotrophin-4 (NT4), are unknown. We have investigated their expression and regulation in developing human and mouse ovaries. BDNF expression increased with increasing gestation, expression of human NTF4 and of both Ntf5 and Bdnf in the mouse was unchanged. Bdnf expression was dramatically lower than Ntf5 in the mouse, but levels were comparable in the human. Human fetal ovarian somatic cells expressed BDNF. Activin A selectively regulated BDNF and Ntf5 expression in human and mouse, respectively, identifying an oocyte/somatic signaling pathway which might mediate the pro-survival effects of activin. These data reveal that expression and regulation of the TrkB ligands are differentially controlled in the developing ovaries of humans and mice, and identify BDNF as a potential regulator of germ cell fate in the human fetal ovary.

N- and E-cadherin expression in human ovarian and urogenital duct development.

OBJECTIVE: To investigate expression of N- and E-cadherin in the developing human ovary. DESIGN: The expression of N- and E-cadherin was analyzed in 18 human fetal ovaries between 8 and 20 weeks' gestation using immunohistochemistry. Fetal human male and rat urogenital tracts were used for comparison of expression. SETTING: Academic research institute. PATIENT(S): Women undergoing termination of pregnancy. INTERVENTION(S): Immunofluorescent analysis of cadherin expression. RESULT(S): In fetal ovary, N- and E-cadherins were expressed at all gestations with overlapping but not identical patterns. Expression was associated with germ cells and adjacent somatic cells, including within newly formed primordial follicles, but neither cadherin was expressed in the somatic cell cords. The epithelia of the müllerian and wolffian ducts expressed only N- and E-cadherin, respectively, in a mutually exclusive fashion. This pattern of cadherin expression was found to be conserved between human and rat fetuses of both genders. CONCLUSION(S): The demonstration of N- and E-cadherin expression in the human fetal ovary indicates likely roles in gonadal development from germ cell proliferation to primordial follicle formation, as well as in the development of the urogenital ducts of both genders. This is consistent with animal studies identifying cadherins as key regulators of early germ cell development.

Prostaglandin E2 as a regulator of germ cells during ovarian development.

CONTEXT: The formation of primordial follicles occurs during fetal life yet is critical to the determination of adult female fertility. Prior to this stage, germ cells proliferate, enter meiosis, and associate with somatic cells. Growth and survival factors implicated in these processes include activin A (INHBA), the neurotrophins BDNF and NT4 (NTF5), and MCL1. The prostaglandins have pleiotrophic roles in reproduction, notably in ovulation and implantation, but there are no data regarding roles for prostaglandins in human fetal ovarian development. OBJECTIVE: The aim of the study was to investigate a possible role for prostaglandin (PG) E(2) in human fetal ovary development. DESIGN: In vitro analysis of ovarian development between 8 and 20 wk gestation was performed. MAIN OUTCOME MEASURE(S): The expression patterns of PG synthesis enzymes and the PGE(2) receptors EP2 and EP4 in the ovary were assessed, and downstream effects of PGE(2) on gene expression were analyzed. RESULTS: Ovarian germ cells express the PG synthetic enzymes COX2 and PTGES as well as the EP2 and EP4 receptors, whereas COX1 is expressed by ovarian somatic cells. Treatment in vitro with PGE(2) increased the expression of BDNF mRNA 1.7 +/- 0.16-fold (P = 0.004); INHBA mRNA, 2.1 +/- 0.51-fold (P = 0.04); and MCL1 mRNA, 1.15 +/- 0.06-fold (P = 0.04), but not that of OCT4, DAZL, VASA, NTF5, or SMAD3. CONCLUSIONS: These data indicate novel roles for PGE(2) in the regulation of germ cell development in the human ovary and show that these effects may be mediated by the regulation of factors including BDNF, activin A, and MCL1.