Fgfs direct embryogenesis of several organs, including the lung, limb, and anterior pituitary. Here we report male-to-female sex reversal in mice lacking Fibroblast growth factor 9 (Fgf9), demonstrating a novel role for FGF signaling in testicular embryogenesis. Fgf9(-/-) mice also exhibit lung hypoplasia and die at birth. Reproductive system phenotypes range from testicular hypoplasia to complete sex reversal, with most Fgf9(-/-) XY reproductive systems appearing grossly female at birth. Fgf9 appears to act downstream of Sry to stimulate mesenchymal proliferation, mesonephric cell migration, and Sertoli cell differentiation in the embryonic testis. While Sry is found only in some mammals, Fgfs are highly conserved. Thus, Fgfs may function in sex determination and reproductive system development in many species.

Recently, we demonstrated that loss of Fgf9 results in a block of testis development and a male to female sexreversed phenotype; however, the function of Fgf9 in sex determination was unknown. We now show that Supplemental data available online

Growth factor signaling leads to the induction or repression of immediate early genes, but how these genes act collectively as effectors of downstream processes remains unresolved. We have used gene trap-coupled microarray analysis to identify and mutate multiple platelet-derived growth factor (PDGF) intermediate early genes in mice. Mutations in these genes lead to a high frequency of phenotypes that affect the same cell types and processes as those controlled by the PDGF pathway. We conclude that these genes form a network that controls specific processes downstream of PDGF signaling.

The platelet-derived growth factor (PDGF) signaling pathway regulates numerous lineages of mesenchymal cell origin during development and in the adult. The transcriptional targets of this pathway have been shown to be required in several PDGF-dependent processes, but the roles of these targets in specific tissues is just beginning to be identified. In this study, we show that five different PDGF target genes are essential for male and/or female fertility. Mutations in each of these five different genes lead to defects in the steroid-producing cells in the testis and/or ovary and altered hormone production, suggesting that the PDGF pathway controls steroidogenesis through these genes in both sexes. Furthermore, conditional mutations of both PDGF receptors revealed a requirement in steroid-producing cells in multiple organs, including the testis, ovary, and adrenal cortex. Therefore, PDGF signaling may constitute a common mechanism in the control of multiple steroidogenic lineages.[Keywords: PDGF; testis; ovary; steroid hormone; Leydig cell; theca cell] Supplemental material is available at http://www.genesdev.org. Steroidogenesis and the development of the steroid-producing cells in the gonads is a tightly controlled process in both sexes, requiring regulation at many stages of development through endocrine, autocrine, and paracrine mechanisms. Defects in these processes lead to infertility, malformation of the reproductive tracts, and abnormal secondary sexual characteristics. In males, low testosterone production leads to abnormalities in spermatogenesis, undescended testes, ambiguous genitalia, and infertility (Habert et al. 2001). In females, the production of estrogen and progesterone is essential for ovulation and the maintenance of pregnancy (Fisher et al. 1998;Toda et al. 2001). Altered levels of steroid hormones are known to be associated with many of the common types of infertility in both men and women, such as hypogonadism and Polycystic Ovary Syndrome (PCOS), yet many of the mechanisms that control steroidogenic cell development and hormone production are not well understood.In the gonads, steroid hormones are synthesized by specialized endocrine cells: the Leydig cells in the testis (Habert et al. 2001) and theca cells in the ovary (Magoffin 2005). In the testis, Leydig cells have at least two clearly defined waves of development, as fetal and adult Leydig cells. Fetal Leydig cells appear very early after sex determination, by embryonic day 12.5 (E12.5) in the mouse, and testosterone production from these cells is necessary for the masculinization of the fetus. Postnatally, fetal Leydig cells are replaced by adult Leydig cells, which are required for the progression and maintenance of spermatogenesis. In the ovary, the production of steroid hormones requires cooperation between two cell types, the theca and granulosa cells (Magoffin 2005). Theca cells are steroidogenic, as they initiate steroid synthesis by importing cholesterol to the mitochondrial membrane and synthesize steroid hormones de novo. ...

Cell proliferation has been shown to have multiple functions in development and pattern formation, including roles in growth, morphogenesis, and gene expression. Previously, we determined that the earliest known morphological event downstream of the male sex determining gene, Sry, is the induction of proliferation. In this study, we used proliferation inhibitors to block cell division during early gonad development, at stages before the XY gonad has committed to the testis pathway. Using the expression of sex-specific genes and the formation of testis morphology as markers of testis determination, we found that proliferation within a specific 8-h window was critical for the establishment of the male pathway and the formation of the testis. Inhibition of proliferation before or after this critical period led to smaller gonads, but did not block testis formation. The critical period of proliferation coincides with the initiation of Sry expression and is essential for the differentiation of Sertoli cells, suggesting that proliferation is a vital component of the initiation of the male pathway by Sry. We believe these studies suggest that proliferation is involved not only in the elaboration of organ pattern, but also in the choice between patterns (male and female) in the bipotential gonad.

Ghrelin is a unique peptide gut hormone that requires post-translational modification to stimulate both feeding and growth hormone release. Ghrelin O-acyltransferase (GOAT) was identified as a specific acyl-transferase for ghrelin, and recent genetic deletion studies of the Goat gene (Goat(-/-)) uncovered the role of ghrelin in the regulation of glucose homeostasis. To further understand the physiological functions of the GOAT/ghrelin system, we have conducted a metabolomic and microarray profile of Goat-null mice, as well as determined Goat expression in different tissues using the lacZ reporter gene. Serum metabolite profile analysis revealed that Goat(-/-) mice exhibited increased secondary bile acids >2.5-fold. This was attributed to increased mRNA and protein expression of the ileal sodium-dependent bile acid transporter (ISBT) in the intestinal and biliary tract. Increased expression of additional solute carrier proteins, including Slc5a12 (>10-fold) were also detected in the small intestine and bile duct. Goat staining was consistently observed in the pituitary glands, stomach, and intestines, and to a lesser extent in the gallbladder and pancreatic duct. This is the first report that the GOAT/ghrelin system regulates bile acid metabolism, and these findings suggest a novel function of GOAT in the regulation of intestinal bile acid reabsorption..

SummaryDuring vertebrate development the gonad has two possible fates, the testis or the ovary. The choice between these fates is made by a variety of sex-determining mechanisms, from the sexdetermining gene on the Y chromosome (Sry) in mammals, to nongenetic temperature-dependent systems in many reptiles. Despite the differences in the mechanisms at the top of the sexdetermining cascade, the resulting morphology and many genes involved in early testis and ovarian development are common to most vertebrates, leading to the hypothesis that the underlying processes of sex determination are conserved. In this study, we examined the early steps of gonad development in the red-eared slider turtle (Trachemys scripta), a species that uses the temperature of egg incubation to determine sex. A dramatic increase in cell proliferation was observed in the male gonad during the earliest stages of sex determination. Using the localization of Wilms' Tumor suppressor 1 (WT1), we determined that this proliferation increase occurred in a population that contained pre-Sertoli cells. The proliferation of pre-Sertoli cells has been documented during sex determination in both mice and alligators, suggesting that proliferation of this cell type has an important role in vertebrate testis organogenesis and the determination of male fate.

No abstract