Sex Determination and Differentiation Chapter 7 Sex Determination and Differentiation © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 7.1 (A) Proposed mechanism for the evolution of sex chromosomes from a pair of autosomes. (B) Structure of the human Y chromosome indicating the position of the SRY gene. PA, pseudoautosomal region; MSY, male-specific region of the Y; euchrom, euchromatic region; heterochrom, heterochromatic region; cent, centromere. Source: (Adapted from Ref. 248). © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 7. 2 XX male sex reversal with an Sry transgene FIGURE 7.2 XX male sex reversal with an Sry transgene. (A) On the left is a control XY male and on the right is his littermate, an XX transgenic carrying a 14-kb genomic fragment containing the mouse Sry gene. The external and internal genitalia are indistinguishable except for the testis, which is smaller in the transgenic animal due to the lack of germ cells (see insets, in which crosssections through the testis of each mouse are shown). (B) PCR analysis of genomic DNA from these mice as well as an XX sibling control. Bands for Sry and the DNA loading control (myogenin) are present in the XX transgenic animal but the Y chromosome marker Zfy-1 is missing. M, size marker. Soure: Adapted from Ref. 6. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 7.3 The four core genotypes (FCG) model separates the effects of chromosome complement from those of gonadal sex. (A) Breeding scheme for generation of FCG mice. XX female mice are crossed with XY male mice in which Sry has been deleted from the Y chromosome (Y−) and reinserted on an autosome (Sry). Progeny of four different genotypes are generated. Their phenotype, chromosome complement, and X imprinting status are listed below. (B) A 2 × 2 schematic demonstrates how the FCG mice can be used to determine the cause of phenotypic differences observed. Source: Figure reprinted with permission from Ref. 249. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 7. 4 Regulation of Sox9 expression at the TESCO enhancer FIGURE 7.4 Regulation of Sox9 expression at the TESCO enhancer. (A) Binding of SF1 to the TESCO enhancer is sufficient for initiation of Sox9 expression. (B) Expression is subsequently upregulated by synergistic action of SF1 and SRY, which may physically interact at the enhancer. (C) Once SRY expression ceases, Sox9 expression is maintained by an autoregulatory loop in which SOX9 itself binds to TESCO and interacts with SF1 to promote expression. (D) In female embryos, FOXL2 and estrogen receptor (ER) bind to TESCO, acting synergistically to inhibit Sox9 expression. In addition, DAX1 competes with SF1 for binding sites on TESCO, preventing Sox9 expression. Source: Adapted from Sekido and Lovell-Badge, 2008.251 © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 7.5 XYPOS mice on a C57Bl/6 background exhibit ovotestis formation. Brightfield images of wild-type female (A) and male (B) gonads from embryos at E14.5. Testicular cords are clearly visible in the male gonad at this stage. (C) Ovotestis formation in XYPOS mice on a C57Bl/6 background. Male testicular cords can be seen in the central portion of the gonad while the ovarian portion is found at both poles. Source: Pictures taken from Ref. 250. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 7.6 Differentiation of the embryonic testis from a bipotential precursor. This figure is reproduced in color in the color plate section. (A) Confocal image of a gonad and mesonephros stained with an antibody to laminin at a stage before morphological changes take place (E11.5). (B–H) Morphology of the embryonic testis. (B, C) The Sertoli and Leydig cells of the E13.5 gonad are marked by whole-mount in situ hybridization for the expression of the Sertoli cell marker AMH (B) and the Leydig cell marker Cyp11a1 (C). The structure of the testicular cords is seen in the confocal image of an E12.5 gonad that was stained with an antibody against SOX9 in green (D). Germ cells are found within the testicular cords as marked by the antibody stain for PECAM in red (D). In the interstitium, epithelial cells, as marked by the antibody stain for PECAM in red (D), and Leydig cells, as marked by the section of the whole mount in situ hybridization on a gonad from a E14 embryo for the expression of Cyp11a1 (E), are found. (F, G) Mesonephric cell migration is observed in the XY (F) but not the XX (G) gonad, as shown by organ culture samples where the mesonephros but not the gonad is derived from transgenic mice that express GFP ubiquitously. (H) The formation of male-specific vasculature as shown by a whole-mount antibody stain to PECAM, which marks endothelial cells, of gonad and mesonephros from an E14 embryo. mt, mesonephric tubules; g, gonad; m, mesonephros; tc, testis cord; cbv, coelomic blood vessel. Source: Adapted from Ref. 252; confocal image (D) courtesy of Blanche Capel. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 7. 7 Stages of adult Leydig cell development FIGURE 7.7 Stages of adult Leydig cell development. Pictorial representations of the morphology of the developing adult Leydig cell, with defining characteristics tabulated below. Source: Taken from Ref. 253. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 7.8 Initiation and maintenance of sexspecific gonadal phenotypes. Initially, a male versus female gonadal fate is dependent upon expression of Sry from the Y chromosome, and genes including Sox9, Fgf9, and Pgd2 promote testis organogenesis. Male-promoting genes negatively regulate female-promoting genes including members of the Wnt pathway, and vice versa. In the adult, negative regulatory loops remain, and are now thought to involve female fate-promoting Foxl2 and ERα/β genes, and male-specific Dmrt1. Source: Taken from Ref. 149. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition

FIGURE 7.9 Sexual differentiation of the internal and external genitalia. The bipotential gonad develops into an ovary in the absence of SRY or a testis if SRY is present. Three main sexually dimorphic cell types are found in the gonad: germ cells, supporting cells (Sertoli cells and follicle cells), and steroidogenic cells (Leydig and theca cells). In the male, products from the testis, AMH, Insl3, and testosterone, induce the differentiation of the male-specific internal and external genitalia. Source: Confocal images of laminin stained gonads were adapted from Ref. 254. © 2015, Elsevier, Inc., Plant and Zeleznik, Knobil and Neill's Physiology of Reproduction, Fourth Edition