The endocrine control of male phenotypic development

Male and female embryos develop in an identical fashion during the initial portion of gestation. If the indifferent gonad differentiates into an ovary (or if no gonad is present), a female phenotype is formed. Male phenotypic differentiation, however, requires the presence of an endocrinologically active testis. Two secretions of the foetal testis, Mullerian-inhibiting substance and testosterone, are responsible for male development. Testosterone itself is responsible for virilization of the Wolffian duct system into the epididymis, vas deferens, and seminal vesicle, whereas dihydrotestosterone induces development of the prostate and male external genitalia. Thus, impairment of dihydrotestosterone formation results in a characteristic phenotype consisting of predominantly female external genitalia but normally virilized Wolffian ducts. The molecular mechanisms by which testosterone and dihydrotestosterone act during foetal development appear to involve the same high affinity receptor, a protein that transports both testosterone and dihydrotestosterone to the nucleus of target cells. When this receptor is either absent, deficient, or structurally abnormal, the actions of both testosterone and dihydrotestosterone are impaired, and the resulting developmental anomalies involve both internal and external genital structures.     

Reproductive/urogenital organ development and molecular genetic cascades: glamorous developmental processes of bodies

At the beginning of the 21st century, developmental biologists together with medical researchers in a wide range of fields are witnessing rapid progress in molecular developmental biology. For example, conditional gene knockout systems are being designed to tackle questions about organogenesis and body plan formation in experimental mouse models and experimental designs include several compound mutant analyses and genome modification strategies. On the other hand, several fields remain relatively unexplored. Molecular mechanisms of sex differentiation are one of the unexplored huge area. Unanswered questions include the molecular genetic cascade of gonad formation, reproductive organ formation, uterus, external genitalia and mammary gland formation, and also the molecular mechanisms of signal transduction, and gene regulation by nuclear hormone receptors. This special thematic review series entitled, "Reproductive/urogenital organ development and molecular genetic cascades: glamorous developmental processes of bodies," covers such a wide range of topics. For this special issue, I have asked active researchers to contribute reviews of these topics which I believe will be useful not only for molecular developmental biologists, but also for researchers in biochemistry and cell biology. It will be my great pleasure if this special thematic issue encourages scientists to study this exciting research field.     

Cellular and molecular mechanisms of development of the external genitalia

The limb and external genitalia are appendages of the body wall. Development of these structures differs fundamentally in that masculine development of the external genitalia is androgen dependent, whereas development of the limb is not. Despite this fundamental difference in developmental regulation, epithelial-mesenchymal interactions play key roles in the development of both structures, and similar regulatory molecules are utilized as mediators of morphogenetic cell-cell interactions during development of both the limb and external genitalia. Given the relatively high incidence of hypospadias, a malformation of penile development, it is appropriate and timely to review the morphological, endocrine, and molecular mechanisms of development of the genital tubercle (GT), the precursor of the penis in males and the clitoris in females. Morphological observations comparing development of the GT in humans and mouse emphasize the validity of the mouse as an animal model of GT development and validate the results of experimental studies. Accordingly, the use of mutant mice provides important insights into the roles of specific regulatory molecules in development of the external genitalia. While our current understanding of the morphological and molecular mechanisms of mammalian external genitalia development is still rudimentary, this review summarizes the current state of our knowledge and whenever possible draws from the rich experimental embryology literature on other relevant organs such as the developing limb. Future research on the hormonal and molecular mechanisms of GT development may yield strategies to prevent or reduce the incidence of hypospadias and to elucidate the molecular genetic mechanisms of GT morphogenesis, especially in relation to common organogenetic pathways utilized in other organ systems.     

Role of gonadal hormones in development of the sexual phenotypes

Summary Male and female embryos develop in an identical fashion during the initial portion of gestation. If the indifferent gonad differentiates into an ovary (or if no gonad is present), a female phenotype is formed. Male phenotypic differentiation, however, requires the presence of an endocrinologically active testis. Two secretion of the fetal testis, Müllerian inhibiting substance and testosterone, are responsible for male development. Studies of single gene mutations that interfere with androgen action indicate that testosterone itself is responsible for virilization of the Wolffian duct system into the epididymis, vas deferens, and seminal vesicle, whereas the testosterone metabolite dihydrotestosterone induces development of the prostate and male external genitalia. Thus, impairment of dihydrotestosterone formation results in a characteristic phenotype consisting of predominantly female external genitalia but normally virilized Wolffian ducts. The molecular mechanisms by which testosterone and dihydrotestosterone act during fetal development appear to involve the same high affinity receptor, a protein that transports both testosterone and dihydrotestosterone to the nucleus of target cells. When this receptor is either absent, deficient, or structurally abnormal, the actions of both testosterone and dihydrotestosterone are impaired, and the resulting developmental anomalies involve both internal and external genital structures.The original work described in this review was supported by grant AM 03892 from the National Institutes of Health     

Unique functions of Sonic hedgehog signaling during external genitalia development.

Coordinated growth and differentiation of external genitalia generates a proximodistally elongated structure suitable for copulation and efficient fertilization. The differentiation of external genitalia incorporates a unique process, i.e. the formation of the urethral plate and the urethral tube. Despite significant progress in molecular embryology, few attempts have been made to elucidate the molecular developmental processes for external genitalia. The sonic hedgehog (Shh) gene and its signaling genes have been found to be dynamically expressed during murine external genitalia development. Functional analysis by organ culture revealed that Shh could regulate mesenchymally expressed genes, patched 1 (Ptch1), bone morphogenetic protein 4 (Bmp4), Hoxd13 and fibroblast growth factor 10 (Fgf10), in the anlage: the genital tubercle (GT). Activities of Shh for both GT outgrowth and differentiation were also demonstrated. Shh(-/-) mice displayed complete GT agenesis, which is compatible with such observations. Furthermore, the regulation of apoptosis during GT formation was revealed for the first time. Increased cell death and reduced cell proliferation of the Shh(-/-) mice GT were shown. A search for alterations of Shh downstream gene expression identified a dramatic shift of Bmp4 gene expression from the mesenchyme to the epithelium of the Shh mutant before GT outgrowth. Regulation of mesenchymal Fgf10 gene expression by the epithelial Shh was indicated during late GT development. These results suggest a dual mode of Shh function, first by the regulation of initiating GT outgrowth, and second, by subsequent GT differentiation.     

Control of adventitious root formation: insights into synergistic and antagonistic hormonal interactions

Plants have evolved sophisticated root systems that help them to cope with harsh environmental conditions. They are typically composed of a primary root and lateral roots (LRs), but may also include adventitious roots (ARs). Unlike LRs, ARs may be initiated not only from pericycle cells, but from various cell types and tissues depending on the species. Phytohormones, together with many other internal and external stimuli, coordinate and guide every step of AR formation from the first event of cell reprogramming until emergence and outgrowth. In this review, we summarize recent advances in the molecular mechanisms controlling AR formation and highlight the main hormonal cross talk involved in its regulation under different conditions and in different model systems.     

Neuronal models for sleep-wake regulation and synaptic reorganization in the sleeping hippocampus

In this article, we discuss mathematical models that address the control of sleep-wake behavior in the infant and adult rodent and a model that addresses changes in single-cell firing patterns in the hippocampus across wake and rapid eye movement (REM) sleep states. Each of the models describes the dynamics of experimentally identified neuronal components--either the firing activity of wake-and sleep-promoting neuronal populations or the spiking activity of hippocampal pyramidal neurons. Our discussion of each model illustrates how a mathematical model that describes the temporal dynamics of the modeled neuronal components can reveal specifics about proposed neuronal mechanisms that underlie sleep-wake regulation or sleep-specific firing patterns. For example, the dynamics of the models developed for sleep-wake regulation in the infant rodent lend insight into the involved brain-stem neuronal populations and the evolution of the network during maturation. The results of the model for sleep-wake regulation in the adult rodent suggest distinct properties of the involved neuronal populations and their interactions that account for long-lasting and brief waking bouts. The dynamics of the model for sleep-specific hippocampal neural activity proposes neural mechanisms to account for observed activity changes that can invoke synaptic reorganization associated with learning and memory consolidation.     

Identification and functional characterization of doublesex gene in the testis of Spodoptera litura

Fusion of the testis occurs in most Lepidoptera insects, including Spodoptera litura, an important polyphagous pest. Testicular fusion in S. litura is advantageous for male reproduction, and the molecular mechanism of fusion remains unknown. Doublesex influences the formation of genitalia, the behavior of courtship, and sexually dimorphic traits in fruit-fly and silkworm, and is essential for sexual differentiation. However, its purpose in the testis of S. litura remains unknown. The doublesex gene of S. litura (Sldsx) has male-specific SldsxM and female-specific SldsF isoforms, and exhibits a higher expression level in the male testis. At the testicular fusion stage (L6D6), Sldsx attained the highest expression compared to the pre-fusion and post-fusion periods. Moreover, Sldsx had a higher expression in the peritoneal sheaths of testis than that of germ cells in the follicle. CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/Cas9) was applied to S. litura to determine the role of Sldsx. A mixture of single guide RNA messenger RNA and Cas9 protein (300 ng/μL each) was injected into eggs within 2 h following oviposition. CRISPR/Cas9 successfully induced genomic mutagenesis of Sldsx at Go generation. The mutant males had smaller testis surrounded by less tracheae. Moreover, the mutant males had abnormal external genitalia and could not finish mating with wild-type females. Additionally, testes were fused for almost all mutant males. The results showed that Sldsx was not related to testicular fusion, and is required for both testis development and the formation and function of external genitalia in S. litura. The main roles of doublesex on the male are similar to other insects.     

Molecular mechanisms of external genitalia development

External genitalia development occurs through a combination of hormone independent, hormone dependent, and endocrine pathways. Perturbation of these pathways can lead to abnormal external genitalia development. We review human and animal mechanisms of normal and abnormal external genitalia development, and we evaluate abnormal mechanisms that lead to hypospadias. We also discuss recent laboratory findings that further our understanding of animal models of hypospadias.     

Steroid deficiency syndromes in mice with targeted disruption of Cyp11a1

Steroid deficiencies are diseases affecting salt levels, sugar levels, and sexual differentiation. To study steroid deficiency in more detail, we used a gene-targeting technique to insert a neo gene into the first exon to disrupt Cyp11a1, the first gene in steroid biosynthetic pathways. Cyp11a1 null mice do not synthesize steroids. They die shortly after birth, but can be rescued by steroid injection. Due to the lack of feedback inhibition by glucocorticoid, their circulating ACTH levels are exceedingly high; this results in ectopic Cyp21 gene expression in the testis. Male Cyp11a1 null mice are feminized with female external genitalia and underdeveloped male accessory sex organs. Their testis, epididymis, and vas deferens are present, but undersized. In addition, their adrenals and gonads accumulate excessive amounts of lipid. The lack of steroid production, abnormal gene expression, and aberrant reproductive organ development resemble various steroid deficiency syndromes, making these mice good models for studies of steroid function and regulation.     

精子发生过程中基因表达转录水平的调控

哺乳动物精子发生于睾丸的生精小管, 是一个高度复杂的细胞分裂和分化过程, 涉及到错综复杂的基因表达调控过程, 包括转录和转录后水平的调控, 其中任何一个环节出错都可能导致雄性不育。因此, 揭示精子发生过程中的分子调控机理, 对发现新的男性避孕方法及治疗不育症有重要意义。文章重点综述了近年有关雄激素及其受体、雌激素及其受体、转录因子和染色质相关因子在精子发生转录水平调控的研究进展。     

Anthropometric study of male external genitalia of 320 healthy Nigerian adults

Five basic measurements of the male external genitalia were studied in 320 healthy male medical students belonging to the various parts of Nigeria (West Africa). Their ages range from 17 to 23 years. The measurements were as follows: average length of the penis (81.6 +/- 0.94 mm); circumference of the penis (88.3 +/- 0.02 mm); circumference of the scrotum (212.6 +/- 2.48 mm); length of right testis (46.8 +/- 0.54 mm); width of right testis (32.4 +/- 0.37 mm); length of left testis (46.0 +/- 0.53 mm); and width of left testis (31.4 +/- 0.36 mm). The size of the genitalia increases with the increase in age in younger year groups. The adult stages of genitalia development are reached at the age of 21 years in 89.0% of the individuals. The growth of the genitalia is continued with the increasing height and weight, but this growth slows down after attaining a definite height and weight.     

肾脏发育的分子调控机制

随着分子生物学技术的迅猛发展和广泛应用,参与肾脏发育过程的新基因相继被发现,肾脏发育过程中复杂的分子信号调控机制也得到进一步的研究,为阐明肾脏疾病的发病机制及从基因水平开展治疗提供了新的思路。文章对肾脏发育的3个阶段,即输尿管芽的发生和分支形成、生后肾原基的早期上皮性分化、肾小球血管球的发生和发育的分子信号调控研究进展进行了总结,主要涉及多种转录因子、生长因子及细胞因子,同时细胞外基质和黏附分子也参与其调控。     

Systematic analyses of murine masculinization processes based on genital sex differentiation parameters

Murine reproductive tissues of the external genitalia and perineum develop with remarkably distinctive characteristics in males and females. Although many researches on such mouse organ development have been reported, there are still limited parameters that evaluate the developmental sexual differences of external genitalia and perineum. Furthermore, elucidation of the recent developmental signals for the external genitalia and perineum requires up‐to‐date knowledge of gene functions in reproductive science. To promote researches on reproductive organ formation, establishment of parameters for the androgen‐mediated formation of external genitalia and perineum is essential. In this study, we propose genital sex differentiation parameters (GSDP), a set of developmental parameters based on systematic three‐dimensional tissue reconstruction and cumulative histological analyses. We define the sexual differences of external genitalia and perineum by GSDP through analyzing mouse models, androgen inhibitor‐induced feminization experiments and Mafb mutant mouse with defective urethral differentiation. The urethral parameters displayed prominent reduction by the androgen inhibitor (finasteride) treatment. However, genital tubercle (GT) size parameters were not affected by such treatment. These results indicated that sensitivity to dihydrotestosterone was different between embryonic GT size and urethral formation. Furthermore, we evaluated the extent of urethral defects of Mafb mutant mice by GSDP. Thus, GSDP is a set of useful parameters to define the sexual differences during external genitalia and perineum development.