Development of the external genitalia in rat fetuses

Development of the external genitalia in rat fetuses was studied with special reference to the formation of the labia pudenda and the determination of the stage at which the sex difference could be recognized from changes in the external structures. The urogenital fold located on either side of the external structures. The urogenital fold located on either side of the urogenital groove gradually enlarges and begins to enclose the genital tubercle with its counter fold on day 20 of gestation. Thus, the urogenital folds, which are known to become the labia minora and the prepuce of clitoris in the human, are differentiated only into the prepuce of clitoris in the rat. The genital swellings situated caudally to the urogenital folds are not well developed and come to be inconspicuously flat in situ at the end of gestation. However, the labia majora are formed by the time of puberty when the vagina opens. Therefore, it seems that the genital swellings contribute to the formation of the labia majora after birth. Sex difference in development of the external genitalia is recognized on day 17 of gestation; a small oval urogenital orifice is larger in male than in female and the genital swellings are better developed in male than in female.     

Tissue-specific requirements of beta-catenin in external genitalia development

External genitalia are body appendages specialized for internal fertilization. Their development can be divided into two phases, an early androgen-independent phase and a late androgen-dependent sexual differentiation phase. In the early phase, the embryonic anlage of external genitalia, the genital tubercle (GT), is morphologically identical in both sexes. Although congenital external genitalia malformations represent the second most common birth defect in humans, the genetic pathways governing early external genitalia development and urethra formation are poorly understood. Proper development of the GT requires coordinated outgrowth of the mesodermally derived mesenchyme and extension of the endodermal urethra within an ectodermal epithelial capsule. Here, we demonstrate that beta-catenin plays indispensable and distinct roles in each of the aforementioned three tissue layers in early androgen-independent GT development. WNT-beta-catenin signaling is required in the endodermal urethra to activate and maintain Fgf8 expression and direct GT outgrowth, as well as to maintain homeostasis of the urethra. Moreover, beta-catenin is required in the mesenchyme to promote cell proliferation. By contrast, beta-catenin is required in the ectoderm to maintain tissue integrity, possibly through cell-cell adhesion during GT outgrowth. The fact that both endodermal and ectodermal beta-catenin knockout animals develop severe hypospadias in both sexes raises the possibility that the deregulation of any of these functions can contribute to the etiology of congenital external genital defects in humans.     

Bilateral rhomboid flaps for reconstruction of the external genitalia in epispadias-exstrophy

In ten young males with the epispadias-exstrophy complex, a new technique of bilateral rhomboid flaps was used for penile elongation and genital reconstruction. This approach offers less chance of injury to the verumontanum and ejaculatory ducts and accurately defines the penopubic angle. Cosmetic and functional results were satisfactory in all patients.     

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.     

东亚飞蝗外生殖器的显微结构

利用扫描电镜技术观测了东亚飞蝗Locusta migratoria manilensis(Meyen)雌雄个体外生殖器的显微构造,描述了雌雄两性外生殖器的具体结构以及其表面上感受器的分布情况。雌性的外生殖器由背、腹产卵瓣构成,雄性的外生殖器由外骨骼所包被的阳具基背片和阳具复合体构成。在雌雄两性的外生殖器表面着生有大量的感受器,包括毛形、刺形、锥形,主要是机械感受器,还有少量化学感受器。     

Development of the external genitalia in fetuses of the southern minke whale, Balaenoptera acutorostrata

The developmental changes of the anogenital distance and external genitalia were studied in 81 fetuses of the southern minke whale. It was difficult to sex the fetuses with less than 55.8 mm crown-rump length (CRL) even by histological means, but it was easy in the fetuses with more than 77.0 mm CRL and less than 110.0 mm CRL. The histologically determined male fetuses had a ratio of anogenital distance to CRL or body length of more than 5%, while females had a value of less than 4%. At later stages with a CRL of more than 113.0 mm, male fetuses had an umbilicus-directed genital tubercle, while in females a tail-directed tubercle was observed. The present study suggests that the stage with sexual dimorphism might be earlier in the southern minke whale than that previously reported.     

A procedure for the fusion of cells in suspension by means of polyethylene glycol

The nuclei of chick and human fibroblasts are readily distinguishable in Leishman stained heterokaryons. The use of these two types of cell has allowed development of a method for fusion in suspension based on the use of polyethylene glycol (PEG) of MW 1000 in Dulbecco's medium containing 15% dimethylsulfoxide (DMSO).