Rat gonadal and ovarioan organogenesis with and without germ cells. An ultrastructural study

Quantitation of sex chromosomal influence(s) on the somatic growth of fetal gonads in vivo

Matings between mice carrying the heterozygous autosomal gene Steel produce 25% homozygous Sl/Sld mutants having agametic gonads composed of somatic tissue alone. Mutants show a normal 1:1 male:female sex ratio and gonadal sex corresponds to genotypic sex. Gonads from both normal and mutant male and female fetuses were obtained on a daily basis from the twelfth day of gestation to birth and morphometrically evaluated for determination of the quantitative expression of XY and XX chromosomal combinations on growth of gonadal somatic tissue. Growth of testicular soma was found to be independent of a germ cell influence throughout the entire course of gestation whereas a germ cell influence on growth of ovarian gonadal soma was apparent from day 18 and thereafter. By birth, testicular somatic growth displayed a ten-fold increase over that of the ovary. These results suggest that early gonadal somatic growth is independent of a germ cell influence. The significant impact of a Y-chromosomal influence on gonadal somatic growth may suggest that male-specific gene product(s) regulate growth as well as differentiation of the somatic elements of the fetal testis.

Morphogenesis and fibronectin in sexual differentiation of rat embryonic gonads

The possible role of fibronectin in the organization of the sex-specific gonadal components was studied by immunocytochemistry combined with electron and light microscopy in rat fetuses at the ages of 12-15 days. Fibronectin was evenly distributed in both sexes under the basal lamina of the surface epithelium. Other basal laminae were not seen using light or electron microscopy inside the gonadal ridges at the age of 12 days. As the first sign of sexual differentiation, fibronectin-negative gonadal cords appeared in 13-day-old fetuses. In the males the cords were bigger than those in the females. The cords were clearly separated from the interstitium in 15-day-old fetuses of both sexes. A continuous layer of fibronectin had formed between the testicular surface epithelium and the elongated cords indicating the formation of a tunica albuginea. In females the surface epithelium-cord connection was maintained at all stages. Connections of the gonadal cords to mesonephric tubuli were seen in the rete region of both sexes. The electron optical basal lamina around the gonadal cords became continuous by the age of 15 days. The present results suggest that fibronectin is intimately involved in the sexual differentiation of the gonads, but not under the regulation of H-Y antigen or other testis-organizing factor.

Development of the ovarian surface and associated germ cells in the human fetus. A correlated study by scanning and transmission electron microscopy

The ovarian surface and associated germ cells have been studied in human fetuses from 12 weeks of age until near term, using light, TEM and SEM techniques. The surface epithelium and related cords proliferate extensively, especially at midterm. The cords of the ovarian cortex appear to be linked with ingrowths from the surface epithelium, and both structures have a common basal lamina. Germ cells are always interspersed among the somatic cells of the surface epithelium and associated cords. These results indicate that both the proliferating cords and surface epithelium may contribute to the formation of early follicles. Furthermore, the occurrence, of elements having some of the features of primitive steroidogenic cells in the regions of cord-surface epithelium continuity, suggests that both structures (surface epithelium and cords) contribute somatic cells, which in addition to becoming granulosa cells, might also contribute to the provision of primitive interstitial cells. Gonocytes tend to migrate through the developing ovarian tissue towards the surface where they become extruded into the peritoneal cavity. This phenomenon might contribute to the reduction in the number of germ cells at birth and parallels the atretic processes within the ovary.

The capacity of testicular cells of the postnatal rat to reorganize into histotypic structures

Cell reorganization experiments in vitro were performed with dissociated rat testes at different ages of postnatal development namely, newborn, 8-10, 18-25, 35-40, and 90 days. Only newborn and juvenile rat testicular cells reassociated into testicular-like organization in rotation culture. Puberal and adult rat testicular cells show morphogenetic organization when they were deprived or germ cells by busulphan pretreatment. A factor present in testicular tissue of puberal and adult rats inhibits reorganization. The inhibitor is confined to the spermatic cell fraction in the testis.

Cell to cell relationships in the seminiferous epithelium in the mouse embryo

Germ cells and Sertoli cells in embryonic mouse testes (day 14 to 20 of gestation) were examined by sectioning and freeze-fracture. Intercellular cytoplasmic bridges between the germ cells are observed in day 14 and older embryos. Membrane specializations with dense fuzzy material similar to the so-called "desmosome-like structures" are found between Sertoli cells and germ cells. A cell contact area with dense opposed membranes is also found between adjacent germ cells. Asymmetrical dense fuzzy lining of both Sertoli and germ cell membranes is noted. Pinocytotic pits or caveolae are frequently found in the Sertoli cell membrane. Between adjacent Sertoli cells, gap junctions of various sizes and focal meshworks of the occluding junctions are found. Most of the occluding junctional particles are located in the center of the grooves in the E face, and are similar to those in postnatal and adult Sertoli cell junctions. In addition, on both fractured faces there are ridges and grooves devoid of particles which are continuous with occluding junctions with particles, suggesting an initial stage in the formation of occluding junctions of the Sertoli cells. Particles gathered at the site of desmosome-like structures are present on the P face of the Sertoli cell.

The origin, migration and fine morphology of human primordial germ cells

Human primordial germ cells (PGCs) were observed ultrastructurally in stages from their endodermal to gonadal locations. Primitive PGCs in the hind-gut epithelium of the 4-week embryo, were recognized as well demarcated cells from the neighboring cells. At the time fo separation, the basal lamina of the epithelium was broken, then, through the gap so opened, the PGCs started to escape into the outer mesenchyme. In embryos at five weeks, PGCs were in the migration stage, and were found in the dorsal mesentery, at the coelomic angle and in the forming germinal ridge. In embryos at six weeks or later, almost all PGCS were accumulated in the gonad. The PGC was characterized by its large size and the large and round nucleus with conspicuous nucleolus, and by the presence of abundant glycogen particles and a considerable number of lipid droplets in the cytoplasm. Alkaline phosphatase activity was demonstrated selectively on the plasma membrane of the PGC. The shape of PGC was irregular, often had pseudopodia in PGCs in the separation and migration stages, suggesting their amoeboid movement in vivo, but was generally round or elliptic in PGCs in the settlement stage. The PGC was usually surrounded by and in close association with adjacent somatic cells.

Serous cysts of the aging guinea pig ovary. I. Light microscopy and origin

Ovaries from guinea pigs of different ages have been examined by light microscopy. Serous cysts measuring between 1 mm and 2.5 cm are present in all animals over one year of age. The cysts are fewer in number and size at six months, are least developed at ten weeks and are not apparent in the near-term fetus. The cysts arise from the rete ovarii. They are lined with a simple cuboidal to columnar epithelium composed of cells bearing solitary cilia or tufts of cilia. The structure and origin of these cysts is discussed and compared with what is known of the human serous cystadenoma.

The onset of testicular differentiation in the rat: An ultrastructural study

The structure of developing rat testes was studied by light and electron microscopy. Ultrastructural differentiation of Sertoli and Leydig cells was followed from 14 days of gestation through birth. Specialized morphology in Sertoli cells was first seen at 16 days of gestation. In these cells the rough endoplasmic reticulum increased and became organized as numerous short cisternae loaded with a homogenous material. Typical Leydig cells were found among the stromal cells, around day 17 of gestation. There is good correlation between the time of appearance of ultrastructural specialization and published data on secretory capacity of the fetal testes, in respect to the inhibition and differentiation of the Müllerian and Wolffian ducts.