Developmental changes in interstitial collagens of fetal rat genital ducts

Cellular mechanisms of Müllerian duct formation in the mouse

Regardless of their sex chromosome karyotype, amniotes develop two pairs of genital ducts, the Wolffian and Müllerian ducts. As the Müllerian duct forms, its growing tip is intimately associated with the Wolffian duct as it elongates to the urogenital sinus. Previous studies have shown that the presence of the Wolffian duct is required for the development and maintenance of the Müllerian duct. The Müllerian duct is known to form by invagination of the coelomic epithelium, but the mechanism for its elongation to the urogenital sinus remains to be defined. Using genetic fate mapping, we demonstrate that the Wolffian duct does not contribute cells to the Müllerian duct. Experimental embryological manipulations and molecular studies show that precursor cells at the caudal tip of the Müllerian duct proliferate to deposit a cord of cells along the length of the urogenital ridge. Furthermore, immunohistochemical analysis reveals that the cells of the developing Müllerian duct are mesoepithelial when deposited, and subsequently differentiate into an epithelial tube and eventually the female reproductive tract. Our studies define cellular and molecular mechanisms for Müllerian duct formation.

Collagens and collagen-related matrix components in the human and mouse eye

The three-dimensional structure of the eye plays an important role in providing a correct optical environment for vision. Much of this function is dependent on the unique structural features of ocular connective tissue, especially of the collagen types and their supramolecular structures. For example, the organization of collagen fibrils is largely responsible for transparency and refraction of cornea, lens and vitreous body, and collagens present in the sclera are largely responsible for the structural strength of the eye. Phylogenetically, most of the collagens are highly conserved between different species, which suggests that collagens also share similar functions in mice and men. Despite considerable differences between the mouse and the human eye, particularly in the proportion of the different tissue components, the difficulty of performing systematic histologic and molecular studies on the human eye has made mouse an appealing alternative to studies addressing the role of individual genes and their mutations in ocular diseases. From a genetic standpoint, the mouse has major advantages over other experimental animals as its genome is better known than that of other species and it can be manipulated by the modern techniques of genetic engineering. Furthermore, it is easy, quick and relatively cheap to produce large quantities of mice for systematic studies. Thus, transgenic techniques have made it possible to study consequences of specific mutations in genes coding for structural components of ocular connective tissues in mice. As these changes in mice have been shown to resemble those in human diseases, mouse models are likely to provide efficient tools for pathogenetic studies on human disorders affecting the extracellular matrix. This review is aimed to clarify the role of collagenous components in the mouse and human eye with a closer look at the new findings of the collagens in the cartilage and the eye, the so-called "cartilage collagens".

Molecular mechanisms of hormone-mediated Mullerian duct regression: involvement of beta-catenin

Regression of the Mullerian duct in the male embryo is one unequivocal effect of anti-Mullerian hormone, a glycoprotein secreted by the Sertoli cells of the testis. This hormone induces ductal epithelial regression through a paracrine mechanism originating in periductal mesenchyme. To probe the mechanisms of action of anti-Mullerian hormone, we have studied the sequence of cellular and molecular events involved in duct regression. Studies were performed in male rat embryos and in transgenic mice overexpressing or lacking anti-Mullerian hormone, both in vivo and in vitro. Anti-Mullerian hormone causes regression of the cranial part of the Mullerian duct whereas it continues to grow caudally. Our work shows that this pattern of regression is correlated with a cranial to caudal gradient of anti-Mullerian hormone receptor protein, followed by a wave of apoptosis spreading along the Mullerian duct as its progresses caudally. Apoptosis is also induced by AMH in female Mullerian duct in vitro. Furthermore, apoptotic indexes are increased in Mullerian epithelium of transgenic mice of both sexes overexpressing the human anti-Mullerian hormone gene, exhibiting a positive correlation with serum hormone concentration. Inversely, apoptosis is reduced in male anti-Mullerian hormone-deficient mice. We also show that apoptosis is a decisive but not sufficient process, and that epitheliomesenchymal transformation is an important event of Mullerian regression. The most striking result of this study is that anti-Mullerian hormone action in peri-Mullerian mesenchyme leads in vivo and in vitro to an accumulation of cytoplasmic beta-catenin. The co-localization of beta-catenin with lymphoid enhancer factor 1 in the nucleus of peri-Mullerian mesenchymal cells, demonstrated in primary culture, suggests that overexpressed beta-catenin in association with lymphoid enhancer factor 1 may alter transcription of target genes and may lead to changes in mesenchymal gene expression and cell fate during Mullerian duct regression. To our knowledge, this is the first report that beta-catenin, known for its role in Wnt signaling, may mediate anti-Mullerian hormone action.

Ultrastructure of mullerian and wolffian ducts of fetal rabbit in vivo and in organ culture

Emphasis is put on programmed cell death in the epithelial cells of mullerian and wolffian ducts, in rabbit fetuses, by observations on the timing and ultrastructural characteristics of cell degeneration. Genital tracts were collected on days 17 to 25 post-coitum and processed for electron microscopy. An organ culture assay was performed on fetal ducts and testis or ovary, for 4 days. Then, ducts and gonads were processed for electron microscopy. The involution of male mullerian and female wolffian ducts in culture and in vivo follows a similar pattern. Cell degeneration is initialized by an increase in the number of lysosomes which are subsequently involved in invading autophagic vacuoles. Cytochemical localizations of acid phosphatase and aminopeptidase indicate the presence of new lysosomes within the cells. In conclusion, this cell degeneration seems to be due to a double lysosome system in the rabbit urogenital ridge: A mullerian one spontaneously inactive when mullerian inhibiting substance is absent, and a wolffian one, spontaneously active when testosterone is absent. The organ culture is reliable for further attempts to study the responses to substances known to act on lysosome formation or activity.

Expression of type I and III collagen during morphogenesis of fetal rat testis and ovary

The distribution of interstitial collagen type I and III was studied immunocytochemically and ultrastructurally in the fetal rat testis and ovary from the undifferentiated stage (day 12) until birth. The results suggest that there is a correlation between the differentiation, organization, and abundance of the mesenchyme and the differentiation of the testicular vs. ovarian cords. Type III collagen was already present in the undifferentiated gonadal mesenchyme, and it appeared at an early stage around the organizing gonadal cords. Type I collagen appeared later in a similar mesenchymal distribution as type III collagen. Fragmentation of the subepithelial basement membrane in the gonads starting morphogenesis was considered to indicate that the surface epithelium participates in the gonadal cord formation. The expression of type III collagen at first on the surface of the developing testicular cords and later around the ovarian cords suggests that the mesenchymal premyoid cells are actively involved in the male cord formation. Focal discontinuities were found in the basement membrane of the ovarian cords, which in part were separated from each other by a ramified and relatively sparse mesenchyme. A complex linkage between the cytoskeleton and the extracellular matrix is illustrated both in the cord forming Sertoli and granulosa cells, and in the adjacent mesenchymal cells. Depletion of the mesenchyme and the basement membrane around the germ cell-granulosa cell associations of the wide ovarian medullary cords may be causal for their subsequent degeneration.

Epithelial and mesenchymal cell differentiation in the fetal rat genital ducts: changes in the expression of cytokeratin and vimentin type of intermediate filaments and desmosomal plaque proteins

Mesonephric and paramesonephric ducts develop in different ways in male and female fetuses. We have analyzed the changes in the expression of cytokeratin and vimentin type of intermediate filaments and desmosomal plaque proteins in progressing and regressing genital ducts of rat fetuses. The concomitant changes in the basement membranes were detected by laminin antibody. Epithelial cells of the indifferent (Day 15) male and female mesonephric and paramesonephric ducts contained faint vimentin positivity which, however, later disappeared. Indifferent mesonephric duct epithelium stained strongly for cytokeratin, whereas in the corresponding paramesonephric duct only a weak and spotty positivity was seen. Immunocytochemical localization of cytokeratin filaments and desmosomal plaque proteins correlated with the ultrastructural differences in the apical junctional complexes of the mesonephric and paramesonephric ducts. Regardless of the ongoing regression of the male paramesonephric duct, cytokeratin positivity increased in the disorganizing epithelium; the most weak and a granular immunoreaction was seen in the cells found in the intensively vimentin-positive periductal mesenchyme. In the regressing female mesonephric duct cytokeratin positivity was lost before the final dissolution of the basement membrane. Immunoblotting analysis of cytokeratin and vimentin polypeptides of the individual genital ducts were in agreement with the immunocytochemical results obtained in 15- and 16-day-old fetuses. The results suggest that the expression of vimentin type intermediate filaments is an indication of the mesothelial origin of the genital ducts. The increase in cytokeratin positivity of the regressing paramesonephric duct epithelium suggests that the degenerative changes are initiated by the mesenchyme. Cytokeratin-positive cells found in the periductal mesenchyme of the male paramesonephric duct may be epithelial cells transforming into mesenchyme. The results emphasize a close relationship between the changes of the intermediate filament system and extracellular matrix upon differentiation of the fetal genital ducts.