[Show abstract][Hide abstract] ABSTRACT: We cloned a cDNA encoding Vasa, a member of the DEAD (Asp-Glu-Ala-Asp) family of proteins, from the ovary of the frog Rana rugosa. Comparative alignment of amino acid sequences with known Vasa from several species of vertebrate showed that the R. rugosa orthologue shares eight conserved regions with Vasa from other vertebrates. Vasa gene expression was restricted to the testis and ovary among ten different tissues examined. Vasa expression showed no sexual dimorphism during sex determination in R. rugosa, but became higher in the ovary thereafter. By Western blot analysis, a single Vasa band with a molecular weight of 80.9 kDa was detected. The same antibody immunohistochemically detected Vasa in a few cells in the embryonic endoderm at stage 15; the beginning of closure of neural folds, and in the cytoplasm of spermatogonia in the testis, and oocytes in the ovary of tadpoles at stage XX; marked by one or both forelegs protruded. Together, these results suggest that Vasa is a highly specific marker of germ cells and hence useful for studies of germ cell specification and function in amphibians as it already is in other species of both invertebrates and vertebrates such as Drosophila and zebrafish.
No preview · Article · Aug 2010 · Journal of Experimental Zoology Part A Ecological Genetics and Physiology
[Show abstract][Hide abstract] ABSTRACT: Here we report that structural changes in gonadal basement membranes during sex differentiation in the frog Rana rugosa are revealed using an antibody to its laminin component. Immunohistochemical staining indicated that the first sexual dimorphism appeared in testicular cords and ovarian cavities in differentiating gonads of tadpoles at St. 25-3W, three weeks after they reached St. 25. During development, as the testis enlarged, testicular cord partitions appeared to form by invagination of the testicular epithelium. Ovarian cavities also increased in volume. Laminin-positive basement membranes initially surrounded a partial surface of oocytes close to the ovarian cavity, fully covering growing oocytes by St. X. Laminin-reactive signals were present in somatic cells outside seminiferous tubules in the testis and outside oocytes in one-year-old frogs. BrdU-labeling showed that the number of dividing germ cells increased continuously in male gonads but increased in females only up to St. V, declining at St. X and thereafter. The number of dividing germ cells declined when the basement membranes had fully covered the oocytes. Together, these findings suggest that the first sexual dimorphism in the gonad of R. rugosa first appears as a structural change in the basement membranes. Finally, we speculate that the basement membrane on the surface of oocytes may affect their proliferation in this species.
No preview · Article · Jul 2010 · Journal of Experimental Zoology Part A Ecological Genetics and Physiology