Mature Xenopus laevis spermatozoa are capable of binding plasmid pAPrC carrying the complete Rous sarcoma virus (RSV) DNA. Each sperm cell associates, on an average, with 70-160 molecules of the plasmid DNA in a DNase resistant form, if the spermatozoa were exposed to the DNA at a concentration of 1.0-1.4 micrograms/10(7) sperm cells. Fertilization with pAPrC-treated spermatozoa induced developmental malformations in 25-30% of embryos. Immunohistochemical analysis of tissue sections from defective animals revealed aberrations in myotomal structures, and increased expression of pp60src protein in myoblasts, neuronal tube, and epidermis. The presence of characteristic v-src and RSV-long terminal repeat (LTR) sequences in X. laevis DNA was detected by PCR analysis. Embryonic RNA hybridized with a src-specific and an RSV-LTR specific probes indicating expression of the viral DNA. Plasmid DNAs without the v-src gene (pATV9) or completely free of any RSV sequences (pBR322) did not induce any changes in embryonic development. Our results provide evidence that the pBR322-cloned DNA form of the RSV genome associates with frog sperm cells in a DNase-resistant manner suggesting internalization and may be subsequently carried into eggs during the process of artificial fertilization. Correlation between the defective morphogenesis of X. laevis and increased expression of the src gene as well as an interference of RSV DNA with the developmental programs of frog embryos are discussed.
The distribution of tubulin and/or tubulin-containing structures was examined in separate classes of Xenopus laevis oocytes and in germinal vesicles isolated from them. Although a monoclonal antibody has been used, the technique applied on paraffin sections does not allow clear-cut definition of the state of tubulin present (monomeric, dimeric or polymerized form); however, the probable existence of assembled microtubules is indicated by supplementary techniques, i.e. histology and immunoperoxidase staining. Immunofluorescence reveals maximum tubulin concentration in the Balbiani body and in a ring-shaped formation around the nucleus in young oocytes. The Balbiani body disintegrates in the course of vitellogenesis, granules formed from its periphery migrate into the cytoplasm and gradually fill the entire cytoplasm as radial cords. In the ring-shaped formation around the nucleus strongly fluorescent cords and fibres are formed, particularly on the future vegetal-half-facing part of the nucleus. Reorganization of tubulin may be related to the establishment of a structure directing two-way shifts (1) of cytoplasmic organelles from the Balbiani body to the cytoplasm, and (2) of yolk proteins containing endosomes derived from the endocytically active oolemma to the yolk platelets. A distinct fluorescent fibrillar network is found inside the isolated germinal vesicles,- near the nucleus membrane. Peripheral nucleoli, often present in nuclear membrane protuberances, seem to be surrounded by this material, which is oriented along the surface, and as a basket towards the inside of the nucleus. It is assumed that the structures may participate in the transport of nucleoli from the nucleus to the cytoplasm via the nuclear envelope.
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