Signaling from germ cells mediated by the rhomboid homolog stet organizes encapsulation by somatic support cells

Germ cells normally differentiate in the context of encapsulating somatic cells. However, the mechanisms that set up the special relationship between germ cells and somatic support cells and the signals that mediate the crucial communications between the two cell types are poorly understood. We show that interactions between germ cells and somatic support cells in Drosophila depend on wild-type function of the stet gene. In males, stet acts in germ cells to allow their encapsulation by somatic cyst cells and is required for germ cell differentiation. In females, stet function allows inner sheath cells to enclose early germ cells correctly at the tip of the germarium. stet encodes a homolog of rhomboid, a component of the epidermal growth factor receptor signaling pathway involved in ligand activation in the signaling cell. The stet mutant phenotype suggests that stet facilitates signaling from germ cells to the epidermal growth factor receptor on somatic cells, resulting in the encapsulation of germ cells by somatic support cells. The micro-environment provided by the surrounding somatic cells may, in turn, regulate differentiation of the germ cells they enclose.     

Theory of the continuity of germ plasma according to the findings of modern biology

The main principles on the theory of germ plasma by A. Weismann are briefly presented; a number of his genetic-embryological hypotheses proved to be prophetic. Modern notions on the germ plasma are critically discussed, as well as the resulting from them the conception on continuity of totipotent cells (the source of germ cells) in the line of generations, that is historically connected with M. Nussbaum--A. Weismann's notions on continuity of the embryonic pathway. The term totipotency is sometimes used inaccurately; it means ability to formation of a whole organism. In Metazoa zygota and isolated blastomeres, at a regulative type of development, and groups of somatic cells or fragments of the organism, at an asexual reproduction and somatic embryogenesis, possess this ability. In ontogenesis totipotency is lost both by the somatic and by the germ cells because of their specialization and is recreated with the beginning of every ontogenesis when zygota is formed. The germ cells are always a product of the organism--unicellular or multicellular, and their specialization in all its manifestations is the result of integrative influences of the organism as a whole of them. Certain reasons are presented for supporting ideas on germ cells as one of the lines of cell differentiation. The main, if not the only contradiction in the problem concerning relation of the germ and somatic cells is, at the present time, the thesis on continuity of totipotent cells in the line of generations.     

Analysis of nuclear reprogramming in cloned miniature pig embryos by expression of Oct-4 and Oct-4 related genes

Xenotransplantation is a rapidly expanding field of research and cloned miniature pigs have been considered as a model animal for it. However, the efficiency of somatic cell nuclear transfer (SCNT) is extremely low, with most clones resulting in early lethality and several kinds of aberrant development. A possible explanation for the developmental failure of SCNT embryos is insufficient reprogramming of the somatic cell nucleus by the oocyte. In order to test this, we analyzed the reprogramming capacity of differentiated fibroblast cell nuclei and embryonic germ cell nuclei with Oct-4 and Oct-4 related genes (Ndp5211, Dppa2, Dppa3, and Dppa5), which are important for embryonic development, Hand1 and GATA-4, which are important for placental development, as molecular markers using RT-PCR. The Oct-4 expression level was significantly lower (P<0.05) in cloned hatched blastocysts derived from fibroblasts and many of fibroblast-derived clones failed to reactivate at least one of the tested genes, while most of the germ cell clones and control embryos correctly expressed these genes. In conclusion, our results suggest that the reprogramming of fibroblast-derived cloned embryos is highly aberrant and this improper reprogramming could be one reason of the early lethality and post-implantation anomalies of somatic cell-derived clones.