Oocyte, fertilization unfertilized

Fig. 2 NP-based transgenic strategies. NP-loaded DNA may be transfected into sperm for sperm-mediated gene transfer (i), microinjected into unfertilized or fertilized oocytes (2) ormagenofected into early cleavage-stage to blastocyst-stage embryos (4). Alternatively, DNA-loaded NPs may be delivered into stem cells (5) for production of transgenic embryos by morula aggregation of blastocyst injection...

Later experiments provided the initial evidence to suggest that the synthetic passivity of the ribosomes of unfertilized oocytes could be due to absence of interaction between templates of protein synthesis and mRNA molecules, or to the presence of too few templates, as a result of which the ribosomes were uncharged and did not form polysomes (Nemer, 1962 Wilt and Hultin, 1962 Nemer and Bard, 1963 Hultin, 1964). When synthetic systems were created in vitro and mRNA molecules were replaced by synthetic polynucleotides, no significant differences were found between the ribosomes of fertilized and unfertilized oocytes. It was soon shown, however, that the messenger RNA synthesized during oogenesis can combine with ribosomes, but cannot exercise its functions because of special protein membranes, which evidently break up during activation of the oocytes as a result of increased protease activity (Monroy et al., 1965). 

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