Mosaic oocytes

This phenomenon, which has been called ooplasmic segregation, may be demonstrated particularly clearly in the so-called mosaic oocytes in which physiological and biochemical differentiation of the cytoplasm is particularly clearly defined, being accompanied by other additional external characteristics pigmentation, granule-formation, etc. This phenomenon has become a classical object of study in embryology, and the subject of much research, so that I shall mention only one or two typical examples by way of illustration. 

Recently, Tazima and associates compared chemically induced mutations with those induced by radiation for embryonic lethality. In this experiment, mutations were induced as mosaics by treating oocytes with ethyl methanesulfonate (EMS) or diethylsulfate (DES) and led to homozygotes in order to examine embryonic lethality. The data are given in Table 1, together with those previously obtained by irradiating the corresponding stages of oocytes. 

On the other hand, Asselbergs et al. (1980) observed translational competition between globin mRNA, lens crystallin mRNAs, and turnip yellow mosaic virus RNA in the micrococcal nuclease-treated reticulocyte lysate, but not after microinjection into Xenopus oocytes (Asselbergs et al., 1979). The reason for this discrepancy is not clear, as Laskey et al. (1977) have shown that in oocytes, a component of the translation machinery, and not mRNA, limits the rate of protein synthesis. 

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