Control of Nuclear Function by Cytoplasmic Factors

In Gurdon s experiments (Gurdon, 1970, 1971) transplantation of amphibian nuclei convincingly demonstrated that factors in the cytoplasm regulate nuclear function. For instance, autoradiography showed that the neurula stage nucleus which synthesizes all types of RNA s will terminate this synthesis 1 h after its transplantation into egg cytoplasms. RNA and DNA synthesis rates were determined with the aid of labeled precursors (Table 27). 

The original method for cultivating isolated Xenopus laevis cells was found by Shiokawa and co-workers (Shiokawa et al., 1967). They dissociated cells of the blastula (B-cells) and late neurula (N-cells) stages. The cultivated B-cells synthesize tRNA, but are not able to synthesize rRNA (the ratio of rRNA/tRNA is 0.5-0.8). N-cells synthesize both types of RNA s and the ratio of rRNA to tRNA is more than 5.0. This ratio is reduced to 2.0 if N-cells are cultivated together with B-cells 

Chromosomal activity arid cell-type Chromosomal activity of transplanted nuclei 

RNA Mitosis DNA+ + Mid-blastula RNA Mitosis DNA Growing oocyte RNA- + Mitosis DNA  

RNA+ Condensed chromosomes Adult brain RNA Condensed chromosomes Maturing oocyte RNA Condensed chromosomes  

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