Xenopus gene amplification

The question, whether the discrepancy between the rDNA values for brain and liver tissues of the rat is the result of technical errors or represents true rDNA amplification, has been answered unequivocally by Mohan et al. (1969). Cross-hybridization between rRNA and DNA from rat liver and brain in all combinations resulted in identical saturation plateaus within the limits of measurement. This result clearly indicates that rDNA amplification does not take place in rat brain tissue. Furthermore, Ryffel et al. (1973) have shown that the number of rRNA genes remains unchanged in liver and tail muscle of Xenopus laevis larvae during thyroxine-induced metamorphosis, although the synthesis of rRNA is increased in larval tissues in response to hormone treatment. This observation casts some doubt on the validity of the interpretation by Koeh and Cruceanu (1971), especially because they used exceedingly high concentrations of the hormone. 

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