Exploitation of a Sensitive Test System with Oocytes

Exploitation of a Sensitive Test System with Oocytes 

When eggs were soaked in 0.01 M KNO2 aqueous solution, almost all were killed when the pH was 4.2, but the effect was negligible when the pH was 5.6.  

It was not known, however, to what extent chemical compounds can pass through the chorion. Hence, the penetrating amount was assessed with MMC. The chemical was injected into the hemocoele of female pupae 1 day before emergence, and mutation frquencies were obtained at the marked loci. An almost linear relationship was obtained between administered dose and mutation frequency, but mutation frequencies observed were not as high as expected from other experiments. Perhaps penetration of the chemical was impeded by the chorion to an appreciable extent. 

To increase the amount of the compound that is incorporated into the egg plasm, injection was performed at various developmental stages of the cells from 1 day before to 5 days before emergence. As has been shown in Table 7, injection 3 days before emergence was about 10 times and injection 5 days before emergence was more than 100 times as effective as injection 1 day before. 

The mutagenic effectiveness appeared to be negatively correlated with chorion formation, which starts about 5 days before and is completed 1 day before emergence. High mutation frequencies obtained by injection at earlier stages seemed to indicate that a relatively large amount of the chemical was incorporated into the egg plasm, but after the chorion was completed, the incorporated amount decreased appreciably. This view was based on the assumption that injected chemicals react with egg nuclei at their most sensitive stage, perhaps around meiotic metaphases I and II. 

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