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Propagation d'un Virus Sigma Défectif au Niveau de Disques Imaginaux d'Aile Implantés dans des Drosophiles Adultes

Laboratoire de génétique des virus du CNRS, 91-Gif-sur-Yvette, France

A variant of virus defective for maturation functions was studied. Stabilized flies for this virus were called ultra- flies. They were not CO₂-sensitive and extracts were not infectious. The presence of the virus was detected because it conferred to imagos a characteristic immunity against a superinfecting virus: these flies were not immunized against a superinfecting virus of the same group, such as vesicular stomatitis virus.

Wing discs were taken from larvae of two ultra- strains (U-46 and U-751) and were exposed to superinfection by implantation into hosts infected with a non-defective virus. The blastemas were then implanted into a detector host able to support virus multiplication until the symptom appeared showing superinfection. Control experiments were made with originally virus-free discs. We have thus shown that the characteristic ultra- immunity is present in the imaginal wing disc of ultra- larvae. It is concluded that embryonic blastema cells contain ultra- virus genomes.

In tests on the persistence of immunity through successive transfer generations the results differed with the ultra- strain used. The detector hosts implanted with U-46 blastemas were classified as early CO₂-sensitive and CO₂-resistant; the number of CO₂-resistant hosts did not decrease and the U-46 immunity was therefore stable. On the other hand, the detector hosts implanted with U-751 blastemas were of three classes: early CO₂-resistant and late sensitive hosts decreased as a function of time indicating that U-751 immunity was unstable. This instability suggests that blastemas giving late sensitivity are mosaics of ultra- cells and virus-free cells.

Received 24 November 1968; accepted 8 May 1970.