Expression of the Drosophila retrovirus gypsy as ultrastructurally detectable particles in the ovaries of flies carrying a permissive flamenco allele (original) (raw)

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Abstract

The endogenous retrovirus gypsy is controlled by the Drosophila gene flamenco (flam). New insertions of gypsy occur in any individual Drosophila if its mother is homozygous for the flam 1 permissive allele and contains functional gypsy proviruses. The ovaries of flam 1 females also contain high amounts of gypsy RNAs. Unexpectedly however, gypsy derepression does not occur in the flam 1 female germline proper but in the somatic follicular epithelium of the ovary. Since extracts from these females are able to efficiently infect the germ-line of a strain devoid of active gypsy proviruses, we assume that a similar kind of germ-line infection, which would occur inside the flam 1 females themselves, could be required for gypsy insertions to occur in their progeny. This hypothesis was confirmed by electron microscopy observations showing that non-enve-loped intracytoplasmic particles containing gypsy RNAs accumulate in the apical region of the flam 1 follicle cells, close to specific membrane domains to which the gypsy envelope proteins are targeted, whereas both are absent in the flam controls. Low amounts of similar virus-like particles were also observed in flam 1 oocytes, but it is not yet known whether they entered passively or as a result of membrane fusion. This is the first report of the beginning of a retrovirus cycle in invertebrates and these observations should be taken into account when explaining the maternal effect of the flamenco gene on the multiplication of gypsy proviruses.

• Published Online:01/09/1997

© Society for General Microbiology Ltd 1997

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