Distribution and conservation of sequences homologous to the 1731 retrotransposon in Drosophila

The distribution of 1731 retrotransposon-hybridizing sequences in thefamily Drosophilidae has been studied using a 1731 probe from Drosophilamelanogaster. Squash blot and Southern blot analyses of 42 species revealthat the 1731 sequences are widespread within both the Sophophora andDrosophila subgenera and are also present in the genera Scaptomyza andZaprionus. Hence the 1731 retrotransposon family appears to have a longevolutionary history in the Drosophilidae genome. Differences ofhybridization signal intensity suggested that the 1731 sequence is wellconserved only in the three species most closely related to D. melanogaster(D. simulans, D. mauritiana, and D. sechellia). A survey of insertion sitesin numerous different populations of the previous four species by in situhybridization to polytene chromosomes has shown in all cases bothchromocentric hybridizations and a low number of sites (0-5) on thechromosomal arms. This number of sites is among the lowest observed in D.melanogaster and D. simulans when 1731 is compared with otherretrotransposon families. In addition, we have observed species-specificpatterns of the chromocentric hybridization signal, suggesting rapidmodifications of the beta-heterochromatin components since the radiation ofthe melanogaster subgroup.