Regulation of I-transposon activity in Drosophila: evidence for cosuppression of nonhomologous transgenes and possible role of ancestral I-related pericentromeric elements.
We have previously shown that the activity of functional I retrotransposons (I factors) introduced into Drosophila devoid of such elements can be repressed by transgenes containing an internal fragment of the I factor itself and that this repressing effect presents the characteristic features of homology-dependent gene silencing or cosuppression. Here we show that the same transgenes can induce silencing of a nonhomologous reporter gene containing as the sole I-factor sequence its 100-bp promoter fragment. Silencing of the nonhomologous reporter gene shows strong similarities to I-factor cosuppression: It does not require any translation product from the regulating transgenes, sense and antisense constructs are equally potent, and the silencing effect is only maternally transmitted and fully reversible. A search for genomic I-like sequences containing domains with similarities to those of both the regulating and the reporter transgenes led to the identification of four such elements, which therefore could act as intermediates-or relays-in the cosuppression machinery. These results strongly suggest that ancestral transposition-defective I-related elements, which are naturally present in the Drosophila genome, may participate per se in the natural conditions of I-factor silencing.
Jensen
Silke
S
CNRS UMR 1573, Institut Gustave Roussy, 94805 Villejuif Cedex, France.
Gassama
Marie-Pierre
MP
Dramard
Xavier
X
Heidmann
Thierry
T
D000818:Animals; D001483:Base Sequence; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D004251:DNA Transposable Elements; D004330:Drosophila / Q000235:genetics* / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology*; D020868:Gene Silencing / Q000502:physiology; D017930:Genes, Reporter / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D019076:Transgenes
D004251:DNA Transposable Elements; D015500:Chloramphenicol O-Acetyltransferase