Ingrowth by photoreceptor axons induces transcription of a retrotransposon in the developing Drosophila brain
The development of the lamina, the first optic ganglion of the fly visual system, depends on inductive cues from the innervating photoreceptor axons. lacZ expression from a P-element insertion, A72, occurs in the anlage of the lamina coincident with axon ingrowth from the eye imaginal disc. In eyeless mutants lacking photoreceptor axons, lacZ expression did not occur. The P-element was found to have inserted within the 3′ long terminal repeat (LTR) of a '17.6′ type retrotransposon. The expression pattern of 17.6 transcripts in the brain in wild-type and eyeless mutants paralleled the expression of the lacZ reporter. Analysis of 17.6 cis-regulatory sequences indicates that the lamina-specific expression is due to the combined action of an enhancer element in the LTR and a repressor element within the internal body of the retrotransposon. The regulation of the 17.6 retrotransposon provides a model for the study of innervation-dependent gene expression in postsynaptic cells during neurogenesis.
© 1994 The Company of Biologists Limited. Accepted 18 January 1994. The authors wish to thank the members of the Benzer lab for suggestions during the course of this work and for critical reading of this manuscript. The excellent technical assistance of Rosalind Young, Julia Chang and Evelyn Eichenberger are most appreciated. Thanks to Ward Odenwald for pointing out the TAAT sequence and Harold Gainer for support at NIH. This work was supported by postdoctoral fellowship EY067161 from the National Eye Institute to B. A. M. and grants to S. B. from the National Science Foundation (BCS-8908154), the National Eye Institute (EY0 9278), and the James G. Boswell Foundation.
Published - MOZdev94.pdf