charlatan, a gene encoding a Zn-finger factor involved in nervous system development. L.M. Escudero ¹, K.L. Schulze ², H.J. Bellen ², J. Modolell ¹. 1) Centro Biologia Molecular S.O., C.S.I.C., Madrid, Madrid, Spain; 2) HHMI, Baylor College of Medicine, One Baylor Plaza, Houston TX 77030 USA.

   In a search for new genes involved in the development of the Drosophila PNS, we have examined the overexpression phenotypes of several new EP lines that alter the pattern of sensory organs at the notum. When one of these lines, EPIL#6, is overexpressed with several GAL4 drivers, it causes the appearance of ectopic macrochaetae. The insertion lies within charlatan (chn), a gene previously identified by Kania et al. (1995; Genetics 139: 1663-1678) by a P-element insertion allele that alters the morphology of the chordotonal organ clusters of the embryonic PNS. chn gives rise to at least two transcripts, one that encodes a zinc-finger transcription factor and a second one that should produce a putative protein without recognizable similarity to known proteins. In the wild-type, the first transcript is expressed in the embryonic and larval CNS and PNS. In the wing imaginal disc, it is expressed in proneural clusters, and we find that is positively regulated by the proneural achaete and scute genes. A chn loss-of-function mutation removes elements from the embryonic PNS and CNS and, with low penetrance, suppresses notum bristles. These phenotypes are rescued by overexpression of the transcript that encodes the zinc finger transcription factor. In the wing disc, misexpression of chn promotes ectopic expression of scute. Our working hypothesis is that within proneural clusters chn helps achaete and scute genes to reach levels of expression effective in neurogenesis.