KRUPPEL TARGET GENE KNOCKOUT PARTICIPATES IN THE PROPER INNERVATION OF A SPECIFIC SET OF DROSOPHILA LARVAL MUSCLES

Kruppel (Kr) encodes a zinc finger-type transcription factor expressed in spatially and temporally restricted patterns during Drosophila emb ryogenesis. Molecular targets and the mechanism of Kr action have been studied extensively during the early segmentation process, but only l ittle is known about Kr requirement during later development. We repor t the identification of a target gene of Kr, termed knockout (ko), iso lated by virtue of Kruppel in vitro binding sites. Loss and gain of fu nction experiments show that Kr activity maintains ko expression in a subset of muscles. ko encodes a novel protein expressed in several emb ryonic tissues including Kr-expressing muscles. Movements of embryos d eficient for ko activity are uncoordinated. Their muscle pattern is no rmal, but the patterns of neuromuscular innervation are specifically d isarranged. The results suggest that the Kr target gene ko is required for proper innervation of specific muscles by RP motoneurons.