Analysis of the antennal phenotype in the Drosophila mutant lozenge.

Previous work on the lozenge (lz) gene complex of D. melanogaster has focused on the compound eye. Here we study the effects of 22 lz mutations on the antennal sensilla. The antenna of strong lz alleles is characterized by a lack of basiconic sensilla and by a significantly increased density of coeloconic sensilla. Intermediate alleles have few basiconic sensilla, they exhibit a highly increased density of trichoid sensilla, but a normal coeloconic density. Basiconic sensilla on the maxillary palps are weakly affected even by strong lz alleles. The antennal phenotype for most of the strong and intermediate mutants is partially dominant over wild type. Although this complicates the interpretation of complementation data, 12 selected mutants that were studied in heteroallelic combinations seem to define a single cistron. Temperature shifts of the lztsl allele showed that gene activity is crucial from about 87% of the third larval instar up to 7% of pupal life. Applying restrictive temperature early during this period results in a 'novel' phenotype that is characterized by a dramatic decrease in the density of trichoid sensilla, whereas a late pulse of restrictive temperature leads to a 'normal' intermediate phenotype. Our data suggest that the lz gene controls at least five different functions in the antenna: the size of the third antennal segment, the overall number and density of sensilla, the proportions of the 3 types of sensilla, and the generation of basiconic sensilla.