Timing of expression of a gene in the adult Drosophila is regulated by mechanisms independent of temperature and metabolic rate.

The examination of beta-galactosidase (beta-gal) expression in the third segment of the antenna of the 2216 enhancer trap line in Drosophila melanogaster reveals two distinct spatial and temporal regulatory patterns of expression during adult life. Type 1 expression is characterized by a decline in the level of beta-gal expression with increasing age. Starting from a maximal level of expression at the time of adult emergence, there is a decrease in the number of cells that express beta-gal so that by 40-50 days of adult life few cells express beta-gal. Varying the ambient temperature and using hyperactivity mutants (Hyperkinetic, Shaker) demonstrates that the rate of this decline is independent of temperature and metabolic rate. Type II expression is distinctly different in spatial distribution and temporal regulation from the first pattern. Type II expression is restricted in the antenna to a small (< 20-30) set of cells whose level of expression changes in a periodic manner with time. The regulation of this periodicity appears to be linked to ambient temperature.