Daily behavioral and
physiological rhythms in most animals are regulated by a circadian clock. In
the fruit fly, Drosophila melanogaster, this clock consists of a network
of about 150 cerebral neurons. Different parameters of the fruit fly circadian
locomotion are attributed to specific neuronal subsets and the molecular
rhythms of clock genes and proteins within them. To understand the clock
machinery, many clock mutant flies have been used. yellow white (y w) mutation in D. melanogaster cause impaired
melanisation, eye pigmentation loss, and behavioral alterations including
changes in circadian locomotion. This study investigates the possible molecular
background for these circadian alterations. Results revealed that in the output
pathway of the clock, the Pigment-Dispersing Factor (PDF) expression was
suppressed in y w mutant fruit flies compared to Canton S (CS) wild-type in the PDF⁺ clock neurons. On
the other hand, the degradation of the PERIOD (PER) protein was significantly
delayed in  y
w mutants and their levels was higher, especially at
the transition from dark to light. The combined effect of elevated PER levels
and suppressed PDF signaling provides an explanation for the delayed morning
locomotor activity peak (M) and advanced evening peak (E) of y w flies
compared to CS.
It could be concluded that mutations affecting eye pigmentation like the y w mutation
could have profound effects on the circadian regulation of behavior and their
underlying molecular oscillations in clock neurons. These effects reduce the
plasticity and robustness of the circadian clock and expose the flies to higher
levels of the environmental risk of desiccation.