The NF-kappa B-like Relish gene is complex, with four transcripts that are all located within an intron of the Nmdmc gene. Using deletion mutants, we show that Relish is specifically required for the induction of the humoral immune response, including both antibacterial and antifungal peptides. As a result, the Relish mutants are very sensitive to infection. A single cell of E. cloacae is sufficient to kill a mutant fly, and the mutants show increased susceptibility to fungal infection. In contrast, the blood cell population, the hematopoietic organs, and the phagocytic, encapsulation, and melanization responses are normal. Our results illustrate the importance of the humoral response in Drosophila immunity and demonstrate that Relish plays a key role in this response.

Certain of the rhythm mutations in Drosophila melanogaster lead to arrhythmic locomotor activity (and aperiodic eclosion) in constant conditions. In light-dark (LD) cycles, however, such mutants exhibit clear fluctuations between high levels of activity when the lights are on and much lower ones when they are off. Our data, in contrast to some previous conclusions, strongly suggest that period0 (per0) adults are, in LD conditions, merely being "forced" into exhibiting periodic behavior. These experiments involved application of 8-, 12-, 16-, and 24-hr LD cycles, in which the arrhythmic mutant could have any of these periodicities imposed upon it, whereas wild-type flies tended to exhibit periods of about 24 hr in cycling conditions whose T values were > 8 hr different from 24. In phase-shift experiments, it was found that Drosophila expressing genotypes associated with rhythmicity achieved a 5-hr advance over a 2-day period following an advanced lights-on; per0 adults altered the phase of their locomotor peaks more rapidly. Against a background of the fact that eyeless or blind flies exhibit normal entrainment, it was hypothesized that double-mutant flies--carrying such visual mutations and per0 as well--should not synchronize to LD cycles, if the forced rhythms seen in the latter single-mutant type are mediated solely by light input through the external photoreceptors. Since an appreciable proportion of the double mutants did synchronize (to LD 12:12), it is thus suggested that the visual cues involved in forcing rhythmicity could be input through the same extraocular photoreceptors that, in general, subserve the fly's rhythm system.

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