Involvement of the period Gene in Developmental Time-Memory: Effect of the per^Short Mutation on Phase Shifts Induced by Light Pulses Delivered to Drosophila Larvae

Abstract

Phases of circadian locomotor activity rhythms of adult Drosophila reared in constant darkness have been shown to be set by a light stimulus delivered as early as the first-instar larval stage. This implies that a circadian clock functions continuously throughout postembryonic development. The clock genes period (per) and timeless (tim) are expressed cyclically in the larval central nervous system of Drosophila, and daily oscillations of per expression persist throughout metamorphosis in a group of cells, which gives rise to the pacemaker cells underlying locomotor activity rhythms of adults. Therefore, PER and TIM cyclings in these neurons may be responsible for the phenomenon of "larval time-memory." In the absence of any evidence for the involvement of these genes in such a developmental clock, and because circadian-pacemaker functions are underanalyzed in terms of the functions during development, the authors tested the time-memory of a fast-clock period mutant. They show that dark-reared perS mutant individuals as well as wild-type flies can be entrained as larvae and that a brief light pulse given to such entrained larvae can induce phase shifts in animals of either genotype. However, the direction and magnitude of phase shifts were different between wild type and perS, suggesting that a clock under the control of period gene participates in the regulation of developmental time-memory. The authors show that the relevant clock can be entrained by two light input pathways, one involving the phospholipase C encoded by the norpA gene, the other mediated by the blue-light receptor cryptochrome. Phase shifts of molecular oscillations during the larval stage were smaller than those measured by adult behavior, suggesting molecularly transient responses during development.

Genetic analysis of the circadian system in Drosophila melanogaster and mammals

“…Strikingly, this study also showed convincingly that this is not the case for larval pacemaker neurons: here PER and TIM cycle robustly in cry b mutant flies, both in LD (cf. Kaneko et al, 2000) and DD conditions, similar to what has been shown for the adult behavioral pacemaker neurons (Stanewsky et al, 1998;Helfrich-Förster et al, 2001). …”

“…In fact, cry is coexpressed with other clock genes and pdf within these pacemaker neurons, suggesting that these important cells contain a circadian photoreceptor, the central clock-works, and output functions (Emery et al, 2000). Yet, in another subset of these pacemaker neurons-in fact, the ones projecting to the dorsal brain area, where rhythmic PDF release is thought to control locomotor behavior-TIM cycling and its degradation by light is not impaired by cry b pointing to a contribution of other pigments (Stanewsky et al, 1998;Kaneko et al, 2000;Helfrich-Förster et al, 2001;Ivanchenko et al, 2001). Only after removal of all other retinal and extraretinal photoreceptors can cry b flies no longer entrain to LD cycles.…”

Rhythm Defects Caused by Newly Engineered Null Mutations in Drosophila's cryptochrome Gene

“…In contrast, Mealey-Ferrara et al (2003) showed that that mutation allows for LD entrainment of cultures such that they exhibited solidly periodic eclosion in (subsequent) DD. Another matter addressed by the study just cited: the fact that norpA 1 function contributes to synchronization of clock-protein cycling in developing Drosophila; this phenomenon operates in larval brain neurons (Kaneko et al 2000). But the simultaneous presence of a norpA mutation and cry b left developing animals synchronizable for periodic eclosion if they were exposed to LD after the larval stage before proceeding into DD (Mealey-Ferrara et al (2003).…”

Splicing of the period Gene 3′-Terminal Intron Is Regulated by Light, Circadian Clock Factors, and Phospholipase C

“…Early work clearly established an important role for the light-induced degradation of TIM as a key primary clock-specific photoresponse in the entrainment of Drosophila clocks to daily light-dark cycles (26,35,38,49,54,55). The putative blue-light photoreceptor CRYPTO-CHROME (CRY) enhances the light-induced degradation of TIM in most, if not all, clock cells (18,25,27,28,48,51). CRY functions as a deep-brain photoreceptor (15) that apparently directly interacts with TIM (4), presumably leading to the rapid ubiquitination and destruction of TIM by the proteasome (39).…”