TIMELESS: A link between fly's circadian and photoperiodic clocks?

Abstract

Abstract. Potential involvement of circadian clock genes in so far unknown mechanism of photoperiodic time measurement is an important question of insect life-cycle regulation science. Here we report about the cloning of full-length cDNA of the structural homologue of the Drosophila's timeless gene in Chymomyza costata. Its expression was compared in two strains: a wild-type strain, responding to short days by entering larval diapause and a «pd-mutant strain, showing no photoperiodic response. The timeless mRNA transcripts were not detectable by Northern blot analysis in the fly heads of «pd-mutants, while they were detectable and showed typical daily oscillations in the wild-type strain. After disrupting the normal process of timeless transcription in the wild-type strain by injection of timeless double-strandRNA into early embryos of wild-type (RNAi method: Kennerdell & Carthew 1998, 2000, a certain proportion of the individuals adopted a «pd-mutant phenotype, showing no-diapause in response to short-daylength. Cloning of genomic DNA fragments revealed that «pd-mutants carry a different allele, timeless"1 "1, with a 13-bp insertion in an intron positioned within the 5'-leader sequence. Genetic linkage analysis showed that the 13-bp insertion (a marker for timeless"1 "1) and the absence of response to short days (a marker for «pd-phenotype) are strictly co-inherited in the F2 progeny of the reciprocal crosses between wild-type and «pd-mutant flies. Such results indicated that the locus «pd could code for the timeless gene in C. costata and its product might thus represent a molecular link between circadian and photoperiodic clock systems in this fly.

Quantitative Trait Loci Associated with Photoperiodic Response and Stage of Diapause in the Pitcher-Plant Mosquito, Wyeomyia smithii

“…The mutation at the period locus renders flies behaviorally arrhythmic but they remain normally photoperiodic if they possess wild-type timeless. The double mutant is both behaviorally arrhythmic and nonphotoperiodic (Pavelka et al 2003). Flesh flies (Sarcophaga bullata) that have elevated expression of period and timeless are behaviorally arrhythmic and nonresponsive to short days for the induction of diapause (Goto et al 2006).…”

Period gene expression in relation to seasonality and circadian rhythms in the linden bug, Pyrrhocoris apterus (Heteroptera)

“…Although there may be no causal relationship between the per gene itself and photoperiodic regulation of diapause, as is suggested for D. melanogaster (Saunders, 1990), it is likely that the photoperiodic regulation of per gene expression, as revealed in P. apterus, reflects responses of other molecular components of the circadian system to photo period. It will be important to study how photoperiod affects other circadian clock-related genes, particularly in the view of a recent finding that the photoperiodic insen sitivity in a drosophilid fly, C. costata, may be caused by an inability to transcribe the timeless (tim) gene (Pavelka et al, 2003). A higher (about twice) peak level of tim mRNA under short daylength relative to long daylength was demonstrated in adult heads of the flesh fly, Sarcophaga crassipalpis (Goto & Denlinger, 2002).…”

“…On the other hand, day length affects the expression of per mRNA (Maj ercak et al, 1999), as well as the T of locomotor rhythm in D. melanogaster (Tomioka et al, 1997). The effect of day length is mediated through the photosensi tive timeless protein (Maj ercak et al, 1999), and the time less locus is thought to be causally involved in the photoperiodic induction of larval diapause in another drosophilid, Chymomyza costata (Kostal & Shimada, 2001;Pavelka et al, 2003). These results indicate that the cir cadian clock governing overt rhythms and mechanisms decoding photoperiodic time may share common molecular components.…”

The involvement of the brain region containing pigment-dispersing factor-immunoreactive neurons in the photoperiodic response of the bean bugRiptortus pedestris

“…Circadian clock genes and their protein products are expressed in a variety of tissues, but only a small number of neurons in the brain are responsible for the circadian clock regulating locomotor activity (Helfrich-Förster, 2003;Tomioka et al, 2012). While the involvement of the circadian clock genes in the photoperiodic response has been demonstrated in several insect species (Pavelka et al, 2003;Sakamoto et al, 2009;Ikeno et al, 2010;Ikeno et al, 2011b;Ikeno et al, 2011c;Ikeno et al, 2013;Bajgar et al, 2013a;Bajgar et al, 2013b), less is known about the neuronal mechanism of the circadian clock underlying photoperiodism (Shiga, 2012).…”