Rhythms In Drosophila Research Articles

Daily and circadian rhythms of synaptic frequency in the first visual neuropile of the housefly’s ( Musca domestica L.) optic lobe

Photoreceptors of the fly's compound eye generally show no very obvious daily or circadian rhythms, a lack which prompted us to examine whether their function might be regulated not in the retina, but at the site of transmission in the first visual neuropile, or lamina. Here, photoreceptor terminals (R1-R6) are reciprocally interconnected with one class of lamina monopolar cell, L2: L2 receives input from R1-R6 at so-called tetrad synapses, and in turn is presynaptic to R1-R6 at feedback synapses. We have calculated the mean frequencies of these synaptic profiles in electron micrographs of single lamina sections. L2 feedback synapses were more numerous at night than during the day, whereas the number of tetrads showed only small modulations between day and night. These changes persisted amongst feedback synapses in flies held in constant darkness, and are thus circadian. In contrast to the slow modulations during a 24 h cycle, the number of L2 feedback synapses after 1 h light pulse in flies held in constant darkness showed no clear change, whereas it increased the number of tetrad profiles. These findings support the occurrence of cyclical daily and circadian changes amongst the two lamina synaptic populations, with tetrads showing rather weak modulations in frequency, but more pronounced responses to the light pulse than feedback synapses.

On Kyriacou & Hall's defence of courtship song rhythms in Drosophila

Commentaires et critiques sur les resultats obtenus par Kyriacou et Hall concernant leurs etudes sur les rythmes du chant de cour chez Drosophila melanogaster

Changes in abundance or structure of the per gene product can alter periodicity of the Drosophila clock

The period (per) locus, which controls biological rhythms in Drosophila, was originally defined by three chemically induced mutations. Flies carrying the pero mutation were arrhythmic, whereas pers and perl mutants had circadian behavioural rhythms with 19-hour and 29-hour periodicities, respectively. Wild-type flies have 24-hour rhythms. Here we compare the per locus DNA sequences of the three mutants with the parental wild-type. The pers and perl mutations lead to amino-acid substitutions, whereas pero introduces an early translation stop (amber). The results indicate that the protein product of per controls biological rhythms. We also report that the abundance of this protein may set the pace of the Drosophila clock. Although circadian rhythms are restored when arrhythmic (per-) Drosophila are transformed with per locus DNA, flies receiving identical transforming DNA segments can produce rhythms with periods that differ by more than 12 hours. Transcription studies reveal a tenfold variation in the level of per RNA among transformed lines. Levels of per RNA are inversely correlated with period length, so that flies with lowest levels of the per product have slow-running biological clocks. On the basis of the combined studies we suggest that perl and pers mutants produce hypoactive and hyperactive per proteins, respectively.

An unusual coding sequence from a Drosophila clock gene is conserved in vertebrates

The per locus has a fundamental involvement in the expression of biological rhythms in Drosophila. Mutations at this locus can shorten, lengthen or eliminate a variety of rhythmic activities that range from circadian behaviours, exemplified by eclosion and locomotor activities, to short-period behaviour such as the 55-s rhythm of courtship song. DNA from the per locus has been cloned, and we have used P-element-mediated DNA transformation to establish that a 7.1-kilobase(kb) HindIII fragment contains a functional copy of the gene. This transforming DNA contains a single transcription unit which gives rise to a 4.5-kb poly(A)+ RNA. Here we report the results of a search for sequences homologous to the per locus DNA in the genomic DNA of several species of vertebrates. An unusual, tandemly repeated sequence forming a portion of the 4.5-kb per transcript is homologous to DNA in chicken, mouse and man. Cloned DNAs from the mouse and Drosophila are related by long, uninterrupted tandem repetitions of the sequence ACNGGN. At the per locus, these tandem repeats are predicted to code for poly(Thr-Gly) tracts up to 48 amino acids long. These repeated sequences are also transcribed in the mouse. Several long tracts of poly(Thr-Gly) appear to be encoded by DNA cloned from the mouse.

Genetic analysis of the circadian oviposition rhythm inDrosophila melanogaster: Effects of drift in laboratory strains

Under photoperiodic conditions, flies recently collected in nature exhibit, at the beginning of the scotophase, an oviposition peak which has a higher amplitude in Afrotropical than in European temperate populations. Several old laboratory strains failed, however, to show this peak. In each cross between genetically different strains, the oviposition curves of F1 and F2 were usually close to the midparent curve. Ten isofemale lines from an Afrotropical populations were submitted to inbreeding and drift. After 100 generations, two of the four surviving lines had retained the high peak typical of the origin population while the two others had lost it. Chromosome substitutions between these lines demonstrated a polygenic inheritance with a significant effect of the three major chromosomes. Presumably, the variations of amplitude of the oviposition peak were not caused by a modification of the ovarian activity but by a behavioral change toward the external signals of the environment.

The function of courtship song rhythms in Drosophila

The courtship songs of Drosophila are produced by the male's wing vibration and consist of a series of pulses, with an inter-pulse interval (IPI) of 34 ms for D. melanogaster and 48 ms for D. simulans. The IPI's are not constant in length during courtship, but oscillate sinusoidally with 55-s cycles in the former species and 35-s cycles in the latter. We have stimulated D. melanogaster females with artificially generated courtship songs, and have observed that they mate fastest when the song incorporates a 55-s oscillation superimposed on a 34-ms IPI. D. simulans females, on the other hand, mate fastest with a 48-ms IPI and a 35-s oscillation period. Consequently these newly-discovered song cycles produce significant mating enhancement in these species, with the females showing a preference for songs which carry both the species-specific IPI and the species-specific IPI rhythm.

Evidence for the functional involvement of carotenoids in the photoperiodic reaction of spider mites.

PHOTOPERIODISM in insects and mites depends on the presence of light-absorbing pigments, which are probably located in the central nervous system; photoperiodic responses are mediated by the direct action of light on these nervous elements1. Until now, pigments involved in photoperiodic processes such as diapause and polymorphism have not been identified. Different groups of pigments have been named by various authors as possible candidates for this function. A biologically active role based mainly on action spectra studies and the absorption characteristics of isolated pigments has been suggested for pterins2, carotenoids3, a combination of carotenoproteins, flavoproteins and haemoproteins4 and bile pigments5. Carotenoids, pterins and flavins have also been proposed as possible photoreceptor pigments in studies on the spectral sensitivity of circadian rhythms6. According to Lees1, however, the usefulness of action spectra in identifying the light acceptor is limited, as spectra for photoperiodic action cannot at present be matched against absorption curves. A different approach was used by Zimmerman and Goldsmith7, who reared Drosophila on a carotenoid-free diet and showed that in one generation the sensitivity of the visual receptors was lowered by 3 log units because of lack of rhodopsin. At the same time the photosensitivity of the rhythm of pupal eclosion in the cultures was not affected, from which it was concluded that the pigment involved in mediating light effects on the circadian rhythm in Drosophila is not a carotenoid derivative. We demonstrate here that carotenoids are functionally involved in the photoperiodic induction of diapause in the spider mite Tetranychus urticae using a method involving pigment mutants.

Acute temperature sensitivity of the circadian rhythm in Drosophila

The circadian rhythm of eclosion in fruitfly populations has a temperature-compensated 24 hr period, but it is not temperature insensitive: large steady-state phase shifts result from several hour's incubation 8° above ambient.

Oviposition rhythm in Drosophila melanogaster and its alteration by a change in the photoperiodicity.

La mesure toutes les 3, 6, 12 ou 24 h, sous deux photoperiodicites distinctes, de la ponte journaliere deDrosophila melanogaster a montre que la ponte presente un cycle journalier bien marque et que celui-ci peut-etre modifie par un changement de la photoperiodicite.

Action spectra for phase shifts of a circadian rhythm in Drosophila.

Action spectra were determined for lightinduced phase shifts of the circadian rhythm of adult emergence in Drosophila pseudoobscura. The action spectra for advance and delay phase shifts are similar; the most effective wavelengths are in the blue region, with a sharp cutoff above 500 nanometers. This similarity suggests that the same photoreceptive pigment mediates both advance and delay phase shifts.

Effect of light and dark pulses on the emergence rhythm ofDrosophila pseudoobscura

BeiDrosophila pseudoobscura synchronisiert ein einmaliger Ubergang von Dauerdunkel zu Dauerlicht und von Dauerlicht zu Dauerdunkel das Schlupfen der Fliegen aus dem Puparium (Figur 2). Die Ergebnisse von Licht-Puls- und Dunkel-Puls-Experimenten lassen sich als Uberlagerung solcher einfachen Stufeneffekte erklaren.