PubMed Health⌕ Search

Biomedical subjects

C P Kyriacou

Publications and source records attributed to C P Kyriacou.

At least 19 recordsLinked to original sources
PubMed2002

Molecular evolution of the period gene in sandflies.

The molecular evolution of the clock gene period was studied in Phlebotomine sandflies (Diptera: Psychodidae). Comparison of the synonymous and nonsynonymous substitution rates between sandflies and Drosophila revealed a significantly higher evolutionary rate in the latter in three of the four regions analyzed. The differences in rate were higher in the sequences flanking the Thr-Gly repetitive domain, a region that has expanded in Drosophila but remained stable and short in sandflies, a result consistent with the coevolutionary scenario proposed for this region of the gene. An initial phylogenetic analysis including eight neotropical sandfly species and one from the Old World was also carried out. The results showed that only the subgenus Nyssomyia is well supported by distance (neighbor-joining) and maximum parsimony analysis. The grouping of the other species from the subgenus Lutzomyia and Migonei group shows very low bootstrap values and is not entirely consistent with classical morphological systematics of the genus Lutzomyia.

Amino Acid Sequence↗
PubMed2002

Molecular evolution of the cacophony IVS6 region in sandflies.

A number of insects produce acoustic signals during courtship. Genes involved in the control of the courtship song are particularly interesting from an evolutionary viewpoint because interspecific variation in this signal is potentially important as a reproductive isolation mechanism and, as a consequence, in the speciation process. The cacophony gene was identified by a mutation affecting the "lovesong" in Drosophila melanogaster. Phlebotomine sandflies (Diptera: Psychodidae) also produce acoustic stimuli during courtship and therefore cacophony can be used as an interesting molecular marker in evolutionary studies in these important disease vectors. In this paper we have studied the molecular evolution of the IVS6 region of cacophony in sandflies. We compared the level of divergence in the exon sequences encoding this conserved domain in Drosophila and Phlebotomines. We also analysed the high level of variation in an intron that is present in sandflies but that was lost in Drosophila during evolution. The available cacophony sequences were also used for a phylogenetic analysis of some species of the Neotropical genus Lutzomyia.

Amino Acid Sequence↗
PubMed2002

The period gene and genetic differentiation between three Brazilian populations of Lutzomyia longipalpis.

Lutzomyia longipalpis (Diptera: Psychodidae: Phlebotominae), the main vector of visceral leishmaniasis in the Americas, is a putative species complex. Molecular polymorphism was characterized in a 266 bp fragment of L. longipalpis homologous to period, a 'speciation gene' from Drosophila. Samples from the Brazilian localities of Jacobina (BA), Lapinha (MG) and Natal (RN) were analysed and the data indicate that the three populations are highly differentiated, with a very low level of gene flow between them. These results are in agreement with published pheromone and copulation song studies that suggest the existence of a sibling species complex in Brazil.

Amino Acid Sequence↗
PubMed2001

Flies, clocks and evolution.

The negative feedback model for gene regulation of the circadian mechanism is described for the fruitfly, Drosophila melanogaster. The conservation of function of clock molecules is illustrated by comparison with the mammalian circadian system, and the apparent swapping of roles between various canonical clock gene components is highlighted. The role of clock gene duplications and divergence of function is introduced via the timeless gene. The impressive similarities in clock gene regulation between flies and mammals could suggest that variation between more closely related species within insects might be minimal. However, this is not borne out because the expression of clock molecules in the brain of the giant silk moth, Antheraea pernyi, is not easy to reconcile with the negative feedback roles of the period and timeless genes. Variation in clock gene sequences between and within fly species is examined and the role of co-evolution between and within clock molecules is described, particularly with reference to adaptive functions of the circadian phenotype.

Adaptation, Physiological↗
PubMed2001

Light-dependent interaction between Drosophila CRY and the clock protein PER mediated by the carboxy terminus of CRY.

BACKGROUND: The biological clock synchronizes the organism with the environment, responding to changes in light and temperature. Drosophila CRYPTOCHROME (CRY), a putative circadian photoreceptor, has previously been reported to interact with the clock protein TIMELESS (TIM) in a light-dependent manner. Although TIM dimerizes with PERIOD (PER), no association between CRY and PER has previously been revealed, and aspects of the light dependence of the TIM/CRY interaction are still unclear. RESULTS: Behavioral analysis of double mutants of per and cry suggested a genetic interaction between the two loci. To investigate whether this was reflected in a physical interaction, we employed a yeast-two-hybrid system that revealed a dimerization between PER and CRY. This was further supported by a coimmunoprecipitation assay in tissue culture cells. We also show that the light-dependent nuclear interactions of PER and TIM with CRY require the C terminus of CRY and may involve a trans-acting repressor. CONCLUSIONS: This study shows that, as in mammals, Drosophila CRY interacts with PER, and, as in plants, the C terminus of CRY is involved in mediating light responses. A model for the light dependence of CRY is discussed.

Animals↗
PubMed2001

Efficient and heritable functional knock-out of an adult phenotype in Drosophila using a GAL4-driven hairpin RNA incorporating a heterologous spacer.

We have developed a modified RNA interference (RNAi) method for generating gene knock-outs in Drosophila melanogaster. We used the sequence of the yellow (y) locus to construct an inverted repeat that will form a double-stranded hairpin structure (y-IR) that is under the control of the upstream activating sequence (UAS) of the yeast transcriptional activator GAL4. Hairpins are extremely difficult to manipulate in Escherichia coli, so our method makes use of a heterologous 330 bp spacer encoding sequences from green fluorescent protein to facilitate the cloning steps. When the UAS-y-IR hairpin is expressed under the control of different promoter-GAL4 fusions, a high frequency of y pigment phenocopies is obtained in adults. Consequently this method for producing gene knock-outs has several advantages over previous methods in that it is applicable to any gene within the fly genome, greatly facilitates cloning of the hairpin, can be used if required with GAL4 drivers to avoid lethality or to induce RNAi in a specific developmental stage and/or tissue, is useful for generating knock-outs of adult phenotypes as reported here and, finally, the system can be manipulated to investigate the trans-acting factors that are involved in the RNAi mechanism.

Animals↗
PubMed2001

New molecular markers for phlebotomine sand flies.

Using degenerate-primers PCR we isolated and sequenced fragments from the sand fly Lutzomyia longipalpis homologous to two behavioural genes in Drosophila, cacophony and period. In addition we identified a number of other gene fragments that show homology to genes previously cloned in Drosophila. A codon usage table for L. longipalpis based on these and other genes was calculated. These new molecular markers will be useful in population genetics and evolutionary studies in phlebotomine sand flies and in establishing a preliminary genetic map in these important leishmaniasis vectors.

Amino Acid Sequence↗
PubMed2001

Keeping time with the human genome.

The cloning and characterization of 'clock gene' families has advanced our understanding of the molecular control of the mammalian circadian clock. We have analysed the human genome for additional relatives, and identified new candidate genes that may expand our knowledge of the molecular workings of the circadian clock. This knowledge could lead to the development of therapies for treating jet lag and sleep disorders, and add to our understanding of the genetic contribution of clock gene alterations to sleep and neuropsychiatric disorders. The human genome will also aid in the identification of output genes that ultimately control circadian behaviours.

Animals↗
PubMed2001

Keystone clocks.

Explore the source record for details and available documents.

Animals↗
PubMed2001

Comparative analysis of the nonA region in Drosophila identifies a highly diverged 5' gene that may constrain nonA promoter evolution.

A genomic fragment from Drosophila virilis that contained all the no-on-transientA (nonA) coding information, plus several kilobases of upstream material, was identified. Comparisons of nonA sequences and the gene nonA-like in D. melanogaster, a processed duplication of nonA, suggest that it arose before the split between D. melanogaster and D. virilis. In both species, another gene that lies <350 bp upstream from the nonA transcription starts, and that probably corresponds to the lethal gene l(1)i19, was identified. This gene encodes a protein that shows similarities to GPI1, which is required for the biosynthesis of glycosylphosphatidylinositol (GPI), a component for anchoring eukaryotic proteins to membranes, and so we have named it dGpi1. The molecular evolution of nonA and dGpi1 sequences show remarkable differences, with the latter revealing a level of amino acid divergence that is as high as that of transformer and with extremely low levels of codon bias. Nevertheless, in D. melanogaster hosts, the D. virilis fragment rescues the lethality associated with a mutation of l(1)i19e, as well as the viability and visual defects produced by deletion of nonA(-). The presence of dGpi1 sequences so close to nonA appears to have constrained the evolution of the nonA promoter.

Amino Acid Sequence↗
PubMed2001

The nonA gene in Drosophila conveys species-specific behavioral characteristics.

The molecular basis of species-specific differences in courtship behavior, a critical factor in preserving species boundaries, is poorly understood. Genetic analysis of all but the most closely related species is usually impossible, given the inviability of hybrids. We have therefore applied interspecific transformation of a single candidate behavioral locus, no-on-transient A (nonA), between Drosophila virilis and D. melanogaster, to investigate whether nonA, like the period gene, might encode species-specific behavioral information. Mutations in nonA can disrupt both visual behavior and the courtship song in D. melanogaster. The lovesong of nonA(diss) mutant males superficially resembles that of D. virilis, a species that diverged from D. melanogaster 40-60 mya. Transformation of the cloned D. virilis nonA gene into D. melanogaster hosts carrying a synthetic deletion of the nonA locus restored normal visual function (the phenotype most sensitive to nonA mutation). However, the courtship song of transformant males showed several features characteristic of the corresponding D. virilis signal, indicating that nonA can act as a reservoir for species-specific information. This candidate gene approach, together with interspecific transformation, can therefore provide a direct avenue to explore potential speciation genes in genetically and molecularly tractable organisms such as Drosophila.

Animals↗
PubMed2000

The clock gene period of the housefly, Musca domestica, rescues behavioral rhythmicity in Drosophila melanogaster. Evidence for intermolecular coevolution?

In Drosophila, the clock gene period (per), is an integral component of the circadian clock and acts via a negative autoregulatory feedback loop. Comparative analyses of per genes in insects and mammals have revealed that they may function in similar ways. However in the giant silkmoth, Antheraea pernyi, per expression and that of the partner gene, tim, is not consistent with the negative feedback role. As an initial step in developing an alternative dipteran model to Drosophila, we have identified the per orthologue in the housefly, Musca domestica. The Musca per sequence highlights a pattern of conservation and divergence similar to other insect per genes. The PAS dimerization domain shows an unexpected phylogenetic relationship in comparison with the corresponding region of other Drosophila species, and this appears to correlate with a functional assay of the Musca per transgene in Drosophila melanogaster per-mutant hosts. A simple hypothesis based on the coevolution of the PERIOD and TIMELESS proteins with respect to the PER PAS domain can explain the behavioral data gathered from transformants.

Amino Acid Sequence↗
PubMed1999

Different period gene repeats take 'turns' at fine-tuning the circadian clock.

The repetitive region of the circadian clock gene period in Drosophila pseudoobscura consists predominantly of a pentapeptide sequence whose consensus is NSGAD. In D. melanogaster, this region is replaced by a dipeptide Thr-Gly repeat, which plays a role in the thermal stability of the circadian phenotype. The Thr-Gly repeat has been shown to form a type II or III beta-turn, whose conformational monomer is (Thr-Gly)3. Here we report, using conformational analyses, that both an NSGAD pentapeptide, and a polymer of the same sequence, form type II beta-turns. Thus two peptide sequences, whose amino-acid composition is very different, nevertheless form the same secondary structure. The implications of these structures for clock function are discussed.

Animals↗
PubMed1998

Molecular coevolution within a Drosophila clock gene.

The period (per) gene in Drosophila melanogaster provides an integral component of biological rhythmicity and encodes a protein that includes a repetitive threonine-glycine (Thr-Gly) tract. Similar repeats are found in the frq and wc2 clock genes of Neurospora crassa and in the mammalian per homologues, but their circadian functions are unknown. In Drosophilids, the length of the Thr-Gly repeat varies widely between species, and sequence comparisons have suggested that the repeat length coevolves with the immediately flanking amino acids. A functional test of the coevolution hypothesis was performed by generating several hybrid per transgenes between Drosophila pseudoobscura and D. melanogaster, whose repetitive regions differ in length by about 150 amino acids. The positions of the chimeric junctions were slightly altered in each transgene. Transformants carrying per constructs in which the repeat of one species was juxtaposed next to the flanking region of the other were almost arrhythmic or showed a striking temperature sensitivity of the circadian period. In contrast, transgenes in which the repeat and flanking regions were conspecific gave wild-type levels of circadian rescue. These results support the coevolutionary interpretation of the interspecific sequence changes in this region of the PER molecule and reveal a functional dimension to this process related to the clock's temperature compensation.

Amino Acid Sequence↗
PubMed1998

Functional and evolutionary implications of natural variation in clock genes.

Nearly all studies of natural variation within clock genes involve the period (per) locus, which was originally isolated in the fruit-fly. Intra- and interspecific work on per has focused mostly on a region of Thr-Gly or Ser-Gly repeats, which show rapid length and sequence evolution. The functional implications of nucleotide variation in this repetitive array have been characterised using behavioural, molecular, ecological, structural and statistical analyses. A population genetics approach to variation in per has also been useful in defining species histories within Drosophilids and, in some cases, in implicating selective processes in the evolution of the per gene. Interspecific analysis of per expression patterns reveals evolutionary alterations in this clock gene's regulation.

Animals↗