Search

Background: Light is the major environmental signal for the entrainment of circadian rhythms. In Drosophila melanogaster, the period(per) and timeless (tim) genes are required for circadian behavioural rhythms and their expression levels undergo circadian fluctuations. Light signals can entrain these rhythms by shifting their phases. However, little is known about the molecular mechanism for the perception and transduction of the light signal. The members of the photolyase/cryptochrome family contain flavin adenine dinucleotide (FAD) as chromophore and are involved in two diverse functions, DNA repair and photoreception of environmental light signals., Results: We report the cloning of a new member of this family, dcry, from Drosophila. Northern blot analysis shows that this gene is expressed in various tissues. The dcry mRNA is expressed in a circadian manner in adult heads, while such rhythmic fluctuation is abolished in the clock-defective per0 and tim0 mutants. The circadian expression is dampened down in constant darkness. The over-expression of the dcry gene alters the light-induced phase delay in the locomotor activity rhythms of flies., Conclusion: These results suggest that DCRY is a circadian photoreceptor and that its expression is regulated by circadian clock genes.

In Drosophila sensory organ development, the balance of activities between proneural genes and repressor genes defines a proneural cluster as a population of competent cells for neural development. In this study, we report the isolation and analysis of the tamou (tam) gene that encodes a cell-cell junction-associated protein, which is homologous to mammalian ZO-1, a member of the membrane-associated guanylate kinase homolog family. The tam mutation reduces the transcription of a repressor gene, extramacrochaetae, and causes enlargement of a proneural cluster where supernumerary precursor cells emerge, resulting in extra mechanosensory organs in the fly. These results suggest that the membrane-associated Tam protein is involved in the signaling pathway that activates emc expression.

To study the general physiological role of the Mo25 gene, which has been cloned from mouse cleavage-stage embryos, we isolated a Drosophila equivalent, dMo25, cDNA from an embryo cDNA library. The 2,222 nucleotides contained a single open reading frame encoding a polypeptide of 339 amino acid residues with a calculated molecular mass of 39,278 daltons. The deduced amino acid sequence of the dMo25 cDNA had 69.3% identity with mouse Mo25. A homology search revealed that these were similar to a protein encoded in an open reading frame near the calcineurin B subunit gene on chromosome XI in Saccharomyces cerevisiae. In particular, the carboxy-terminal region was highly conserved in Drosophila, mouse, and yeast. The dMo25 gene was mapped to the left arm of the third chromosome at 73AB, and 2.3- and 1.8-kb mRNA bands were detected during development and in adult Drosophila. Conservation of the gene structure and the wide expression profile indicated that the function of the gene is likely to be fundamental in many cell types as well as during development.

The canoemisty1 (cnomis1) mutation was isolated by virtue of its severe rough eye phenotype from approximately 500 fly lines, each harboring a single autosomal insertion of a P element (Bm delta w). Excision of the P element generated a lethal, null allele, cnomis10, together with many revertants with normal eye morphology. Ommatidia homozygous for cnomis10, produced in an otherwise wild-type eye by somatic recombination, typically contain a reduced number of outer photoreceptors. Some cnomis1 homozygous adults bear extra macrochaetes on the head, notum, humerus and/or scutellum. cnomis1 hemizygotes often show conspicuous wing phenotypes such as a notched blade and the loss of a cross vein. The sequence of cno cDNA clones isolated from an embryonic cDNA library revealed a long open reading frame that potentially encodes a 1893-amino-acid protein with the GLGF/DHR motif, a conserved sequence in Discs large, Dishevelled, and some other proteins associated with cellular junctions. Flies doubly mutant for cnomis1 and scabrous1 (sca1) and those for cnomis1 and the split (spl) allele of Notch (N) always have rumpled wings curved downward. The spl; cnomis1 double mutant flies also exhibit a "giant socket" phenotype. These phenotypes are rarely observed flies singly mutant for either cnomis1, sca1 or spl. The wing vein gaps caused by Abruptex1, a N allele producing an activated form of N protein, are dominantly suppressed by cnomis1. Heterozygosity for shaggy and myospheroid promotes formation of extra wing veins in cnomis1 homozygotes. The genetic interactions suggest that cno participates with members of the N pathway in regulating adhesive cell-cell interactions for the determination of cell fate.

Northern blot and nucleotide sequence analyses of copia RNA from a transfectant made by introducing a genomic copia into copia-free cells showed that the 2 kb RNA, one of the major transcripts of copia, is generated through splicing. Using the polymerase chain reaction (PCR), we have also found that the position of the splice sites used in Drosophila larvae and cultured cells originally containing copia is the same as that used in the transfectant. To investigate the function of the 2 kb RNA, we constructed mutant copias which harboured a single point mutation at the splice site or approximately 3 kb deletion of the internal region corresponding to the spliced out sequence. Analyses of transfectants made by introducing these mutant copias into copia-free cells demonstrated that the spliced 2 kb RNA contains sufficient information to make copia virus-like particles (VLPs). Furthermore, when copia RNA corresponding to the spliced RNA was translated in vitro, the major VLP protein was found to be released autocatalytically from its own precursor. A single amino acid substitution at the putative protease active site in the precursor prevented the processing, and resulted in accumulation of the mutant precursor in vitro. From these results, we conclude that copia VLPs are produced through autocatalytic processing of the precursor polyprotein encoded by the spliced copia RNA.