Comparative analysis of Pdf-mediated circadian behaviors between Drosophila melanogaster and D. virilis

CLOCK deubiquitylation by USP8 inhibits CLK/CYC transcription in Drosophila

A conserved transcriptional feedback loop underlies animal circadian rhythms. In Drosophila, the transcription factors CLOCK (CLK) and CYCLE (CYC) activate the transcription of direct target genes like period (per) and timeless (tim). They encode the proteins PER and TIM, respectively, which repress CLK/CYC activity. Previous work indicates that repression is due to a direct PER-CLK/CYC interaction as well as CLK/CYC phosphorylation. We describe here the role of ubiquitin-specific protease 8 (USP8) in circadian transcriptional repression as well as the importance of CLK ubiquitylation in CLK/CYC transcription activity. usp8 loss of function (RNAi) or expression of a dominant-negative form of the protein (USP8-DN) enhances CLK/CYC transcriptional activity and alters fly locomotor activity rhythms. Clock protein and mRNA molecular oscillations are virtually absent within circadian neurons of USP8-DN flies. Furthermore, CLK ubiquitylation cycles robustly in wild-type flies and peaks coincident with maximal CLK/CYC transcription. As USP8 interacts with CLK and expression of USP8-DN increases CLK ubiquitylation, the data indicate that USP8 deubiquitylates CLK, which down-regulates CLK/CYC transcriptional activity. Taken together with the facts that usp8 mRNA cycles and that its transcription is activated directly by CLK/CYC, USP8, like PER and TIM, contributes to the transcriptional feedback loop cycle that underlies circadian rhythms.

Divergent functions through alternative splicing: the Drosophila CRMP gene in pyrimidine metabolism, brain, and behavior

DHP and CRMP proteins comprise a family of structurally similar proteins that perform divergent functions, DHP in pyrimidine catabolism in most organisms and CRMP in neuronal dynamics in animals. In vertebrates, one DHP and five CRMP proteins are products of six genes; however, Drosophila melanogaster has a single CRMP gene that encodes one DHP and one CRMP protein through tissue-specific, alternative splicing of a pair of paralogous exons. The proteins derived from the fly gene are identical over 90% of their lengths, suggesting that unique, novel functions of these proteins derive from the segment corresponding to the paralogous exons. Functional homologies of the Drosophila and mammalian CRMP proteins are revealed by several types of evidence. Loss-of-function CRMP mutation modifies both Ras and Rac misexpression phenotypes during fly eye development in a manner that is consistent with the roles of CRMP in Ras and Rac signaling pathways in mammalian neurons. In both mice and flies, CRMP mutation impairs learning and memory. CRMP mutant flies are defective in circadian activity rhythm. Thus, DHP and CRMP proteins are derived by different processes in flies (tissue-specific, alternative splicing of paralogous exons of a single gene) and vertebrates (tissue-specific expression of different genes), indicating that diverse genetic mechanisms have mediated the evolution of this protein family in animals.

The genomic response to courtship song stimulation in female Drosophila melanogaster

Courtship behaviour involves a complex exchange of signals and responses. These are usually studied at the phenotypic level, and genetic or transcriptional responses to courtship are still poorly understood. Here, we examine the gene-expression changes in Drosophila melanogaster females in response to one of the key male courtship signals in mate recognition, song produced by male wing vibration. Using long oligonucleotide microarrays, we identified several genes that responded differentially to the presence or absence of acoustic courtship stimulus. These changes were modest in both the number of genes involved and fold-changes, but notably dominated by antennal signalling genes involved in olfaction as well as neuropeptides and immune response genes. Second, we compared the expression patterns of females stimulated with synthetic song typical of either conspecific or heterospecific (Drosophila simulans) males. In this case, antennal olfactory signalling and innate immunity genes were also enriched among the differentially expressed genes. We confirmed and investigated the time course of expression differences of two identified immunity genes using real-time quantitative PCR. Our results provide novel insight into specific molecular changes in females in response to courtship song stimulation. These may be involved in both signal perception and interpretation and some may anticipate molecular interactions that occur between the sexes after mating.

Characterization, expression, and evolutionary aspects of Corazonin neuropeptide and its receptor from the House Fly, Musca domestica (Diptera: Muscidae)

In this article, we characterized structure and expression of genes encoding the neuropeptide Corazonin (MdCrz) and its putative receptor (MdCrzR) in the House Fly, Musca domestica. The MdCrz gene contains two introns, one within the 5' untranslated region and the other within the open reading frame. The 150-amino-acid precursor consists of an N-terminal signal peptide, and mature Crz followed by Crz-associated peptide (CAP). The CAP region is highly diverged from those of other insect precursors, whereas the mature Crz is identical in other dipteran members. In situ hybridization and immunohistochemistry consistently found a group of three MdCrz-producing neurons in the dorso-lateral protocerebrum, and eight pairs of bi-lateral neurons in the ventral nerve cord in the larvae. In adults, the expression was found exclusively in a cluster of five to seven neurons per brain lobe. Comparable expression patterns observed in other dipteran species suggest conserved regulatory mechanisms of Crz expression and functions during the course of evolution. MdCrzR deduced from the full-length cDNA sequence is a 655-amino acid polypeptide that contains seven trans-membrane (TM) domains and other motifs that are characteristics of Class-A G-protein coupled receptors. Although the TMs and loops between the TMs are conserved in other CrzRs, N-terminal extracellular domain is quite dissimilar. Tissue-specific RT-PCR revealed a high level of MdCrzR expression in the larval salivary glands and a moderate level in the CNS. In adults, the receptor was expressed both in the head and body, suggesting multifunctionality of the Crz signaling system.

Signalling through pigment dispersing hormone-like peptides in invertebrates

During recent decades, several research teams engaged in unraveling the molecular structure and the physiological significance of pigment dispersing hormone-like peptides, particularly with respect to colour change and biological rhythms. In this review, we first summarise the entire history of pigment dispersing hormone-like peptide research, thus providing a stepping stone for those who are curious about this growing area of interest. Next, we try to bring order in the plethora of experimental data on the molecular structure of the various peptides and receptors and also discuss immunolocalization, time-related expression and suggested functions in crustaceans, insects and nematodes. In addition, a brief comparison with the vertebrate system is made.

Dissecting differential gene expression within the circadian neuronal circuit of Drosophila

Behavioral circadian rhythms are controlled by a neuronal circuit consisting of diverse neuronal subgroups. To understand the molecular mechanisms underlying the roles of neuronal subgroups within the Drosophila circadian circuit, we used cell-type specific gene-expression profiling and identified a large number of genes specifically expressed in all clock neurons or in two important subgroups. Moreover, we identified and characterized two circadian genes, which are expressed specifically in subsets of clock cells and affect different aspects of rhythms. The transcription factor Fer2 is expressed in ventral lateral neurons; it is required for the specification of lateral neurons and therefore their ability to drive locomotor rhythms. The Drosophila melanogaster homolog of the vertebrate circadian gene nocturnin is expressed in a subset of dorsal neurons and mediates the circadian light response. The approach should also enable the molecular dissection of many different Drosophila neuronal circuits.