Noncircadian regulation and function of clock genes period and timeless in oogenesis of Drosophila melanogaster

Circadian clock genes are ubiquitously expressed in the nervous system and peripheral tissues of complex animals. While clock genes in the brain are essential for behavioral rhythms, the physiological roles of these genes in the periphery are not well understood. Constitutive expression of the clock gene period was reported in the ovaries of Drosophila melanogaster; however, its molecular interactions and functional significance remained unknown. This study demonstrates that period (per) and timeless (tim) are involved in a novel noncircadian function in the ovary. PER and TIM are constantly expressed in the follicle cells enveloping young oocytes. Genetic evidence suggests that PER and TIM interact in these cells, yet they do not translocate to the nucleus. The levels of TIM and PER in the ovary are affected neither by light nor by the lack of clock-positive elements Clock (Clk) and cycle (cyc). Taken together, these data suggest that per and tim are regulated differently in follicle cells than in clock cells. Experimental evidence suggests that a novel fitness-related phenotype may be linked to noncircadian expression of clock genes in the ovaries. Mated females lacking either per or tim show nearly a 50% decline in progeny, and virgin females show a similar decline in the production of mature oocytes. Disruption of circadian mechanism by either the depletion of TIM via constant light treatment or continuous expression of PER via GAL4/UAS expression system has no adverse effect on the production of mature oocytes.     

Common functional elements of Drosophila melanogaster seminal peptides involved in reproduction of Drosophila melanogaster and Helicoverpa armigera females

Sex peptide (SP) and Ductus ejaculatorius peptide (Dup) 99B are synthesized in the retrogonadal complex of adult male Drosophila melanogaster, and are transferred in the male seminal fluid to the female genital tract during mating. They have been sequenced and shown to exhibit a high degree of homology in the C-terminal region. Both affect subsequent mating and oviposition by female D. melanogaster. SP also increases in vitro juvenile hormone (JH) biosynthesis in excised corpora allata (CA) of D. melanogaster and Helicoverpa armigera. We herein report that the partial C-terminal peptides SP(8-36) and SP(21-36) of D. melanogaster, and the truncated N-terminal SP(6-20) do not stimulate JH biosynthesis in vitro in CA of both species. Both of these C-terminal peptides reduce JH-III biosynthesis significantly. Dup99B, with no appreciable homology to SP in the N-terminal region, similarly lacks an effect on JH production by H. armigera CA. In contrast, the N-terminal peptides - SP(1-11) and SP(1-22) - do significantly activate JH biosynthesis of both species in vitro. We conclude that the first five N-terminal amino acid residues at the least, are essential for allatal stimulation in these disparate insect species. We have previously shown that the full-length SP(1-36) depresses pheromone biosynthesis in H. armigera in vivo and in vitro. We now show that full-length Dup99B and the C-terminal partial sequence SP(8-36) at low concentrations strongly depress (in the range of 90% inhibition) PBAN-stimulated pheromone biosynthesis of H. armigera. In addition, the N-terminal peptide SP(1-22), the shorter N-terminal peptide SP(1-11) and the truncated N-terminal SP(6-20) strongly inhibit pheromone biosynthesis at higher concentrations.     

Short-day and long-day expression patterns of genes involved in the flesh fly clock mechanism: period,timeless, cycle and cryptochrome

Though our knowledge of the molecular details of the circadian clock has advanced rapidly, the functional elements of the photoperiodic clock remain largely unknown. As a first step to approach this issue, we report here the sequences and expression patterns of period (per), timeless (tim), cycle (cyc) and cryptochrome (cry) mRNAs in the flesh fly Sarcophaga crassipalpis. Nucleotide and deduced amino acid sequences of the genes in S. crassipalpis show high similarity to homologous genes in other insects that have been investigated. S. crassipalpis TIM has a unique C-terminus that contains a poly Q region. A diel rhythmicity of per and tim mRNA abundance was detected in the adult heads (peak during scotophase), while cry and cyc mRNA abundance remained fairly constant throughout. The abundance of cyc mRNA was quite low when compared to per, tim and cry mRNA. Rearing temperature affected the amount of per and tim mRNAs: abundance of per mRNA increased at 20 °C when compared to 25 °C, but that of tim mRNA decreased. Photoperiod influenced the expression patterns of per and tim mRNA: the peak of per mRNA expression shifted in concert with onset of the scotophase, while a shift in tim mRNA expression was less pronounced. The amplitude of tim mRNA was severely dampened under long daylength, but that of per mRNA was not affected. These distinct patterns of expression suggest that this information could be used to determine photoperiodic responses such as diapause.     

Spatial and temporal patterns of neurogenesis in the central nervous system of Drosophila melanogaster

Neurogenesis in the ventral CNS of Drosophila was studied using staining with toluidine blue and birth dating of cells monitored by incorporation of bromodeoxyuridine into DNA. The ventral CNS of the larva contains sets of neuronal stem cells (neuroblasts) which are thought to be persistent embryonic neuroblasts. Each thoracic neuromere has at least 47 of these stem cells whereas most abdominal neuromeres possess only 6. They occur in stereotyped locations so that the same neuroblast can be followed from animal to animal. The thoracic neuroblasts begin enlarging at 18-26 hr of larval life, DNA synthesis commences by 31-36 hr, and the first mitoses occur shortly thereafter. Mitotic activity continues through the remainder of larval life with the neuroblasts showing a minimum cell cycle time of less than 55 min during the late third larval instar. By 12 hr after pupariation each neuroblast has produced approximately 100 progeny which are collected with it into a discrete packet. The progeny accumulate in an immature, arrested state and only finish their differentiation into mature neurons with the onset of metamorphosis. Most of the abdominal neuroblasts differ from their thoracic counterparts in their minimum cell cycle time (less than 2 hr) and the duration of proliferation (from about 50 to 90 hr of larval life). Neurons produced during the larval stage account for more than 90% of the cells found in the ventral CNS of the adult.     

Gene expression patterns accompanying a dietary shift in Drosophila melanogaster

The ability of many organisms to switch to new hosts can be critical to their survival in the wild. However, the genetic mechanisms underlying such shifts are poorly understood. In this study, we used complementary DNA (cDNA) microarrays to ask if changes in gene expression are observed in response to a dietary shift in Drosophila melanogaster, a dietary generalist. We found significant and repeatable differential expression in a number of genes related to metabolic function and stress, suggesting that a functional genomics approach will be useful in seeking loci involved in the ability of flies to utilize different resources.     

Transposable elements and fitness in Drosophila melanogaster

Transposable elements constitute a significant fraction of the Drosophila melanogaster genome. The five families of moderately repeated transposable elements identified to date occupy dispersed and variable genomic locations, but have relatively constant copy numbers per individual. What effect to these elements have on the fitness of the individuals harboring them? Experimental evidence relating to this question is reviewed. The relevant data fall into two broad categories. The first involves the determination of the distribution of transposable elements in natural populations, by restriction mapping or in situ hybridization, and the comparison of the observed distribution with different theoretical expectations. The second approach is to study directly the effects of new transposable element-induced mutations on fitness. The P family of transposable elements is a particularly efficient mutagen, and the results of experiments in which initially P-free chromosomes are contaminated with P elements are discussed with regard to P-induced fitness mutations.     

黒腹果蝇中嵌合新基因的进化命运和表达模式

新基因的起源和进化对基因组多样性的产生具有重要的贡献.新基因起源常常通过外显子重排而形成嵌合的基因结构,以产生具有新功能的蛋白质.该文调查了在黒腹果蝇中的14个新起源的嵌合基因在群体中的多态性,发现其中8个在群体中的核苷酸多态性会引起提前终止子,而其他6个在群体中编码框都完整且其中4个受到负选择.研究结果表明,嵌合新基因起源后可能存在两种命运:积累提前终止子突变而假基因化,或者表现出一定功能而受自然选择固定下来.基因表达的数据显示,与RNA介导外显子重排(逆转座)形成的新基因不一样,这些由DNA水平外显子重排产生的新基因没有精巢或者雄性特异性表达模式,而是表现出更为多样性的时空表达模式,这提示尽管通过DNA水平外显子重排产生的新基因可能正在变成假基因或者非蛋白质编码的RNA基因,但它们依然可能具有进化出广泛的生物学功能的潜力.     

Evolutionary fate and expression patterns of chimeric new genes in Drosophila melanogaster

Origin and evolution of new genes contribute a lot to genome diversity. New genes usually form chimeric gene structures through DNA-based exon shuffling and generate proteins with novel functions. We investigated polymorphism of 14 chimeric new genes in Drosophila melanogaster populations and found that eight have premature stop codons in some individuals while six are intact in the population, four of which are under negative selection, suggesting the two evolutionary fates of new chimeric genes after origination: accumulate premature stop codons and pseudolize, or acquire functions and get fixed by natural selection. Different from new genes originated through RNA-based duplication (retroposition) which are usually testis-specific or male-specific expressed, the expression patterns of these new genes through DNA-based exon shuffling are temporally and spatially diverse, implying that they may have the potential to evolve various biological functions despite that they may become pseudogenes or non-protein-coding RNA genes.     

A model-based analysis of chemical and temporal patterns of cuticular hydrocarbons in male Drosophila melanogaster

Drosophila Cuticular Hydrocarbons (CH) influence courtship behaviour, mating, aggregation, oviposition, and resistance to desiccation. We measured levels of 24 different CH compounds of individual male D. melanogaster hourly under a variety of environmental (LD/DD) conditions. Using a model-based analysis of CH variation, we developed an improved normalization method for CH data, and show that CH compounds have reproducible cyclic within-day temporal patterns of expression which differ between LD and DD conditions. Multivariate clustering of expression patterns identified 5 clusters of co-expressed compounds with common chemical characteristics. Turnover rate estimates suggest CH production may be a significant metabolic cost. Male cuticular hydrocarbon expression is a dynamic trait influenced by light and time of day; since abundant hydrocarbons affect male sexual behavior, males may present different pheromonal profiles at different times and under different conditions.     

Structure and genomic organization of I elements involved in I-R hybrid dysgenesis in Drosophila melanogaster.

I-R hybrid dysgenesis in D. melanogaster is controlled by transposable elements known as I factors which terminate at their 3' ends by an A-rich sequence. Inducer strains contain active I factors. Both reactive and inducer stocks possess defective I elements. We have cloned various I elements from both categories of strains. The I elements having recently transposed in inducer strains have a structure closely related to that of active I factors. However we have isolated one such I element that is truncated at its 5' end. The I elements common to reactive and inducer strains are affected by various rearrangements and many point mutations. They do not appear to be simple derivatives of complete I factors.