Egg-laying strategy under natural conditions of Leptopilina boulardi, a hymenopteran parasitoid of Drosophila spp

The hypothesis of optimal host species selection predicts that when a parasitoid has the choice between two host species, it will choose the species thay gives the best survival chances for its progeny. We confirmed this hypothesis by laboratory experiments with Leptopilina boulardi Barb. et al., a cynipid parasitoid which prefers Drosophila melanogaster Meigen (the host species most suitable for parasitoid survival) above D. simulans Sturt. As far as fitness parameters are concerned, the fertility of L. boulardi is higher with D. melanogaster; the egg laying can be spread out over a long period when this host is relatively scarce. This does not occur with D. simulans in which parasitic oviposition stops soon when this host is not abundant.Investigations of this foraging strategy were done under more complex natural conditions. We found that L. boulardi has a type III functional response with D. melanogaster only; furthermore, it seems that a switching effect may exist with this host. Parasitoid females appear to distribute their eggs more regularly on D. melanogaster, thus avoiding superparasitism. This seems to be independent of the relative frequency of this host. However, superparasitism of D. simulans did occur more frequently when this host was scarce.

---

Stratégie de ponte de Leptopilina boulardi (hyménoptère parasite de drosophiles) dans les conditions naturelles

Résumé Le concept de réponse optimale d'un parasite vis-à-vis de l'hôte le plus favorable pour son développement demeure surtout théorique et n'a pu être vérifié que dans les conditions de laboratoire. Nous avons montré que Drosophila melanogaster s'avère être, par rapport à D. simulans, l'hôte le plus favorable pour le développement du cynipide parasite Leptopilina boulardi. Une étude sur le terrain a démontré que ce parasite présente une réponse fonctionnelle densité dépendante vis-à-vis de D. melanogaster et non vis-à-vis de D. simulans, avec un effet de bascule. D'autre part, il s'avère que ce parasite exploite beaucoup mieux son hôte, en évitant le superparasitisme, ceci étant démontré au laboratoire et dans la nature. Enfin, il apparaît qu'il est capable d'allonger sa période de ponte lorsque cet hôte est rare, ce qui ne se produit pas avec D. simulans.

     

Cell proliferation, survival, and death in the Drosophila eye

The Drosophila retina has a precise repeating structure based on the unit eye, or ommatidium. This review summarizes studies of the cell proliferation and survival episodes that affect the number of cells available to make each ommatidium. Late in larval development, as differentiation and patterning begin, the retinal epithelium exhibits striking regulation of the cell cycle including a transient G1 arrest of all cells, followed by a ‘Second Mitotic Wave’ cell cycle that is regulated at the G2/M transition by local intercellular signals. Reiterated episodes of cell death also contribute to precise regulation of retinal cell number. The EGF receptor homolog has multiple roles in retinal proliferation and survival.     

RNA干扰技术在果蝇中的应用

RNA干扰是双链RNA特异诱导的转录后期基因沉默.该技术随着不断完善而越来越被广泛地运用于果蝇的功能基因组研究上,双链RNA已经成为果蝇中功能基因的一个十分有效的抑制子,势必使RNA干扰技术成为研究果蝇体内基因功能的强有力的反向遗传学研究技术.     

Postembryonic Hematopoiesis in Drosophila

We have investigated the blood cell types present in Drosophila at postembryonic stages and have analysed their modifications during development and under immune conditions. The anterior lobes of the larval hematopoietic organ or lymph gland contain numerous active secretory cells, plasmatocytes, few crystal cells, and a number of undifferentiated prohemocytes. The posterior lobes contain essentially prohemocytes. The blood cell population in larval hemolymph differs and consists mainly of plasmatocytes which are phagocytes, and of a low percentage of crystal cells which reportedly play a role in humoral melanisation. We show that the cells in the lymph gland can differentiate into a given blood cell lineage when solicited. Under normal nonimmune conditions, we observe a massive differentiation into active macrophages at the onset of metamorphosis in all lobes. Simultaneously, circulating plasmatocytes modify their adhesion and phagocytic properties to become pupal macrophages. All phagocytic cells participate in metamorphosis by ingesting doomed larval tissues. The most dramatic effect on larval hematopoiesis was observed following infestation by a parasitoid wasp. Cells within all lymph gland lobes, including prohemocytes from posterior lobes, massively differentiate into a new cell type specifically devoted to encapsulation, the lamellocyte.     

Molybdoenzymes in Drosophila. IV. Further characterization of the cinnamon phenotype

Summary Mutations at the cin gene display drastically lowered levels of the molybdoenzymes, xanthine dehydrogenase (XDH) and aldehyde oxidase (AO), and lack pyridoxal oxidase (PO) and sulfite oxidase (SO) activities. Certain mutations at cin also display varying degrees of female sterility, which is maternally affected. Here we characterize five new cin alleles with respect to the molybdoenzyme activities as well as the molybdenum cofactor, commonly required for molybdoenzyme activity. In complementing cin heterozygotes we find that, in addition to the previously reported unusually high levels of XDH and AO activities, there are unusually elevated levels of SO activity, as well as complementation for PO activity. The levels of immunologically crossreacting material in such heterozygotes indicate that the elevated levels of molybdoenzyme activities cannot be due to increases in the number of enzyme molecules. Measurements of the level of molybdenum cofactor activity normally present in XDH, AO, PO, and SO point to the possibility that a larger fraction of the enzyme molecules are active in these heterozygotes. The possible role of SO with respect to cinnamon's female sterility is also discussed.     

Genotoxicity is modulated by ascorbic acid: Studies using the wing spot test in Drosophila

The ability of ascorbic acid (Vitamin C) to modulate the genotoxic action of several mutagens was investigated in the wing spot test of Drosophila melanogaster. In this assay, 3-day-old transheterozygous larvae for the multiple wing hairs (mwh, 3-0.3) and flare (flr, 3-38.8) genes were treated with three reference mutagenic compounds, namely cobalt chloride (CoCl₂), 4-nitroquinoline 1-oxide (4-NQO) and potassium dichromate (K₂Cr₂O₇). The results obtained show that the three reference mutagens tested were clearly genotoxic in the Drosophila wing somatic mutation and recombination test (SMART). None of the three concentrations tested of ascorbic acid (25, 75 and 250 mM) induced significant increases in the frequency of the mutant clones recorded. When co-treatment experiments with ascorbic acid were carried out, different results were found. Thus, ascorbic acid was effective in reducing the genotoxicity of K₂Cr₂O₇ virtually to the control level; on the contrary, it did not show any antigenotoxic effect on the genotoxicity of 4-NQO. Finally, co-treatments with CoCl₂ and ascorbic acid show a significant increase in the frequency of mutant clones over the values obtained with CoCl₂ alone.     

Specific expression of the Drosophila midline-jumper retro-transposon in embryonic CNS midline cells

Here we describe of a novel Drosophila LTR-type retrotransposon that is expressed in the embryonic CNS midline glia and in the embryonic germ cells. The element is related to the gypsy and burdock retrotransposons and was termed midline-jumper. In addition to cDNA clones generated from internal retrotransposon sequences, we have identified one cDNA clone that appears to reflect a transposition event, indicating that the midline-jumper retrotransposon is not only transcribed but also able to transpose during Drosophila development.     

以果蝇模型研究人类神经退行性疾病

人类神经退行性疾病是一类以神经元退行性病变导致个体行为异常乃至死亡为主要特征的疾病.果蝇以其独特的分子遗传学优势成为研究人类神经退行性疾病的理想模型.通过对果蝇模型的研究不仅可以揭示神经退行性疾病发生的细胞分子通路,还可以研究对疾病有调控作用的基因及其表达产物,寻找可能的药物作用靶点并进行药物筛选,为防治人类神经退行性疾病提供新的方法和有效的药物.     

果蝇学习记忆行为的分子机制

分子遗传学技术的应用一方面发展了新的神经组织学方法,使果蝇脑中的细微结构得以展示;另一方面,对记忆从形成到提取过程中信息处理的研究,表明蘑菇体可能在形成长时程记忆方面起重要作用,而一对背内侧核团（dorsal paired medial cells）与蘑菇体之间的信息传递对于记忆的“提取(retrieval)”是至关重要的.行为功能检测为视觉信号整和的研究提供了新的实验依据,从而使果蝇蘑菇体的高级脑中枢功能逐渐被揭示出来.     

Host-age discrimination during host location byCotesia glomerata, a larval parasitoid ofPieris brassicae

Some parasitoids are restricted with respect to the host stage that they attack and even to a certain age within a stage. In this paper we investigate whether the parasitoidCotesia glomerata can discriminate between old and young caterpillar instars of its host,Pieris brassicae, before contacting these hosts, since contacts with older instars are very risky with a chance of being killed, due to the aggressive defensive behaviour of the caterpillars. Flight chamber dual choice tests showed that volatile chemicals emitted by Brussels sprouts plants (Brassica oleracea var. gemmifera) after feeding damage by 1st and 5th larval instars are equally attractive to the wasps. Simulated herbivore damage by 2nd and 5th larval instars, obtained by treating mechanically damaged leaves with carterpillar regurgitant, was also equally attractive, even when the wasps were exposed to repeated experience on different larval instars to increase their discriminatory ability. In contrast, single choice contact bioassays showed that the time spent searching on a leaf with feeding damage of 1st instar larvae was significantly longer than the time spent on 5th instar feeding damage or on mechanically damaged leaves. Both flight and contact bioassays did not show any effect of egg-related infochemicals. The results demonstrate thatC. glomerata can discriminate between young and old larval instars ofP. brassicae, without contacting the caterpillars. This is not done through volatile herbivore-induced synomones but through cues that are contacted after arrival at a caterpillar-infested leaf.     

Search for Drosophila genes encoding a conserved domain present in the achaete-scute complex and myc proteins

Summary Several genes of the achaete-scute complex (ASC) of Drosophila melanogaster encode a 60 amino acids long conserved domain which shares a significant homology with a region of the vertebrate myc proteins. Based on these results, the existence of a family of Drosophila genes that would share both this conserved domain and the neurogenic function of the AS-C has been postulated. To test this proposal, we have searched a D. melanogaster genomic library with a probe that encodes the conserved domain. Only under very low stringency hybridization conditions, clones not belonging to the AS-C cross-hybridized with the probe. Those that gave the strongest signals were characterized. Sequencing of the cross-hybridizing regions showed that they had no significant homology with the conserved domain, the sequence similarity extending at the most for 37 nucleotides. Although our results do not conclusively disprove the existence of a family of AS-C-like genes, they indicate that the conservation of the domain would be lower than that found for shared motifs in other families of Drosophila developmental genes.     

Retention of autonomous replicating plasmids in cultured Drosophila cells

Summary Six kinds of autonomously replicating sequences (ARSs) derived from Drosophila or tobacco were inserted into the vector pDSV, constructed with pSV2-gpt and the copia long terminal repeat (LTR). The resulting ARS-containing plasmids, pDSV-ARSs, were transfected into the cultured Drosophila cells of GM1 S1cl1. Most of the plasmids remained for about 2 weeks and some for about 1 month in these cells. The retention time of the plasmid was not directly correlated with autonomously replicating activity of ARSs detected in the yeast. Two plasmids, one carrying ARS of Drosophila nuclear DNA and the other carrying tobacco DNA, showed the longest retention time in transformed cells and replication was confirmed in these cells. Some of these long lived plasmids were recovered, however, as modified forms. Other plasmids had disappeared 1 month after transfection. Two months following transfection, none of plasmids were recovered but they were detected in nuclear DNA as the integrated form. The integration patterns in all the cells transformed by different kinds of ARS-containing plasmids were similar to each other, and to the distribution pattern of copia LTR in the genome. These results suggest that copia LTR sequences contained in the pDSV-ARSs may participate in the integration process of these plasmids into Drosophila DNA.     

Functional interactions between the gene tetanic and the Shaker gene complex of Drosophila

Different phenotypes associated with the tetanic (tta) mutation such as appendage contraction, maternal effect and low viability and fertility are enhanced by one extra dose of the Shaker gene complex (ShC). The tta mutation is lethal with two extra doses of ShC. In addition, tta embryos have a defective nervous system. In this paper, I analyse the interaction between tta and ShC to gain insight into their relationship. Aneuploid analysis suggests that the lethality is due to an interaction of the tta mutation with the maternal effect (ME) region of this gene complex. Mutations in the ME region of ShC partially suppress this interaction. Trans-heterozygous combinations of MEI[l(1)305] and MEIII [l(1)459] mutations causes dominant lethality in a tta background. Trans-heterozygous combinations of an MEII [l(1)1359] mutation with the cited MEI and MEIII mutations are lethal in a tta background. Double mutant combinations and gene dosage experiments, suggest that tta also interacts with the viable (V) region of ShC. These specific genetic interactions indicate that tta and the ME and V regions of ShC are functionally related. These results, together with the previous electrophysiological, molecular and biochemical studies on these mutants suggest an interaction at the protein level. Thus, in the case of the V region, the tta gene product may modulate the activity of the K⁺ channels encoded in this region. Furthermore, the extreme dosage sensitivity of the interaction between tta and ShC suggests a stoichiometric requirement for the different gene products involved, which might be physically associated and form heteromultimers.     

A gain-of-function screen identifies wdb and lkb1 as lifespan-extending genes in Drosophila

The insulin/insulin-like growth factor (IGF) and the target of rapamycin (TOR) signaling pathways are known to regulate lifespan in diverse organisms. However, only a limited number of genes involved in these pathways have been examined regarding their effects on lifespan. Through a gain-of-function screen in Drosophila, we found that overexpression of the wdb gene encoding a regulatory subunit of PP2A, and overexpression of the lkb1 gene encoding a serine/threonine kinase, reduced organ size and extended lifespan. Overexpression of wdb also reduced the level of phosphorylated AKT, while overexpression of lkb1 increased the level of phosphorylated AMPK and decreased the level of phosphorylated S6K. Taken together, our results suggest that wdb- and lkb1-dependent lifespan extension is mediated by downregulation of S6K, a downstream component of the insulin/IGF and TOR signaling pathways.     

Phenotypic suppression of the Drosophila mitochondrial disease-like mutant tko by duplication of the mutant gene in its natural chromosomal context

A mutation in the Drosophila gene technical knockout (tko^25t), encoding mitoribosomal protein S12, phenocopies human mitochondrial disease. We isolated three spontaneous X-dominant suppressors of tko^25t (designated Weeble), exhibiting almost wild-type phenotype and containing overlapping segmental duplications including the mutant allele, plus a second mitoribosomal protein gene, mRpL14. Ectopic, expressed copies of tko^25t and mRpL14 conferred no phenotypic suppression. When placed over a null allele of tko, Weeble retained the mutant phenotype, even in the presence of additional transgenic copies of tko^25t. Increased mutant gene dosage can thus compensate the mutant phenotype, but only when located in its normal chromosomal context.     

Microspatial genetic differentiation for tolerance and utilization of various alcohols and acetic acid in Drosophila species from India

In five Indian localities, it was possible to collect D. melanogaster in two different types of habitats, namely ordinary domestic and alcohol rich ones. Tolerance and utilization capacity of several alcohols and of acetic acid were analyzed in a total of 10 local populations. Results on two other species (D. repleta and D. immigrans) were also available from one place. In each locality, the population from alcohol rich habitat proved to be more tolerant to all the investigated products and also to be more capable of using them as a resource. Alcohols toxicity increased with increasing carbon chain length and secondary alcohols were more toxic than primary ones. Utilization capacity of all products was relatively independent of their toxicity. Especially acetic acid, the toxicity of which was low and similar to that of ethanol, was always a fairly poor resource. From a genetic point of view, tolerance and utilization capacity appeared as two relatively independent traits. Natural selection, which is responsible for the genetic differentiation of local populations, is likely to act simultaneously on both traits. This revised version was published online in July 2006 with corrections to the Cover Date.     

JNK protects Drosophila from oxidative stress by trancriptionally activating autophagy

JNK signaling functions to induce defense mechanisms that protect organisms against acute oxidative and xenobiotic insults. Using Drosophila as a model system, we investigated the role of autophagy as such a JNK-regulated protective mechanism. We show that oxidative stress can induce autophagy in the intestinal epithelium by a mechanism that requires JNK signaling. Consistently, artificial activation of JNK in the gut gives rise to an autophagy phenotype. JNK signaling can induce the expression of several autophagy-related (ATG) genes, and the integrity of these genes is required for the stress protective function of the JNK pathway. In contrast to autophagy induced by oxidative stress, non-stress related autophagy, as it occurs for example in starving adipose or intestinal tissue, or during metamorphosis, proceeds independently of JNK signaling. Autophagy thus emerges as a multifunctional process that organisms employ in a variety of different situations using separate regulatory mechanisms.     

Responses of a generalist and a specialist parasitoid (Hymenoptera: Eucoilidae) to Drosophilid larval kairomones

Foraging parasitoids are thought to need more specific information than generalists on the presence, identity, availability, and suitability of their insect host species. In the present paper, we compare responses to host kairomones by two phylogenetically related parasitoid species that attack Drosophilidae and that differ in the width of their host range. As predicted, the behavioral response of the parasitoids to host kairomones reflected their difference in host range. The response of the specialist parasitoid Leptopilina boulardiwas restricted to contact kairomones from its natural hosts and one closely related species. In contrast, the generalist parasitoid Leptopilina heterotomaresponded to contact kairomones of a variety of Drosophilidae species.