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.     

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.     

Molybdenum hydroxylases in Drosophila

Summary The molybdenum hydroxylases are a ubiquitous class of enzymes which contain molybdenum in association with a low molecular weight cofactor. Genetic evidence suggests that the Drosophila loci, ma-1, cin and lxd are concerned with this cofactor because mutants for any one of these loci simultaneously interrupt activity for two molybdenum hydroxylases, XDH and A0. A third enzyme activity, P0, is also absent in each of the three mutants but evidence classifying P0 as a molybdoenzyme has been lacking. This study utilizes the known tungsten sensitivity of molybdoenzymes to demonstrate directly that pyridoxal oxidase is also a molybdoenzyme. The low molecular weight molybdenum cofactor is found to be severely reduced in extracts of the lxd and cin mutants but ma-1 mutants have high levels of cofactor. A partially purified preparation of XDH crossreacting material from ma-1 was also shown to contain the molybdenum cofactor. These results, considered with data from other workers are taken to indicate that the functions of all three of the loci examined could be concerned with some aspect of cofactor biosynthesis.This work was supported by PHS grant GM 23736 to V. Finnerty     

Molybdenum hydroxylases in Drosophila

Summary A reliable method for visualizing the Drosophila enzyme pyridoxal oxidase in polyacrylamide gels is described. Antiserum to pyridoxal oxidase has been produced and used in quantitative immunoelectrophoresis to determine the relative amounts of pyridoxal oxidase cross reacting material (CRM) in several mutants including lpo, lxd, ma-l and cin. The lpo variant did not have CRM for PO, thus further supporting the idea that it represents a structural gene for pyridoxal oxidase in Drosophila. CRM for PO was found in ma-l and lxd indicating that their effects upon the enzyme are probably post-translational. No CRM for PO could be found in the cin mutants.This work was supported by PHS grant GM 23736 to V. Finnerty     

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.     

The Drosophila genome

The past year has been a spectacular one for Drosophila research. The sequencing and annotation of the Drosophila melanogaster genome has allowed a comprehensive analysis of the first three eukaryotes to be sequenced—yeast, worm and fly—including an analysis of the fly's influences as a model for the study of human disease. This year has also seen the initiation of a full-length cDNA sequencing project and the first analysis of Drosophila development using high-density DNA microarrays containing several thousand Drosophila genes. For the first time homologous recombination has been demonstrated in flies and targeted gene disruptions may not be far off.     

The ribosomes of Drosophila

Summary One- and two-dimensional gel electrophoresis was employed to characterize and compare ribosomal subunit proteins from wild-type D. melanogaster and several mutants, including suppressor-offorked and four X-linked cold sensitive lethals. The sibling species D. simulans was also studied. We found the electropherogram patterns indistinguishable in all cases.This work was supported by grants from the National Institutes of Health (GM 18910, GM 22866) and the National Science Foundation (BM S75-11890) to Edward Berger     

The ribosomes of Drosophila

Summary The assembly of proteins and RNA into mature ribosomal subunits has been studied in Drosophila cell cultures by pulse-chase experiments. Pulse labeled rRNA has a transit time of 3 h, while the transfer of ribosomal protein occurs completely within 30 min. Inhibition of protein synthesis by cycloheximide results in an almost immediate cessation of ribosome assembly, a result which indicates that no large pool of free ribosomal proteins exists in the cell. Substituting pre-ribosomal RNA with the analogue 5-fluorouridine (5-FU) results in a cessation of ribosome maturation. Under these conditions at least three large subunit proteins continue to accumulate on pre-existing cytoplasmic subunits, indicating an exchange. A portion of ribosomal subunit proteins synthesized in the presence of 5-FU can be recovered in cytoplasmic subunits once the effect of 5-FU has been reversed. This is most easily interpreted in terms of their stabilization on substituted pre-rRNA within the nucleolus, and subsequent utilization on unsubstituted RNA.Work supported by a grant from the NIH (GM 22866)     

The bithorax complex—A model for cell determination in Drosophila

The bithorax complex is postulated to be the structural gene for an allosteric protein whose function is to translate a position in the developing egg into the expression of a unique set of genes characterizing the determined state of cells arising in that region of the egg. This is accomplished through the binding of inducer molecules, which exist in an anterior-posterior gradient in the egg, to the allosteric bithorax protein. Depending upon the nature of the inducer binding sites occupied, an expressor binding site on the bithorax protein is activated to one of a number of possible states. Depending upon the state of the expressor binding site, the bithorax protein binds to one of a number of classes of expressors. Binding of the bithorax protein to an expressor leads to the expression of those genes controlled by the expressor.     

Molecular cloning and characterization of Drosophila genes encoding small GTPases of the rab and rho families

We have isolated eight genes from Drosophila, small GTPases. They can be classified into three rab family genes (Drab2, Drab5, Drab11) and five rho family genes (Drac1a, Drac1b, Drac3, Dcdc42, DrhoA). While Drac3 is a novel type of rac gene, others are homologues of known mammalian genes for small GTPases. Northern blot analyses showed that all the genes are expressed throughout all developmental stages from embryo to adult. In situ hybridization to embryos revealed that Drab2, Drac1b, and Drac3 are highly expressed in the nervous system, in the trunk mesoderm, and in the cephalic mesoderm, respectively. Since hemocytes are derived from the cephalic mesoderm, we carried out double stainings using a hemocyte marker – anti-peroxidasin antibody – and Drac3 in situ hybridization. We found that Drac3 is expressed in hemocyte precursor cells. In the Drac3 deficiency embryos, the hemocyte precursor cells start to differentiate normally, but never develop into mature hemocytes, indicating that Drac3 is essential for their maturation. The DrhoA and Dcdc42 genes complemented S. cerevisiae rho1 and cdc42 mutations in the same manner as human rhoA and CDC42, respectively. These results suggest functional similarity between Drosophila and mammalian small GTPase genes. Received: 7 May 1996 / Accepted: 6 January 1997     

Sex-specific non-pheromonal taste receptors in Drosophila

Taste receptorshave recently been reported in Drosophila [1] and [2], but little is known of the relation between receptor and response. Morphological studies of the distribution of chemosensory sensilla indicate that the fruit fly has two major sites of gustation: the proboscis and the legs [3]. The taste sensilla on both these sites are similar in structure and each sensillum generally houses four gustatory neurons [4]. Early anatomical observations have demonstrated a sexual dimorphism in the number of tarsal sensilla [5] and in their central projections [6]. We measured the electrophysiological responses of the prothoracic taste sensilla to non-pheromonal substances—salts, sugars and water—and found a clear sexual dimorphism. From the response profile of individual sensilla, we were able to distinguish three types of tarsal sensilla in females as against only two types in males. The female-specific type, which responded specifically to sugar, was absent in males except when male gustatory neurons were genetically feminised. The fact that tarsal gustatory hairs exhibit a sexual dimorphism that affects the perception of non-pheromonal compounds suggests that sexual identity is more complex than has previously been thought [7] and [8].     

Abnormal centrosomes in cold-treated Drosophila embryos

In this study we examine the effect on the centrosomes of cold treatment of early Drosophila embryos. Prolonged cold treatment during the mitotic divisions which lead to the formation of the blastoderm causes arrest at metaphase of the nuclear divisions. When examined with immunofluorescence microscopy the mitotic spindles show marked pole splitting with the formation of supernumerary and irregularly sized centers, all able to nucleate microtubules. In embryos recovered for longer periods the additional organizing centers become ring-shaped and lose their nucleating properties. Cold treatment of embryos during the cellularization of the blastoderm results in marked fragmentation of the centrosomes, but nucleating capacity is preserved. Sometimes the centrioles come away from the pericentriolar material and their structure is seen to be modified.     

Neuronal differentiation in the Drosophila ommatidium

Using monoclonal and polyclonal antibodies as differentiation markers, we have found that the eight photoreceptors of the Drosophila ommatidium differentiate in a fixed sequence. The foundation photoreceptor, R8, expresses neural antigens first. The paired photoreceptors R2/5 are next to express, followed by the pair R3/4, followed by the pair R1/6; R7 is the final photoreceptor to differentiate. From previous studies it is known that Drosophila photoreceptors use local, positional cues to select their identities. Together with the morphological picture of ommatidial development, the sequential order of photoreceptor differentiation demonstrated here suggests that these cues may be encoded in the particular combination of cells an undetermined cell finds itself in contact with.     

Microfilament distribution in cold-treated Drosophila embryos

Cold treatment of Drosophila embryos is observed to result in general alteration of microfilament distribution leading to deformation of the surface caps and to perturbation of the process of cleavage furrow extension. After exposure to low temperature the cortical actin caps underwent several morphological changes, despite the arrested nuclear cycle. These observations are discussed in relation to centrosome behavior during the cell cycle.