Fine structure of a sensory organ in the arista of Drosophila melanogaster and some other dipterans

Summary The arista, a characteristic appendage of dipteran antennae, consists of 2 short segments at the base and a long distal shaft. A small sensory ganglion, from which arises the aristal nerve, is located proximally in the shaft. The fine structure of the aristal sensory organ was studied in detail in the fruitfly (Drosophila) and for comparison in the housefly (Musca) and the blowfly (Calliphora). In Drosophila, the aristal sense organ consists of 3 identical sensilla that terminate in the hemolymph space of the aristal shaft, and not in an external cuticular apparatus. Each sensillum comprises 2 bipolar neurons and 2 sheath cells; a third sheath cell envelops the somata of all six neurons of the ganglion. The neurons have long slender dendrites with the usual subdivision into an inner and an outer segment. One of the outer segments is highly lamellated and bears small particles (BOSS-structures) on the outside of its cell membrane; the other outer segment is unbranched and has a small diameter. The fine structure of the first dendrite is strongly reminiscent of thermoreceptors known from the antennae of other insects. These thermoreceptors are often coupled with hygroreceptors; however, we can only speculate whether the second dendrite of the aristal organ also has this function. Our present results argue against mechanoreceptive functions, as formerly postulated. The aristal sense organs in Musca and Calliphora are similar to those in Drosophila, but contain more sensilla (12 in Musca, 18 in Calliphora).     

Drosophila purine auxotrophy: New alleles ofadenosine2 exhibiting a complex visible phenotype

New mutant alleles of theadenosine2 locus (ade2; 2–17.7) have been isolated using the eye-color phenotype exhibited by the prototype auxotrophic alleleade2 ¹ as the screening criterion. The new mutants form a single complementation group, suggesting that they all exhibit purine auxotrophy and defective formylglycineamide ribotide amidotransferase enzyme, likeade2 ¹. Tests carried out on particular new alleles confirm these suggestions. The new mutants all exhibit more extreme physical defects than the prototype. They have wing abnormalities like mutants defective in pyrimidine biosynthesis and reduced bristles like those defective in protein synthesis; thus they exhibit the combined visible phenotype ofrudimentary wings,rosy eyes, andbobbed bristles. Cytogenetic analysis places the locus in the interband proximal to26B1-2.This work was supported by NSERC Operating Grant A3269 to D.N., an Alberta Heritage Foundation for Medical Research Postdoctoral Fellowship to S.Y.K.T., and National Institute on Aging Grant AG00029 to D.P.     

Use of the polymerase chain reaction to identify mosquito species of the Anopheles gambiae complex

A nonradiometric method has been developed for distinguishing between the sibling species Anopheles gambiae Giles and An. arabiensis Patton, two important Afrotropical vectors of malaria. DNA fragments of species diagnostic length are amplified by polymerase chain reaction (PCR) from a small amount of unknown DNA and three different PCR primers. All three PCR primers are based on ribosomal DNA (rDNA) sequences. A universal plus-strand primer (A0) is derived from a conserved region at the 3' end of the 28S rDNA coding region. Two species-specific minus-strand primers (Aa0.5 and Ag1.3) are derived from sequences in the intergenic spacers. The Ag1.3 sequence is approximately 1.3 kb downstream of A0; the Aa0.5 sequence is about 0.5 kb downstream of A0. When mosquito DNA is amplified in the presence of all three primers, a 1.3 kb fragment is produced if An. gambiae DNA is used as template, and a 0.5 kb fragment is produced if An. arabiensis DNA is used. Amplification of DNA from An.gambiae/An. arabiensis hybrids produces both the 1.3 kb and the 0.5 kb fragments. Neither diagnostic fragment is produced when DNA from other species in the An. gambiae complex is used as template.     

Synchronized endocytosis studied in the oocyte of a temperature-sensitive mutant of Drosophila melanogaster

Summary This study demonstrates that endocytosis in the oocyte of Drosophila melanogaster is reversibly blocked at the stage of pit formation by the temperature-sensitive, single-gene mutant, shibire ^ts1. Uptake of horseradish peroxidase conjugated with wheat-germ agglutinin was observed to be normal in mutant oocytes at 19°C, but was blocked at 29°C. After 10 min at 29°C, there was a build-up of coated pits along invaginations of the plasma membrane. Also, the endosomal compartment consisting of tubules, bulbs, and small yolk spheres, disappeared. Lowering the temperature to 19°C after 10 min at 29°C released a synchronized wave of endocytosis into a cytoplasm cleared of uptake-related organelles. By observing this synchronized wave after exposure to 19°C for varying durations, we determined that endocytosis proceeds as follows: coated pits/vesiclestubulessmall yolk spheresmature yolk spheres. The observations suggest that these organelles transform one into another within this sequence.     

The development of the sensory organs of the legs in the blowfly,Phormia regina

Summary The development of the sensory neurons of the legs of the blowfly,Phormia regina has been described from the third instar larva to the late pupa using immunohistochemical staining. The leg discs of the third instar larva contain 8 neurons of which 5 come to lie in the fifth tarsomere of the developing leg. Whereas 2 neurons persist at least to the late pupa, the other cells degenerate. The first neurons of gustatory sensilla arise in the fifth tarsomere at about 1.5 h after formation of the puparium. Most of these sensilla, however, appear within a short time period beginning at about 18 h. The femoral chordotonal sensory neurons first appear at the time of formation of the puparium, as a mass of cells situated in the distal femur. During later pupal development 2 groups of these cells come to lie at the femur-trochanter border, where they become the proximal femoral chordotonal organ of the adult; the remaining cells become the distal femoral chordotonal organ. Other scolopidial neurons appear later in development. The nerve pathways of the late pupal leg are established either by the axons of the cells that are present in the larval leg disc or by new outgrowing processes of sensory neurons. In the tibia, the initial direction of new outgrowth differs in different regions of the segment: proximal tibial neurons grow distally, while distal tibial neurons grow initially proximally.     

Structure of retinular cells in a Drosophila melanogaster visual mutant,rdgA, at early stages of degeneration

Summary A Drosophila visual mutant rdgA has photoreceptive cells which degenerate gradually after eclosion. Fine structure of the retinular cells of rdgA ^KS60 and rdgA ^K014 was studied during early stages of degeneration to determine the initial morphological defects. The retinular cells of these two alleles showed the following structural abnormality within 1 day after eclosion: (1) rhabdomeres were small and irregular in shape; (2) cisternae of the rough endoplasmic reticulum were more numerous than those in normal retinular cells; (3) submicrovillar cisternae were absent; and (4) lysosomes were fewer than normal. Three-dimensional reconstruction of serial sections of the ommatidia showed that the degeneration of mutant rhabdomeres proceeds more rapidly in regions remote from the nuclei. These results suggest that the process of turnover of rhabdomeric microvilli is abnormal in rdgA. We also confirmed an increase of lysosomes and destruction of cellular organelles, as reported by previous investigators at more advanced stages of degeneration.     

On the mechanism of speed and altitude control in Drosophila melanogaster

ABSTRACT The total power output of tethered flying Drosophila melanogaster in still air depends on translational velocity components of image flow on the eye, whereas the orientation of the average flight force in the midsagittal plane of the fly is widely independent of visual input (Götz, 1968). The fly does not seem to control the vertical and the horizontal force component independently. Freely flying flies nevertheless generate different ratios between lift and thrust, simply by changing the inclination of their body. By the combined adjustment of the body angle and the total power output a fly appears to be able to stabilize height and speed (David, 1985). Here a possible mechanism is proposed by which the appropriate torque about the transverse body axis could be generated. Translational pattern motion influences the posture of the abdomen and the plane of wing oscillation. Thus the position of the centre of gravity relative to the flight force vector is changed. When abdomen and stroke plane deviate from an equilibrium state, a lever is generated by which the force vector will rotate the fly about its transverse axis.     

Native Molecular Forms of Head Acetylcholinesterase from Adult Drosophila melanogaster: Quaternary Structure and Hydrophobic Character

The native molecular forms of acetylcholinesterase (AChE) present in adult Drosophila heads were characterized by sedimentation analysis in sucrose gradients and by nondenaturing electrophoresis. The hydrophobic properties of AChE forms were studied by comparing their migration in the presence of Triton X100, 10-oleyl ether, or sodium deoxycholate, or in the absence of detergent. We examined the polymeric structure of AChE forms by disulfide bridge reduction. We found that the major native molecular form is an amphiphilic dimer which is converted into hydrophilic dimer and monomer on autolysis of the extracts, or into a catalytically active amphiphilic monomer by partial reduction. The latter component exists only as trace amounts in the native enzyme. Two additional minor native forms were identified as hydrophilic dimer and monomer. Although a significant proportion of AChE was only solubilized in high salt, following extractions in low salt, this high salt-soluble fraction contained the same molecular forms as the low salt-soluble fractions: thus, we did not detect any molecular form resembling the asymmetric forms of vertebrate cholinesterases.     

Melatonin Biosynthesis in Drosophila: Its Nature and Its Effects

Drosophila melanogaster homogenates incubated with tritiated 5-hydroxytryptophan, 5-hydroxytryptamine, or N-acetylserotonin have the ability of converting them into labelled indolamines, including melatonin. All these compounds were characterized by two-dimensional thin-layer chromatography by comparison with nonradiolabelled standards, and melatonin by mass spectrometry and radioimmunoassay. On the other hand, the injection of pharmacological doses of melatonin into 2-day-old female flies diminishes the mating speed and the oviposition rate.