Fruit Fly Brain Research Articles

The neuroarchitecture of the circadian clock in the brain of Drosophila melanogaster.

Neuroethologists try to assign behavioral functions to certain brain centers, if possible down to individual neurons and to the expression of specific genes. This approach has been successfully applied for the control of circadian rhythmic behavior in the fruit fly Drosophila melanogaster. Several so-called "clock genes" are expressed in specific neurons in the lateral and dorsal brain where they generate cell-autonomous molecular circadian oscillations. These clusters are connected with each other and contribute differentially to the control of behavioral rhythmicity. This report reviews the latest work on characterizing individual circadian pacemaker neurons in the fruit fly's brain that control activity and pupal eclosion, leading to the questions by which neuronal pathways they are synchronized to the external light-dark cycle, and how they impose periodicity on behavior.

Embryonic and larval development of the Drosophila mushroom bodies: concentric layer subdivisions and the role of fasciclin II.

Mushroom bodies (MBs) are the centers for olfactory associative learning and elementary cognitive functions in the arthropod brain. In order to understand the cellular and genetic processes that control the early development of MBs, we have performed high-resolution neuroanatomical studies of the embryonic and post-embryonic development of the Drosophila MBs. In the mid to late embryonic stages, the pioneer MB tracts extend along Fasciclin II (FAS II)-expressing cells to form the primordia for the peduncle and the medial lobe. As development proceeds, the axonal projections of the larval MBs are organized in layers surrounding a characteristic core, which harbors bundles of actin filaments. Mosaic analyses reveal sequential generation of the MB layers, in which newly produced Kenyon cells project into the core to shift to more distal layers as they undergo further differentiation. Whereas the initial extension of the embryonic MB tracts is intact, loss-of-function mutations of fas II causes abnormal formation of the larval lobes. Mosaic studies demonstrate that FAS II is intrinsically required for the formation of the coherent organization of the internal MB fascicles. Furthermore, we show that ectopic expression of FAS II in the developing MBs results in severe lobe defects, in which internal layers also are disrupted. These results uncover unexpected internal complexity of the larval MBs and demonstrate unique aspects of neural generation and axonal sorting processes during the development of the complex brain centers in the fruit fly brain.

Effects of tyrosine hydroxylase mutants on locomotor activity in Drosophila: a study in functional genomics.

The brain of the adult fruit fly, Drosophila melanogaster, contains tyrosine hydroxylase, the rate-limiting enzyme required for catecholamine biosynthesis, as well as dopa decarboxylase. Catecholamines, principally dopamine, are also present. We have previously shown that pharmacological inhibition of tyrosine hydroxylase with alpha-methyl-p-tyrosine results in a dose-related inhibition of locomotor activity in adult organisms. Similar results were found with reserpine, a well-known inhibitor of catecholamine uptake into storage granules. The drug-induced inhibition could be prevented in each case by the concomitant administration of L-dopa. The single-copy gene coding for tyrosine hydroxylase in Drosophila is pale (ple). Both null and temperature-sensitive loss of function mutant alleles of ple are recessive embryonic lethals. Heterozygous null mutant flies have normal locomotor activity demonstrating that only a single dose of the wild type form of ple is required to support normal function. Both hemizygous and homozygous temperature-sensitive ple mutants (ple(ts1)) also show normal locomotor activity at the permissive temperature for this mutant allele (18 degrees C), which progressively declines as the temperature is increased to its restrictive level (29 degrees C). These abnormal locomotor effects are reversible by L-dopa. Thus the effects on locomotor activity resulting from the pharmacological inhibition of catecholamine synthesis or storage are the same as those resulting from lack of tyrosine hydroxylase expression. These findings indicate that brain catecholamine loss decreases locomotor activity in the fly, as it does in mammals, and demonstrate the ability of functional genomic studies to mimic that of pharmacological inhibition of enzyme function or other similar processes.

Neurobiology. Learning how a fruit fly forgets.

There are three stages to memory: acquisition, storage, and retrieval. But distinguishing which brain structures are involved in each stage has been very difficult. In their Perspective, [Waddell and Quinn][1] discuss new findings showing that synaptic output from structures in the fruit fly brain called mushroom bodies is required for memory recall but not for its acquisition and storage ([ McGuire et al .][2]). [1]: http://www.sciencemag.org/cgi/content/full/293/5533/1271 [2]: http://www.sciencemag.org/cgi/content/short/293/5533/1330

Immunodetection of Parkin protein in vertebrate and invertebrate brains: a comparative study using specific antibodies

Parkin is an intracellular protein that plays a significant role in the etiopathogenesis of autosomal recessive juvenile parkinsonism. Using immunoblot methods, we found Parkin isoforms varying from 54 to 58 kDa in rat, mouse, bird, frog and fruit-fly brains. Immunocytochemical studies carried out in rats, mice and birds demonstrated multiple cell types bearing the phenotype for Parkin throughout telencephalic, diencephalic, mesencephalic and metencephalic brain structures. While in some instances Parkin-containing neurons tended to be grouped into clusters, the majority of these labeled nerve cells were widely scattered throughout the neuraxis. The topographical distribution and organizational pattern of Parkin within major functional brain circuits was comparable in both rats and mice. However, the subcellular localization of Parkin was found to vary significantly as a function of antibody reactivity. A consistent cytoplasmic labeling for Parkin was observed in rodent tissue incubated with a polyclonal antibody raised against the human Parkin protein and having an identical amino-acid sequence with that of the rat. In contrast, rodent tissue alternately incubated with a polyclonal antibody raised against a different region of the same human Parkin protein but having 10 mismatched amino-acid sequence changes with those of the rat and mouse, resulted in nuclear labeling for Parkin in rat but not mouse neurons. This difference in epitope recognition, however, was reversed when mouse brain tissue was heated at 80°C, apparently unmasking target epitopes against which the antisera were directed. Collectively, these results show a high degree of conservation in the cellular identity of Parkin in animals as different as drosophilids and mammals and points to the possibility that the biochemical specificities of Parkin, including analogous functional roles, may have been conserved during the course of evolution.

Avermectin chemistry and action: ester- and ether-type candidate photoaffinity probes

Avermectin B1a (1 ) is a potent anthelmintic, insecticide, miticide and chloride channel activator on interaction with a specific nerve membrane site analyzed by binding assays with [3H]1. Candidate photoaffinity probes were prepared replacing the dioleandrosyl substituent with potential isosteric esters and ethers approximating the original overall atom length and terminating in a phenyl moiety substituted with azido, iodo or hydroxy. Several of the candidates met the goal of high potency on mouse, housefly and fruit fly brain chloride channels with IC50 values of 7–57 nM in competing for the [3H]1 binding site.

Multiple Clocks Keep Time in Fruit Fly Tissues

Neuroscientists have focused on the brain as the master timekeeper for biological rhythms, controlling everything from normal fluctuations in body temperature to midafternoon slumps. But on page 1632, researchers report new evidence indicating that fruit flies have independent clocks throughout their bodies. By harnessing recently developed techniques for imaging proteins in living cells, they tracked the production of a timekeeping protein, called PER. Previous work had shown that per, the gene that makes the protein, cycles on and off in the fruit fly brain to establish the body9s daily rhythms; now this cycling appears to be widespread in fruit fly tissues. Other research has also revealed preliminary evidence for such tissue clocks in higher organisms, including mammals. These new clocks may help individual tissues tailor their protein production to the needs of the hour, while the brain clock oversees rhythms involving coordination of two or more different responses.

Circadian Clock Neurons in the Silkmoth Antheraea pernyi: Novel Mechanisms of Period Protein Regulation

We examined Period (PER) protein regulation in the brain of the silkmoth Antheraea pernyi. PER expression is restricted to the cytoplasm and axons of eight neurons, with no evidence of temporal movement into the nucleus. These neurons appear to be circadian clock cells, because PER and per mRNA are colocalized and their levels oscillate in these cells, Timeless protein immunoreactivity is coexpressed in each PER-positive neuron, and clock protein and mRNA oscillations are all suppressed in these neurons by constant light. A per antisense RNA oscillation was detected that is spatially restricted to PER-expressing cells, suggesting a novel mechanism of PER regulation. PER-positive neurons and their projections are strategically positioned for regulating prothoracicotropic hormone and eclosion hormone, two neurohormones under circadian control. Differences in the molecular details of PER expression and regulation between the brains of silkmoths and fruitflies provide insights into the mechanisms of clock gene regulation.

A period (per)-like protein exhibits daily rhythmicity in the suprachiasmatic nuclei of the rat

The period (per) gene of Drosophila melanogaster is considered an important biological clock gene, since it regulates multiple behavioral rhythms. Per mRNA and protein exhibit circadian rhythms in the fruitfly brain and these rhythms appear to influence each other through a feedback loop. More recently, using the same antibody as was used in the Drosophila studies, PER-like proteins were detected in the suprachiasmatic nuclei (SCN) of male rats. This region of the brain is considered to be a major neural circadian pacemaker in mammals. The purpose of this study was to confirm that PER-like proteins are detectable in the SCN of female rats and to determine whether PER-like proteins exhibit a circadian rhythm. Female rats were killed at several times of day under both light/dark and constant conditions. Using the same anti-PER antibody in Western blots with Enhanced Chemiluminescence (Western-ECL) detection, the levels of the PER-like proteins were quantified in the SCN and cerebral cortex. The antibody identified a doublet band of approximately 170-160 kDa and a single band at 115 kDa. Of the three PER-like proteins only the largest exhibited a daily rhythm in the SCN, which peaked in the middle of the dark and attained its nadir around lights off; levels during the light were intermediate with a tendency towards a second drop around lights on. This rhythm did not persist under constant dim red light. The data demonstrate that an antigen similar to PER exhibits a daily rhythm in the pacemaker region of the rat brain and suggest that it may play a role in the maintenance of 24-h rhythmicity in mammals.