The regulation of phosphorylation of a specific protein in synaptosomal fractions from Drosophila heads: the effects of light and two visual mutants

Differential centrifugation-based biochemical fractionation of the Drosophila adult CNS

Drosophila is widely used as a genetic model in questions of development, cellular function and disease. Genetic screens in flies have proven to be incredibly powerful in identifying crucial components for synapse formation and function, particularly in the case of the presynaptic release machinery. Although modern biochemical methods can identify individual proteins and lipids (and their binding partners), they have typically been excluded from use in Drosophila for technical reasons. To bridge this essential gap between genetics and biochemistry, we developed a fractionation method to isolate various parts of the synaptic machinery from Drosophila, thus allowing it to be studied in unprecedented biochemical detail. This is only possible because our protocol has unique advantages in terms of enriching and preserving endogenous protein complexes. The procedure involves decapitation of adult flies, homogenization and differential centrifugation of fly heads, which allow subsequent purification of presynaptic (and to a limited degree postsynaptic) components. It is designed to require only a rudimentary knowledge of biochemical fractionation, and it takes ∼3.5 h. The yield is typically 4 mg of synaptic membrane protein per gram of Drosophila heads.

Importin-beta11 regulates synaptic phosphorylated mothers against decapentaplegic, and thereby influences synaptic development and function at the Drosophila neuromuscular junction

Importin proteins act both at the nuclear pore to promote substrate entry and in the cytosol during signal trafficking. Here, we describe mutations in the Drosophila gene importin-beta11, which has not previously been analyzed genetically. Mutants of importin-beta11 died as late pupae from neuronal defects, and neuronal importin-beta11 was present not only at nuclear pores but also in the cytosol and at synapses. Neurons lacking importin-beta11 were viable and properly differentiated but exhibited discrete defects. Synaptic transmission was defective in adult photoreceptors and at larval neuromuscular junctions (NMJs). Mutant photoreceptor axons formed grossly normal projections and synaptic terminals in the brain, but synaptic arbors on larval muscles were smaller while still containing appropriate synaptic components. Bone morphogenic protein (BMP) signaling was the apparent cause of the observed NMJ defects. Importin-beta11 interacted genetically with the BMP pathway, and at mutant synaptic boutons, a key component of this pathway, phosphorylated mothers against decapentaplegic (pMAD), was reduced. Neuronal expression of an importin-beta11 transgene rescued this phenotype as well as the other observed neuromuscular phenotypes. Despite the loss of synaptic pMAD, pMAD persisted in motor neuron nuclei, suggesting a specific impairment in the local function of pMAD. Restoring levels of pMAD to mutant terminals via expression of constitutively active type I BMP receptors or by reducing retrograde transport in motor neurons also restored synaptic strength and morphology. Thus, importin-beta11 function interacts with the BMP pathway to regulate a pool of pMAD that must be present at the presynapse for its proper development and function.

Identification of a Drosophila gene encoding a calmodulin-binding protein with homology to the trp phototransduction gene

We have isolated a number of Drosophila cDNAs on the basis of their encoding calmodulin-binding proteins. A full-length cDNA clone corresponding to one of these genes has been cloned and sequenced. Conservation of amino acid sequence and tissue-specific expression are observed between this gene and the transient receptor potential (trp) gene. We propose the name transient receptor potential-like (trpl) to describe this newly isolated gene. The trpl protein contains two possible calmodulin-binding sites, six transmembrane regions, and a sequence homologous to an ankyrin-like repeat. Structurally, the trpl and trp proteins resemble cation channel proteins, particularly the brain isoform of the voltage-sensitive Ca2+ channel. The identification of a protein similar to the trp gene product, yet also able to bind Ca2+/calmodulin, allows for a reinterpretation of the phenotype of the trp mutations and suggests that both genes may encode light-sensitive ion channels.

In vitro protein phosphorylation in head preparations from normal and mutant Drosophila melanogaster

We have characterized protein phosphorylation in vitro in subcellular fractions from Drosophila melanogaster heads. Optimal conditions for the incorporation of 32P into proteins, and its dependence on ATP, divalent cations, and cyclic nucleotides have been determined, as well as the effect of inhibitors of ATPase, protein phosphatase, and protein kinase on protein phosphorylation. Among these inhibitors, Zn2+ was found to affect the incorporation of 32P into specific bands and p-hydroxymercuribenzoate was found to be most suited for freezing the activity of both kinases and phosphatases. Cyclic AMP-dependent protein kinase (cAMP-dPK) activity was present in both supernatant (S2) and particulate (P2) fractions, with the majority (60-85%, depending on the homogenization medium) being associated with S2, as determined by phosphorylation of exogenous synapsin I. cAMP-dPK catalyzed the phosphorylation of at least 18 endogenous polypeptides in S2 and at least 10 endogenous polypeptides in P2. These proteins could be classified on the basis of the extent of stimulation of phosphorylation by cyclic nucleotides, dependence on cyclic nucleotide concentration, and rate of phosphorylation. A phosphoprotein of 51 kilodaltons (pp51) was a major component of the S2 and P2 fractions and displayed properties expected from the regulatory subunit of the cAMP-dPK, R-II. A phosphoprotein doublet of approximately 37 kilodaltons (pp37) was stimulated to the largest extent by cAMP in the P2 and S2 fractions. The phosphorylation of several proteins in both fractions was significantly lowered by the mammalian Walsh inhibitor of cAMP-dPK, whereas in some cases the stimulation of phosphorylation of the same proteins by exogeneous cAMP was relatively small. Phosphoproteins from two learning mutants known to be deficient in cAMP metabolism, dnc and rut, were analyzed for their extent of phosphorylation in the presence of a stable cAMP analogue; no significant differences from normal were detected, suggesting that the genetic defect in cAMP metabolism is not accompanied by constituent abnormalities in phosphorylated substrates in the adult fly, and that the physiological defects in these mutants result from aberrations in the interaction of the cAMP cascade with normal substrates. The majority of Ca2+/calmodulin kinase activity (80-90%, depending on the homogenization procedure) was associated with S2, as revealed by phosphorylation of exogenous synapsin I. Two endogenous substrates for this kinase in P2 had molecular masses of approximately 45 and 87 kilodaltons. At least 11 substrates for the Ca2+/calmodulin-dependent kinase were detected in S2.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of the genes shaking-B, small optic lobes, sluggish-A, stoned and stress-sensitive-C to a well-defined region on the X-chromosome of Drosophila melanogaster

Using deletion mapping and complementation tests, we have localized 5 behavioral mutations: shaking-B2, small optic lobesKS58, sluggish-AEE85, stonedts1, and stress-sensitive-C1 to 4 genetic complementation groups at the base of the X-chromosome. Shaking-B2 is an allele of the lethal complementation group R-9-29 near band 19E3; small optic lobesKS58 and sluggish-AEE85 belong to adjacent complementation groups, between lethals W2 and A112 near band 19F4; and stonedts1 and stress-sensitive-C1 are both alleles of the 8P1 lethal complementation group between lethals 114 and 13E3 near bands 20B-C.

Sexual dimorphism and electrophoretic variation in the form I cyclic nucleotide phosphodiesterase from Drosophila melanogaster

We have investigated the form I cyclic nucleotide phosphodiesterase (PDE) from Drosophila melanogaster and shown that whereas heads and male thoraces and abdomens contain high levels of Ca2+-stimulated enzyme, female thoraces and abdomens contain little Ca2+-stimulated activity. The electrophoretic patterns of form I PDE from these 3 sources have also been studied and reveal that heads, and male thoraces and abdomens, produce two bands of form I PDE both of which are stimulated by Ca2+. Extracts of female thoraces and abdomens, on the other hand, show only a single, faster running band of PDE activity which is only marginally stimulated by Ca2+, if at all. Surveying wild-type strains of Drosophila has revealed that one strain, Swedish, shows altered electrophoretic mobility of the PDE band from female thoraces and abdomens. The alteration is such that the Swedish PDE band runs more anodally than the Oregon-R and Canton-S PDE activities. Mixing experiments, using co-homogenization of heads with female thoraces and abdomens, yield a single faster running band on electrophoresis. This band contains only Ca2+-insensitive PDE. Attempts to reconstruct this loss of Ca2+-sensitive PDE without electrophoresis have failed. The Swedish electrophoretic variation of the PDE from female thoraces and abdomens has been found to be recessive with respect to the Canton-S phenotype, but the variation is observed to re-emerge and segregate with the third chromosome in the F2 generation. The results indicate that electrophoretic variation in the form I PDE is, by itself, insufficient to allow the location of the structural gene for this enzyme.