A member of the p38 mitogen-activated protein kinase family is responsible for transcriptional induction of Dopa decarboxylase in the epidermis of Drosophila melanogaster during the innate immune response

Drosophila innate immunity is controlled primarily by the activation of IMD (immune deficiency) or Toll signaling leading to the production of antimicrobial peptides (AMPs). IMD signaling also activates the JUN N-terminal kinase (JNK) cascade, which is responsible for immune induction of non-antimicrobial peptide immune gene transcription though the transcription factor AP-1. Transcription of the Dopa decarboxylase (Ddc) gene is induced in response to gram-negative and gram-positive septic injury, but not aseptic wounding. Transcription is induced throughout the epidermis and not specifically at the site of infection. Ddc transcripts are detectible within 2 h and remain high for several hours following infection with either gram-negative or gram-positive bacteria. Using Ddc-green fluorescent protein (GFP) reporter gene constructs, we show that a conserved consensus AP-1 binding site upstream of the Ddc transcription start site is required for induction. However, neither the Toll, IMD, nor JNK pathway is involved. Rather, Ddc transcription depends on a previously uncharacterized member of the p38 mitogen-activated protein kinase family, p38c. We propose that the involvement of DDC in a new pathway involved in Drosophila immunity increases the levels of dopamine, which is metabolized to produce reactive quinones that exert an antimicrobial effect on invading bacteria.

Identification and characterization of an aromatic amino acid decarboxylase from the filarial nematode, Dirofilaria immitis

A novel secreted aromatic amino acid decarboxylase-like molecule was identified in the excretory/secretory products of L3/L4 larvae as well as in an extract of adult Dirofilaria immitis. The secretion of the enzyme was developmentally regulated. Peak enzyme activities were detected in the culture medium before and after the molting of L3 larvae in vitro. The enzyme was purified from D. immitis adult extracts and the excretory/secretory products of L3/L4 larvae using different chromatographic methods followed by isoelectric focusing and SDS-PAGE. The enzyme has a molecular mass of 48 kDa and a pI of 5.6, and shows a specific enzymatic activity towards the aromatic amino acid substrates phenylalanine, tyrosine and tryptophan. The enzyme's activity did not show an absolute requirement for exogenous pyridoxal-5-phosphate. However, addition of pyridoxal-5-phosphate at 5 microM in the reaction increased the enzyme activity greatly. The enzyme had the ability to catalyze the formation of dopamine from L-dopa. Studies on the effects of inhibitors on the enzyme activity showed that the enzyme was sensitive to Pefabloc and p-chloromercuribenzoic acid, but not to diisopropyl flurophosphate. The Km values of the enzyme for H-Phe-AMC, H-Tyr-AMC and H-Trp-AMC were calculated to be 32.1 microM, 35.1 microM and 29.1 microM, respectively.

Reproduction and development in Drosophila are dependent upon catecholamines

Drosophila melanogaster, maintained on culture media containing alpha-methyl-p-tyrosine (alpha-MT) at millimolar levels for 7 days, fail to produce viable progeny. Lesser concentrations delay development. This effect of alpha-MT, an inhibitor of tyrosine hydroxylase (TH), is partially reversible by co-administration of L-dihydroxyphenylalanine, the product of TH. Potent inhibitors of other steps in the pathway for catecholamine biosynthesis are inactive except for a partial effect with dopamine B-hydroxylase inhibition. the effect of alpha-MT is due to a combination of ovulation suppression coupled with decreases in embryonic and larval viability. Effects similar to those of alpha-MT are found with millimolar levels of reserpine, prazosin and to a lesser extent, rauwolscine. No significant effects are found with propranolol, chlorpromazine, sulpiride and SK&F 83566. Mutant alleles of the gene coding for TH are known to be lethal at the embryonic stage when homozygous in both Drosophila and mice. Taken together, these results indicate that in addition to their established roles in the nervous system catecholamines function in animal development via an action mediated through alpha-adrenoceptors.

Mosquito dopa decarboxylase cDNA characterization and blood-meal-induced ovarian expression

Dopa decarboxylase (DDC) functions in insect catecholamine biochemistry to produce materials essential for cross-linking reactions that result in tanning and/or melanization, include tanning of the mosquito egg chorion and encapsulation of parasites. We have cloned Ddc from the mosquito, Aedes aegypti, and studied its expression in response to blood-feeding, which initiates events necessary for egg maturation in mosquitoes. The Ae. aegypti Ddc cDNA was isolated via heterologous screening using a clone from Drosophila melanogaster. A resulting 1.87 kilobase (kb) clone was sequenced to reveal an open reading frame of 1464 bp, as well as 5'- and 3'-untranslated segments. The inferred amino acid sequence of this clone shares 81% identity with the published Drosophila Ddc cDNA, including complete identity with twenty-four contiguous amino acids encompassing the pyridoxal-5-phosphate cofactor binding domain. Analysis of an F2 intercross population derived from a parental cross between two Ae. aegypti strains (Hamburg and Moyo-In-Dry) allowed us to map Ddc to a locus on linkage group 2. Expression studies demonstrated the presence of a 2.1 kb message, the majority of which occurs in the ovaries where Ddc-specific mRNA is up-regulated in response to ingestion of a blood meal. The potential for egg-tanning in anautogenous mosquitoes as a model for understanding specific genetic events in the regulation of catecholamine metabolism is addressed.

Effects of Ddc cluster lethal alleles on ovary growth, attachment, and egg production in Drosophila

The Ddc cluster of genes on the left arm of chromosome 2 in Drosophila has been extensively characterized by Wright and coworkers (Wright, '87b). Many of the genes in the cluster are associated with the pigmentation and sclerotization of the cuticle, and at least 12 have been shown to play a role in female fertility. To characterize further the actions of genes in the cluster, we have investigated the effect on fertility of a total of five of the previously untested genes (l(2)37Be, Bb, Bg, Bd, and Cg), and three of the partially characterized genes (l(2)37Ce, Ddc, and amd). Each allele was crossed to Df(2L)TW130 or49h flies in order to make it hemizygous over the 8-12 band deficiency covering the Ddc region, 37B9-C1,2;37D1-2. Ovaries taken from larvae produced by this cross were transplanted into female larval hosts of y f mal genotype, that were then mated to v f mal males. The wild type allele of mal in implanted tissue allowed identification and study of surviving implants by staining for the presence of aldehyde oxidase. Of the 18 alleles available, amdH149, l(2)37Bb1, Bb9, Bb11, Bd6, Be1, Bd7, Be2, Be3, Ce4, and Cg1 did not allow enough growth to form transplantable ovaries; l(2)37Bg1, Bg2, and Cgts1 prevented development of transplanted ovaries in their hosts; l(2)37Ce5 allowed implanted ovaries to attach to oviducts and grow, but insufficiently for production of eggs; and DdcN27, amd29, and l(2)37Bd4 appeared not to restrict ovary development. Heteroallelic heterozygotes of Bd7 x Bd4 also produced fully fertile ovaries, but no other heteroallelic combinations did so.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in the activities of tyrosinase, N-acetyltransferase, and tyrosine aminotransferase in immune reactive larvae of Drosophila melanogaster

The activities of three enzymes, tyrosinase (monophenol oxidase, MPO), N-acetyltransferase (NAT), and tyrosine aminotransferase (TAT), were studied during eumelanotic encapsulation in host larvae of Drosophila melanogaster parasitized by the wasp, Leptopilina boulardi. At 24 h postinfection there was a tenfold increase in the MPO, whereas the activities of NAT and TAT were lower than those of nonparasitized controls. The data suggest that certain developmental processes are temporarily interrupted and alterations made in the metabolism of tyrosine to provide the metabolites necessary for a successful immune response. Two strains of D. melanogaster, R and Tyr-1, were parasitized and found to be immune reactive. The Tyr-1 strain is deficient in tyrosinase during the adult stage, but this mutation was found not to affect the immune capacity of the larvae. This is the first study to document concurrent alterations in the activities of various catecholamine-metabolizing enzymes during an immune response in an insect.

Vitelline membrane biogenesis in Drosophila requires the activity of the alpha-methyl dopa hypersensitive gene (I(2)amd) in both the germline and follicle cells

The vitelline membrane of Drosophila eggs is composed of a family of proteins which are cross linked into an insoluble matrix with an overlying waxy layer that prevents desiccation. We present here three sets of experiments which show that integrity of the vitelline membrane requires the activity of the alpha methyl dopa hypersensitive (I(2)amdH or amd) gene in both egg chambers and follicle cells. We show that loss of amd activity either by dietary administration of inhibitors or in genetic mosaics of either the germ line or follicle cells leads to production of defective vitelline membranes and by in situ hybridization, that amd is expressed in both nurse cells and follicle cells. The amd gene product is the first non-structural protein gene described whose activity is required for vitelline membrane biosynthesis. Given its unique role in insects and its demonstrated sensitivity to dietary inhibitors, the amd gene product poses an attractive target for insect control.

Reduced cellular immune competence of a temperature-sensitive dopa decarboxylase mutant strain of Drosophila melanogaster against the parasite Leptopilina boulardi

1. The melanotic encapsulation response made by larvae of a temperature-sensitive dopa decarboxylase (DDC) mutant strain of Drosophila against the parasitic wasp Leptopilina was severely compromised in hosts with reduced levels of DDC. 2. Dopa and 5,6-dihydroxyindole (DHI) were two hemolymph components identified in hosts exhibiting a melanotic encapsulation response. 3. This is the first study to implicate DDC in insect cellular immune responses, and to provide chemical evidence that the pigment formed during such responses is eumelanin derived from tyrosine.

Developmental expression and spatial distribution of dopa decarboxylase in Drosophila

Regulation of the dopa decarboxylase gene of Drosophila has been studied at the genetic and molecular levels. Here we report a direct assay for the tissue and temporal regulation of Ddc. A dopa decarboxylase (DDC) peptide was obtained by bacterial expression of a portion of the DDC gene in a pUC plasmid. Antisera raised against this biologically purified DDC peptide react specifically with Drosophila DDC in histological preparations and protein blots. The levels of DDC cross-reacting material closely parallel the levels of enzyme activity observed during development, indicating that DDC is degraded during periods of declining activity. We find that DDC is expressed in only two tissues, namely, the epidermis and the nervous system of the larva and adult. Epidermal DDC was found within the epidermal cells and was not detected in the overlying cuticle. DDC-containing neurons were observed in the central as well as in the visceral nervous system. Paired and unpaired midline neurons in the ventral ganglia are arranged in a segmental pattern. A subset of the DDC-positive neurons appears to correlate with the serotonin-positive neurons suggesting that the others are producing only dopamine. We find that the DDC activity associated with the proventriculus and ovary is due to the presence of DDC in the stomatogastric and caudal system neurons specifically associated with those structures.

A genetic analysis of glutamatergic function in Drosophila

Neurotransmitters are essential for communication between neurons and hence are vital in the overall integrative functioning of the nervous system. Previous work on acetylcholine metabolism in the fruit fly, Drosophila melanogaster, has also raised the possibility that transmitter metabolism may play a prominent role in either the achievement or maintenance of the normal structure of the central nervous system in this species. Unfortunately, acetylcholine is rather poorly characterized as a neurotransmitter in Drosophila; consequently, we have begun an analysis of the role of glutamate (probably the best characterized transmitter in this organism) in the formation and/or maintenance of nervous system structure. We present here the results of a series of preliminary analyses. To suggest where glutamatergic function may be localized, an examination of the spatial distribution of high affinity [3H]-glutamate binding sites are presented. We present the results of an analysis of the spatial and temporal distribution of enzymatic activities thought to be important in the regulation of transmitter-glutamate pools (i.e., glutamate oxaloacetic transaminase, glutaminase, and glutamate dehydrogenase). To begin to examine whether mutations in any of these functions are capable of affecting glutamatergic activity, we present the results of an initial genetic analysis of one enzymatic function, glutamate oxaloacetic transaminase (GOT), chosen because of its differential distribution within the adult central nervous system and musculature.

Developmental control of transduced dopa decarboxylase genes in D. melanogaster

Seventeen new euchromatic integration sites of the dopa-decarboxylase gene (Ddc) have been generated using p-mediated transduction. The developmental expression of the integrated genes was examined by monitoring the embryonic induction of dopa decarboxylase enzyme activity (DDC) and by monitoring the developmental pattern of DDC activity from late third instar to eclosion. The majority of inserts are regulated correctly within about 30% of controls. Several cases of multiple insertion events were recovered and these show correspondingly elevated levels of activity and are regulated normally. The pattern of expression of one insert (15C) falls outside the normal range. Multiple copies of transduced Ddc genes are used to test for effects of elevated gene dose on levels of expression. One insert on the X chromosome shows little or no dosage compensation. Possible reasons for the differences between the regulation of transduced genes in Drosophila and the regulation of transformed genes in mammalian systems are discussed.

An analysis of dopa decarboxylase expression during embryogenesis in Drosophila melanogaster

Dopa decarboxylase (DDC) activity appears near the end of embryogenesis in Drosophila. High titers of 20-OH-ecdysone on the other hand are found at midembryogenesis. Several explanations for this lag were investigated, since this hormone has been shown to induce a rapid increase in DDC activity at pupariation (G. P. Kraminsky, W. C. Clark, M. A. Estelle, R. D. Gietz, B. A. Sage, J. D. O'Connor, and R. B. Hodgetts, 1980, Proc. Natl. Acad. Sci. USA 77, 4175-4179). Using immunological and genetical criteria, it was shown that the same structural gene encodes DDC in embryos, mature larvae, and young adults. This rules out the existence of a distinct embryonic DDC gene unresponsive to 20-OH-ecdysone. Second, no evidence was found to support the hypothesis that a delay in the translation of DDC transcripts, produced in response to the elevated titer of 20-OH-ecdysone at midembryogenesis, caused the lag. Northern analysis of the RNA molecules homologous to cloned genomic sequences revealed that DDC transcripts were present at two different times during embryogenesis. A transcript was found in both ovaries and 0- to 2-hr embryos. However, this species disappeared by 4 hr and DDC transcript levels remained low until late in embryogenesis, when a significant increase occurred. This increase was presumably responsible for the appearance of the enzyme at this time. The northern blotting revealed nine DDC transcript species were present during embryogenesis and hybridization to intron-specific probes indicated that five of these contained at least part of one (or both) of the two introns. Three putative mature mRNA species were identified by their small size, relative abundance, apparent lack of intron sequence, and their presence on polysomes. The two mature species found during the late stages were postulated to differ in the length of their poly(A)+ tails. The third mature species was found only in ovaries and very young embryos and may well be of maternal origin. Data are examined in light of the possibility that this species is derived from a precursor initiated at a novel promotor.

Identification of a cholinergic synapse in the giant fiber pathway of Drosophila using conditional mutations of acetylcholine synthesis

Temperature-sensitive mutations of the choline acetyltransferase (Cha) gene, which lead to reduced choline acetyltransferase (ChAT) activity and acetylcholine (ACh) levels, have been used in an attempt to identify the neurotransmitter at a chemical synapse in the giant fiber pathway (GFP) of Drosophila melanogaster. Prolonged incubation of adult mutant flies at non-permissive temperatures blocked the response of this pathway to brain stimulation, whereas shorter incubation times disturbed various parameters of the normal response. Even at permissive temperature subnormal responses were still evident. These defects in the giant fiber pathway's function suggest a specific cholinergic synapse within the pathway, the first synapse of this type implicated in Drosophila. When the function of this synapse was experimentally stressed, disruptions of GFP function paralleling decreased ChAT activity began to appear at enzyme levels estimated to be approximately 80% of wild-type.

Genetics of the nervous system in Drosophila

The genetic analysis ofDrosophilaneurobiology has expanded into a considerable field. A host of genetic variants is now available for analyzing the development, structure, physiology, and chemistry of the fly's excitable cells and tissues and how they control the animal's behavior.

The genetics of dopa decarboxylase in Drosophila melanogaster. IV. The genetics and cytology of the 37B10-37D1 region

Of 204 mutations located in the 8-12 band Df(2L)130 region, 37B9-C1,2;37D1-2, 199 have been assigned to twelve lethal genes and one visible gene (hook). The 13 genes are not evenly distributed. Twelve, (possibly all thirteen) are in the seven band region 37B10-C4 giving a gene-to-band ratio of almost two. Only one gene, 1(2)37Cf, may be in the four band region 37C5-7, and none are localized in band 37D1. In situ hybridization places the dopa decarboxylase structural gene, Ddc, in or very close to band 37C1,2 (Hirsh and Davidson, 1981). The chi methyl dopa hypersensitive gene, 1(2) and, is 0.002 map units distal to Ddc. Df(2L)VA17, 37C1,2; 37F5-38A1 may actually break in the 37C1,2 singlet. It places six genes, hook, 1(2) and, and four lethal genes, in a maximum of five bands, 37B10, 11, 12, 13 and perhaps part of the 37C1,2 singlet and localizes six genes, Ddc plus five lethal genes, in a maximum of three bands; probably part of the 37C1,2 singlet plus bands, C3, and C4. Wild type activity of five of twelve lethal genes is necessary for female fertility. --Band 37C5 puffs at the time of pupariation; Puff Stages 8-10. Twelve of eighteen alleles of 1(2)37Cf have been examined as heterozygotes over CyO and none affect the appearance of a homozygous 37C5 puff. --Of the 204 mutations considered here only one Ddcpl, affects the function of more than one gene. It eliminates Ddc+ and 1(2)37Ca+ function and at 30 degrees C reduces 1(2)37Ce+ function. It is not a deficiency but could be a polar mutant.