The lysozyme locus in Drosophila melanogaster: an expanded gene family adapted for expression in the digestive tract

Adult midgut expressed sequence tags from the tsetse fly Glossina morsitans morsitans and expression analysis of putative immune response genes

BACKGROUND

Tsetse flies transmit African trypanosomiasis leading to half a million cases annually. Trypanosomiasis in animals (nagana) remains a massive brake on African agricultural development. While trypanosome biology is widely studied, knowledge of tsetse flies is very limited, particularly at the molecular level. This is a serious impediment to investigations of tsetse-trypanosome interactions. We have undertaken an expressed sequence tag (EST) project on the adult tsetse midgut, the major organ system for establishment and early development of trypanosomes.

RESULTS

A total of 21,427 ESTs were produced from the midgut of adult Glossina morsitans morsitans and grouped into 8,876 clusters or singletons potentially representing unique genes. Putative functions were ascribed to 4,035 of these by homology. Of these, a remarkable 3,884 had their most significant matches in the Drosophila protein database. We selected 68 genes with putative immune-related functions, macroarrayed them and determined their expression profiles following bacterial or trypanosome challenge. In both infections many genes are downregulated, suggesting a malaise response in the midgut. Trypanosome and bacterial challenge result in upregulation of different genes, suggesting that different recognition pathways are involved in the two responses. The most notable block of genes upregulated in response to trypanosome challenge are a series of Toll and Imd genes and a series of genes involved in oxidative stress responses.

CONCLUSIONS

The project increases the number of known Glossina genes by two orders of magnitude. Identification of putative immunity genes and their preliminary characterization provides a resource for the experimental dissection of tsetse-trypanosome interactions.

Asymmetric sequence divergence of duplicate genes

Much like humans, gene duplicates may be created equal, but they do not stay that way for long. For four completely sequenced genomes we show that 20%-30% of duplicate gene pairs show asymmetric evolution in the amino acid sequence of their protein products. That is, one of the duplicates evolves much faster than the other. The greater this asymmetry, the greater the ratio Ka/Ks of amino acid substitutions (Ka) to silent substitutions (Ks) in a gene pair. This indicates that most asymmetric divergence may be caused by relaxed selective constraints on one of the duplicates. However, we also find some candidate duplicates where positive (directional) selection of beneficial mutations (Ka/Ks > 1) may play a role in asymmetric divergence. Our analysis rests on a codon-based model of molecular evolution that allows a test for asymmetric divergence in Ka. The method is also more sensitive in detecting positive selection (Ka/Ks > 1) than models relying only on pairwise gene comparisons.

Lysozyme from the gut of the soft tick Ornithodoros moubata: the sequence, phylogeny and post-feeding regulation

Sequence of a tick gut lysozyme (TGL) from the soft tick Ornithodoros moubata was determined by cloning and sequencing of overlapping polymerase chain reaction (PCR) and RACE PCR products. It is the first lysozyme sequence representing the subphylum Chelicerata. The resulting open reading frame codes for a putative signal peptide of 22 amino-acid residues and a mature protein composed of 124 amino-acids. Calculated mass of the protein is 14037.75 Da and a theoretical isoelectric point is 8.16. The phylogenetic analysis revealed that the TGL belongs to the c-type lysozymes. It forms a distinct monophyletic group together with multiple lysozyme-like sequences found in the gene products agCP6542 from Anopheles gambiae strain PEST and CG8492-PA from Drosophila melanogaster. This group is referred to as an H-branch due to a unique histidine residue at position 52 which replaces the highly conserved tyrosine present in the vast majority of c-type lysozymes. TGL seems to be an interesting case in which the features of lysozymes with anti-bacterial and digestive function are combined. Semi-quantitative RT-PCR and Northern blotting analysis demonstrated that TGL is strongly up-regulated at the transcriptional level after a bloodmeal. The maximum lysozyme mRNA level was detected 16 h post bloodmeal and the message remained stable for 5 days and then it slowly dropped down to the level of non-fed ticks within 2 weeks.

Lysozyme of the beet armyworm, Spodoptera exigua: activity induction and cDNA structure

Lysozyme of the beet armyworm, Spodoptera exigua, was characterized in its up-regulation pattern, and its cDNA was cloned by RT-PCR using degenerate primers designed from some conserved amino acid regions shared with related lepidopteran species. Lysozyme activity of the non-immunized S. exigua had developmental variation, with the highest level in the fifth instar larvae. The basal level of the lysozyme activity was significantly enhanced by the injection of laminarin or lipopolysaccharide (LPS). Among different LPSs tested, the extract from an entomopathogenic bacterium, Xenorhabdus nematophilus, proved to be the most potent. Fat body was the major tissue to express the lysozyme in S. exigua. Even though there was a significantly elevated level of lysozyme in the hemolymph at 12 h after laminarin injection, the transcript ( approximately 1.1 kbp) was found in the fat body as early as 6 h after injection. The cDNA of the lysozyme was cloned as 602 bp with a deduced 141-amino-acid residue open reading frame containing two introns. Except for a signal peptide with 20 amino acid residues, the estimated molecular weight and isoelectric point of the lysozyme was 14313.83 Da and 8.59, respectively. Only a single copy gene of the lysozyme was found in S. exigua genome from Southern analysis. The amino acid sequence of S. exigua lysozyme showed higher similarity (88.7%) with noctuid species compared to other lepidopteran species.

Isolation and characterization of a cDNA encoding for a lysozyme from the gut of the reduviid bug Triatoma infestans

We have isolated and characterised a Triatoma infestans cDNA encoding a lysozyme. A 174-bp fragment was amplified by PCR using degenerate oligodeoxyribonucleotide primers derived from the known amino acid sequences of lysozyme from other insects. This PCR fragment was used to screen a cDNA gut library of T. infestans. A clone containing the 3'-end of the lysozyme cDNA (219 bp) was isolated and sequenced. RACE was used to amplify the 5'-end of the lysozyme cDNA. After sequencing the complete lysozyme cDNA, the deduced 417 amino acid sequence showed high identity (40-50%) with other chicken-type lysozymes. The amino acid residues responsible for the catalytic activity and the binding of the substrate were essentially conserved. The expression pattern of the lysozyme gene in bugs at different molting and feeding states showed that this gene was upregulated in the digestive tract directly after the molt and after feeding. Additionally, this lysozyme gene was expressed differently in the different regions of the digestive tract, strongly in the cardia and stomach, the anterior regions of the midgut, and only traces of lysozyme mRNA could be detected in the small intestine, the posterior region of the midgut.

Characterization and cDNA cloning of an immune-induced lysozyme from cultured Aedes albopictus mosquito cells

Protein chemistry and cDNA sequencing were used to identify an Aedes albopictus mosquito lysozyme secreted after treatment of cultured cells with heat-killed bacteria. On acid gels, the putative lysozyme activity ran just ahead of the cecropin band. Elution of this activity yielded a single band on SDS gels, with a mass of approximately 14 kDa. Mass spectral analysis of the silver-stained band uncovered five tryptic peptides with masses that matched peptides from an Aedes aegypti lysozyme, which we had previously characterized from the Aag-2 mosquito cell line. Based on this tentative identification, the Ae. albopictus lysozyme cDNA was cloned using PCR-based approaches. The full length cDNA sequence was used to deduce the sequences and masses of theoretical tryptic peptides that would be detected after matrix-assisted laser desorption ionization time of flight (MALDI-TOF) and tandem mass spectrometry (MS/MS). In aggregate, this analysis uncovered seven peptides that encoded 75 of the 125 amino acids in the mature Ae. albopictus lysozyme. In a phylogenetic analysis, the Aedes lysozymes were most closely related to the Anopheles lysozymes. As a group the mosquito lysozymes were more closely related to lysozymes from various Lepidopteran species than to those from higher Diptera such as Drosophila and Musca, which have evolved a digestive function.

Molecular cloning of lysozyme-encoding cDNAs expressed in the salivary gland of a wood-feeding termite, Reticulitermes speratus

Two kinds of PCR-product cDNAs that encode premature lysozyme peptides (Rs-Lys1 and Rs-Lys2) were cloned from workers of a Japanese damp-wood termite, Reticulitermes speratus. The Rs-Lys1 and Rs-Lys2 cDNAs encoded deduced sequences of 170 and 164 amino acids, respectively. Alignment of these sequences with those of other insect lysozymes showed that the cDNAs encode lysozyme homologues with putative signal peptides, insertions eight amino acids long, and a relatively long C-terminus (13-17 amino acids). A maximum likelihood tree, constructed using the cDNA sequences, indicated that the termite lysozymes are related to those of mosquitoes and lepidopterans. Southern-blotting analysis identified single copies of these lysozyme genes in the termite. Reverse transcript (RT)-PCR and in situ hybridization experiments showed that Rs-Lys1 and Rs-Lys2 are expressed in the salivary glands of worker termites. Here, we discuss the possible digestive function of these lysozymes.

Localization of Der f 2 in the gut and fecal pellets of Dermatophagoides farinae

BACKGROUND

House dust mite derived materials are known to be the most potent agent inducing allergic diseases. Localization of Der f 2 was attempted to specify the sites and concentrations of Der f 2 within the mite, which may indicate the importance of secreted materials and nonexcreted body components as allergen sources.

METHODS

Serial cryostat sections of embedded live mites and the fecal pellets, collected by brush, were immunoprobed using monoclonal antibody (mAb) 2F38 raised against recombinant (r) Der f 2.

RESULTS

Highest concentrations were found in the anterior midgut, implying that this is the site of Der f 2 synthesis and secretion. Digestive material and defecated fecal pellets were also labeled with mAb.

CONCLUSIONS

Our results show that the major allergen, Der f 2, found in the house dust mite D. farinae is derived from the digestive tract, and is concentrated in the feces.

Gliogenesis inDrosophila: genome-wide analysis of downstream genes ofglial cells missingin the embryonic nervous system

In Drosophila, the glial cells missing (gcm) gene encodes a transcription factor that controls the determination of glial versus neuronal fate. In gcm mutants, presumptive glial cells are transformed into neurons and, conversely, when gcm is ectopically misexpressed, presumptive neurons become glia. Although gcm is thought to initiate glial cell development through its action on downstream genes that execute the glial differentiation program, little is known about the identity of these genes. To identify gcm downstream genes in a comprehensive manner, we used genome-wide oligonucleotide arrays to analyze differential gene expression in wild-type embryos versus embryos in which gcm is misexpressed throughout the neuroectoderm. Transcripts were analyzed at two defined temporal windows during embryogenesis. During the first period of initial gcm action on determination of glial cell precursors, over 400 genes were differentially regulated. Among these are numerous genes that encode other transcription factors, which underscores the master regulatory role of gcm in gliogenesis. During a second later period, when glial cells had already differentiated, over 1200 genes were differentially regulated. Most of these genes, including many genes for chromatin remodeling factors and cell cycle regulators, were not differentially expressed at the early stage, indicating that the genetic control of glial fate determination is largely different from that involved in maintenance of differentiated cells. At both stages, glial-specific genes were upregulated and neuron-specific genes were downregulated, supporting a model whereby gcm promotes glial development by activating glial genes, while simultaneously repressing neuronal genes. In addition, at both stages, numerous genes that were not previously known to be involved in glial development were differentially regulated and, thus, identified as potential new downstream targets of gcm. For a subset of the differentially regulated genes, tissue-specific in vivo expression data were obtained that confirmed the transcript profiling results. This first genome-wide analysis of gene expression events downstream of a key developmental transcription factor presents a novel level of insight into the repertoire of genes that initiate and maintain cell fate choices in CNS development.

Regulation of midgut defensin production in the blood-sucking insect Stomoxys calcitrans

The Stomoxys midgut defensin (Smd) family of genes are exclusively expressed in the anterior midgut of adult flies. Their putative function is protection of the stored bloodmeal from microbial attack. Smd genes are constitutively expressed, up-regulated in response to a bloodmeal and further up-regulated by immune stimulation per os but only in the presence of a bloodmeal not a sugar meal. Smd genes are down-regulated in response to a systemic immune challenge. Smd gene constructs transfected into l(2)mbn cells undertake constitutive expression but are not up-regulated by immune challenge. Electrophoretic mobility shift assays (EMSA) suggest the rel-like sites in the proximal promoter region of Smd genes do not bind midgut factors and so are non-functional.

Genome-wide analysis of the Drosophila immune response by using oligonucleotide microarrays

To identify new Drosophila genes involved in the immune response, we monitored the gene expression profile of adult flies in response to microbial infection by using high-density oligonucleotide microarrays encompassing nearly the full Drosophila genome. Of 13,197 genes tested, we have characterized 230 induced and 170 repressed by microbial infection, most of which had not previously been associated with the immune response. Many of these genes can be assigned to specific aspects of the immune response, including recognition, phagocytosis, coagulation, melanization, activation of NF-kappaB transcription factors, synthesis of antimicrobial peptides, production of reactive oxygen species, and regulation of iron metabolism. Additionally, we found a large number of genes with unknown function that may be involved in control and execution of the immune response. Determining the function of these genes represents an important challenge for improving our knowledge of innate immunity. Complete results may be found at http://www.fruitfly.org/expression/immunity/.

Molecular cloning, expression and evolution of the Japanese flounder goose-type lysozyme gene, and the lytic activity of its recombinant protein

In this study, we cloned the goose-type (g-type) lysozyme gene from the Japanese flounder genomic DNA library, the first such data in fish and only the second after the chicken g-type lysozyme gene. The Japanese flounder g-type lysozyme gene was 1252 bp in length from the transcription site to the polyadenylation site, coded for 758 bp of mRNA and 195 deduced amino acids, which contain five exons and four introns. A phylogenetic analysis based on amino acid sequences showed that the flounder gene was closer to g-type lysozyme, followed by phage-type lysozyme and then chicken-type (c-type) lysozyme. Although exon 1 of the flounder gene differs from exons 1 and 2 of the chicken g-type lysozyme gene, three catalytic residues, as well as their neighboring amino acids were conserved between the Japanese flounder and the four avian g-type lysozymes. In a Southern blot analysis using the genomic DNA of homo-cloned Japanese flounder, the flounder g-type lysozyme gene showed a simple pattern, suggesting that it is encoded by a single copy gene. A Northern blot analysis showed that this gene was expressed in all tissues of Japanese flounder that we examined in this study and showed major differences from those expressed tissues of the chicken g-type gene. Japanese flounder g-type lysozyme mRNA levels in the intestine, heart and whole blood increased after injecting the fish with Edwardsiella tarda. Recombinant flounder g-type lysozyme, which has an optimal pH and temperature of pH 6.0 and 25 degrees C, possessed lytic activity against Micrococcus lysodeikticus and several fish pathogenic bacteria. This is the first report of a g-type lysozyme gene other than for reported avian species.

The gene of chlamysin, a marine invertebrate-type lysozyme, is organized similar to vertebrate but different from invertebrate chicken-type lysozyme genes

In a recent publication we reported the protein purification, characterization, and the gene isolation of a cDNA encoding the antibacterial cold-active lysozyme-like protein chlamysin from the marine bivalve Chlamys islandica. A 4.2 kb genomic chlamysin gene has now been amplified and sequence-analyzed. By comparison to the cDNA sequence and its translation product, the coding region was found separated in four exons of 38-252 bp. The introns range in size from 0.8 to 1.5 kb, and have traditional spliceosomal intron 5'-GT donor and 3'-AG acceptor sites for splicing. Two of the introns contain multiple copies of three sequence motifs not found repeated in other published genes. The over-all gene organization of chlamysin resembles chicken-type (c-type) lysozyme genes in vertebrates, but is different from the three-exon structure in invertebrate c-type lysozyme genes. A phylogenetic analysis of invertebrate-type (i-type) and c-type lysozyme proteins demonstrated a large evolutionary distance between the i-type and the c-type enzyme classes. Exons of the i-type genes are not equally organized according to their homolog protein domains.

Immune activation upregulates lysozyme gene expression in Aedes aegypti mosquito cell culture

After stimulation with heat-killed bacteria, cultured cells from the mosquito Aedes aegypti (Aag-2 cells) secreted an induced protein with a mass of approximately 16 kDa that cross-reacted with antibody to chicken egg lysozyme. To investigate whether lysozyme messenger RNA is induced in bacteria-treated cells, we used polymerase chain reaction-based approaches to obtain the complete lysozyme cDNA from Aag-2 cells. The deduced protein contained 148 amino acids, including a 23 amino acid signal sequence. The calculated mass of the precursor protein is 16 965 Da, which is processed to yield a mature lysozyme of 14 471 Da with a calculated pI of 10.1. The lysozyme from Ae. aegypti shared 50% amino acid identity with lysozymes from Anopheles gambiae and Anopheles darlingi, which in turn shared 70% identity between each other. Northern analysis with the lysozyme cDNA probe showed induction of a 1.3 kb messenger RNA during the first 3 h after treatment of Aag-2 cells with heat-killed bacteria, followed by maximal expression 12-36 h after treatment. Southern analysis suggested that the gene likely occurs as a single copy in the genome of Aag-2 cells.

Genes that fight infection: what the Drosophila genome says about animal immunity

From deciphering the principles of heredity to identifying the genes that control development, the fruit fly Drosophila melanogaster is being used to deconstruct an increasing number of biological processes. Genetic studies of Drosophila responses to microbial infection have identified regulators of innate immunity that are functionally conserved in mammals. These recent findings highlight the ancient origins of animal immune responses and demonstrate the potential of Drosophila for dissecting host-pathogen interactions. The sequencing of the Drosophila genome both enhances genetic approaches and provides new clues for the identification of key components of innate immunity. This article summarizes how information gained from genomic analysis contributes to our understanding of how animals cope with infectious disease.

Cysteine-rich antimicrobial peptides in invertebrates

Antimicrobial peptides are pivotal elements of the innate immune defense against bacterial and fungal infections. Within the impressive list of antimicrobial peptides available at present, more than half have been characterized in arthropods. Cysteine-rich antimicrobial peptides represent the most diverse and widely distributed family among arthropods and, to a larger extent, among invertebrates. Proeminent groups of cysteine-rich peptides are peptides with the CS alpha beta motif and peptides forming an hairpin-like beta-sheet structure. Although these substances exhibit a large structural diversity and a wide spectrum of activity, they have in common the ability to permeabilize microbial cytoplasmic membranes. Drosophila has proved a remarkable system for the analysis of the regulation of expression of gene encoding antimicrobial cysteine-rich peptides. These studies have unraveled the striking parallels that exist between insect immunity and innate immunity in mammals that point to a common ancestry of essential aspects of innate immunity.

Purification and characterization of the lysozyme from the gut of the soft tick Ornithodoros moubata

The gut of the adult soft ticks Ornithodoros moubata displays high lytic activity against the bacteria Micrococcus luteus. The activity differed in the range of two orders of magnitude among individual animals and increased on average 4 fold during the first week following ingestion. In homogenates of first instar nymphs the activity was much lower increasing exponentially as nymphs neared the first molt. The protein responsible for this activity was purified out of gut contents of adult ticks by means of affinity adsorption on magnetic-chitin followed by two chromatography steps on cation exchange FPLC column MonoS. The homogeneous active protein has a mass of 14006 +/- 20 Daltons as determined by MALDI-TOF mass spectrometry. The N-terminal amino-acid sequence of this protein is K-V-Y-D-R-C-S-L-A-S-E-L-R with the highest similarity to the lysozyme from liver of rainbow trout and to lysozymes from digestive tracts of several mammals. The motif DRCSLA is specific for the digestive lysozymes of several dipteran insects. Based on this evidence, we have identified the protein as the tick gut lysozyme. The tick gut lysozyme has a pI near 9.7 and retains its full activity after treatment at 60 degrees C for 30 minutes. The pH optimum of the tick lysozyme was in the range from pH 5-7. Only marginal activity could be detected at pH > 8 which raises the question about the function of lysozyme in anti-bacterial defense in the environment of the tick gut.

Induction of carboxylesterase isozymes in Bombyx mori by E. coli infection

Many proteins, including antibacterial peptides in the hemolymph, are induced by bacterial infections. We found two bacterially inducible carboxylesterases (CEs) in the hemolymph of the silkworm, Bombyx mori. CEs Est-1 and 2 were induced by lipopolysaccharide injection after 6 hours as well as E. coli infection. We found that bacterially inducible CEs clearly differed from noninducible CEs, including juvenile hormone esterases, in pI values, migration on analytical native PAGE, and inhibitor sensitivity. We are now studying the features and functions of these CEs.

Antimicrobial and cytolytic polypeptides of amoeboid protozoa--effector molecules of primitive phagocytes

Amoebae are primitive, actively phagocytosing eukaryotic cells, many of which use bacteria as a major nutrient source. One may suppose that amoebae possess an array of potent antimicrobial molecules acting in synergy to combat bacterial growth inside their phagosomes. Lysosome-like granular vesicles of Entamoeba histolytica contain a family of 77-residue peptides with a compact alpha-helical, disulfide-bonded fold. These polypeptides, named amoebapores, exhibit antibacterial and cytolytic activity by forming pores in membranes of various origin. It is of particular interest that amoebapores are structurally and functionally most similar to polypeptides of mammalian cytotoxic lymphocytes. In addition, amoebic granules contain bacteriolytic proteins with lysozyme-like properties. Some amoebic polypeptides may represent archaic analogs of effector molecules from invertebrates and vertebrates.

The amino acid sequence of wood duck lysozyme

The amino acid sequence of wood duck (Aix sponsa) lysozyme was analyzed. Carboxymethylated lysozyme was digested with trypsin and the resulting peptides were sequenced. The established amino acid sequence had the highest similarity to duck III lysozyme with four amino acid substitutions, and had eighteen amino acid substitutions from chicken lysozyme. The valine at position 75 was newly detected in chicken-type lysozymes. In the active site, Tyr34 and Glu57 were found at subsites F and D, respectively, when compared with chicken lysozyme.

Identification and characterization of kraken, a gene encoding a putative hydrolytic enzyme in Drosophila melanogaster

Kraken, a novel Drosophila gene isolated from a 4-8-h-old Drosophila embryo cDNA library, shows homology to a family of serine hydrolases whose common feature is that they all catalyse breakage of substrates with a carbonyl-containing group. It is a single-copy gene with at least two introns and maps to position 21D on polytene chromosomes. kraken is a member of a conserved gene family. Messenger RNA of kraken is expressed ubiquitously in early embryogenesis. Later, it is concentrated in the foregut and the posterior midgut primordium. Towards the end of embryogenesis, expression of kraken is confined to the gastric caeca. During the third-instar larval stage, kraken is expressed at low levels in the gastric caeca and parts of the gut, and at higher levels in the fat body. We suggest a role for Kraken in detoxification and digestion during embryogenesis and larval development.

Molecular characterization of an exceptionally acidic lysozyme-like protein from the protozoon Entamoeba histolytica

The protozoan parasite Entamoeba histolytica contains a second antibacterial protein with lysozyme-like properties. The newly recognized bacteriolytic protein was purified from extracts of amoebic trophozoites to allow amino-terminal sequencing. Subsequent molecular cloning revealed that it is an isoform of the amoeba lysozyme described previously but also demonstrated a substantial sequence divergence of the two forms. As lysozymes typically are basic proteins, the novel amoebic protein differs markedly in having a pI of 4.5. There is no significant similarity of both amoeba lysozymes with any bacteriolytic protein of other organisms reported so far; however, striking sequence identity is found with predicted gene products of unknown function derived from the bacteria-feeding nematode Caenorhabditis elegans.

The amino acid sequence of monal pheasant lysozyme and its activity

The amino acid sequence of monal pheasant lysozyme and its activity were analyzed. Carboxymethylated lysozyme was digested with trypsin and the resulting peptides were sequenced. The established amino acid sequence had one amino acid substitution at position 102 (Arg to Gly) comparing with Indian peafowl lysozyme and four amino acid substitutions at positions 3 (Phe to Tyr), 15 (His to Leu), 41 (Gln to His), and 121 (Gln to His) with chicken lysozyme. Analysis of the time-courses of reaction using N-acetylglucosamine pentamer as a substrate showed a difference of binding free energy change (-0.4 kcal/mol) at subsites A between monal pheasant and Indian peafowl lysozyme. This was assumed to be caused by the amino acid substitution at subsite A with loss of a positive charge at position 102 (Arg102 to Gly).

The genes encoding the antibacterial sex-specific peptides ceratotoxins are clustered in the genome of the medfly Ceratitis capitata

Ceratotoxins are antibacterial peptides produced in the female reproductive accessory glands of the medfly Ceratitis capitata. Their expression is not affected by bacterial infection, but is enhanced after mating and is modulated by juvenile hormone. Three different peptides, named ceratotoxins A, B and C, have been previously purified from the female accessory gland secretion and their amino acid and cDNA sequences have been determined. We report here the complete nucleotide sequences of four genes encoding closely related ceratotoxin peptides. One of them encodes a novel peptide, which we named ceratotoxin D. Restriction and nucleotide sequence analysis indicate that these ceratotoxin genes are organized in a large cluster spanning more than 26 kilobases of DNA. All ceratotoxin genes are coordinately expressed. Ceratotoxin transcripts appear in 2-3 day old adult females, and they reach a maximum in 6-7 day old females. The presence of highly conserved motifs in the upstream regions of all the sequenced ceratotoxin genes suggests the presence of common regulatory elements for all ceratotoxins.

Protein purification and nucleotide sequence of a lysozyme from the bacteria-induced larvae of the fall webworm, Hyphantria cunea

A protein with lytic activity against Micrococcus luteus was purified from the hemolymph of the fall webworm, Hyphantria cunea, larvae challenged with live E. coli. A bacteriolytic protein of about 14,000 daltons in mass was purified by cation exchange chromatography and reverse-phased HPLC. The optimum pH and optimum temperature range for activity were around pH 6.2 and 50 degrees C, respectively, in a 100 mM phosphate buffer. The amino-terminal amino acid sequence of this protein was determined and the corresponding cDNA was isolated and analyzed. The deduced protein of 142 amino acid residues was composed of a putative leader sequence of 20 residues and the mature enzyme of 122 residues. The cloned lysozyme gene was strongly induced in response to bacterial injection, implying that the enzyme is a part of the immune response of H. cunea. Comparison with other known lysozyme sequences shows that our lysozyme belongs to the chicken lysozyme.

Structural deviations in a bovine low expression lysozyme-encoding gene active in tissues other than stomach

Lysozyme-encoding genes (Lys) constitute a gene-family in ruminants. While several of these genes are highly expressed in stomach (sLys), few other copies are weakly expressed in other tissues, notably in polymorphnuclear granulocytes and macrophages (mLys). Searching an understanding for these grossly different levels of expression, we isolated the bovine variant of the gene being expressed in granulocytes and characterized it by sequencing, together with its promoter. Spanning about 9 kb of genomic DNA, the gene is found to be segmented into four exons, in common with all other Lys, as known from vertebrates. Sequence homologies between all bovine sLys-variants exceeds 70% over much of the entire coding sequence and promoter region. This indicates (i) that bovine lysozymes expressed either in stomach or granulocyte originate from a common ancestral gene and (ii) also excludes the possibility that the observed weak expression of the mLys gene is due to major structural rearrangements within the promoter segment. However, primer extension analysis based on RNA isolated from kidney locates the transcription startpoint (tsp of that gene) 44 nt further upstream than observed in both, bovine stomach lysozyme RNA or any of the homologous genes in mice and man. The observed weak expression of this bovine mLys gene appears to be a consequence of both the presence of an extra ATG codon in the extended 5'-UTR, and a severe down mutation of the ancestral TATA-box which is only partially compensated for by the presence of another mutation further upstream resulting in a weak substitute promoter sequence.

Molecular characterization of ceratotoxin C, a novel antibacterial female-specific peptide of the ceratotoxin family from the medfly Ceratitis capitata

Ceratotoxins A and B are antibacterial peptides produced by the sexually mature females of Ceratitis capitata. The gene expression is restricted to the female reproductive accessory glands, and is not affected by bacterial infection, but is enhanced by mating. We report here the purification and the amino acid sequence of ceratotoxin C, a novel member of the ceratotoxin family, the cloning of its cDNA and the analysis of its expression. Ceratotoxin C is coordinately expressed with the other members of the ceratotoxin family. Its antibacterial activity is directed against both Gram-negative and Gram-positive bacterial strains but it is lower than that of ceratotoxin A. We demonstrate in the genome of C. capitata the presence of at least three ceratotoxin genes which express, in the female accessory glands, a set of peptides presumably involved in the protection of the genital tract during fertilization.

Analysis of a lysozyme gene from the malaria vector mosquito, Anopheles gambiae

A genomic DNA sequence encoding a basic lysozyme was isolated from the malaria vector mosquito Anopheles gambiae by screening a library with a probe prepared by PCR of reverse transcribed adult RNA. The sequence consists of an upstream region of about 2 kb, a coding region containing three exons and two introns, and a short 3' untranslated region. The coding region indicates that this mosquito lysozyme consists of a signal peptide of 20 residues followed by an 120 aa mature protein which is very similar to other basic lysozymes. The two small introns, 67 and 76 bp, are located at evolutionarily conserved sites. RT-PCR indicated that this gene is expressed abundantly in sugar-fed adults, and at considerably lower levels when females have fed on blood. Although it remains to be seen whether this gene is induced by bacterial infection, the surrounding sequence contains six sequence motifs very similar to the consensus binding sites for a transcription factor similar to NF-kappa B that are found associated with most insect immune response genes. This lysozyme gene maps to division 27 on the left arm of polytene chromosome 2L. An ORF unrelated to any animal protein in current data bases was found at the 5' end of the clone.

Molecular cloning of an alpha-esterase gene cluster on chromosome 3r of Drosophila melanogaster

All or part of the alpha-esterase gene cluster in Drosophila melanogaster has been isolated by screening a YAC clone that spans cytological region 84D3-10 with consensus carboxyl/cholinesterase oligonucleotides. The cluster encompasses 11 putative esterase genes within 65 kb of genomic DNA and is one of the largest clusters of related protein-coding genes yet reported in Drosophila. The cluster must include the gene encoding the major alpha-esterase isozyme, EST9, which has previously been mapped to 84D3-5. It probably also includes the genes encoding the EST23, MCE and ALI esterases that have previously been mapped to 84D3-E2. The latter three are homologs of genes involved in organophosphate insecticide resistance in the sheep blowfly, Lucilia cuprina and the housefly, Musca domestica. Sequencing of one of the putative esterase genes in the Drosophila cluster, alpha E1, shows that it would encode features characteristic of an active carboxyl/cholinesterase, including the so-called catalytic triad, the nucleophilic elbow and oxyanion hole. It also shows that the closest relative of alpha E1 amongst previously published esterase sequences is ESTB1, which confers organophosphate resistance in Culex mosquitoes. We argue that we have cloned the D. melanogaster version of a major cluster of esterase genes which have variously mutated to confer organophosphate resistance in diverse Diptera.

Adaptive evolution of lysozyme: changes in amino acid sequence, regulation of expression and gene number

Adaptive evolution of lysozyme has involved remodelling of amino acid sequences and changes in patterns of gene expression and in gene number. Following an outline of the phenomena likely to be indicative of adaptive evolution and how one can assess them, this chapter focuses on four cases in which lysozyme c has been recruited as a digestive enzyme in the stomachs of creatures needing to retrieve nutrients from microorganisms in fermented food. For each case-ruminant artiodactyls, leaf-eating monkeys, a leaf-eating bird, and fruit flies-the factors likely to be of primary importance in lysozyme's adaptation are examined. Additional examples of apparent adaptation for digestion or antimicrobial defense in animals as diverse as mice, moths, and molluscs are summarized. This chapter considers also the case of three internally clustered residues which among galliform bird lysozymes c occur either as Thr 40, Ile 55, and Ser 91 (TIS) or as Ser 40, Val 55, and Thr 91 (SVT). Reconstruction and testing of six possible intermediate proteins and development of the concept of a neutral corridor of protein traits are described.

Insect lysozymes

Lysozymes, related to the chicken-type lysozymes in vertebrates, are ubiquitous components in the bacteriolytic armamentarium of insects. The enzyme is normally present in the blood, and together with other bactericidal factors lysozyme is often strongly induced when the insect is infected. This response is regulated by mechanisms that are related to those that activate inflammatory, acute-phase and immune responses in mammals, and the induction of lysozyme and other factors is now being investigated as a model for innate immune reactions in general. A special adaptation is seen in flies like Musca and Drosophila. These animals live on the microorganisms in decompositing matter, and they have developed a specialized set of lysozymes that are expressed in the alimentary tract. In Drosophila, at least seven different lysozyme genes are clustered in a small region on the third chromosome. The different genes are expressed in different parts of the digestive tract, and at different time points during development, and they are highly divergent in sequence. The major lysozymes in the fly gut have acidic isoelectric points and/or pH optima, and their evolution provides an interesting parallel to the ruminants.

Animal lysozymes c and g: an overview

Amino acid sequences for 88 distinct lysozymes c, obtained from members of four vertebrate classes and two orders of insects, are summarized. A model for the relationships and origins of major lineages within the lysozyme c superfamily-which consists of conventional lysozymes c, calcium-binding lysozymes c, and alpha-lactalbumin-is presented and supported by evolutionary analyses. Pioneering events in the discovery and sequencing of lysozymes c are traced, and salient contributions to knowledge made by sequences from various kinds of animals highlighted. A summary of the four known amino acid sequences of bird lysozymes g and an outline of the investigations on this very different kind of vertebrate lysozyme are provided. Areas of future research aimed at further elucidating early events in the evolutionary history of the lysozyme c superfamily and at understanding differences in patterns of lysozyme gene expression are outlined.

Isolation, cultivation, and partial characterization of the ELB agent associated with cat fleas

ELB rickettsiae from cat flea homogenates were recovered in tissue culture cells following sequential passage through laboratory rats and the yolk sacs of embryonated chicken eggs. Seven days after inoculation of ELB from the infected yolk sacs, Vero cells and L929 cells were observed to contain intracellular bacteria as demonstrated by Diff Quik and indirect immunofluorescence assay staining. The rickettsial and ELB identity of the cultured agent was confirmed by PCR detection of the 16S rRNA and citrate synthase genes and PCR-restriction fragment length polymorphism analysis of the 17-kDa conserved rickettsial antigen gene. The ELB rickettsiae induced plaques in Vero cells on day 11 postinfection. Rat anti-ELB serum reacted at 1:4,096 to cultured ELB and had lower reactivity to Rickettsia typhi Wilmington (1:1,024), Rickettsia akari Kaplan (1:512), and Rickettsia australis JC (1:64). Spotted fever group polyclonal sera also exhibited lower reactivity to ELB than to the homologous antigen. Coomassie blue-stained sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of the ELB isolate and two R. typhi strains were identical.

Isolation and characterization of the lysozyme-encoding gene from the silkworm Bombyx mori

We have isolated and characterized a Bombyx mori (Bm) cDNA encoding a lysozyme (Lyz). A 90-bp DNA fragment was amplified by PCR using degenerate oligodeoxyribonucleotide primers derived from the known amino acid (aa) sequence of the Bm Lyz. These PCR fragments were used to screen a fat body cDNA library. A clone containing the complete lys cDNA (1294 bp) was isolated and completely sequenced. The deduced 137-aa sequence showed high homology with other chicken-type Lyz. Bm lys gene expression was constitutive in fat body, cuticular epidermal tissue and at a very low level in hemocytes. This gene expression was up-regulated in fat body, hemocytes and cuticular epidermal tissue following the injection of Gram+ bacteria.

Innate immunity of insects

Insects are particularly resistant to microorganisms. Their host-defense system relies on several innate reactions: upon injury, the immediate onset of two proteolytic cascades leading to localized blood clotting and to melanization, the latter process involving production of cytotoxic molecules (namely reactive oxygen intermediates); the phagocytosis of bacteria and the encapsulation of larger parasites by blood cells; the induced synthesis by the fat body of a battery of potent antimicrobial peptides/polypeptides which are secreted into the hemolymph where they act synergistically to kill the invading microorganisms. The insect host defence system shares many of the basic characteristics of the mammalian acute phase response, especially at the level of the coordinate control of gene expression, where similar cis-regulatory and inducible transactivators appear to play key functions. The powerful techniques developed to study the genetics of Drosophila provide a unique opportunity to dissect the development and differentiation of this primordial immune system and may contribute to our understanding of the innate immune response in higher organisms.