Developmental expression of the glucose dehydrogenase gene in Drosophila melanogaster

Post-eclosion growth in the Drosophila ejaculatory duct is driven by Juvenile hormone signaling and is essential for male fertility

The Drosophila Ejaculatory duct (ED) is a secretory tissue of the somatic male reproductive system. The ED is involved in the secretion of seminal fluid components and ED-specific antimicrobial peptides that aid in fertility and the female post-mating response. The ED is composed of secretory epithelial cells surrounded by a layer of innervated contractile muscle. The ED grows in young adult males during the first 24 h post-eclosion, but the cell cycle status of the ED secretory cells and the role of post-eclosion ED growth have been unexplored. Here, we show that secretory cells of the adult Drosophila ED undergo variant cell cycles lacking mitosis called the endocycle, that lead to an increase in the cell and organ size of the ED post eclosion. The cells largely exit the endocycle by day 3 of adulthood, when the growth of the ED ceases, resulting in a tissue containing cells of ploidies ranging from 8C to 32C. The size of the ED directly correlates with the ploidy of the secretory cells, with additional ectopic endocycles increasing organ size. When endoreplication is compromised in ED secretory cells, it leads to reduced organ size, reduced protein synthesis and compromised fertility. We provide evidence that the growth and endocycling in the young adult male ED is dependent on Juvenile hormone (JH) signaling and we suggest that hormone-induced early adult endocycling is required for optimal fertility and function of the ED tissue. We propose to use the ED as a post-mitotic tissue model to study the role of polyploidy in regulating secretory tissue growth and function.

Post-eclosion growth in the Drosophila Ejaculatory Duct is driven by Juvenile Hormone signaling and is essential for male fertility

The Drosophila Ejaculatory duct (ED) is a secretory tissue of the somatic male reproductive system. The ED is involved in the secretion of seminal fluid components and ED-specific antimicrobial peptides that aid in fertility and the female post-mating response. The ED is composed of secretory epithelial cells surrounded by a layer of innervated contractile muscle. The ED grows in young adult males during the first 24h post-eclosion, but the cell cycle status of the ED secretory cells and the role of post-eclosion ED growth have been unexplored. Here, we show that secretory cells of the adult Drosophila ED undergo variant cell cycles lacking mitosis called the endocycle, that lead to an increase in the cell and organ size of the ED post eclosion. The cells largely exit the endocycle by day 3 of adulthood, when the growth of the ED ceases, resulting in a tissue containing cells of ploidies ranging from 8C-32C. The size of the ED directly correlates with the ploidy of the secretory cells, with additional ectopic endocycles increasing organ size. When endoreplication is compromised in ED secretory cells, it leads to reduced organ size, reduced protein synthesis and compromised fertility. We provide evidence that the growth and endocycling in the young adult male ED is dependent on Juvenile hormone (JH) signaling and we suggest that hormone-induced early adult endocycling is required for optimal fertility and function of the ED tissue. We propose to use the ED as a post-mitotic tissue model to study the role of polyploidy in regulating secretory tissue growth and function.

Honey Bee Larval Hemolymph as a Source of Key Nutrients and Proteins Offers a Promising Medium for Varroa destructor Artificial Rearing

Varroa destructor, a major ectoparasite of the Western honey bee Apis mellifera, is a widespread pest that damages colonies in the Northern Hemisphere. Throughout their lifecycle, V. destructor females feed on almost every developmental stage of their host, from the last larval instar to the adult. The parasite is thought to feed on hemolymph and fat body, although its exact diet and nutritional requirements are poorly known. Using artificial Parafilm™ dummies, we explored the nutrition of V. destructor females and assessed their survival when fed on hemolymph from bee larvae, pupae, or adults. We compared the results with mites fed on synthetic solutions or filtered larval hemolymph. The results showed that the parasites could survive for several days or weeks on different diets. Bee larval hemolymph yielded the highest survival rates, and filtered larval plasma was sufficient to maintain the mites for 14 days or more. This cell-free solution therefore theoretically contains all the necessary nutrients for mite survival. Because some bee proteins are known to be hijacked without being digested by the parasite, we decided to run a proteomic analysis of larval honey bee plasma to highlight the most common proteins in our samples. A list of 54 proteins was compiled, including several energy metabolism proteins such as Vitellogenin, Hexamerin, or Transferrins. These molecules represent key nutrient candidates that could be crucial for V. destructor survival.

Impact of Nosema ceranae and Nosema apis on individual worker bees of the two host species (Apis cerana and Apis mellifera) and regulation of host immune response

Nosema apis and Nosema ceranae are obligate intracellular microsporidian parasites infecting midgut epithelial cells of host adult honey bees, originally Apis mellifera and Apis cerana respectively. Each microsporidia cross-infects the other host and both microsporidia nowadays have a worldwide distribution. In this study, cross-infection experiments using both N. apis and N. ceranae in both A. mellifera and A. cerana were carried out to compare pathogen proliferation and impact on hosts, including host immune response. Infection by N. ceranae led to higher spore loads than by N. apis in both host species, and there was greater proliferation of microsporidia in A. mellifera compared to A. cerana. Both N. apis and N. ceranae were pathogenic in both host Apis species. N. ceranae induced subtly, though not significantly, higher mortality than N. apis in both host species, yet survival of A. cerana was no different to that of A. mellifera in response to N. apis or N. ceranae. Infections of both host species with N. apis and N. ceranae caused significant up-regulation of AMP genes and cellular mediated immune genes but did not greatly alter apoptosis-related gene expression. In this study, A. cerana enlisted a higher immune response and displayed lower loads of N. apis and N. ceranae spores than A. mellifera, suggesting it may be better able to defend itself against microsporidia infection. We caution against over-interpretation of our results, though, because differences between host and parasite species in survival were insignificant and because size differences between microsporidia species and between host Apis species may alternatively explain the differential proliferation of N. ceranae in A. mellifera.

Structural analysis of fungus-derived FAD glucose dehydrogenase

We report the first three-dimensional structure of fungus-derived glucose dehydrogenase using flavin adenine dinucleotide (FAD) as the cofactor. This is currently the most advanced and popular enzyme used in glucose sensor strips manufactured for glycemic control by diabetic patients. We prepared recombinant nonglycosylated FAD-dependent glucose dehydrogenase (FADGDH) derived from Aspergillus flavus (AfGDH) and obtained the X-ray structures of the binary complex of enzyme and reduced FAD at a resolution of 1.78 Å and the ternary complex with reduced FAD and D-glucono-1,5-lactone (LGC) at a resolution of 1.57 Å. The overall structure is similar to that of fungal glucose oxidases (GOxs) reported till date. The ternary complex with reduced FAD and LGC revealed the residues recognizing the substrate. His505 and His548 were subjected for site-directed mutagenesis studies, and these two residues were revealed to form the catalytic pair, as those conserved in GOxs. The absence of residues that recognize the sixth hydroxyl group of the glucose of AfGDH, and the presence of significant cavity around the active site may account for this enzyme activity toward xylose. The structural information will contribute to the further engineering of FADGDH for use in more reliable and economical biosensing technology for diabetes management.

Differential expression of immune genes of adult honey bee (Apis mellifera) after inoculated by Nosema ceranae

Nosema ceranae is a microsporidium parasite infecting adult honey bees (Apis mellifera) and is known to affects at both the individual and colony level. In this study, the expression levels were measured for four antimicrobial peptide encoding genes that are associated with bee humoral immunity (defensin, abaecin, apidaecin, and hymenoptaecin), eater gene which is a transmembrane protein involved cellular immunity and gene encoding female-specific protein (vitellogenin) in honey bees when inoculated by N. ceranae. The results showed that four of these genes, defensin, abaecin, apidaecin and hymenoptaecin were significantly down-regulated 3 and 6days after inoculations. Additionally, antimicrobial peptide expressions did not significantly differ between control and inoculated bees after 12days post inoculation. Moreover, our results revealed that the mRNA levels of eater and vitellogenin did not differ significantly following N. ceranae inoculation. Therefore, in this study we reaffirmed that N. ceranae infection induces host immunosuppression.

Salicyl alcohol oxidase of the chemical defense secretion of two chrysomelid leaf beetles. Molecular and functional characterization of two new members of the glucose-methanol-choline oxidoreductase gene family

Salicyl alcohol oxidase is an extracellular enzyme that occurs in glandular reservoirs of chrysomelid leaf beetle larvae and catalyzes the formation of salicylaldehyde, a volatile deterrent used by the larvae against predators. Salicyl alcohol is the hydrolysis product of salicin, a plant-derived precursor taken up by the beetle larvae from the leaves of willow and poplar trees. The cDNA encoding salicyl alcohol oxidase from two related species Chrysomela tremulae and Chrysomela populi has been identified, cloned, and expressed in an active form in Escherichia coli. The open reading frame of 623 amino acids begins in both enzymes with an N-terminal signal peptide of 21 amino acids. Sequence comparison has revealed that salicyl alcohol oxidase belongs to the family of glucose-methanol-choline oxidoreductase-like sequences with mostly unknown function. Enzymes of this family share similar overall structure with an essentially identical FAD-binding site but possess different catalytic activities. The data suggest that salicyl alcohol oxidase, essential for the activation of the plant-derived precursor salicin, was originally recruited from an oxidase involved in the autogenous biosynthesis of iridoid monoterpenes and found in related chrysomelid leaf beetle species.

Expansion and evolution of insect GMC oxidoreductases

Background

The GMC oxidoreductases comprise a large family of diverse FAD enzymes that share a homologous backbone. The relationship and origin of the GMC oxidoreductase genes, however, was unknown. Recent sequencing of entire genomes has allowed for the evolutionary analysis of the GMC oxidoreductase family.

Results

Although genes that encode enzyme families are rarely linked in higher eukaryotes, we discovered that the majority of the GMC oxidoreductase genes in the fruit fly (D. melanogaster), mosquito (A. gambiae), honeybee (A. mellifera), and flour beetle (T. castaneum) are located in a highly conserved cluster contained within a large intron of the flotillin-2 (Flo-2) gene. In contrast, the genomes of vertebrates and the nematode C. elegans contain few GMC genes and lack a GMC cluster, suggesting that the GMC cluster and the function of its resident genes are unique to insects or arthropods. We found that the development patterns of expression of the GMC cluster genes are highly complex. Among the GMC oxidoreductases located outside of the GMC gene cluster, the identities of two related enzymes, glucose dehydrogenase (GLD) and glucose oxidase (GOX), are known, and they play major roles in development and immunity. We have discovered that several additional GLD and GOX homologues exist in insects but are remotely similar to fungal GOX.

Conclusion

We speculate that the GMC oxidoreductase cluster has been conserved to coordinately regulate these genes for a common developmental or physiological function related to ecdysteroid metabolism. Furthermore, we propose that the GMC gene cluster may be the birthplace of the insect GMC oxidoreductase genes. Through tandem duplication and divergence within the cluster, new GMC genes evolved. Some of the GMC genes have been retained in the cluster for hundreds of millions of years while others might have transposed to other regions of the genome. Consistent with this hypothesis, our analysis indicates that insect GOX and GLD arose from a different ancestral GMC gene than that of fungal GOX.

Impact of an ectoparasite on the immunity and pathology of an invertebrate: evidence for host immunosuppression and viral amplification

Varroa mites (Varroa destructor) are ectoparasites of honey bees (Apis mellifera) and cause serious damage to bee colonies. The mechanism of how varroa mites kill honey bees remains unclear. We have addressed the effects of the mites on bee immunity and the replication of a picorna-like virus, the deformed wing virus (DWV). The expression of genes encoding three antimicrobial peptides (abaecin, defensin, and hymenoptaecin) and four immunity-related enzymes (phenol oxidase, glucose dehydrogenase, glucose oxidase, and lysozyme) were used as markers to measure the difference in the immune response. We have demonstrated an example of an ectoparasite immunosuppressing its invertebrate host with the evidence that parasitization significantly suppressed expression of these immunity-related genes. Given that ticks immunosuppress their vertebrate hosts, our finding indicates that immunosuppression of hosts may be a common phenomenon in the interaction and coevolution between ectoparasites and their vertebrate and invertebrate hosts. DWV viral titers were significantly negatively correlated with the expression levels of the immunity-related enzymes. All bees had detectable DWV. Mite-infested pupae developed into adults with either normal or deformed wings. All of the deformed-wing bees were greatly infected by DWV (approximately 10(6) times higher than varroa-infested but normal-winged bees). Injection with heat-killed bacteria dramatically promoted DWV titers (10(5) times in 10 h) in the mite-infested, normal-winged bees to levels similar to those found in mite-infested, deformed-wing bees. Varroa mites may cause the serious demise of honey bees by suppressing bee immunity and by boosting the amplification of DWV in bees exposed to microbes.

A genomic analysis of Drosophila somatic sexual differentiation and its regulation

In virtually all animals, males and females are morphologically, physiologically and behaviorally distinct. Using cDNA microarrays representing one-third of Drosophila genes to identify genes expressed sex-differentially in somatic tissues, we performed an expression analysis on adult males and females that: (1) were wild type; (2) lacked a germline; or (3) were mutant for sex-determination regulatory genes. Statistical analysis identified 63 genes sex-differentially expressed in the soma, 20 of which have been confirmed by RNA blots thus far. In situ hybridization experiments with 11 of these genes showed they were sex-differentially expressed only in internal genital organs. The nature of the products these genes encode provides insight into the molecular physiology of these reproductive tissues. Analysis of the regulation of these genes revealed that their adult expression patterns are specified by the sex hierarchy during development, and that doublesex probably functions in diverse ways to set their activities.

Glucose dehydrogenase is required for normal sperm storage and utilization in femaleDrosophila melanogaster

Female sperm storage is a key factor for reproductive success in a variety of organisms, including Drosophila melanogaster. The spermathecae,one of the Drosophila sperm storage organs, has been suggested as a long-term storage organ because its secreted substances may enhance the quality of sperm storage. Glucose dehydrogenase (GLD) is widely expressed and secreted in the spermathecal ducts among species of the genus Drosophila. This highly conserved expression pattern suggests that this enzyme might have an important role in female fertility. Here, we examine the function of GLD in sperm storage and utilization using Gld-null mutant females. The absence of GLD reduced the amount of sperm stored in the spermathecae and led to a highly asymmetrical sperm distribution in the two spermathecal capsules of the mutant females. The storage defect was especially severe when the mutant females were crossed to a Gld-mutant male that had previously mated a few hours before the experimental cross. Under this mating condition, the mutant females stored in the spermathecae only one-third of the sperm amount of the wild-type control females. In addition, the mutant females used stored sperm at a slower rate over a longer period compared with wild-type females. Thus, our results indicate that GLD facilitates both sperm uptake and release through the spermathecal ducts.

Discovery of genes with highly restricted expression patterns in the Drosophila wing disc using DNA oligonucleotide microarrays

The Drosophila wing disc is divided along the proximal-distal axis into regions giving rise to the body wall (proximal), wing hinge (central) and wing blade (distal). We applied DNA microarray analysis to discover genes with potential roles in the development of these regions. We identified a set of 94 transcripts enriched (two fold or greater) in the body wall and 56 transcripts enriched in the wing/hinge region. Transcripts that are known to have highly restricted expression patterns, such as pannier, twist and Bar-H1 (body wall) and knot, nubbin and Distal-less (wing/hinge), showed strong differential expression on the arrays. In situ hybridization for 50 previously uncharacterized genes similarly revealed that transcript enrichment identified by the array analysis was consistent with the observed spatial expression. There was a broad spectrum of patterns, in some cases suggesting that the genes could be targets of known signaling pathways. We show that three of these genes respond to wingless signaling. We also discovered genes likely to play specific roles in tracheal and myoblast cell types, as these cells are part of the body wall fragment. In summary, the identification of genes with restricted expression patterns using whole genome profiling suggests that many genes with potential roles in wing disc development remain to be characterized.

Distribution of nonrandom associations between pairs of protein loci along the third chromosome of Drosophila melanogaster

The within-chromosome distribution of gametic disequilibrium (GD) between protein loci, and the underlying evolutionary factors of this distribution, are still largely unknown. Here, we report a detailed study of GD between a large number of protein loci (15) spanning 87% of the total length of the third chromosome of Drosophila melanogaster in a large sample of haplotypes (600) drawn from a single natural population. We used a sign-based GD estimation method recently developed for multiallelic systems, which considerably increases both the statistical power and the accuracy of estimation of the intensity of GD. We found that strong GD between pairs of protein loci was widespread throughout the chromosome. In total, 22% of both the pairs of alleles and pairs of loci were in significant GD, with mean intensities (as measured by D' coefficients) of 0.43 and 0.31, respectively. In addition, strong GD often occurs between loci that are far apart. By way of illustration, 32% of the allele pairs in significant GD occurred within pairs of loci separated by effective frequencies of recombination (EFRs) of 15-20 cM, the mean D' value being 0.49. These observations are in sharp contrast with previous studies showing that GD between protein loci is rarely found in natural populations of outcrossing species, even between very closely linked loci. Interestingly, we found that most instances of significant interallelic GD (68%) involved functionally related protein loci. Specifically, GD was markedly more frequent between protein loci related by the functions of hormonal control, molybdenum control, antioxidant defense system, and reproduction than between loci without known functional relationship, which is indicative of epistatic selection. Furthermore, long-distance GD between functionally related loci (mean EFR 9 cM) suggests that epistatic interactions must be very strong along the chromosome. This evidence is hardly compatible with the neutral theory and has far-reaching implications for understanding the multilocus architecture of the functional genome. Our findings also suggest that GD may be a useful tool for discovering networks of functionally interacting proteins.

Complex organization of promoter and enhancer elements regulate the tissue- and developmental stage-specific expression of the Drosophila melanogaster Gld gene

The Drosophila melanogaster Gld gene has multiple and diverse developmental and physiological functions. We report herein that interactions among proximal promoter elements and a cluster of intronically located enhancers and silencers specify the complex regulation of Gld that underlies its diverse functions. Gld expression in nonreproductive tissues is largely determined by proximal promoter elements with the exception of the embryonic labium where Gld is activated by an enhancer within the first intron. A nuclear protein, GPAL, has been identified that binds the Gpal elements in the proximal promoter region. Regulation of Gld in the reproductive organs is particularly complex, involving interactions among the Gpal proximal promoter elements, a unique TATA box, three distinct enhancer types, and one or more silencer elements. The three somatic reproductive organ enhancers each activate expression in male and female pairs of reproductive organs. One of these pairs, the male ejaculatory duct and female oviduct, are known to be developmentally homologous. We report evidence that the other two pairs of organs are developmentally homologous as well. A comprehensive model to explain the full developmental regulation of Gld and its evolution is presented.

An evolutionarily conserved palindrome in the Drosophila Gld promoter directs tissue-specific expression

A conserved palindromic sequence (Gpal) in the promoter region of the Drosophila Gld directs expression of a heterologous reporter gene in transgenic flies to the anterior spiracular glands of third instar larvae and to the ejaculatory bulb of adult males. The Gld gene is normally expressed at high levels in the anterior spiracular glands but is not expressed in the ejaculatory bulb of Drosophila melanogaster. However, Gld promoters from other Drosophila species contain the Gpal element and express glucose dehydrogenase (GLD) in the adult male ejaculatory bulb. A gene fusion composed of the D. melanogaster Gld promoter and the lacZ gene is expressed in the anterior spiracular glands of transgenic larvae. Mutations of the Gpal sequence element in this gene fusion block expression of beta-galactosidase in the anterior spiracular gland. Together these experiments demonstrate that Gpal is necessary and sufficient for tissue-specific expression in the anterior spiracular glands. Based upon the tissue distribution and function of GLD, it is speculated that expression of GLD in the anterior spiracular glands represents the ancestral state and that GLD expression in other tissues arose as a fortuitous consequence of a shared combinatorial regulatory network.

Correlated evolution of the cis-acting regulatory elements and developmental expression of the Drosophila Gld gene in seven species from the subgroup melanogaster

The tissue-specific expression patterns of glucose dehydrogenase (GLD) exhibit a high degree of interspecific variation in the adult reproductive tract among the species in the genus Drosophila. We chose to focus on the evolution of GLD expression and the evolution of the Gld promoter in seven closely related species in the melanogaster subgroup as a means of elucidating the relationship of changes in cis-acting regulatory elements in the Gld promoter region with changes in tissue-specific expression. Although little variation in tissue-specific patterns of GLD was found in nonreproductive tissues during development, a surprisingly high level of variation was observed in the expression of GLD in both developing and mature reproductive organs. In some cases this variation is correlated with changes in sequence elements in the Gld promoter which were previously shown to direct tissue-specific expression in the reproductive tract. In particular D. teissieri adult males do not express GLD in their ejaculatory ducts, atypical of the melanogaster subgroup species. The Gld promoter region of D. teissieri specifically lacks all three of the TTAGA regulatory elements present in D. melanogaster. The TTAGA elements were previously shown to direct reporter gene expression to the ejaculatory duct. Together these data suggest the absence or presence of the TTAGA elements may be responsible for variation in the absence or presence of GLD in the ejaculatory duct among species.

Tissue-specific regulatory elements of the Drosophila Gld gene

Putative cis-acting regulatory elements immediately upstream of the Gld promoter were identified by comparative analysis of three Drosophila species. A 509 bp region containing these elements and the Gld promoter region was shown to confer tissue-specific regulation to a reporter gene similar to the pattern observed for Gld mRNA and protein. A dispersed repeat with a core motif of TTAGA was also capable of directing the expression of a reporter gene to several epidermally derived tissues in which GLD is normally expressed. These tissues include male and female somatic reproductive organs. The TTAGA elements and a palindromic element act antagonistically to block expression of reporter gene in some tissues. Previously reported mutations of the heat shock response element resulted in the creation of three TTAGA elements. This mutated hsp70 promoter directs expression of a reporter gene to many of the same tissues as does the Gld TTAGA elements. We have found TTAGA elements near the promoter of two other genes which show an identical expression pattern in the male ejaculatory duct as Gld and the mutant hsp70.

The Drosophila melanogaster stranded at second (sas) gene encodes a putative epidermal cell surface receptor required for larval development

Several lethal mutations were identified previously in the 84BD interval of the Drosophila melanogaster third chromosome (Lewis et al., 1980; Cavener et al., 1986b). We have examined the l(3)84Cd complementation group and found that mutants exhibit novel cuticular defects and die during larval development. The lethal phase occurs during the first larval molt or subsequently during the second instar larval stage; hence, we have named the gene stranded at second (sas). There are no apparent effects on the rate of development of embryos or first instar larvae. Second instar larvae which survive the molt exhibit a marked reduction in growth and eventually die as small second instar larvae. Incomplete penetrance in some weak sas alleles can yield fertile adults. In addition to the lethal phenotype, a segmentally repeated pattern of tanned spots is found within the ventral setal belts of mutant larvae. The position of the spots is always either between the fourth and fifth row of setae (cuticular projections) or between the first and second row of setae. The spots are adjacent to the muscle attachment sites in the setal belt region. Another common larval phenotype is the abnormal tanning of the ventral surface of the pharynx. The sas gene was cloned, and both the cuticular tanning and the larval lethal phenotypes were complemented by P-element-mediated transformation with a genomic DNA-cDNA construct. Three major sas transcripts are expressed throughout development in cuticle secreting epidermal tissues. The sas transcripts show stage- and tissue-specific patterns of expression with switches in transcript patterns occurring at the molts. The inferred 1348-amino-acid sequence suggests that sas encodes a cell surface protein which functions as a receptor. The putative extracellular region contains four tandem repeats of a cysteine-rich motif which is similar to a cysteine pattern present in procollagen and in thrombospondin. Following this region are at least three copies of a fibronectin type III class repeat. The short (35 amino acids) intracellular domain contains a sequence (NPXY) that has been implicated in endocytosis via coated pits.

Organ-specific patterns of gene expression in the reproductive tract of Drosophila are regulated by the sex-determination genes

The sex-determination genes of Drosophila act to repress the developmental pathway for the internal somatic reproductive organs of the opposite sex. By misregulating this pathway during preadult development, the organ-specific expression pattern of the glucose dehydrogenase gene (Gld) in the reproductive tract of adult flies has been changed without a concomitant sexual transformation of the reproductive organs. Misregulation of the tra, tra-2, and dsx genes leads to very similar patterns of ectopic expression of Gld. The induced ectopic patterns of Gld expression at the adult stage occur in a small subset of organs which all normally express the Gld gene during their morphogenesis. These ectopic patterns are irrevocably set during late larval-early pupal development. The normal pattern of Gld expression in several other Drosophila species is quite similar to the ectopic patterns which we have generated in D. melanogaster, suggesting that the interspecific variation in Gld expression may result from variation in the expression of the sex-determination genes.