Analysis of Drosophila yellow-B cDNA reveals a new family of proteins related to the royal jelly proteins in the honeybee and to an orphan protein in an unusual bacterium Deinococcus radiodurans

Reminiscences on the honeybee genome project and the rise of epigenetic concepts in insect science

The sequencing of the honeybee genome in 2006 was an important technological and logistic achievement experience. But what benefits have flown from the honeybee genome project? What does the annotated genomic assembly mean for the study of behavioural complexity and organismal function in honeybees? Here, I discuss several lines of research that have arisen from this project and highlight the rapidly expanding studies on insect epigenomics, emergent properties of royal jelly, the mechanism of nutritional control of development and the contribution of epigenomic regulation to the evolution of sociality. I also argue that the term 'insect epigenetics' needs to be carefully redefined to reflect the diversity of epigenomic toolkits in insects and the impact of lineage-specific innovations on organismal outcomes. The honeybee genome project helped pioneer advances in social insect molecular biology, and fuelled breakthrough research into the role of flexible epigenomic control systems in linking genotype to phenotype.

RNAi of yellow-y, required for normal cuticle pigmentation, impairs courtship behavior and oviposition in the German cockroach (Blattella germanica)

The insect cuticle plays a key role in maintaining the insect's physiological function and behavior. Herein, the yellow-y protein is required to produce black melanin, and is expressed in a pattern that correlates with the distribution of this pigment. However, yellow-y can also have other functions, for instance, in insect behavior, but not much is known. In this study, we have studied the yellow-y gene in one important model and pest species, namely the German cockroach (Blattella germanica), which is to our knowledge the first time reported. In essence, we identified the yellow-y gene (BgY-y) and characterized its function by using RNA interference (RNAi). Silencing of BgY-y gene led to different developmental abnormalities (body weight and wings) in both genders. Specifically, there was an abundant decrease in melanin, turning the body color in pale yellow and the cuticle softer and more transparent. Interestingly, we also observed that the knockdown of BgY-y impaired the male cockroaches to display a weaker response to female-emitted contact sex pheromones, and also that the oviposition ability was weakened in the RNAi females. This study comprehensively analyzed the biological functions of the yellow-y gene in German cockroaches from the perspectives of development, body color, courtship behavior and oviposition, and as a consequence, this may opens new avenues to explore it as a novel pest control gene.

Transcriptome analysis and screening of putative sex-determining genes in the invasive pest, Frankliniella occidentalis (Thysanoptera: Thripidae)

The invasive insect pest, Frankliniella occidentalis, is a well-known vector that transmits a variety of ornamental and vegetable viruses. The mechanistic basis of sex determination in F. occidentalis is not well understood, and this hinders our ability to deploy sterile insect technology as an integrated pest management strategy. In this study, six cDNA libraries from female and male adults of F. occidentalis (three biological replicates each) were constructed and transcriptomes were sequenced. A total of 6000 differentially-expressed genes were identified in the two sexes including 2355 up- and 3645 down-regulated genes. A total of 149 sex-related genes were identified based on GO enrichment data and included transformer-2 (tra2), fruitless (fru), male-specific lethal (msl) and sex lethal (sxl); several of these exhibited sex-specific and/or sex-biased expression in F. occidentalis. This study contributes to our understanding of the sex-determined cascade in F. occidentalis and other members of the Thysanoptera.

Yellow-b, -c, -d, and -h are required for normal body coloration of Henosepilachna vigintioctopunctata

The involvement of yellow genes y-b, y-c, y-e, and y-h in cuticle tanning has poorly been clarified. In the present paper, six putative yellow (y-y, y-b, y-c, y-e y-f, and y-h) genes were identified in Henosepilachna vigintioctopunctata. Hvy-b, Hvy-c, Hvy-e, and Hvy-h were abundantly transcribed at early larval and late pupal stages, especially in the epidermis. Accordingly, RNA interference (RNAi) experiments were performed by an injection of dsy-b, dsy-c, dsy-e, or dsy-h into the second instar larvae and 1-day-old pupae. The head capsule, scoli and strumae, and legs in the fourth-instar larvae became blacker; the blackish spots in the pupae were darkened and widened after RNAi of Hvy-b, compared with those of dsegfp-treated controls. Depletion of Hvy-b at the 1-day-old pupal stage expanded two pair of black markings on the sternum of the metathorax, and darkened the black patched on the sterna of the abdomen segments I-VI in the resultant adults. Depletion of Hvy-e caused darker pigmented adult body and elytral cuticles than those of dsegfp-introduced controls. However, there was no obvious difference in pigmentation of the black markings. Hvy-h-deficient larvae displayed dark yellow body color, whereas the body color of the dsegfp-injected control was pale yellow. There was no obvious difference in coloration of larval specific-black markings or pupal cuticle between dsHvy-h- and dsegfp-treated animals. Moreover, silence of Hvy-c at the second instar larval stage lightened black markings in the resulting larvae and pupae, but had no influence on pale yellow body color. Our results demonstrated their different roles of the four yellow genes during body pigmentation: HvY-b and HvY-c, respectively, inhibit and facilitate the coloration within dark markings, whereas HvY-e and HvY-h, respectively, repress the pigmentation in adult and larval body cuticles outside the black patches in H. vigintioctopunctata.

Anopheles dirus yellow-g mediates Plasmodium vivax infection

OBJECTIVE

Our previous transcriptome analysis of Anopheles dirus revealed upregulation of the An. dirus yellow-g gene upon ingestion of Plasmodium vivax-infected blood. This gene belongs to the yellow gene family, but its role regarding P. vivax infection is not known and remains to be validated. The aim of this study was to investigate the role of the An. dirus yellow-g gene in P. vivax infection.

METHODS

The qRT-PCR was used to detect the expression of the yellow-g gene in many organs of both male and female mosquitos. The yellow-g gene silencing was performed by dsRNA membrane feeding to An. dirus. These mosquitoes were later challenged by P. vivax-infected blood. The oocyst numbers were determined.

RESULTS

The yellow-g transcript was detected in several organs of both male and female An. dirus mosquitoes. Successful knockdown of yellow-g was achieved and resulted in reduced P. vivax infection in the mosquitoes. The decrease in yellow-g expression had no effect on the life span of the mosquitoes.

CONCLUSIONS

These results support the yellow-g gene as having an important function in Plasmodium development in Anopheles mosquitoes.

Identification of a transcription factor that functions downstream of corazonin in the control of desert locust gregarious body coloration

Corazonin (Crz) is a neuropeptide that controls phase-dependent body color polyphenism in locusts. The Crz signaling pathway is responsible for the development of gregarious black patterns in nymphs and determination of the morphometric ratio F/C (F = hind femur length, C = maximum head width) in adults. However, little information is available regarding the mediator and effector proteins regulated by Crz. In this study, we identified a novel transcription factor, Loct, which functions downstream of Crz in Schistocerca gregaria and Locusta migratoria. In S. gregaria, we detected a variant of Loct lacking the N-terminal region. Protein-protein interaction assays showed that both the long and short Loct variants formed a complex with themselves. LOCT knockdown in gregarious nymphs reduced the intensity of their black patterning, but did not affect F/C ratios in adults. LOCT was exclusively expressed in the integument of gregarious nymphs, suggesting that Loct is involved in melanin production. In addition, we found that the melanization-associated protein Yellow (YEL) and the albino-related takeout protein (ALTO) are expressed in the integument and function downstream of Crz. However, Crz injection failed to influence LOCT, YEL, and ALTO expression. Therefore, additional factors probably cooperate with Crz to induce these genes. The gene expression profiles of YEL and ALTO in LOCT-knockdown nymphs suggest that Loct does not directly control the transcription of YEL or ALTO. In summary, we present a working model of the Crz pathway, which is active in crowded S. gregaria nymphs.

EGFR gene methylation is not involved in Royalactin controlled phenotypic polymorphism in honey bees

The 2011 highly publicised Nature paper by Kamakura on honeybee phenotypic dimorphism, (also using Drosophila as an experimental surrogate), claims that a single protein in royal jelly, Royalactin, essentially acts as a master “on-off” switch in development via the epidermal growth factor receptor (AmEGFR), to seal the fate of queen or worker. One mechanism proposed in that study as important for the action of Royalactin is differential amegfr methylation in alternate organismal outcomes. According to the author differential methylation of amegfr was experimentally confirmed and shown in a supportive figure. Here we have conducted an extensive analysis of the honeybee egfr locus and show that this gene is never methylated. We discuss several lines of evidence casting serious doubts on the amegfr methylation result in the 2011 paper and consider possible origins of the author’s statement. In a broader context, we discuss the implication of our findings for contrasting context-dependent regulation of EGFR in three insect species, Apis mellifera, D. melanogaster and the carpenter ant, Camponotus floridanus, and argue that more adequate methylation data scrutiny measures are needed to avoid unwarranted conclusions.

Characteristics of dr1790 disruptant and its functional analysis in Deinococcus radiodurans

Deinococcus radiodurans (DR) is an extremophile that is well known for its resistance to radiation, oxidants and desiccation. The gene dr1790 of D. radiodurans was predicted to encode a yellow-related protein. The primary objective of the present study was to characterize the biological function of the DR1790 protein, which is a member of the ancient yellow/major royal jelly (MRJ) protein family, in prokaryotes. Fluorescence labeling demonstrated that the yellow-related protein encoded by dr1790 is a membrane protein. The deletion of the dr1790 gene decreased the cell growth rate and sensitivity to hydrogen peroxide and radiation and increased the membrane permeability of D. radiodurans. Transcript profiling by microarray and RT-PCR analyses of the dr1790 deletion mutant suggested that some genes that are involved in protein secretion and transport were strongly suppressed, while other genes that are involved in protein quality control, such as chaperones and proteases, were induced. In addition, the expression of genes with predicted functions that are involved in antioxidant systems, electron transport, and energy metabolism was significantly altered through the disruption of dr1790. Moreover, the results of proteomic analyses using 2-DE and MS also demonstrated that DR1790 contributed to D. radiodurans survival. Taken together, these results indicate that the DR1790 protein from the ancient yellow protein family plays a pleiotropic role in the survival of prokaryotic cells and contributes to the extraordinary resistance of D. radiodurans against oxidative and radiation stresses.

Identification, mRNA expression and functional analysis of several yellow family genes in Tribolium castaneum

Querying the genome of the red flour beetle, Tribolium castaneum, with the Drosophila melanogaster Yellow-y (DmY-y) protein sequence identified 14 Yellow homologs. One of these is an ortholog of DmY-y, which is required for cuticle pigmentation (melanization), and another is an ortholog of DmY-f/f2, which functions as a dopachrome conversion enzyme (DCE). Phylogenetic analysis identified putative T. castaneum orthologs for eight of the D. melanogaster yellow genes, including DmY-b, -c, -e, -f, -g, -g2, -h and -y. However, one clade of five beetle genes, TcY-1-5, has no orthologs in D. melanogaster. Expression profiles of all T. castaneum yellow genes were determined by RT-PCR of pharate pupal to young adult stages. TcY-b and TcY-c were expressed throughout all developmental stages analyzed, whereas each of the remaining yellow genes had a unique expression pattern, suggestive of distinct physiological functions. TcY-b, -c and -e were all identified by mass spectrometry of elytral proteins from young adults. Eight of the 14 genes showed differential expression between elytra and hindwings during the last three days of the pupal stage when the adult cuticle is synthesized. Double-stranded RNA (dsRNA)-mediated transcript knockdown revealed that TcY-y is required for melanin production in the hindwings, particularly in the region of the pterostigma, while TcY-f appears to be required for adult cuticle sclerotization but not pigmentation.

Yellow-e determines the color pattern of larval head and tail spots of the silkworm Bombyx mori

Yellow proteins form a large family in insects. In Drosophila melanogaster, there are 14 yellow genes in the genome. Previous studies have shown that the yellow gene is necessary for normal pigmentation; however, the roles of other yellow genes in body coloration are not known. Here, we provide the first evidence that yellow-e is required for normal body color pattern in insect larvae. In two mutant strains, bts and its allele bts2, of the silkworm Bombyx mori, the larval head cuticle and anal plates are reddish brown instead of the white color found in the wild type. Positional cloning revealed that deletions in the Bombyx homolog of the Drosophila yellow-e gene (Bmyellow-e) were responsible for the bts/bts2 phenotype. Bmyellow-e mRNA was strongly expressed in the trachea, testis, and integument, and expression markedly increased at the molting stages. This profile is quite similar to that of Bmyellow, a regulator of neonatal body color and body markings in Bombyx. Quantitative reverse transcription-PCR analysis showed that Bmyellow-e mRNA was heavily expressed in the integument of the head and tail in which the bts phenotype is observed. The present results suggest that Yellow-e plays a crucial role in the pigmentation process of lepidopteran larvae.

Identifying genes related to choriogenesis in insect panoistic ovaries by Suppression Subtractive Hybridization

Background

Insect ovarioles are classified into two categories: panoistic and meroistic, the later having apparently evolved from an ancestral panoistic type. Molecular data on oogenesis is practically restricted to meroistic ovaries. If we aim at studying the evolutionary transition from panoistic to meroistic, data on panoistic ovaries should be gathered. To this end, we planned the construction of a Suppression Subtractive Hybridization (SSH) library to identify genes involved in panoistic choriogenesis, using the cockroach Blattella germanica as model.

Results

We constructed a post-vitellogenic ovary library by SSH to isolate genes involved in choriogenesis in B. germanica. The tester library was prepared with an ovary pool from 6- to 7-day-old females, whereas the driver library was prepared with an ovary pool from 3- to 4-day-old females. From the SSH library, we obtained 258 high quality sequences which clustered into 34 unique sequences grouped in 19 contigs and 15 singlets. The sequences were compared against non-redundant NCBI databases using BLAST. We found that 44% of the unique sequences had homologous sequences in known genes of other organisms, whereas 56% had no significant similarity to any of the databases entries. A Gene Ontology analysis was carried out, classifying the 34 sequences into different functional categories. Seven of these gene sequences, representative of different categories and processes, were chosen to perform expression studies during the first gonadotrophic cycle by real-time PCR. Results showed that they were mainly expressed during post-vitellogenesis, which validates the SSH technique. In two of them corresponding to novel genes, we demonstrated that they are specifically expressed in the cytoplasm of follicular cells in basal oocytes at the time of choriogenesis.

Conclusion

The SSH approach has proven to be useful in identifying ovarian genes expressed after vitellogenesis in B. germanica. For most of the genes, functions related to choriogenesis are postulated. The relatively high percentage of novel genes obtained and the practical absence of chorion genes typical of meroistic ovaries suggest that mechanisms regulating chorion formation in panoistic ovaries are significantly different from those of meroistic ones.

Genomic resources for Myzus persicae: EST sequencing, SNP identification, and microarray design

Background

The green peach aphid, Myzus persicae (Sulzer), is a world-wide insect pest capable of infesting more than 40 plant families, including many crop species. However, despite the significant damage inflicted by M. persicae in agricultural systems through direct feeding damage and by its ability to transmit plant viruses, limited genomic information is available for this species.

Results

Sequencing of 16 M. persicae cDNA libraries generated 26,669 expressed sequence tags (ESTs). Aphids for library construction were raised on Arabidopsis thaliana, Nicotiana benthamiana, Brassica oleracea, B. napus, and Physalis floridana (with and without Potato leafroll virus infection). The M. persicae cDNA libraries include ones made from sexual and asexual whole aphids, guts, heads, and salivary glands. In silico comparison of cDNA libraries identified aphid genes with tissue-specific expression patterns, and gene expression that is induced by feeding on Nicotiana benthamiana. Furthermore, 2423 genes that are novel to science and potentially aphid-specific were identified. Comparison of cDNA data from three aphid lineages identified single nucleotide polymorphisms that can be used as genetic markers and, in some cases, may represent functional differences in the protein products. In particular, non-conservative amino acid substitutions in a highly expressed gut protease may be of adaptive significance for M. persicae feeding on different host plants. The Agilent eArray platform was used to design an M. persicae oligonucleotide microarray representing over 10,000 unique genes.

Conclusion

New genomic resources have been developed for M. persicae, an agriculturally important insect pest. These include previously unknown sequence data, a collection of expressed genes, molecular markers, and a DNA microarray that can be used to study aphid gene expression. These resources will help elucidate the adaptations that allow M. persicae to develop compatible interactions with its host plants, complementing ongoing work illuminating plant molecular responses to phloem-feeding insects.

Differential gene expression between adult queens and workers in the ant Lasius niger

Ants and other social insects forming large societies are generally characterized by marked reproductive division of labour. Queens largely monopolize reproduction whereas workers have little reproductive potential. In addition, some social insect species show tremendous lifespan differences between the queen and worker caste. Remarkably, queens and workers are usually genotypically identical, meaning that any phenotypic differences between the two castes arise from caste-specific gene expression. Using a combination of differential display, microarrays and reverse Northern blots, we found 16 genes that were differentially expressed between adult queens and workers in the ant Lasius niger, a species with highly pronounced reproductive division of labour and a several-fold lifespan difference between queens and workers. RNA ligase mediated rapid amplification of cDNA ends (RLM-RACE) and gene walking were used to further characterize these genes. On the basis of the molecular function of their nearest homologues, three genes appear to be involved in reproductive division of labour. Another three genes, which were exclusively overexpressed in queens, are possibly involved in the maintenance and repair of the soma, a candidate mechanism for lifespan determination. In-depth functional analyses of these genes are now needed to reveal their exact role.

Evolution of the Yellow/Major Royal Jelly Protein family and the emergence of social behavior in honey bees

The genomic architecture underlying the evolution of insect social behavior is largely a mystery. Eusociality, defined by overlapping generations, parental brood care, and reproductive division of labor, has most commonly evolved in the Hymenopteran insects, including the honey bee Apis mellifera. In this species, the Major Royal Jelly Protein (MRJP) family is required for all major aspects of eusocial behavior. Here, using data obtained from the A. mellifera genome sequencing project, we demonstrate that the MRJP family is encoded by nine genes arranged in an approximately 60-kb tandem array. Furthermore, the MRJP protein family appears to have evolved from a single progenitor gene that encodes a member of the ancient Yellow protein family. Five genes encoding Yellow-family proteins flank the genomic region containing the genes encoding MRJPs. We describe the molecular evolution of these protein families. We then characterize developmental-stage-specific, sex-specific, and caste-specific expression patterns of the mrjp and yellow genes in the honey bee. We review empirical evidence concerning the functions of Yellow proteins in fruit flies and social ants, in order to shed light on the roles of both Yellow and MRJP proteins in A. mellifera. In total, the available evidence suggests that Yellows and MRJPs are multifunctional proteins with diverse, context-dependent physiological and developmental roles. However, many members of the Yellow/MRJP family act as facilitators of reproductive maturation. Finally, it appears that MRJP protein subfamily evolution from the Yellow protein family may have coincided with the evolution of honey bee eusociality.

Towards a molecular definition of worker sterility: differential gene expression and reproductive plasticity in honey bees

We show that differences in the reproductive development of honey bee workers are associated with locus-specific changes to abundance of messenger RNA. Using a cross-fostering field experiment to control for differences related to age and environment, we compared the gene expression profiles of functionally sterile workers (wild-type) and those from a mutant strain in which workers are reproductively active (anarchist). Among the set of three genes that are significantly differentially expressed are two major royal jelly proteins that are up-regulated in wild-type heads. This discovery is consistent with sterile workers synthesizing royal jelly as food for developing brood. Likewise, the relative underexpression of these two royal jellies in anarchist workers is consistent with these workers' characteristic avoidance of alloparental behaviour, in favour of selfish egg-laying. Overall, there is a trend for the most differentially expressed genes to be up-regulated in wild-type workers. This pattern suggests that functional sterility in honey bee workers may generally involve the expression of a suite of genes that effectively 'switch' ovaries off, and that selfish reproduction in honey bee workers, though rare, is the default developmental pathway that results when ovary activation is not suppressed.

Identification and analysis of YELLOW protein family genes in the silkworm, Bombyx mori

Background

The major royal jelly proteins/yellow (MRJP/YELLOW) family possesses several physiological and chemical functions in the development of Apis mellifera and Drosophila melanogaster. Each protein of the family has a conserved domain named MRJP. However, there is no report of MRJP/YELLOW family proteins in the Lepidoptera.

Results

Using the YELLOW protein sequence in Drosophila melanogaster to BLAST silkworm EST database, we found a gene family composed of seven members with a conserved MRJP domain each and named it YELLOW protein family of Bombyx mori. We completed the cDNA sequences with RACE method. The protein of each member possesses a MRJP domain and a putative cleavable signal peptide consisting of a hydrophobic sequence. In view of genetic evolution, the whole Bm YELLOW protein family composes a monophyletic group, which is distinctly separate from Drosophila melanogaster and Apis mellifera. We then showed the tissue expression profiles of Bm YELLOW protein family genes by RT-PCR.

Conclusion

A Bombyx mori YELLOW protein family is found to be composed of at least seven members. The low homogeneity and unique pattern of gene expression by each member among the family ensure us to prophesy that the members of Bm YELLOW protein family would play some important physiological functions in silkworm development.

Purine and folate metabolism as a potential target of sex-specific nutrient allocation in Drosophila and its implication for lifespan-reproduction tradeoff

The reallocation of metabolic resources is important for survival during periods of limited nutrient intake. This has an influence on diverse physiological processes, including reproduction, repair, and aging. One important aspect of resource allocation is the difference between males and females in response to nutrient stress. We identified several groups of genes that are regulated in a sex-biased manner under complete or protein starvation. These range from expected differences in genes involved in reproductive physiology to those involved in amino acid utilization, sensory perception, immune response, and growth control. A striking difference was observed in purine and the tightly interconnected folate metabolism upon protein starvation. From these results, we conclude that the purine and folate metabolic pathway is a major point of transcriptional regulation during resource allocation and may have relevance for understanding the physiological basis for the observed tradeoff between reproduction and longevity.

Organization and potential function of the mrjp3 locus in four honeybee species

Royal jelly is a nutritious secretion produced by nurse honeybees to provision queens and growing larvae. Major proteins of royal jelly are mutually similar, and they all belong to the MRJP/yellow protein family (pfam03022). The mrjp3 loci in four traditional honeybee species (Apis mellifera, Apis cerana,Apis dorsata, and Apis florea) were sequenced and found to share high sequence and structural similarities. PCR analyses confirmed the presence of an extensive repetitive region, which showed size and sequence polymorphisms in all species. The evolutionary history of mrjp genes and their repetitive regions was reconstructed from their nucleotide sequences. The analyses proved that the repeat region appeared early in the evolution of the mrjp gene family and that the extreme elongation of the repeat is mrjp3 specific. In the MRJPs was documented a correlation between nitrogen content and repeat length. Therefore, it is argued that the repeat occurred due to a selection for an increase in nitrogen storage for a more efficient nutrition of queens and larvae.

Differential gene expression between alate and dealate queens in the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae)

The transition of fire ant queens from alates to dealates, following a mating flight, is associated with numerous important physiological changes. A molecular analysis of gene expression differences that occur between alates and dealates was performed using the suppression subtractive hybridization (SSH) method. 983 SSH clones were arrayed and screened by dot blot hybridization, followed by Northern blot analysis for selected clones. Gene expression profiles throughout fire ant development were determined using semi-quantitative reverse transcriptase polymerase chain reactions (RT-PCR). The cytochrome c oxidase subunit II and STARS (striated muscle activator of Rho signaling) transcripts were expressed at higher levels in dealates compared to alates and may be involved in the programmed cell death of the flight muscles. Three different vitellogenin genes and two unique yellow g-like genes were identified that may be closely associated with the reproductive system and/or nutrient transport. Two putative antibacterial peptides, abaecin and hymenoptaecin precursors, were highly expressed in dealate queens, suggesting that they are present as an immune system component during this important stage of fire ant development. The genes identified in this study may be utilized as novel targets for fire ant control and will also provide molecular markers for studies of other social insects.

Gene amplification as a developmental strategy: isolation of two developmental amplicons in Drosophila

Gene amplification is known to be critical for upregulating gene expression in a few cases, but the extent to which amplification is utilized in the development of diverse organisms remains unknown. By quantifying genomic DNA hybridization to microarrays to assay gene copy number, we identified two additional developmental amplicons in the follicle cells of the Drosophila ovary. Both amplicons contain genes which, following their amplification, are expressed in the follicle cells, and the expression of three of these genes becomes restricted to specialized follicle cells late in differentiation. Genetic analysis establishes that at least one of these genes, yellow-g, is critical for follicle cell function, because mutations in yellow-g disrupt eggshell integrity. Thus, during follicle cell differentiation the entire genome is overreplicated as the cells become polyploid, and subsequently specific genomic intervals are overreplicated to facilitate gene expression.

A gene necessary for normal male courtship, yellow, acts downstream of fruitless in the Drosophila melanogaster larval brain

The fruitless (fru) gene is a member of the Drosophila melanogaster somatic sex determination genetic pathway. Although it has been hypothesized that the primary function of fru is to regulate a genetic hierarchy specifying development of adult male courtship behavior, genes acting downstream of fru have not yet been identified. Here we demonstrate that the yellow (y) gene is genetically downstream of fru in the 3(rd)-instar larval brain. Yellow protein is present at elevated levels in neuroblasts, which also show expression of male-specific FRU proteins, compared to control neuroblasts without FRU. A location for y downstream of fru in a genetic pathway was experimentally demonstrated by analysis of fru mutants lacking transcription of zinc-finger DNA binding domains, and of animals with temporal, spatial, or sexual mis-expression of male-specific FRU. A subset of fru and y mutants is known to reduce levels of a specific behavioral component of the male courtship ritual, wing extension, and FRU and Yellow were detected in the general region of the brain whose maleness is necessary for development of that behavior. We therefore hypothesized that ectopic expression of Yellow in the 3(rd)-instar brain, in a y null background, would rescue low levels of wing extension and male competitive mating success, and this was found to be the case. Overall, these data suggest that y is a downstream member of the fru branch of the D. melanogaster sex determination hierarchy, where it plays a currently unknown role in the development of adult male wing extension during courtship.

Combining mapping and arraying: An approach to candidate gene identification

A combination of quantitative trait locus (QTL) mapping and microarray analysis was developed and used to identify 34 candidate genes for ovariole number, a quantitative trait, in Drosophila melanogaster. Ovariole number is related to evolutionary fitness, which has been extensively studied, but for which few a priori candidate genes exist. A set of recombinant inbred lines were assayed for ovariole number, and QTL analyses for this trait identified 5,286 positional candidate loci. Forty deletions spanning the QTL were employed to further refine the map position of genes contributing to variation in this trait between parental lines, with six deficiencies showing significant effects and reducing the number of positional candidates to 548. Parental lines were then assayed for expression differences by using Affymetrix microarray technology, and ANOVA was used to identify differentially expressed genes in these deletions. Thirty-four genes were identified that showed evidence for differential expression between the parental lines, one of which was significant even after a conservative Bonferroni correction. The list of potential candidates includes 5 genes for which previous annotations did not exist, and therefore would have been unlikely choices for follow-up from mapping studies alone. The use of microarray technology in this context allows an efficient, objective, quantitative evaluation of genes in the QTL and has the potential to reduce the overall effort needed in identifying genes causally associated with quantitative traits of interest.

Evaluation of differential gene expression during behavioral development in the honeybee using microarrays and northern blots

BACKGROUND

The honeybee (Apis mellifera) has been used with great success in a variety of behavioral studies. The lack of genomic tools in this species has, however, hampered efforts to provide genome-based explanations for behavioral data. We have combined the power of DNA arrays and the availability of distinct behavioral stages in honeybees to explore the dynamics of gene expression during adult development in this insect. In addition, we used caffeine treatment, a procedure that accelerates learning abilities in honeybees, to examine changes in gene expression underlying drug-induced behavioral modifications.

RESULTS

Spotted microarrays containing several thousand cDNAs were interrogated with RNAs extracted from newly emerged worker bees, experienced foragers and caffeine-treated bees. Thirty-six differentially expressed cDNAs were verified by northern blot hybridization and characterized in silico by sequencing and database searches. Experienced foragers overexpressed royal jelly proteins, a putative imaginal disc growth factor, a transcriptional regulator (Stck) and several enzymes, including alpha-glucosidases, aminopeptidases and glucose dehydrogenase. Naive workers showed increased expression of members of the SPARC and lectin families, heat-shock cognate proteins and several proteins related to RNA translation and mitochondrial function. A number of novel genes overexpressed in both naive and experienced bees, and genes induced by caffeine, have also been identified.

CONCLUSIONS

We have shown the usefulness of this transcriptome-based approach for gene discovery, in particular in the context of the efficacy of drug treatment, in a model organism in which routine genetic techniques cannot be applied easily.