Genome-wide analysis of the chromatin sites targeted by HEX 70a storage protein in the honeybee brain and fat body.

Hexamerins, the proteins massively stored in the larval haemolymph of insects, are gradually used throughout metamorphosis as a source of raw material and energy for the development of adult tissues. Such behaviour defined hexamerins as storage proteins. Immunofluorescence experiments coupled with confocal microscopy show a hexamerin, HEX 70a, in the nucleus of the brain and fat body cells from honeybee workers, an unexpected localization for a storage protein. HEX 70a colocalizes with fibrillarin, a nucleolar-specific protein and H3 histone, thus suggesting a potential role as a chromatin-binding protein. This was investigated through chromatin immunoprecipitation and high-throughput DNA sequencing (ChIP-seq). The significant HEX 70a-DNA binding sites were mainly localized at the intergenic, promoter and intronic regions. HEX 70a targeted DNA stretches mapped to the genomic regions encompassing genes with relevant functional attributes. Several HEX 70a targeted genes were associated with H3K27ac or/and H3K27me3, known as active and repressive histone marks. Brain and fat body tissues shared a fraction of the HEX 70 targeted genes, and tissue-specific targets were also detected. The presence of overrepresented DNA motifs in the binding sites is consistent with specific HEX 70a-chromatin association. In addition, a search for HEX 70a targets in RNA-seq public libraries of fat bodies from nurses and foragers revealed differentially expressed targets displaying hex 70a-correlated developmental expression, thus supporting a regulatory activity for HEX 70a. Our results support the premise that HEX 70a is a moonlighting protein that binds chromatin and has roles in the brain and fat body cell nuclei, apart from its canonical role as a storage protein.

The nuclear and mitochondrial genomes of Frieseomelitta varia - a highly eusocial stingless bee (Meliponini) with a permanently sterile worker caste.

BACKGROUND: Most of our understanding on the social behavior and genomics of bees and other social insects is centered on the Western honey bee, Apis mellifera. The genus Apis, however, is a highly derived branch comprising less than a dozen species, four of which genomically characterized. In contrast, for the equally highly eusocial, yet taxonomically and biologically more diverse Meliponini, a full genome sequence was so far available for a single Melipona species only. We present here the genome sequence of Frieseomelitta varia, a stingless bee that has, as a peculiarity, a completely sterile worker caste. RESULTS: The assembly of 243,974,526 high quality Illumina reads resulted in a predicted assembled genome size of 275 Mb composed of 2173 scaffolds. A BUSCO analysis for the 10,526 predicted genes showed that these represent 96.6% of the expected hymenopteran orthologs. We also predicted 169,371 repetitive genomic components, 2083 putative transposable elements, and 1946 genes for non-coding RNAs, largely long non-coding RNAs. The mitochondrial genome comprises 15,144 bp, encoding 13 proteins, 22 tRNAs and 2 rRNAs. We observed considerable rearrangement in the mitochondrial gene order compared to other bees. For an in-depth analysis of genes related to social biology, we manually checked the annotations for 533 automatically predicted gene models, including 127 genes related to reproductive processes, 104 to development, and 174 immunity-related genes. We also performed specific searches for genes containing transcription factor domains and genes related to neurogenesis and chemosensory communication. CONCLUSIONS: The total genome size for F. varia is similar to the sequenced genomes of other bees. Using specific prediction methods, we identified a large number of repetitive genome components and long non-coding RNAs, which could provide the molecular basis for gene regulatory plasticity, including worker reproduction. The remarkable reshuffling in gene order in the mitochondrial genome suggests that stingless bees may be a hotspot for mtDNA evolution. Hence, while being just the second stingless bee genome sequenced, we expect that subsequent targeting of a selected set of species from this diverse clade of highly eusocial bees will reveal relevant evolutionary signals and trends related to eusociality in these important pollinators.

Immunity and physiological changes in adult honey bees (Apis mellifera) infected with Nosema ceranae: The natural colony environment.

Nosema ceranae is a microsporidium that infects Apis mellifera, causing diverse physiological and behavioral alterations. Given the existence of individual and social mechanisms to reduce infection and fungal spread in the colony, bees may respond differently to infection depending on their rearing conditions. In this study, we investigated the effect of N. ceranae in honey bee foragers naturally infected with different fungal loads in a tropical region. In addition, we explored the effects of N. ceranae artificially infected young bees placed in a healthy colony under field conditions. Honey bees naturally infected with higher loads of N. ceranae showed downregulation of genes from Toll and IMD immune pathways and antimicrobial peptide (AMP) genes, but hemolymph total protein amount and Vitellogenin (Vg) titers were not affected. Artificially infected bees spread N. ceranae to the controls in the colony, but fungal loads were generally lower than those observed in cages, probably because of social immunity. Although no significant changes in mRNA levels of AMP-encoding were observed, N. ceranae artificially infected bees showed downregulation of miR-989 (an immune-related microRNA), lower vitellogenin gene expression, and decreased hemolymph Vg titers. Our results demonstrate for the first time that natural infection by N. ceranae suppresses the immune system of honey bee foragers in the field. This parasite is detrimental to the immune system of young and old bees, and disease spread, mitigation and containment will depend on the colony environment.

The four hexamerin genes in the honey bee: structure, molecular evolution and function deduced from expression patterns in queens, workers and drones.

BACKGROUND: Hexamerins are hemocyanin-derived proteins that have lost the ability to bind copper ions and transport oxygen; instead, they became storage proteins. The current study aimed to broaden our knowledge on the hexamerin genes found in the honey bee genome by exploring their structural characteristics, expression profiles, evolution, and functions in the life cycle of workers, drones and queens. RESULTS: The hexamerin genes of the honey bee (hex 70a, hex 70b, hex 70c and hex 110) diverge considerably in structure, so that the overall amino acid identity shared among their deduced protein subunits varies from 30 to 42%. Bioinformatics search for motifs in the respective upstream control regions (UCRs) revealed six overrepresented motifs including a potential binding site for Ultraspiracle (Usp), a target of juvenile hormone (JH). The expression of these genes was induced by topical application of JH on worker larvae. The four genes are highly transcribed by the larval fat body, although with significant differences in transcript levels, but only hex 110 and hex 70a are re-induced in the adult fat body in a caste- and sex-specific fashion, workers showing the highest expression. Transcripts for hex 110, hex 70a and hex70b were detected in developing ovaries and testes, and hex 110 was highly transcribed in the ovaries of egg-laying queens. A phylogenetic analysis revealed that HEX 110 is located at the most basal position among the holometabola hexamerins, and like HEX 70a and HEX 70c, it shares potential orthology relationship with hexamerins from other hymenopteran species. CONCLUSIONS: Striking differences were found in the structure and developmental expression of the four hexamerin genes in the honey bee. The presence of a potential binding site for Usp in the respective 5' UCRs, and the results of experiments on JH level manipulation in vivo support the hypothesis of regulation by JH. Transcript levels and patterns in the fat body and gonads suggest that, in addition to their primary role in supplying amino acids for metamorphosis, hexamerins serve as storage proteins for gonad development, egg production, and to support foraging activity. A phylogenetic analysis including the four deduced hexamerins and related proteins revealed a complex pattern of evolution, with independent radiation in insect orders.

Trade-off between immune stimulation and expression of storage protein genes.

Proteins stored in insect hemolymph may serve as a source of amino acids and energy for metabolism and development. The expression of the main storage proteins was assessed in bacterial-challenged honey bees using real-time (RT)-PCR and Western blot. After ensuring that the immune system had been activated by measuring the ensuing expression of the innate immune response genes, defensin-1 (def-1) and prophenoloxidase (proPO), we verified the expression of four genes encoding storage proteins. The levels of vitellogenin (vg) mRNA and of the respective protein were significantly lowered in bees injected with bacteria or water only (injury). An equivalent response was observed in orally-infected bees. The levels of apolipophorin II/I (apoLp-II/I) and hexamerin (hex 70a) mRNAs did not significantly change, but levels of Hex 70a protein subunit showed a substantial decay after bacterial challenge or injury. Infection also caused a strong reduction in the levels of apoLp-III transcripts. Our findings are consistent with a down-regulation of the expression and accumulation of storage proteins as a consequence of activation of the immune system, suggesting that this phenomenon represents a strategy to redirect resources to combat injury or infection.

Evaluation of reference genes for gene expression analysis by real-time quantitative PCR (qPCR) in three stingless bee species (Hymenoptera: Apidae: Meliponini).

Stingless bees are generalist pollinators distributed through the pantropical region. There is growing evidence that their wild populations are experiencing substantial decline in response to habitat degradation and pesticides. Policies for conservation of endangered species will benefit from studies focusing on genetic and molecular aspects of their development and behavior. The most common method for looking at gene expression is real-time quantitative polymerase chain reaction preceded by reverse transcription (RT-qPCR) of the mRNA of interest. This method requires the identification of reliable reference genes to correctly estimate fluctuations in transcript levels. To contribute to molecular studies on stingless bees, we used Frieseomelitta varia, Melipona quadrifasciata, and Scaptotrigona bipunctata species to test the expression stability of eight reference genes (act, ef1-α, gapdh, rpl32, rps5, rps18, tbp, and tbp-af) in RT-qPCR procedures in five physiological and experimental conditions (development, sex, tissues, bacteria injection, and pesticide exposure). In general, the rpl32, rps5 and rps18 ribosomal protein genes and tpb-af gene showed the highest stability, thus being identified as suitable reference genes for the three stingless bee species and defined conditions. Our results also emphasized the need to evaluate the stability of candidate genes for any designed experimental condition and stingless bee species.

Exploring integument transcriptomes, cuticle ultrastructure, and cuticular hydrocarbons profiles in eusocial and solitary bee species displaying heterochronic adult cuticle maturation.

Differences in the timing of exoskeleton melanization and sclerotization are evident when comparing eusocial and solitary bees. This cuticular maturation heterochrony may be associated with life style, considering that eusocial bees remain protected inside the nest for many days after emergence, while the solitary bees immediately start outside activities. To address this issue, we characterized gene expression using large-scale RNA sequencing (RNA-seq), and quantified cuticular hydrocarbon (CHC) through gas chromatography-mass spectrometry in comparative studies of the integument (cuticle plus its underlying epidermis) of two eusocial and a solitary bee species. In addition, we used transmission electron microscopy (TEM) for studying the developing cuticle of these and other three bee species also differing in life style. We found 13,200, 55,209 and 30,161 transcript types in the integument of the eusocial Apis mellifera and Frieseomelitta varia, and the solitary Centris analis, respectively. In general, structural cuticle proteins and chitin-related genes were upregulated in pharate-adults and newly-emerged bees whereas transcripts for odorant binding proteins, cytochrome P450 and antioxidant proteins were overrepresented in foragers. Consistent with our hypothesis, a distance correlation analysis based on the differentially expressed genes suggested delayed cuticle maturation in A. mellifera in comparison to the solitary bee. However, this was not confirmed in the comparison with F. varia. The expression profiles of 27 of 119 genes displaying functional attributes related to cuticle formation/differentiation were positively correlated between A. mellifera and F. varia, and negatively or non-correlated with C. analis, suggesting roles in cuticular maturation heterochrony. However, we also found transcript profiles positively correlated between each one of the eusocial species and C. analis. Gene co-expression networks greatly differed between the bee species, but we identified common gene interactions exclusively between the eusocial species. Except for F. varia, the TEM analysis is consistent with cuticle development timing adapted to the social or solitary life style. In support to our hypothesis, the absolute quantities of n-alkanes and unsaturated CHCs were significantly higher in foragers than in the earlier developmental phases of the eusocial bees, but did not discriminate newly-emerged from foragers in C. analis. By highlighting differences in integument gene expression, cuticle ultrastructure, and CHC profiles between eusocial and solitary bees, our data provided insights into the process of heterochronic cuticle maturation associated to the way of life.

A cuticle protein gene in the honeybee: expression during development and in relation to the ecdysteroid titer.

A cDNA encoding a cuticle protein containing the R&R Consensus was characterized in the honeybee integument. AmelCPR14 developmental expression is distinguished by an on-off-on pattern, the transition from a low to a high level of transcripts occurring as the ecdysteroid titer is declining after the peak that triggers the onset of pharate (pupal and adult) development. The transcript is abundant during cuticle tanning and sclerotization, and persists even in the adult integument, suggesting that the corresponding protein is required for differentiation and maintenance of the adult cuticle. Such developmental pattern suggested that AmelCPR14 gene might be regulated by the titer of ecdysteroids. We confirmed this hypothesis using different experimental strategies. By tying a ligature in early pupae to prevent exposure of abdominal integument to a high ecdysteroid titer, we delayed the accumulation of AmelCPR14 transcripts in the abdominal integument. This is consistent with ecdysteroid priming being required in pupae for the increase in AmelCPR14 expression in pharate adults. By injecting 20-hydroxyecdysone (20E) in early pupae we demonstrated that hormone titer decay after the peak is critical for AmelCPR14 expression induction. Exposure of pupal integument in vitro to a 20E concentration mimicking the pupal ecdysteroid peak repressed AmelCPR14 expression, which was recovered by hormone removal. Taken together, these data are consistent with an ecdysteroid pulse (increase in hormone titer followed by its decline) being critical for a high AmelCPR14 gene expression in pharate adults.

Repeated evolution of soldier sub-castes suggests parasitism drives social complexity in stingless bees.

The differentiation of workers into morphological castes represents an important evolutionary innovation that is thought to improve division of labor in insect societies. Given the potential benefits of task-related worker differentiation, it is puzzling that physical worker castes, such as soldiers, are extremely rare in social bees and absent in wasps. Following the recent discovery of soldiers in a stingless bee, we studied the occurrence of worker differentiation in 28 stingless bee species from Brazil and found that several species have specialized soldiers for colony defence. Our results reveal that worker differentiation evolved repeatedly during the last ~ 25 million years and coincided with the emergence of parasitic robber bees, a major threat to many stingless bee species. Furthermore, our data suggest that these robbers are a driving force behind the evolution of worker differentiation as targets of robber bees are four times more likely to have nest guards of increased size than non-targets. These findings reveal unexpected diversity in the social organization of stingless bees.Although common in ants and termites, worker differentiation into physical castes is rare in social bees and unknown in wasps. Here, Grüter and colleagues find a guard caste in ten species of stingless bees and show that the evolution of the guard caste is associated with parasitization by robber bees.

Molecular cloning and expression of a hexamerin cDNA from the honey bee, Apis mellifera.

A cDNA encoding a hexamerin subunit of the Africanized honey bee (Apis mellifera) was isolated and completely sequenced. In the deduced translation product we identified the N-terminal sequence typical of the honey bee HEX 70b hexamerin. The genomic sequence consists of seven exons flanked by GT/AT exon/intron splicing sites, which encode a 683 amino acid polypeptide with an estimated molecular mass of 79.5 kDa, and pI value of 6.72. Semi-quantitative RT-PCR revealed high levels of Hex 70b message in larval stages, followed by an abrupt decrease during prepupal-pupal transition. This coincides with decaying titers of juvenile hormone (JH) and ecdysteroids that is the signal for the metamorphic molt. To verify whether the high Hex 70b expression is dependent on high hormone levels, we treated 5th instar larvae with JH or 20-hydroxyecdysone (20E). In treated larvae, Hex 70b expression was maintained at high levels for a prolonged period of time than in the respective controls, thus indicating a positive hormone regulation at the transcriptional level. Experiments designed to verify the influence of the diet on Hex 70b expression showed similar transcript amounts in adult workers fed on a protein-enriched diet or fed exclusively on sugar. However, sugar-fed workers responded to the lack of dietary proteins by diminishing significantly the amount of HEX 70b subunits in hemolymph. Apparently, they use HEX 70b to compensate the lack of dietary proteins.

Ventral nerve cord remodeling in a stingless bee (Melipona quadrifasciata anthidioides, Hymenoptera, Apidae) depends on ecdysteroid fluctuation and programmed cell death.

The reorganization of the ventral nerve cord (VNC) during metamorphosis of M. quadrifasciata was observed to be characterized by shortening of connectives and subsequent fusion of the 2nd and 3rd thoracic and the 1st abdominal ganglia. Also, the 5th to 7th abdominal ganglia came into very close contact. These changes were accompanied by increasing levels of endogenous ecdysteroids, as determined by a radioimmunoassay. Incubation of VNC in the presence of 5 microg 20-hydroxyecdysone, caused significant shortening of connectives in the thoracic region, but not in the abdomen, evidencing a segment-specific response to this hormone. Cell death in the ventral ganglia was revealed by transmission electron microscopy and TUNEL-reaction. Detection of labeled cells in the region where contiguous ganglia come into close contact suggests that programmed cell death is involved in ganglionic fusion.

The genomes of two key bumblebee species with primitive eusocial organization.

BACKGROUND: The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats. RESULTS: We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits. CONCLUSIONS: These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation.

The use of Open Reading frame ESTs (ORESTES) for analysis of the honey bee transcriptome.

BACKGROUND: The ongoing efforts to sequence the honey bee genome require additional initiatives to define its transcriptome. Towards this end, we employed the Open Reading frame ESTs (ORESTES) strategy to generate profiles for the life cycle of Apis mellifera workers. RESULTS: Of the 5,021 ORESTES, 35.2% matched with previously deposited Apis ESTs. The analysis of the remaining sequences defined a set of putative orthologs whose majority had their best-match hits with Anopheles and Drosophila genes. CAP3 assembly of the Apis ORESTES with the already existing 15,500 Apis ESTs generated 3,408 contigs. BLASTX comparison of these contigs with protein sets of organisms representing distinct phylogenetic clades revealed a total of 1,629 contigs that Apis mellifera shares with different taxa. Most (41%) represent genes that are in common to all taxa, another 21% are shared between metazoans (Bilateria), and 16% are shared only within the Insecta clade. A set of 23 putative genes presented a best match with human genes, many of which encode factors related to cell signaling/signal transduction. 1,779 contigs (52%) did not match any known sequence. Applying a correction factor deduced from a parallel analysis performed with Drosophila melanogaster ORESTES, we estimate that approximately half of these no-match ESTs contigs (22%) should represent Apis-specific genes. CONCLUSIONS: The versatile and cost-efficient ORESTES approach produced minilibraries for honey bee life cycle stages. Such information on central gene regions contributes to genome annotation and also lends itself to cross-transcriptome comparisons to reveal evolutionary trends in insect genomes.

Phenoloxidase activity in Apis mellifera honey bee pupae, and ecdysteroid-dependent expression of the prophenoloxidase mRNA.

Phenoloxidase (monophenol, l-dopa: oxygen oxidoreductase, EC 1.14.18.1) is a multicopper oxidase, which plays an important role in melanin synthesis, necessary for defense against intruding microorganisms and parasites, wound healing and cuticle pigmentation. A phenoloxidase from the hemolymph of honey bee pupae exhibited an apparent molecular mass of 70 kDa, as estimated by gel filtration and SDS-PAGE. Optimal pH and temperature were 6.5 and 20 degrees C, respectively. Activity was fully stable for 30 min at 50 degrees C. Like phenoloxidases from the hemolymph of other insects, the honey bee enzyme was activated by trypsin and inhibited by protease inhibitors and phenylthiourea. Only high concentrations of sodium azide effectively inhibited the detected activity. A low concentration (5 microM) of Ca2+, Mg2+, and Mn2+ had a stimulatory effect on the activity. Single Michaelis-Menten curves were observed for l-dopa and dopamine oxidation, but the affinity of the enzyme for dopamine was greater than for L-dopa. Semiquantitative RT-PCR and Southern blot analysis using a 359 bp labeled probe, and quantification of the prophenoloxidase mRNA levels by real-time PCR showed increased amounts of transcripts in hemocytes and integument from young pupae injected with 20-hydroxyecdysone.

Developmental regulation of ecdysone receptor (EcR) and EcR-controlled gene expression during pharate-adult development of honeybees (Apis mellifera).

Major developmental transitions in multicellular organisms are driven by steroid hormones. In insects, these, together with juvenile hormone (JH), control development, metamorphosis, reproduction and aging, and are also suggested to play an important role in caste differentiation of social insects. Here, we aimed to determine how EcR transcription and ecdysteroid titers are related during honeybee postembryonic development and what may actually be the role of EcR in caste development of this social insect. In addition, we expected that knocking-down EcR gene expression would give us information on the participation of the respective protein in regulating downstream targets of EcR. We found that in Apis mellifera females, EcR-A is the predominantly expressed variant in postembryonic development, while EcR-B transcript levels are higher in embryos, indicating an early developmental switch in EcR function. During larval and pupal stages, EcR-B expression levels are very low, while EcR-A transcripts are more variable and abundant in workers compared to queens. Strikingly, these transcript levels are opposite to the ecdysteroid titer profile. 20-hydroxyecdysone (20E) application experiments revealed that low 20E levels induce EcR expression during development, whereas high ecdysteroid titers seem to be repressive. By means of RNAi-mediated knockdown (KD) of both EcR transcript variants we detected the differential expression of 234 poly-A(+) transcripts encoding genes such as CYPs, MRJPs and certain hormone response genes (Kr-h1 and ftz-f1). EcR-KD also promoted the differential expression of 70 miRNAs, including highly conserved ones (e.g., miR-133 and miR-375), as well honeybee-specific ones (e.g., miR-3745 and miR-3761). Our results put in evidence a broad spectrum of EcR-controlled gene expression during postembryonic development of honeybees, revealing new facets of EcR biology in this social insect.

Bacterial infection activates the immune system response and dysregulates microRNA expression in honey bees.

In insects, a rapid and massive synthesis of antimicrobial peptides (AMPs) is activated through signaling pathways (Toll and Imd) to combat invading microbial pathogens. However, it is still unclear whether different types of bacteria provoke specific responses. Immune response mechanisms and the activation of specific genes were investigated by challenging Apis mellifera workers with the Gram-negative bacterium Serratia marcescens or the Gram-positive bacterium Micrococcus luteus. The immune system responded by activating most genes of the Toll and Imd pathways, particularly AMP genes. However, genes specifically regulated by M. luteus or S. marcescens were not detected, suggesting an interaction between the signaling pathways that lead to immune effectors synthesis. Despite this finding, kappaB motifs in the 5'-UTRs of selected genes suggest a pathway-specific control of AMP and transferrin-1 gene expression. Regulation by miRNAs was also investigated and revealed a number of candidates for the post-transcriptional regulation of immune genes in bees.

A honey bee hexamerin, HEX 70a, is likely to play an intranuclear role in developing and mature ovarioles and testioles.

Insect hexamerins have long been known as storage proteins that are massively synthesized by the larval fat body and secreted into hemolymph. Following the larval-to-pupal molt, hexamerins are sequestered by the fat body via receptor-mediated endocytosis, broken up, and used as amino acid resources for metamorphosis. In the honey bee, the transcript and protein subunit of a hexamerin, HEX 70a, were also detected in ovaries and testes. Aiming to identify the subcellular localization of HEX 70a in the female and male gonads, we used a specific antibody in whole mount preparations of ovaries and testes for analysis by confocal laser-scanning microscopy. Intranuclear HEX 70a foci were evidenced in germ and somatic cells of ovarioles and testioles of pharate-adult workers and drones, suggesting a regulatory or structural role. Following injection of the thymidine analog EdU we observed co-labeling with HEX 70a in ovariole cell nuclei, inferring possible HEX 70a involvement in cell proliferation. Further support to this hypothesis came from an injection of anti-HEX 70a into newly ecdysed queen pupae where it had a negative effect on ovariole thickening. HEX 70a foci were also detected in ovarioles of egg laying queens, particularly in the nuclei of the highly polyploid nurse cells and in proliferating follicle cells. Additional roles for this storage protein are indicated by the detection of nuclear HEX 70a foci in post-meiotic spermatids and spermatozoa. Taken together, these results imply undescribed roles for HEX 70a in the developing gonads of the honey bee and raise the possibility that other hexamerins may also have tissue specific functions.

Ecdysteroid-dependent expression of the tweedle and peroxidase genes during adult cuticle formation in the honey bee, Apis mellifera.

Cuticle renewal is a complex biological process that depends on the cross talk between hormone levels and gene expression. This study characterized the expression of two genes encoding cuticle proteins sharing the four conserved amino acid blocks of the Tweedle family, AmelTwdl1 and AmelTwdl2, and a gene encoding a cuticle peroxidase containing the Animal haem peroxidase domain, Ampxd, in the honey bee. Gene sequencing and annotation validated the formerly predicted tweedle genes, and revealed a novel gene, Ampxd, in the honey bee genome. Expression of these genes was studied in the context of the ecdysteroid-coordinated pupal-to-adult molt, and in different tissues. Higher transcript levels were detected in the integument after the ecdysteroid peak that induces apolysis, coinciding with the synthesis and deposition of the adult exoskeleton and its early differentiation. The effect of this hormone was confirmed in vivo by tying a ligature between the thorax and abdomen of early pupae to prevent the abdominal integument from coming in contact with ecdysteroids released from the prothoracic gland. This procedure impaired the natural increase in transcript levels in the abdominal integument. Both tweedle genes were expressed at higher levels in the empty gut than in the thoracic integument and trachea of pharate adults. In contrast, Ampxd transcripts were found in higher levels in the thoracic integument and trachea than in the gut. Together, the data strongly suggest that these three genes play roles in ecdysteroid-dependent exoskeleton construction and differentiation and also point to a possible role for the two tweedle genes in the formation of the cuticle (peritrophic membrane) that internally lines the gut.

Developmental characterization, function and regulation of a Laccase2 encoding gene in the honey bee, Apis mellifera (Hymenoptera, Apinae).

In insects, exoskeleton (cuticle) formation at each molt cycle includes complex biochemical pathways wherein the laccase enzymes (EC 1.10.3.2) may have a key role. We identified an Amlac2 gene that encodes a laccase2 in the honey bee, Apis mellifera, and investigated its function in exoskeleton differentiation. The Amlac2 gene consists of nine exons resulting in an ORF of 2193 nucleotides. The deduced translation product is a 731 amino acid protein of 81.5 kDa and a pI of 6.05. Amlac2 is highly expressed in the integument of pharate adults, and the expression precedes the onset of cuticle pigmentation and the intensification of sclerotization. In accordance with the temporal sequence of exoskeleton differentiation from anterior to posterior direction, the levels of Amlac2 transcript increase earlier in the thoracic than in the abdominal integument. The gene expression lasts even after the bees emerge from brood cells and begin activities in the nest, but declines after the transition to foraging stage, suggesting that maturation of the exoskeleton is completed at this stage. Post-transcriptional knockdown of Amlac2 gene expression resulted in structural abnormalities in the exoskeleton and drastically affected adult eclosion. By setting a ligature between the thorax and abdomen of early pupae we could delay the increase in hemolymph ecdysteroid levels in the abdomen. This severely impaired the increase in Amlac2 transcript levels and also the differentiation of the abdominal exoskeleton. Taken together, these results indicate that Amlac2 expression is controlled by ecdysteroids and has a critical role in the differentiation of the adult exoskeleton of honey bees.

Functional and evolutionary insights from the genomes of three parasitoid Nasonia species.

We report here genome sequences and comparative analyses of three closely related parasitoid wasps: Nasonia vitripennis, N. giraulti, and N. longicornis. Parasitoids are important regulators of arthropod populations, including major agricultural pests and disease vectors, and Nasonia is an emerging genetic model, particularly for evolutionary and developmental genetics. Key findings include the identification of a functional DNA methylation tool kit; hymenopteran-specific genes including diverse venoms; lateral gene transfers among Pox viruses, Wolbachia, and Nasonia; and the rapid evolution of genes involved in nuclear-mitochondrial interactions that are implicated in speciation. Newly developed genome resources advance Nasonia for genetic research, accelerate mapping and cloning of quantitative trait loci, and will ultimately provide tools and knowledge for further increasing the utility of parasitoids as pest insect-control agents.