Molecular characterization and functional analysis of novel carboxyl/cholinesterases with GQSAG motif in the silkworm Bombyx mori

Identification and Functions of JHE 6 Specifically Expressed in Bombyx mori Silk Gland

Juvenile hormone esterase (JHE) is the specific enzyme that degrades juvenile hormone (JH) and regulates the JH titer in insects. JH also regulates the development of the silk gland and the synthesis and secretion of silk proteins in Bombyx mori. Here, we identified nine possible JHE family members, Bmjhe1-9. Notably, Bmjhe6 is specifically expressed in the silk gland. Using semi-quantitative, quantitative real-time RT-PCR and Western blot, it was confirmed that Bmjhe6 was specifically expressed in the middle silk gland (MSG) with high levels in the anterior region of the MSG (A-MSG). The immunofluorescence localization analysis revealed that Bmjhe6 is produced within cells, secreted into the gland lumen, and co-transported with silk proteins into the anterior silk gland (ASG). In vitro hormone induction experiments demonstrated that Bmjhe6 responds to a JH analog, increasing its expression after 12-24 h, whereas 20-hydroxyecdysone inhibited it. In addition, Bmjhe6 knockdown using dsBmjhe6 injections accelerated larval development, resulting in increased larval body and silk gland weight. This induced disordered sericin genes (Ser2, Ser3) expression, and key genes in the JH synthesis pathway (BmKr-h1 and BmMet1) were significantly upregulated along with the transcription factors (SGF-1 and Sage). These results indicate that Bmjhe6 plays an important role in silk gland growth and silk protein synthesis by modulating JH signal.

Two single mutations in carboxylesterase 001C improve fenvalerate hydrolase activity in Helicoverpa armigera

Carboxylesterases (CarEs) usually play critical roles in the detoxification of toxic chemicals and therefore may be involved in insecticide resistance in agricultural pests. Previous work has shown that CarE 001C from Helicoverpa armigera was able to metabolize the isomers of cypermethrin and fenvalerate. In this study, seven mutants of CarE 001C with single amino acid substitution were produced and expressed in the Escherichia coli. Enzyme kinetic analysis indicated that all seven mutations dramatically reduced enzymatic activities toward the generic substrate α-naphthyl acetate, but in vitro metabolism assay showed that two of the mutations, H423I and R322L, significantly improved hydrolase activities toward fenvalerate, with their recorded specific activities being 3.5 and 5.1 nM·s^-1·mg ^-1 proteins, respectively. Further, thermostability assay showed that the stability of one mutant enzyme was enhanced. This study will help us better understand the potential of CarEs in insecticide detoxification and resistance in H. armigera.

Molecular characterization and functional analysis of a novel candidate of cuticle carboxylesterase in Spodoptera exigua degradating sex pheromones and plant volatile esters

Odorant-degrading enzymes (ODEs) are considered to play key roles in odorant inactivation to maintain the odorant receptor sensitivity of insects. Some members of carboxylesterase (CXE) is a major sub-family of ODEs. However, only a few CXEs have been functionally characterized so far. In the present study, we cloned the antennal esterase SexiCXE11 cDNA full-length sequences from the male antennae of a notorious crop pest, Spodoptera exigua, and its encoded 538 amino acids. It was similar to other insect esterases and had the characteristics of a carboxylesterase. We expressed recombinant enzyme in High-Five insect cells and obtained the high level purified recombinant protein by affinity column. Furthermore we test enzyme activity toward its two acetate sex pheromone components (Z9,E12-Tetradecadienyl acetate, Z9E12-14:Ac and Z9-Tetradecenyl acetate, Z9-14:Ac) and other 18 ester plant volatiles. Our results demonstrated that SexiCXE11 degraded acetate sex pheromone components with similar degradation activities (about 15.75% with Z9E12-14:Ac and 19.28% with Z9-14:Ac) and plant volatiles with a relatively high activity such as pentyl acetate and (Z)-3-hexenyl caproate. SexiCXE11 had high hydrolytic activity with these two ester odorants (>50% degradation), which is characterized that although a ubiquitous expression esterase SexiCXE11 may be partly involved with olfaction. This study may facilitate a better understanding of moth ODE differentiation and suggest strategies for the development of new pest behavior inhibitors.

The molecular basis for the neofunctionalization of the juvenile hormone esterase duplication in Drosophila

The Drosophila melanogaster enzymes juvenile hormone esterase (DmJHE) and its duplicate, DmJHEdup, present ideal examples for studying the structural changes involved in the neofunctionalization of enzyme duplicates. DmJHE is a hormone esterase with precise regulation and highly specific activity for its substrate, juvenile hormone. DmJHEdup is an odorant degrading esterase (ODE) responsible for processing various kairomones in antennae. Our phylogenetic analysis shows that the JHE lineage predates the hemi/holometabolan split and that several duplications of JHEs have been templates for the evolution of secreted β-esterases such as ODEs through the course of insect evolution. Our biochemical comparisons further show that DmJHE has sufficient substrate promiscuity and activity against odorant esters for a duplicate to evolve a general ODE function against a range of mid-long chain food esters, as is shown in DmJHEdup. This substrate range complements that of the only other general ODE known in this species, Esterase 6. Homology models of DmJHE and DmJHEdup enabled comparisons between each enzyme and the known structures of a lepidopteran JHE and Esterase 6. Both JHEs showed very similar active sites despite low sequence identity (30%). Both ODEs differed drastically from the JHEs and each other, explaining their complementary substrate ranges. A small number of amino acid changes are identified that may have been involved in the early stages of the neofunctionalization of DmJHEdup. Our results provide key insights into the process of neofunctionalization and the structural changes that can be involved.

Tissue-specific expression and silencing phenotypes of mitochondrial phosphate carrier paralogues in several insect species

The mitochondrial phosphate carrier gene (PiC) encodes a membrane protein that mediates the supply of inorganic phosphate from the cytosol into the mitochondrial matrix. This substrate-specific transport system plays an important role in efficient ATP synthesis. Mammals appear to have only one PiC with two alternative splicing variants whose functional differences remain unclear. The present study is the first to characterize the multiple genes that encode PiC in insects. Bombyx mori was found to have two PiC paralogues, one ubiquitous and one testis-specific, the latter seeming to be present only in Lepidoptera. Drosophila melanogaster was found to harbour two PiC paralogues, whereas Liriomyza chinensis, another dipteran, has three PiC paralogues. Two PiCs were found to be present in Plautia stali, and silencing either of these genes affected the normal development of P. stali nymphs, although their expression patterns differed amongst tissues. Schistocerca gregaria and Locusta migratoria have two PiC each, with different expression patterns. Tribolium castaneum was found to have only one PiC, which appears to play an essential role in larval development. Thus, although the inorganic phosphate transport system appears to be conserved across eukaryotes, PiC has become specialized in the different tissues of different insect species.

A whole genome screening and RNA interference identify a juvenile hormone esterase-like gene of the diamondback moth, Plutella xylostella

Juvenile hormone (JH) plays a crucial role in preventing precocious metamorphosis and stimulating reproduction. Thus, its hemolymph titer should be under a tight control. As a negative controller, juvenile hormone esterase (JHE) performs a rapid breakdown of residual JH in the hemolymph during last instar to induce a larval-to-pupal metamorphosis. A whole genome of the diamondback moth (DBM), Plutella xylostella, has been annotated and proposed 11 JHE candidates. Sequence analysis using conserved motifs commonly found in other JHEs proposed a putative JHE (Px004817). Px004817 (64.61 kDa, pI=5.28) exhibited a characteristic JHE expression pattern by showing high peak at the early last instar, at which JHE enzyme activity was also at a maximal level. RNA interference of Px004817 reduced JHE activity and interrupted pupal development with a significant increase of larval period. This study identifies Px004817 as a JHE-like gene of P. xylostella.

Two homologous carboxylesterase genes from Locusta migratoria with different tissue expression patterns and roles in insecticide detoxification

Carboxylesterases (CarEs) play a crucial role in detoxification of xenobiotics and resistance to insecticides in insects. In this study, two cDNAs of CarE genes (LmCesA4 and LmCesA5) were sequenced from the migratory locust, Locusta migratoria. The cDNAs of LmCesA4 and LmCesA5 putatively encoded 538 and 470 amino acid residues, respectively. The deduced amino acid sequences of the two CarE genes showed 45.0% identities, possessed highly conserved catalytic triads (Ser-Glu-His), and clustered in phylogenetic analysis. These results suggest that they are homologous genes. Both CarE genes were expressed throughout the developmental stages. However, LmCesA4 was predominately expressed in the midgut (including the gastric caeca) and fat bodies, whereas LmCesA5 was mainly expressed in the gastric caeca. The in situ hybridization results showed that the transcripts of the two genes were localized in apical and basal regions of the columnar cells in the gastric caeca. Gene silencing followed by insecticide bioassay increased the mortalities of deltamethrin-, malathion-, and carbaryl-treated locusts by 29.5%, 31.0% and 20.4%, respectively, after the locusts were injected with LmCesA4 double-stranded RNA (dsRNA). In contrast, the injection of LmCesA5 dsRNA did not significantly increase the susceptibility of the locusts to any of these insecticides. These results suggest that these genes not only show different tissue expression patterns but also play different roles in insecticide detoxification.

Two adenine nucleotide translocase paralogues involved in cell proliferation and spermatogenesis in the silkworm Bombyx mori

Mitochondrial adenine nucleotide translocase (ANT) specifically acts in ADP/ATP exchange through the mitochondrial inner membrane. This transporter protein thereby plays a significant role in energy metabolism in eukaryotic cells. Most mammals have four paralogous ANT genes (ANT1-4) and utilize these paralogues in different types of cells. The fourth paralogue of ANT (ANT4) is present only in mammals and reptiles and is exclusively expressed in testicular germ cells where it is required for meiotic progression in the spermatocytes. Here, we report that silkworms harbor two ANT paralogues, the homeostatic paralogue (BmANTI1) and the testis-specific paralogue (BmANTI2). The BmANTI2 protein has an N-terminal extension in which the positions of lysine residues in the amino acid sequence are distributed as in human ANT4. An expression analysis showed that BmANTI2 transcripts were restricted to the testis, suggesting the protein has a role in the progression of spermatogenesis. By contrast, BmANTI1 was expressed in all tissues tested, suggesting it has an important role in homeostasis. We also observed that cultured silkworm cells required BmANTI1 for proliferation. The ANTI1 protein of the lepidopteran Plutella xylostella (PxANTI1), but not those of other insect species (or PxANTI2), restored cell proliferation in BmANTI1-knockdown cells suggesting that ANTI1 has similar energy metabolism functions across the Lepidoptera. Our results suggest that BmANTI2 is evolutionarily divergent from BmANTI1 and has developed a specific role in spermatogenesis similar to that of mammalian ANT4.

Functional characterization of an antennal esterase from the noctuid moth, Spodoptera exigua

Odorant-degrading esterases (ODEs) act in the fast deactivation of ester pheromone components and plant volatiles in insects. However, only few ODEs have been characterised to date. In this study, six full-length putative ODE genes (designated SexiCXE4, 5, 17, 18, 20, and 31) were cloned from the male antennae of Spodoptera exigua. The deduced amino acid sequences possessed typical characteristics of a carboxylesterase (CXE) and shared high identities with reported insect CXEs. The tissue and temporal expression patterns were investigated by quantitative real time PCR. Although all six SexiCXEs are expressed in antennae of both sexes, SexiCXE4, 17 and 20 are antennae-enriched; while SexiCXE5 and SexiCXE18 are dominantly expressed in wings, and SexiCXE31 is mainly expressed in proboscises, heads and legs. With the highly biased expression in antennae and proboscises, SexiCXE4 was selected for further functional assay. The recombinant SexiCXE4 were expressed in High-five cells and purified by a Ni(2+) affinity column. SexiCXE4 has much higher enzyme activity against plant volatiles (Z)-3-hexenyl acetate and hexyl acetate than to the sex pheromone components, suggesting that it may function mostly in the degradation of the plant volatiles.

Identification of a novel strong and ubiquitous promoter/enhancer in the silkworm Bombyx mori

Transgenic techniques offer a valuable tool for determining gene functions. Although various promoters are available for use in gene overexpression, gene knockdown, and identification of transgenic individuals, there is nevertheless a lack of versatile promoters for such studies, and this dearth acts as a bottleneck, especially with regard to nonmodel organisms. Here, we succeeded in identifying a novel strong and ubiquitous promoter/enhancer in the silkworm. We identified a unique silkworm strain whose reporter gene showed strong and ubiquitous expression during the establishment of enhancer trap strains. In this strain, the transposon was inserted into the 5'UTR of hsp90, a housekeeping gene that is abundantly expressed in a range of tissues. To determine whether the promoter/enhancer of hsp90 could be used to induce strong gene expression, a 2.9-kb upstream genomic fragment of hsp90 was isolated (hsp90(P2.9k)), and its transcriptional activation activity was examined. Strikingly, hsp90(P2.9k) induced strong gene expression in silkworm cell cultures and also strongly induced gene expression in various tissues and developmental stages of the silkworm. hsp90(P2.9k) also exhibited significant promoter/enhancer activity in Sf9, a cell culture from the armyworm, suggesting that this fragment might possibly be used as a gene expression tool in other Lepidoptera. We further found that 2.0 kb of hsp90(P2.9k) is sufficient for the induction of strong gene expression. We believe that this element will be of value for a range of studies such as targeted gene overexpression, gene knockdown and marker gene expression, not only in the silkworm but also in other insect species.

Molecular and functional characterization of cDNAs putatively encoding carboxylesterases from the migratory locust, Locusta migratoria

Carboxylesterases (CarEs) belong to a superfamily of metabolic enzymes encoded by a number of genes and are widely distributed in microbes, plants and animals including insects. These enzymes play important roles in detoxification of insecticides and other xenobiotics, degradation of pheromones, regulation of neurodevelopment, and control of animal development. In this study, we characterized a total of 39 full-length cDNAs putatively encoding different CarEs from the migratory locust, Locusta migratoria, one of the most severe insect pests in many regions of the world, and evaluated the role of four CarE genes in insecticide detoxification. Our phylogenetic analysis grouped the 39 CarEs into five different clades including 20 CarEs in clade A, 3 in D, 13 in E, 1 in F and 2 in I. Four CarE genes (LmCesA3, LmCesA20, LmCesD1, LmCesE1), representing three different clades (A, D and E), were selected for further analyses. The transcripts of the four genes were detectable in all the developmental stages and tissues examined. LmCesA3 and LmCesE1 were mainly expressed in the fat bodies and Malpighian tubules, whereas LmCesA20 and LmCesD1 were predominately expressed in the muscles and hemolymph, respectively. The injection of double-stranded RNA (dsRNA) synthesized from each of the four CarE genes followed by the bioassay with each of four insecticides (chlorpyrifos, malathion, carbaryl and deltamethrin) increased the nymphal mortalities by 37.2 and 28.4% in response to malathion after LmCesA20 and LmCesE1 were silenced, respectively. Thus, we proposed that both LmCesA20 and LmCesE1 played an important role in detoxification of malathion in the locust. These results are expected to help researchers reveal the characteristics of diverse CarEs and assess the risk of insecticide resistance conferred by CarEs in the locust and other insect species.

Two esterases from the genus Spodoptera degrade sex pheromones and plant volatiles

In moths, high temporal sensitivity in perception of sex pheromones and host plant volatiles suggests the existence of mechanisms acting to maintain antennal sensitivity. The antennal enzymes have been long hypothesized to play a central role in the mechanisms, by rapid metabolism of the odorants soon after the fulfillment of the sensillum receptor activation. In the present study, two putative homologous esterases, SexiCXE13 and SlituCXE13, were cloned by RT–PCR and RACE procedures from Spodoptera exigua and Spodoptera litura, respectively. The phylogenetic tree assigned the two genes into the same group with two previously identified male antennal-specific pheromone-degrading enzymes. SexiCXE13 and SlituCXE13 were expressed in High Five cells, and the enzymatic characteristics and substrate specificity were investigated using the purified recombinant enzymes. Both esterases showed high activity to a variety of acetate substrates, including the sex pheromones, their analogs, and some common plant odorants. Our study, for the first time, provides direct biochemical and molecular evidence that the ubiquitously expressed enzyme has the ability to degrade sex pheromones and plant volatiles, and thus this adds new knowledge to the mechanism underlying the sensitivity of moth olfaction.

Functional characterization of a juvenile hormone esterase related gene in the moth Sesamia nonagrioides through RNA interference

Juvenile hormone esterase (JHE) is a carboxylesterase that has attracted great interest because of its critical role in regulating larval to adult transition in insects and other arthropods. Previously, we characterized an ecdysteroid sensitive and juvenile hormone non-susceptible juvenile hormone esterase related gene (SnJHER) in the corn stalk borer, Sesamia nonagrioides. SnJHER was rhythmically up-regulated close to each molt during the corn stalk borer's larval development. In this paper we attempted to functionally characterize SnJHER using several reverse genetics techniques. To functionally characterize SnJHER, we experimented with different dsRNA administration methods, including hemolymph, bacterial or baculovirus-mediated RNA interference, (RNAi). Our findings indicate the potential implication of SnJHER in the developmental programming of Sesamia nonagrioides. It is still unclear whether SnJHER is closely related to the authentic JHE gene, with different or similar biological functions.

Heterologous expression and biochemical characterisation of fourteen esterases from Helicoverpa armigera

Esterases have recurrently been implicated in insecticide resistance in Helicoverpa armigera but little is known about the underlying molecular mechanisms. We used a baculovirus system to express 14 of 30 full-length esterase genes so far identified from midgut cDNA libraries of this species. All 14 produced esterase isozymes after native PAGE and the isozymes for seven of them migrated to two regions of the gel previously associated with both organophosphate and pyrethroid resistance in various strains. Thirteen of the enzymes obtained in sufficient yield for further analysis all showed tight binding to organophosphates and low but measurable organophosphate hydrolase activity. However there was no clear difference in activity between the isozymes from regions associated with resistance and those from elsewhere in the zymogram, or between eight of the isozymes from a phylogenetic clade previously associated with resistance in proteomic and quantitative rtPCR experiments and five others not so associated. By contrast, the enzymes differed markedly in their activities against nine pyrethroid isomers and the enzymes with highest activity for the most insecticidal isomers were from regions of the gel and, in some cases, the phylogeny that had previously been associated with pyrethroid resistance. Phospholipase treatment confirmed predictions from sequence analysis that three of the isozymes were GPI anchored. This unusual feature among carboxylesterases has previously been suggested to underpin an association that some authors have noted between esterases and resistance to the Cry1Ac toxin from Bacillus thuringiensis. However these three isozymes did not migrate to the zymogram region previously associated with Cry1Ac resistance.

Predisposing factors of hepatocellular carcinoma recurrence following complete remission in response to transarterial chemoembolization

BACKGROUND AND AIM

The aim of our study was to determine the predictors of recurrences in hepatocellular carcinoma (HCC) patients who had achieved complete remission (CR) by transarterial chemoembolization (TACE).

METHODS

A total of 220 consecutive HCC patients who had achieved CR by TACE were followed for a median 72 months. CR was defined as complete lipiodol uptake based on the results of lipiodol-computed tomography 4 weeks after TACE and no additional tumor staining on the follow-up angiography. Recurrence patterns were classified as local recurrence and secondary tumor, respectively, in relation to the location of recurrence; early and late recurrence were classified in relation to recurrence time.

RESULTS

Recurrence of HCC was observed in 169 patients (77 %), of whom 91 (54 %) had local recurrences, 61 (36 %) had secondary tumor, and 17 (10 %) had both. There were 45 (27 %) early and 124 (73 %) late recurrences. Local recurrence developed more frequently in patients with early recurrence than in those with late recurrence (62 vs. 51 %, respectively), while secondary tumor was detected more commonly in patients with late recurrence than in those with early recurrence (39 vs. 29 %, respectively; P < 0.001). In multivariate analyses, multinodularity [hazard ratio (HR) 2.351, P = 0.023] and a persistently high serum alpha-fetoprotein level following CR (HR 3.173, P < 0.001) were significant predictors of early recurrence. Older age (≥ 60 years; HR 1.531, P = 0.043), advanced Child-Pugh class (HR 1.983, P = 0.002), and the association with cirrhosis (HR 1.756, P = 0.028) were predictors of late recurrence following CR.

CONCLUSIONS

Early recurrences following CR by TACE may be due mainly to undetectable remaining tumors, whereas late recurrences may be caused by newly appearing tumors in patients with a background of advanced cirrhotic liver.

Juvenile hormone (JH) esterase of the mosquito Culex quinquefasciatus is not a target of the JH analog insecticide methoprene

Juvenile hormones (JHs) are essential sesquiterpenes that control insect development and reproduction. JH analog (JHA) insecticides such as methoprene are compounds that mimic the structure and/or biological activity of JH. In this study we obtained a full-length cDNA, cqjhe, from the southern house mosquito Culex quinquefasciatus that encodes CqJHE, an esterase that selectively metabolizes JH. Unlike other recombinant esterases that have been identified from dipteran insects, CqJHE hydrolyzed JH with specificity constant (k_cat/K_M ratio) and V_max values that are common among JH esterases (JHEs). CqJHE showed picomolar sensitivity to OTFP, a JHE-selective inhibitor, but more than 1000-fold lower sensitivity to DFP, a general esterase inhibitor. To our surprise, CqJHE did not metabolize the isopropyl ester of methoprene even when 25 pmol of methoprene was incubated with an amount of CqJHE that was sufficient to hydrolyze 7,200 pmol of JH to JH acid under the same assay conditions. In competition assays in which both JH and methoprene were available to CqJHE, methoprene did not show any inhibitory effects on the JH hydrolysis rate even when methoprene was present in the assay at a 10-fold higher concentration relative to JH. Our findings indicated that JHE is not a molecular target of methoprene. Our findings also do not support the hypothesis that methoprene functions in part by inhibiting the action of JHE.

Juvenile hormone esterase: biochemistry and structure

Normal insect development requires a precisely timed, precipitous drop in hemolymph juvenile hormone (JH) titer. This drop occurs through a coordinated halt in JH biosynthesis and increase in JH metabolism. In many species, JH esterase (JHE) is critical for metabolism of the resonance-stabilized methyl ester of JH. JHE metabolizes JH with a high kcat/KM ratio that results primarily from an exceptionally low KM. Here we review the biochemistry and structure of authentic and recombinant JHEs from six insect orders, and present updated diagnostic criteria that help to distinguish JHEs from other carboxylesterases. The use of a JHE-encoding gene to improve the insecticidal efficacy of biopesticides is also discussed.

Molecular characterization of a gene encoding juvenile hormone esterase in the red flour beetle, Tribolium castaneum

Juvenile hormone esterases (JHEs) are required for the degradation of juvenile hormones (JHs) in insects. Here, we report the cloning and analysis of the jhe gene in the red flour beetle, Tribolium castaneum, a model insect of Coleoptera. The Tcjhe gene was strongly expressed at the final instar larva, as would be expected if it functioned to decrease the JH titer at this stage. A recombinant TcJHE protein efficiently degraded JH III, suggesting that the enzyme functions in vivo as a JH-specific degradation enzyme. This is the first report describing the developmental expression profile of the jhe gene whose enzymatic activity was shown in Coleoptera, and the new data reported here will aid elucidation of the mechanism of JH titer regulation in insects.

Genomic analysis of carboxyl/cholinesterase genes in the silkworm Bombyx mori

Background

Carboxyl/cholinesterases (CCEs) have pivotal roles in dietary detoxification, pheromone or hormone degradation and neurodevelopment. The recent completion of genome projects in various insect species has led to the identification of multiple CCEs with unknown functions. Here, we analyzed the phylogeny, expression and genomic distribution of 69 putative CCEs in the silkworm, Bombyx mori (Lepidoptera: Bombycidae).

Results

A phylogenetic tree of CCEs in B. mori and other lepidopteran species was constructed. The expression pattern of each B. mori CCE was also investigated by a search of an expressed sequence tag (EST) database, and the relationship between phylogeny and expression was analyzed. A large number of B. mori CCEs were identified from a midgut EST library. CCEs expressed in the midgut formed a cluster in the phylogenetic tree that included not only B. mori genes but also those of other lepidopteran species. The silkworm, and possibly also other lepidopteran species, has a large number of CCEs, and this might be a consequence of the large cluster of midgut CCEs. Investigation of intron-exon organization in B. mori CCEs revealed that their positions and splicing site phases were strongly conserved. Several B. mori CCEs, including juvenile hormone esterase, not only showed clustering in the phylogenetic tree but were also closely located on silkworm chromosomes. We investigated the phylogeny and microsynteny of neuroligins in detail, among many CCEs. Interestingly, we found the evolution of this gene appeared not to be conserved between B. mori and other insect orders.

Conclusions

We analyzed 69 putative CCEs from B. mori. Comparison of these CCEs with other lepidopteran CCEs indicated that they had conserved expression and function in this insect order. The analyses showed that CCEs were unevenly distributed across the genome of B. mori and suggested that neuroligins may have a distinct evolutionary history from other insect order. It is possible that such an uneven genomic distribution and a unique neuroligin evolution are shared with other lepidopteran insects. Our genomic analysis has provided novel information on the CCEs of the silkworm, which will be of value to understanding the biology, physiology and evolution of insect CCEs.