The use of a juvenile hormone binding protein for the quantitative assay of juvenile hormone

Juvenile hormone promotes locust fat body cell polyploidization and vitellogenesis by activating the transcription of Cdk6 and E2f1

Juvenile hormone (JH) is known to promote cell polyploidization for insect vitellogenesis and egg production, but the underlying mechanisms remain poorly understood. Using the migratory locust Locusta migratoria as a model system, we report here that the expression of cyclin-dependent kinase 6 (Cdk6) and adenovirus E2 factor-1 (E2f1), the core mediators in cell cycle progression is regulated by JH and its receptor Methoprene-tolerant (Met). JH acts through its receptor complex comprised of Met and Taiman to directly activate the transcription of Cdk6 and E2f1. Depletion of Cdk6 or E2f1 results in significantly decreased ploidy, precocious mitotic entry and increased cell numbers in the fat body, accompanied by substantial reduction of Vitellogenin gene expression, blocked ovarian growth and arrested oocyte maturation. These findings indicate a crucial role of Cdk6 and E2f1 in JH-regulated polyploidization and vitellogenesis as well as a novel regulatory machinery for endocycling in insects.

Involvement of Met and Kr-h1 in JH-Mediated Reproduction of Female Bactrocera dorsalis (Hendel)

Juvenile hormone (JH) prevents metamorphosis during insect larval stages and promotes adult reproductive processes. Krüppel-homolog 1 (Kr-h1), a zinc finger transcription factor assumed to be induced by JH via the JH receptor methoprene-tolerant (Met), mediates the antimetamorphic effect of JH in insects, but its function in JH-mediated reproductive processes has not been fully explored. In this study, Met and Kr-h1 involved in the JH signaling pathway were first cloned and identified from the oriental fruit fly, Bactrocera dorsalis, an important pest infesting fruit and vegetables worldwide. Subsequent spatiotemporal expression analysis revealed that Met and Kr-h1 were both highly expressed in 7-day-old adults and fat body of female adults, respectively. Treatment with a JH analog (methoprene) significantly induced the expression of JH signaling and vitellogenin (Vg) genes and accelerated ovary development. RNA interference (RNAi) further revealed that either Met or Kr-h1 depletion at the adult stage of B. dorsalis impeded ovary development, with significantly lower egg production noted as well. In addition, rescue through methoprene application after RNAi stimulated the expression of JH signaling and Vg genes. Although there were still differences in ovary phenotype between rescued insects and the pre-RNAi control, ovary redevelopment with a larger surface area was observed, consistent with the spatiotemporal expression and phenotypes recorded in the original methoprene experiment. Our data reveal the involvement of Met and Kr-h1 in insect vitellogenesis and egg production, thus indicating the crucial role of the JH signaling pathway in insect reproduction.

Juvenile hormone differentially regulates two Grp78 genes encoding protein chaperones required for insect fat body cell homeostasis and vitellogenesis

Juvenile hormone (JH) has a well known role in stimulating insect vitellogenesis (i.e. yolk deposition) and oocyte maturation, but the molecular mechanisms of JH action in insect reproduction are unclear. The 78-kDa glucose-regulated protein (Grp78) is a heat shock protein 70-kDa family member and one of the most abundant chaperones in the endoplasmic reticulum (ER) where it helps fold newly synthesized peptides. Because of its prominent role in protein folding, and also ER stress, we hypothesized that Grp78 might be involved in fat body cell homeostasis and vitellogenesis and a regulatory target of JH. We report here that the migratory locust Locusta migratoria possesses two Grp78 genes that are differentially regulated by JH. We found that Grp78-1 is regulated by JH through Mcm4/7-dependent DNA replication and polyploidization, whereas Grp78-2 expression is directly activated by the JH-receptor complex comprising methoprene-tolerant and Taiman proteins. Interestingly, Grp78-2 expression in the fat body is about 10-fold higher than that of Grp78-1 Knockdown of either Grp78-1 or Grp78-2 significantly reduced levels of vitellogenin (Vg) protein, accompanied by retarded maturation of oocytes. Depletion of both Grp78-1 and Grp78-2 resulted in ER stress and apoptosis in the fat body and in severely defective Vg synthesis and oocyte maturation. These results indicate a crucial role of Grp78 in JH-dependent vitellogenesis and egg production. The presence and differential regulation of two Grp78 genes in L. migratoria likely help accelerate the production of this chaperone in the fat body to facilitate folding of massively synthesized Vg and other proteins.

Juvenile Hormone Is Required in Adult Males for Drosophila Courtship

Juvenile Hormone (JH) has a prominent role in the regulation of insect development. Much less is known about its roles in adults, although functions in reproductive maturation have been described. In adult females, JH has been shown to regulate egg maturation and mating. To examine a role for JH in male reproductive behavior we created males with reduced levels of Juvenile Hormone Acid O-Methyl Transferase (JHAMT) and tested them for courtship. JHAMT regulates the last step of JH biosynthesis in the Corpora Allata (CA), the organ of JH synthesis. Males with reduced levels of JHAMT showed a reduction in courtship that could be rescued by application of Methoprene, a JH analog, shortly before the courtship assays were performed. In agreement with this, reducing JHAMT conditionally in mature flies led to courtship defects that were rescuable by Methoprene. The same result was also observed when the CA were conditionally ablated by the expression of a cellular toxin. Our findings demonstrate that JH plays an important physiological role in the regulation of male mating behavior.

Juvenile Hormone Activates the Transcription of Cell-division-cycle 6 (Cdc6) for Polyploidy-dependent Insect Vitellogenesis and Oogenesis

Although juvenile hormone (JH) is known to prevent insect larval metamorphosis and stimulate adult reproduction, the molecular mechanisms of JH action in insect reproduction remain largely unknown. Earlier, we reported that the JH-receptor complex, composed of methoprene-tolerant and steroid receptor co-activator, acts on mini-chromosome maintenance (Mcm) genes Mcm4 and Mcm7 to promote DNA replication and polyploidy for the massive vitellogenin (Vg) synthesis required for egg production in the migratory locust (Guo, W., Wu, Z., Song, J., Jiang, F., Wang, Z., Deng, S., Walker, V. K., and Zhou, S. (2014) PLoS Genet. 10, e1004702). In this study we have investigated the involvement of cell-division-cycle 6 (Cdc6) in JH-dependent vitellogenesis and oogenesis, as Cdc6 is essential for the formation of prereplication complex. We demonstrate here that Cdc6 is expressed in response to JH and methoprene-tolerant, and Cdc6 transcription is directly regulated by the JH-receptor complex. Knockdown of Cdc6 inhibits polyploidization of fat body and follicle cells, resulting in the substantial reduction of Vg expression in the fat body as well as severely impaired oocyte maturation and ovarian growth. Our data indicate the involvement of Cdc6 in JH pathway and a pivotal role of Cdc6 in JH-mediated polyploidization, vitellogenesis, and oogenesis.

Krüppel-homolog 1 mediates juvenile hormone action to promote vitellogenesis and oocyte maturation in the migratory locust

Juvenile hormone (JH) prevents insect larval metamorphosis and stimulates processes for adult reproduction. Krüppel-homolog 1 (Kr-h1), a zinc finger transcription factor, is shown to mediate the anti-metamorphic effect of JH in both holometabolous and hemimetabolous insects. However, the role of Kr-h1 in JH-mediated reproduction has not been determined. Using the migratory locust, Locusta migratoria, we showed here that Kr-h1 was expressed in response to JH in female adults, and Kr-h1 transcription was directly regulated by the JH-receptor complex comprised of Methoprene-tolerant (Met) and steroid receptor co-activator. We demonstrated that Kr-h1 RNAi phenocopied Met RNAi and JH-deprived condition during post-eclosion development and vitellogenesis of female locusts. Knockdown of Kr-h1 resulted in substantial reduction of Vg expression in the fat body and lipid accumulation in the primary oocytes, accompanied by blocked follicular epithelium development, oocyte maturation and ovarian growth. Our data therefore reveal a crucial role of Kr-h1 in insect vitellogenesis and egg production. This study suggests that JH-Met-Kr-h1 signaling pathway is also functional in insect reproduction.

Argonaute 1 is indispensable for juvenile hormone mediated oogenesis in the migratory locust, Locusta migratoria

Juvenile hormone (JH) is the primary hormone controlling vitellogenesis and oocyte maturation in the migratory locust Locusta migratoria, an evolutionarily primitive insect species with panoistic ovaries. However, molecular mechanisms of locust oogenesis remain unclear and the role of microRNA (miRNA) in JH mediated locust vitellogenesis and oocyte maturation has not been explored. Using miRNA sequencing and quantification with small RNA libraries derived from fat bodies of JH-deprived versus JH analog-exposed female adult locusts, we have identified 83 JH up-regulated and 60 JH down-regulated miRNAs. QRT-PCR validation has confirmed that transcription of selected miRNAs responded to JH administration and correlated with changes in endogenous hemolymph JH titers. Depletion of Argonaute 1 (Ago1), a key regulator of miRNA biogenesis and function by RNAi in female adult locusts dramatically decreased the expression of vitellogenin (Vg) and severely impaired follicular epithelium development, terminal oocyte maturation and ovarian growth. Our data indicate that Ago1 and Ago1-dependent miRNAs play a crucial role in locust vitellogenesis and egg production.

Purification, characterisation and titre of the haemolymph juvenile hormone binding proteins from Schistocerca gregaria and Gryllus bimaculatus

Juvenile hormone binding proteins (JHBPs) were extracted from the haemolymph of adult desert locusts, Schistocerca gregaria, and Mediterranean field crickets, Gryllus bimaculatus. The JHBPs were purified by polyethyleneglycol precipitation, filtration through molecular weight cut off filters and chromatography on a HiTrap heparin column. The juvenile hormone (JH) binding activity of the extracts was measured using a hydroxyapatite assay and the purification progress was monitored by native gel chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The haemolymph JHBPs of both insects are hexamers composed of seemingly identical subunits. The JHBP of the locust has a native Mr of 480 kDa with subunits of 77 kDa, whereas the JHBP of the cricket has a Mr of 510 kDa with subunits of 81 kDa. The locust JHBP binds JH III with moderate affinity (KD = 19 nM). Competition for binding of JH II and JH I was about 2 and 5 times less, respectively. The cricket JHBP also has a moderate affinity for JH III (KD = 28 nM), but surprisingly, competition for binding of JH II was equal to that of JH III and JH I competed about 3 times higher. No sequence information was obtained for the locust JHBP, but the N-terminal sequence of the cricket JHBP shows ca. 56% sequence homology with a hexamerin from Calliphora vicina. Antisera raised against the purified JHBPs were used to measure age- and sex-dependent changes in haemolymph JHBP titres and to confirm that the JHBPs of both species are immunologically different.

The Drosophila takeout gene is regulated by the somatic sex-determination pathway and affects male courtship behavior

The Drosophila somatic sex-determination regulatory pathway has been well studied, but little is known about the target genes that it ultimately controls. In a differential screen for sex-specific transcripts expressed in fly heads, we identified a highly male-enriched transcript encoding Takeout, a protein related to a superfamily of factors that bind small lipophilic molecules. We show that sex-specific takeout transcripts derive from fat body tissue closely associated with the adult brain and are dependent on the sex determination genes doublesex (dsx) and fruitless (fru). The male-specific Doublesex and Fruitless proteins together activate Takeout expression, whereas the female-specific Doublesex protein represses takeout independently of Fru. When cells that normally express takeout are feminized by expression of the Transformer-F protein, male courtship behavior is dramatically reduced, suggesting that male identity in these cells is necessary for behavior. A loss-of-function mutation in the takeout gene reduces male courtship and synergizes with fruitless mutations, suggesting that takeout plays a redundant role with other fru-dependent factors involved in male mating behavior. Comparison of Takeout sequences to the Drosophila genome reveals a family of 20 related secreted factors. Expression analysis of a subset of these genes suggests that the takeout gene family encodes multiple factors with sex-specific functions.

Sequences of elongation factors-1 alpha and -1 gamma and stimulation by juvenile hormone in Locusta migratoria

Two cDNAs encoding the alpha and gamma subunits of translation elongation factor-1 (EF-1) have been cloned and sequenced from the African migratory locust, Locusta migratoria. Southern blotting and real-time PCR analyses indicated that these sequences represent single copy genes. Comparison with sequences from other species indicated greater conservation for EF-1 alpha than for EF-1 gamma. The developmental profiles for EF-1 alpha and -1 gamma mRNA expression in the fat body paralleled reported changes in the hemolymph juvenile hormone (JH) titer in the fifth instar and were elevated during early reproductive maturation in the female adult. In maturing adults, there was a greater accumulation of EF-1 alpha and -1 gamma transcripts in females than in males. The levels of both transcripts were greatly increased by an enriched diet, previously shown to elevate JH titers and accelerate vitellogenin production. Treating JH-deprived adult females with the JH analog, methoprene, resulted in more than doubling of transcript levels of both genes, supporting the hypothesis that JH could stimulate the accumulation of LmEF-1 alpha and -1 gamma transcripts. We suggest that production of elongation factors, increased by JH, may contribute to the massive protein synthesis required for egg production.

Sequence of the hexameric juvenile hormone-binding protein from the hemolymph of Locusta migratoria

The cDNA for the hexameric hemolymph juvenile hormone-binding protein (JHBP) from the migratory locust has been cloned and sequenced. Antiserum raised against purified JHBP was used to identify clones in an expression library. The 4.3-kilobase JHBP mRNA codes for 668 amino acids (74.4 kDa) and contains 2 kilobases of 3'-untranslated region. The derived amino acid sequence reveals that locust JHBP represents a new group within the hexamerin family of arthropod proteins. JHBP appears to be more closely related to arthropod hemocyanins, the believed ancestors of the family, than to the other known insect hexamerins. The mRNA shows a high (89%) bias to codons ending in G or C and the codons ending in A or T are clustered and concentrated toward the 5' end, suggesting a mosaic gene structure. The recombinant bacterially expressed protein bound [3H]JH III with the same affinity as the protein from hemolymph. A truncated version of JHBP lacking 53 amino acids from the N terminus did not bind JH III. Hybridization analysis of fat body JHBP mRNA in locusts that had been treated with precocene and a JH analog did not give clear evidence for regulation by JH.