Regulatory elements in the juvenile hormone binding protein gene from Galleria mellonella — Topography of binding sites for Usp and EcRDBD

Overexpression of BmJHBPd2 Repressed Silk Synthesis by Inhibiting the JH/Kr-h1 Signaling Pathway in Bombyx mori

The efficient production of silkworm silk is crucial to the silk industry. Silk protein synthesis is regulated by the juvenile hormone (JH) and 20-Hydroxyecdysone (20E). Therefore, the genetic regulation of silk production is a priority. JH binding protein (JHBP) transports JH from the hemolymph to target organs and cells and protects it. In a previous study, we identified 41 genes containing a JHBP domain in the Bombyx mori genome. Only one JHBP gene, BmJHBPd2, is highly expressed in the posterior silk gland (PSG), and its function remains unknown. In the present study, we investigated the expression levels of BmJHBPd2 and the major silk protein genes in the high-silk-producing practical strain 872 (S872) and the low-silk-producing local strain Dazao. We found that BmJHBPd2 was more highly expressed in S872 than in the Dazao strain, which is consistent with the expression pattern of fibroin genes. A subcellular localization assay indicated that BmJHBPd2 is located in the cytoplasm. In vitro hormone induction experiments showed that BmJHBPd2 was upregulated by juvenile hormone analogue (JHA) treatment. BmKr-h1 upregulation was significantly inhibited by the overexpression of BmJHBPd2 (BmJHBPd2OE) at the cell level when induced by JHA. However, overexpression of BmJHBPd2 in the PSG by transgenic methods led to the inhibition of silk fibroin gene expression, resulting in a reduction in silk yield. Further investigation showed that in the transgenic BmJHBPd2OE silkworm, the key transcription factor of the JH signaling pathway, Krüppel homolog 1 (Kr-h1), was inhibited, and 20E signaling pathway genes, such as broad complex (Brc), E74A, and ultraspiracle protein (USP), were upregulated. Our results indicate that BmJHBPd2 plays an important role in the JH signaling pathway and is important for silk protein synthesis. Furthermore, our findings help to elucidate the mechanisms by which JH regulates silk protein synthesis.

Itol A May Affect the Growth and Development of Spodoptera frugiperda through Hijacking JHBP and Impeding JH Transport

Isoryanodane and ryanodane diterpenes have a carbon skeleton correlation in structures, and their natural product-oxidized diterpenes show antifeedant and insecticidal activities against Hemiptera and Lepidoptera. While ryanodine mainly acts on the ryanodine receptor (RyR), isoryanodane does not. In this study, we demonstrated that itol A, an isoryanodane diterpenoid, could significantly downregulate the expression level of juvenile hormone-binding protein (JHBP), which plays a vital role in JH transport. RNAi bioassay indicated that silencing the Spodoptera frugipreda JHBP (SfJHBP) gene decreased itol A activity, which confirmed the developmental phenotypic observation. Parallel reaction monitoring (PRM) further confirmed that itol A affected JHBP's expression abundance. Although JHBP is not proven as the direct or only target of itol A, we confirmed that itol A's action effect depends largely on JHBP and that JHBP is a potential target of itol A. We present foundational evidence that itol A inhibits the growth and development of Spodoptera frugiperda mainly through hijacking JHBP.

Involvement of Cis-Acting Elements in Molecular Regulation of JH-Mediated Vitellogenin Gene 2 of Female Periplaneta americana

Vitellogenins (Vgs) are yolk protein precursors that are regulated by juvenile hormone (JH) and/or 20-hydroxyecdysone (20E) in insects. JH acts as the principal gonadotropin that stimulates vitellogenesis in hemimetabolous insects. In this study, we cloned and characterized the Periplaneta americana Vitellogenin 2 (Vg2) promoter. Multiple sites for putative transcription factor binding were predicted for the 1,804 bp Vg2 promoter region, such as the Broad-Complex, ecdysone response element (EcRE), GATA, Hairy, JH response element (JHRE), and Methoprene (Met)-binding motif, among others. Luciferase reporter assay has identified that construct -177 bp is enough to support JH III induction but not 20E suppression. This 38 bp region (from -177 to -139 bp) contains two conserved response element half-sites separated by 2 nucleotides spacer (DR2) and is designated as Vg2RE (^-168GAGTCACGGAGTCGCCGCTG^-149). Mutation assay and luciferase assay data using mutated constructs verified the crucial role of G residues in Vg2RE for binding the isolated fat body nuclear protein. In Sf9 cells, a luciferase reporter placed under the control of a minimal promoter containing Vg2RE was induced by JH III in a dose- and time-dependent manner. Nuclear proteins isolated from previtellogenic female fat body cells bound to Vg2RE, and this binding was outcompeted by a 50-fold excess of cold Drosophila melanogaster DR4 and Galleria mellonella JH binding protein response elements (Chorion factor-I/Ultraspiracle). Affinity pull-down experiment with nuclear extracts of previtellogenic female fat body, using 31-bp probe Vg2RE as bait, yielded a 71 kDa candidate nuclear protein that may mediate the regulatory action of the JH III.

A putative direct repeat element plays a dual role in the induction and repression of insect vitellogenin-1 gene expression

Juvenile hormones (JH) regulate wide-ranging physiological and developmental processes in insects. However, molecular mechanisms underlying JH signaling remain to be determined. Vitellogenin (Vg) is primarily an egg-yolk protein, but recently proposed to serve many functions in insects. In the female American cockroach (Periplaneta americana), vitellogenin (Vg) genes are activated by JH III and suppressed by 20-hydroxyecdysone (20E) via cis-regulatory elements in a dose-dependent manner. In the present study, the upstream promoter region (935 bp) of Vg1 was cloned to elucidate the action of these hormones. A luciferase reporter assay identified an 81 bp region in the promoter region of Vg1 (-120 to -39 bp) that we found to be critical for JH III activation and 20E suppression. This 81 bp region contains a direct repeat separated by a 2-nucleotide spacer-designated Vg1HRE- that is similar to the Drosophila ecdysone response element direct repeat 4. Moreover, nuclear proteins isolated from nymphs, males, females, and Sf9 cells successfully bound to Vg1HRE, while binding was outcompeted by a 100-fold excess of cold probe or dephosphorylated nuclear protein extracts. In addition, binding was outcompeted by other ecdysone and JH response elements with similar half-site sequences (direct repeats) but to varying extents. Ultimately, we postulate that JH III indirectly activates Vg expression by interfering with or inhibiting the phosphorylation of nuclear proteins bound to Vg1HRE. Involvement of JH III in both induction of Vg1 and control of nuclear proteins binding to Vg1HRE suggest the latter to play an important role in JH signaling.

Genome-wide identification and analysis of JHBP-domain family members in the silkworm Bombyx mori

Juvenile hormone (JH) regulates the insect growth and development. JH appears in the hemolymph bound by a specific glycoprotein, juvenile hormone-binding protein (JHBP), which serves as a carrier to release the hormone to target tissues and cells. However, JHBP family candidates, expression patterns, and functional implications are still unclear. In this study, we identified 41 genes-containing conserved JHBP domains distributed across eight chromosomes of the silkworm Bombyx mori. A phylogenetic tree showed that the silkworm JHBP (BmJHBP) genes could be classified into two major branches and four subfamilies. Microarray data revealed that BmJHBP genes exhibit various expression patterns and are expressed in different tissues, periods, and sexes. The expression of BmJHBP genes was generally higher in the head, integument, midgut, fat body, testis, and ovary than in the anterior of the silk gland (ASG), median of the silk gland (MSG), posterior of the silk gland (PSG), hemocyte, and Malpighian tubule. BmJHBPd2, in particular, was investigated by Western Blotting, and immunofluorescent assay and was found to be highly expressed in the PSG cytoplasm on day 3 of the fifth instar, coinciding with silk production. Taken together, our findings will be useful in improving understanding the complexity of the JHBP family, and will lay the foundation of explaining functional characterization for further research.

Different pattern of Galleria mellonella jhbp gene expression in high five and Sf9 cells

Juvenile hormone binding protein (JHBP) is the key element of the system that transmits hormone signals to target tissues. Recently, we found that the core promoter of the jhbp gene is strongly under the control of the TATA box and the transcription start site. In this report, we have shown that the jhbp promoter contains distal regulatory elements whose functionality clearly depends on the particular cell environment and that the scope of research from one cell line is insufficient to generalize the conclusions of the analysis. Cf1/Usp (where Usp is ultraspiracle protein previously known as Cf1, chorion factor 1) elements suppressed transcription of the reporter gene in the High Five cell line but not in the Sf9 cell line. However, upstream from all three Cf1/Usp elements there is a DNA sequence, containing the Zeste element, which activates jhbp in both systems. We found that juvenile hormone strongly inhibited the activity of the jhbp promoter in the Sf9 cell line, whereas it did not have an effect in the High Five cell line. A second key hormone that controls insect development--20-hydroxyecdysone, was also found to suppress the transcription of jhbp. This is the first report describing how these two hormones affect jhbp gene expression in different cell lines.

Molecular characterization and gene expression of juvenile hormone binding protein in the bamboo borer, Omphisa fuscidentalis

Juvenile hormone (JH) plays an important role in many physiological processes in insect development, diapause and reproduction. An appropriate JH titer in hemolymph is essential for normal development in insects. Information concerning its carrier partner protein, juvenile hormone binding protein (JHBP), provides an alternative approach to understanding how JH regulates metamorphosis. In this study, we cloned and sequenced the Omphisa juvenile hormone binding protein (OfJHBP). The full-length OfJHBP cDNA sequence is comprised of 849 nucleotides with an open reading frame of 726bp encoding 242 amino acids. The molecular mass of the protein was estimated to be 26.94kDa. The deduced protein sequence of OfJHBP showed moderate homology with the lepidopteran, Heliothis virescens JHBP (52% amino acid identity) and lower homology with the Bombyx mori JHBP (45%) and the Manduca sexta JHBP (44%). The OfJHBP was expressed mainly in the fat body. OfJHBP transcripts in the fat body was moderately high during 3rd, 4th and 5th instars, then rapidly increased, reaching a peak during early diapause. The expression remained high in mid-diapause, then decreased in late-diapause until the pupal stage. Both juvenile hormone analog (JHA), methoprene, 20-hydroxyecdysone (20E) exhibited a similar stimulatory pattern in OfJHBP expression of diapausing larvae. OfJHBP mRNA levels gradually increased and showed a peak of gene expression on the penultimate, then declined to low levels in the pupal stage. For in vitro gene expression, both of JHA and 20E induced OfJHBP mRNA expression in fat body. Fat body maintenance in vitro in the presence of 0.1μg/50μl JHA induced OfJHBP mRNA expression to high levels within the first 30min whereas 0.1μg/50μl 20E induced gene expression at 120min. To study the synergistic effect of these two hormones, fat body was incubated in vitro with 0.1μg/50μl JHA or 0.1μg/50μl 20E or a combination of both hormone for 30min. Induction of OfJHBP expression by JHA and 20E was significantly greater than that of either hormone alone. These results should contribute to our understanding of how JHBP and JH regulate the termination of larval diapause in the bamboo borer.