BmCbZ, an insect-specific factor featuring a composite DNA-binding domain, interacts with BmC/EBPγ

Interacting C/EBPg and YBP regulate DNA methyltransferase 1 expression in Bombyx mori embryos and ovaries

DNA methylation is an important epigenetic modification. DNA methyltransferases (Dnmts), which catalyze the formation of 5-methylcytosine, play a role in ovarian and embryonic development in some insects. However, the underlying mechanism of Dnmt in mediating ovarian and embryonic development remains unclear. In this study, the regulation and function of Bombyx mori Dnmt1 were investigated. By progressively deleting the sequence upstream of Dnmt1, a region located between -580 and -560 region from the transcription initiation site was found to have the most transcriptional activity. Electrophoretic mobility shift assay and chromatin immunoprecipitation demonstrated that transcription factor Y box binding protein (YBP), a homolog of human Y box binding protein 1 (YBX1), bound to the -580 to -560 region. YBP knockdown and overexpression in a Bombyx cell line indicated that YBP activates Dnmt1 expression. Furthermore, GST-pulldown and co-immunoprecipitation demonstrated that YBP and ovarian CCAAT/enhancer binding protein (C/EBPg) could bind each other. Simultaneous knockdown of C/EBPg and YBP was more effective than single-gene RNAi in inhibiting Dnmt1 expression and reducing the hatching rate. These results demonstrated that the interaction of C/EBPg and YBP activated Dnmt1 expression. Correlated with the expression profiles of the studies genes, our results suggest that high-level expression and interaction of C/EBPg and YBP in ovaries and embryos enhance the expression of Dnmt1, thus ensuring high reproduction rate in B. mori.

20-Hydroxyecdysone receptor-activated Bombyx mori CCAAT/enhancer-binding protein gamma regulates the expression of BmCBP and subsequent histone H3 lysine 27 acetylation in Bo. mori

Cyclic adenosine monophosphate (cAMP) response element binding protein (CREB)-binding protein (CBP or CREBBP) plays important roles in regulating gene transcription and animal development. However, the process by which CBP is up-regulated to impact insect development is unknown. In this study, the regulatory mechanism of Bombyx mori CBP (BmCBP) expression induced by 20-hydroxyecdysone (20E) was investigated. In the Bo. mori cell line, DZNU-Bm-12, 20E enhanced BmCBP transcription and histone H3K27 acetylation. BmCBP RNA interference (RNAi) resulted in decreased histone H3K27 acetylation. Additionally, the luciferase activity analysis revealed that the transcription factor, Bo. mori CCAAT/enhancer-binding protein gamma (BmC/EBPg), activated BmCBP transcription, which was suppressed by BmC/EBPg RNAi and promoted by BmC/EBPg overexpression. Electrophoretic mobility shift assay and chromatin immunoprecipitation results demonstrated that BmC/EBPg could bind to the C/EBP cis-regulatory elements in two positions of the BmCBP promoter. Moreover, BmC/EBPg transcription was enhanced by the 20E receptor (BmEcR), which bound to the BmC/EBPg promoter. BmEcR RNAi significantly inhibited the transcriptional levels of BmC/EBPg and BmCBP in the presence of 20E. Furthermore, the BmEcR-BmC/EBPg pathway regulated the acetylation levels of histone H3K27. Altogether, these results indicate that BmEcR enhances the expression of BmC/EBPg, which binds to the BmCBP promoter, activates BmCBP expression and leads to histone H3K27 acetylation.

Insect Transcription Factors: A Landscape of Their Structures and Biological Functions in Drosophila and beyond

Transcription factors (TFs) play essential roles in the transcriptional regulation of functional genes, and are involved in diverse physiological processes in living organisms. The fruit fly Drosophila melanogaster, a simple and easily manipulated organismal model, has been extensively applied to study the biological functions of TFs and their related transcriptional regulation mechanisms. It is noteworthy that with the development of genetic tools such as CRISPR/Cas9 and the next-generation genome sequencing techniques in recent years, identification and dissection the complex genetic regulatory networks of TFs have also made great progress in other insects beyond Drosophila. However, unfortunately, there is no comprehensive review that systematically summarizes the structures and biological functions of TFs in both model and non-model insects. Here, we spend extensive effort in collecting vast related studies, and attempt to provide an impartial overview of the progress of the structure and biological functions of current documented TFs in insects, as well as the classical and emerging research methods for studying their regulatory functions. Consequently, considering the importance of versatile TFs in orchestrating diverse insect physiological processes, this review will assist a growing number of entomologists to interrogate this understudied field, and to propel the progress of their contributions to pest control and even human health.

The dynamic landscape of gene regulation during Bombyx mori oogenesis

BACKGROUND

Oogenesis in the domestic silkworm (Bombyx mori) is a complex process involving previtellogenesis, vitellogenesis and choriogenesis. During this process, follicles show drastic morphological and physiological changes. However, the genome-wide regulatory profiles of gene expression during oogenesis remain to be determined.

RESULTS

In this study, we obtained time-series transcriptome data and used these data to reveal the dynamic landscape of gene regulation during oogenesis. A total of 1932 genes were identified to be differentially expressed among different stages, most of which occurred during the transition from late vitellogenesis to early choriogenesis. Using weighted gene co-expression network analysis, we identified six stage-specific gene modules that correspond to multiple regulatory pathways. Strikingly, the biosynthesis pathway of the molting hormone 20-hydroxyecdysone (20E) was enriched in one of the modules. Further analysis showed that the ecdysteroid 20-hydroxylase gene (CYP314A1) of steroidgenesis genes was mainly expressed in previtellogenesis and early vitellogenesis. However, the 20E-inactivated genes, particularly the ecdysteroid 26-hydroxylase encoding gene (Cyp18a1), were highly expressed in late vitellogenesis. These distinct expression patterns between 20E synthesis and catabolism-related genes might ensure the rapid decline of the hormone titer at the transition point from vitellogenesis to choriogenesis. In addition, we compared landscapes of gene regulation between silkworm (Lepidoptera) and fruit fly (Diptera) oogeneses. Our results show that there is some consensus in the modules of gene co-expression during oogenesis in these insects.

CONCLUSIONS

The data presented in this study provide new insights into the regulatory mechanisms underlying oogenesis in insects with polytrophic meroistic ovaries. The results also provide clues for further investigating the roles of epigenetic reconfiguration and circadian rhythm in insect oogenesis.

Transcription factor CAAT/enhancer-binding protein is involved in regulation of expression of sterol carrier protein x in Spodoptera litura

The Spodoptera litura sterol carrier protein x (SlSCPx) gene is expressed in various tissues throughout the life cycle and plays important role in sterol absorption and transport. In this study, the effects of insect hormones (20-hydroexcdysone and juvenile hormone) and lipids (arachidonic acid, cholesterol) on the expression of SlSCPx was analysed by reverse-transcriptase PCR. The results showed that none of these substances significantly induced the expression of SlSCPx in Spodoptera litura-221 (Spli-221) cells. To identify the transcription factors responsible for regulation of SlSCPx expression, a 3311-bp promoter sequence of the gene was cloned. Transcriptional activity of the promoter was studied using an in vivo promoter/reporter system and a 29-bp sequence between -1000 and -1029 nucleotides (nt) upstream of this gene was found to be responsible for the up-regulation of the gene. Over-expression of CAAT/enhancer-binding protein (C/EBP) in Spli-221 cells increased the promoter activity 5.57-fold. An electrophoretic mobility shift assay showed that two nuclear proteins bound to this sequence. Recombinant C/EBP specifically bound with a putative cis-regulatory element (CRE). Mutation of the C/EBP CRE abolished the binding of the C/EBP with the CRE. These results suggest that the transcription factor C/EBP may regulate the expression of SlSCPx by binding to the CRE in the promoter of this gene.

Analysis of developmentally regulated chorion gene promoter architecture via electroporation of silk moth follicles

In the silk moth Bombyx mori, chorion genes of the same developmental specificity are organized in divergently transcribed α/β gene pairs, sharing a common 5' flanking promoter region. This bidirectional promoter contains a complete set of cis-elements responsible for developmentally accurate gene expression. In the present paper, based on the observation that Bombyx chorion gene promoters contain cis-elements for the same transcription factors without concrete evidence on which of them are essential, we address the question as to how promoter architecture (number, orientation and position of common factor binding sites) facilitates developmentally accurate chorion gene regulation. To this end, we constructed several mutated promoter regions of an early-middle gene pair and cloned them upstream of a reporter gene to introduce these plasmid constructs into silk moth follicle epithelial cells via electroporation as an efficient and quick method for transient expression. This is the first time that an ex vivo method had been applied to test the impact of systematic cis-element mutations on a chorion gene promoter. Our results confirmed the importance of the HMGA factor and the role of the GATA factor as an early repressor, and led to a more detailed understanding of which C/EBP sites participate in the regulation of early-middle chorion gene expression.

Chorion genes: a landscape of their evolution, structure, and regulation

Differential regulation at the level of transcription provides a means for controlling gene expression in eukaryotes, especially during development. Insect model systems have been extensively used to decipher the molecular basis of such regulatory cascades, and one of the oldest such model systems is the regulation of chorion gene expression during ovarian follicle maturation. Recent experimental and technological advances have shed new light onto the system, allowing us to revisit it. Thus, in this review we try to summarize almost 40 years' worth of studies on chorion gene regulation while-by comparing Bombyx mori and Drosophila melanogaster models-attempting to present a comprehensive, unified model of the various regulatory aspects of choriogenesis that takes into account the evolutionary conservation and divergence of the underlying mechanisms.

Silkmoth chorion gene regulation revisited: promoter architecture as a key player

Regulation of silkmoth chorion genes has long been used as a model system for studying differential gene expression. The large numbers of genes, their overlapping expression patterns and the overall complexity of the system hinted towards an elaborate mechanism for transcriptional control. Recent studies, however, offer evidence of a molecular pathway governed by the interplay between two general transcription factors, CCAAT enhancer binding proteins (C/EBP) and GATA, an architectural protein, high mobility group A and a chromatin remodeller, chromo-helicase/ATPase-DNA binding protein 1. In this review we present a parsimonious model that adequately describes regulation of transcription across all temporally regulated chorion genes, and propose a role for promoter architecture.

Microarray analysis of acaricide-inducible gene expression in the southern cattle tick, Rhipicephalus (Boophilus) microplus

Acaricide-inducible differential gene expression was studied in larvae of Rhipicephalus (Boophilus) microplus using a microarray-based approach. The acaricides used were: coumaphos, permethrin, ivermectin, and amitraz. The microarrays contained over 13 000 probes, having been derived from a previously described R. microplus gene index (BmiGI Version 2; Wang et al., 2007). Relative quantitative reverse transcriptase-PCR, real time PCR, and serial analysis of gene expression data was used to verify microarray data. Among the differentially expressed genes with informative annotation were legumain, glutathione S-transferase, and a putative salivary gland-associated protein.

CHD1 assumes a central role during follicle development

During Bombyx mori follicle development, fine-tuning of chorion gene expression is under the control of bidirectional promoters. In this work, we show that the silkmoth chromo-helicase/ATPase-DNA binding protein 1 (CHD1) ortholog is responsible for repositioning of nucleosomes on chorion promoters, where the factor binds specifically. Chorion genes, occupying a single chromosomal locus, rely on an almost identical set of cis elements for their differential expression. As a direct consequence of remodeling, interaction of C/EBP and TFIID with promoter elements is facilitated and ultimately leads to initiation of transcription. Appending of methylation marks to H3K4 in a temporal-specific manner is dependent on CHD1 binding to cognate cis elements and signifies gene activation. Overall, CHD1 is a critical factor for proper development of the follicular epithelium in terms of whole-cell chromatin arrangement.