Forkhead transcription factors regulate mosquito reproduction

High-throughput sequencing to reveal genes involved in reproduction and development in Bactrocera dorsalis (Diptera: Tephritidae)

BACKGROUND

Tephritid fruit flies in the genus Bactrocera are of major economic significance in agriculture causing considerable loss to the fruit and vegetable industry. Currently, there is no ideal control program. Molecular means is an effective method for pest control at present, but genomic or transcriptomic data for members of this genus remains limited. To facilitate molecular research into reproduction and development mechanisms, and finally effective control on these pests, an extensive transcriptome for the oriental fruit fly Bactrocera dorsalis was produced using the Roche 454-FLX platform.

RESULTS

We obtained over 350 million bases of cDNA derived from the whole body of B. dorsalis at different developmental stages. In a single run, 747,206 sequencing reads with a mean read length of 382 bp were obtained. These reads were assembled into 28,782 contigs and 169,966 singletons. The mean contig size was 750 bp and many nearly full-length transcripts were assembled. Additionally, we identified a great number of genes that are involved in reproduction and development as well as genes that represent nearly all major conserved metazoan signal transduction pathways, such as insulin signal transduction. Furthermore, transcriptome changes during development were analyzed. A total of 2,977 differentially expressed genes (DEGs) were detected between larvae and pupae libraries, while there were 1,621 DEGs between adults and larvae, and 2,002 between adults and pupae. These DEGs were functionally annotated with KEGG pathway annotation and 9 genes were validated by qRT-PCR.

CONCLUSION

Our data represent the extensive sequence resources available for B. dorsalis and provide for the first time access to the genetic architecture of reproduction and development as well as major signal transduction pathways in the Tephritid fruit fly pests, allowing us to elucidate the molecular mechanisms underlying courtship, ovipositing, development and detailed analyses of the signal transduction pathways.

Fork head transcription factor is required for ovarian mature in the brown planthopper, Nilaparvata lugens (Stål)

Background

The brown planthopper (BPH), Nilaparvata lugens, is the most devastating rice pest in many areas throughout Asia. The reproductive system of female N. lugens consists of a pair of ovaries with 24-33 ovarioles per ovary in most individuals which determine its fecundity. The fork head (Fox) is a transcriptional regulatory molecule, which regulates and controls many physiological processes in eukaryotes. The Fox family has several subclasses and members, and several Fox factors have been reported to be involved in regulating fecundity.

Results

We have cloned a fork head gene in N. lugens. The full-length cDNA of NlFoxA is 1789 bp and has an open reading frame of 1143 bp, encoding a protein of 380 amino acids. Quantitative real-time PCR (RT-qPCR) and Reverse Transcription- PCR (RT-PCR) analysis revealed that NlFoxA mRNA was mainly expressed in the fat body, midgut, cuticle and Malpighian tube, and was expressed continuously with little change during all the developmental stages. NlFoxA belongs to the FoxA subfamily of the Fox transcription factors. Knockdown of NlFoxA expression by RNAi using artificial diet containing double-stranded RNA (dsRNA) significantly decreased the number of offspring and impacted the development of ovaries. ELISA and Western blot analyses showed that feeding-based RNAi of NlFoxA gene also resulted in decreased expression of vitellogenin (Vg) protein.

Conclusion

NlFoxA plays an important role in regulation of fecundity and development of ovaries in the BPH via regulating vitellogenin expression.

Nutritional and hormonal regulation of the TOR effector 4E-binding protein (4E-BP) in the mosquito Aedes aegypti

Mosquitoes require blood for egg development, and, as a consequence, they transmit pathogens of devastating diseases. Target of rapamycin (TOR) signaling is a key pathway linking blood feeding and egg development in the mosquito Aedes aegypti. We show that the regulation of the TOR effector translational repressor 4E-BP is finely tuned to the nutritional requirements of the female mosquito, and it occurs at transcriptional and post-translational levels. Immediately after blood feeding, 4E-BP became hyperphosphorylated, suggesting rapid inhibition of its translational repression function. 4E-BP was highly phosphorylated after in vitro incubation of the fat body in the presence of amino acids; this phosphorylation was rapamycin insensitive, in contrast to another TOR target, S6K, phosphorylation of which was rapamycin sensitive. A high level of 4E-BP phosphorylation was also elicited by insulin. Rapamycin and the PI3K inhibitor LY294002 blocked insulin-mediated 4E-BP phosphorylation. RNA-interference depletion of the insulin receptor or Akt resulted in severe reduction of 4E-BP phosphorylation. Phosphorylation and stability of 4E-BP was dependent on its partner eIF4E translation initiation factor. Silencing of 4E-BP resulted in reduction of the life span of adult female mosquitoes. This study demonstrates a dual nutritional and hormonal control of 4E-BP and its role in mosquito egg development.

The forkhead transcription factor FOXL2 is expressed in somatic cells of the human ovary prior to follicle formation

Interactions between germ cells and surrounding somatic cells are central to ovarian development as well as later function. Disruption of these interactions arising from abnormalities in either cell type can lead to premature ovarian failure (POF). The forkhead transcription factor FOXL2 is a candidate POF factor, and mutations in the FOXL2 gene are associated with syndromic and non-syndromic ovarian failure. Foxl2-deficient mice display major defects in primordial follicle activation with consequent follicle loss, and earlier roles in gonadal development and sex determination have also been suggested. However, despite its importance no data presently exist on its expression in the developing human ovary. Expression of FOXL2 mRNA was demonstrated in the human fetal ovary between 8 and 19 weeks gestation, thus from soon after sex determination to primordial follicle development. Expression in the ovary was higher after 14 weeks than at earlier gestation weeks and was very low in the fetal testis at all ages examined. Immunolocalization revealed FOXL2 expression to be confined to somatic cells, both adjacent to germ cells and those located in the developing ovarian stroma. These cells are the site of action of oocyte-derived activin signalling, but in vitro treatment of human fetal ovaries with activin failed to reveal any regulation of FOXL2 transcription by this pathway. In summary, the expression of FOXL2 in somatic cells of the developing human ovary before and during follicle formation supports a conserved and continuing role for this factor in somatic/germ cell interactions from the earliest stages of human ovarian development.

Role of forkhead L2 in transforming growth factor-beta /Smad signaling pathway-mediated activation of hepatic stellate cells

Hepatic fibrosis is characterized by an abnormal hepatic deposition of extracellular matrix (especially collagen). As hepatic fibrosis progresses, cirrhosis will develop. Hepatic stellate cells are the major source of the extracellular matrix (ECM). The activation of hepatic stellate cells is the central event in the development of hepatic fibrosis. The transforming growth factor-beta (TGF-β)/Smad signaling pathway plays an important role in regulating the synthesis of ECM in stellate cells. Recent studies found that forkhead L2 (Fox L2), belonging to the forkhead family, was able to act as a molecular chaperone for Smad complex. Thus, it may enhance the stability between Smad complex and target genes.

Silencing of carbonic anhydrase in an Anopheles gambiae larval cell line, Ag55

RNAi has been used extensively to down-regulate proteins in adult mosquitoes; however, it is not well adapted for use in larvae. Larval mosquitoes can generate a pH as high as 10.5 in the anterior region of their midgut. The mechanisms responsible for the generation and maintenance of this pH are not entirely understood, but members of the carbonic anhydrase (CA) family of enzymes have been implicated. Here we use an An. gambiae larval cell line, Ag55 cells, to demonstrate that application of full-length double-stranded RNA specific to one CA, AgCA9, is sufficient to silence AgCA9 mRNA and down-regulate the corresponding protein. This is a first step towards determining the role(s) of these enzymes in pH regulation.

Evolutionary selection pressure of forkhead domain and functional divergence

Forkhead-box (Fox) genes encode a family of transcription factors defined by a "winged helix" DNA-binding domain which have been identified in many metazoans, and play important roles in diverse biological processes. Here we aimed to extend previous evolutionary selection analysis to fungi, using available sequences from E. cuniculi (Ec), Eremothecium gossypii (Eg), Saccharomyces cerevisiae (Sc), etc. The phylogeny of 335 Fox protein sequences was reconstructed, revealing the existence of 26 orthologous groups that were well supported by gene phylogeny which arose following a series of gene duplication events. Gene conversion events may also play important roles in the evolution of Fox genes. The nonsynonymous to synonymous substitution ratios (dN/dS) for orthologous groups suggested that after gene duplication and/or speciation of forkhead clusters, rapid differentiation and the negative selection have occurred, prompting the formation of distinct Fox subclasses and new functions. SDPpred was used to produce a set of the alignment positions (specificity determining positions) which is involved in conferring differential functional specificity. These findings explained the functional divergence of Fox gene family.