Novel cis-regulatory regions in ecdysone responsive genes are sufficient to promote gene expression in Drosophila ovarian cells

Proteomic profiling for ovarian development and azadirachtin exposure in Spodoptera litura during metamorphosis from pupae to adults

Azadirachtin is one of the most successful botanical pesticides in agricultural pest control. To build a repertoire of proteins and pathways in response to azadirachtin exposure during ovarian development, iTRAQ-based comparative proteomic was conducted. 1423 and 1686 proteins were identified as differentially accumulated proteins (DAPs) by comparing the protein abundance in adult ovary with that in pupal ovary under normal and azadirachtin exposure condition, respectively. Bioinformatics analysis indicated that pupae-to-adult transition requires proteins related to proteasome and branched chain amino acids (BCAAs) degradation for ovary development. Azadirachtin exposure strongly affected glycosylation-related pathway. And proteins related to vitamin B6 synthesis were necessary for ovary development under normal and AZA-exposure condition. RNAi assays confirmed the essential roles of DAPs related to glycosylation and vitamin B6 synthesis in moth growth and ovary development. The results enhance our understanding of the molecular regulatory network for ovary development and provide valuable resources for using AZA-responsive proteins to develop novel bio-rational insecticides.

Pri smORF Peptides Are Wide Mediators of Ecdysone Signaling, Contributing to Shape Spatiotemporal Responses

There is growing evidence that peptides encoded by small open-reading frames (sORF or smORF) can fulfill various cellular functions and define a novel class regulatory molecules. To which extend transcripts encoding only smORF peptides compare with canonical protein-coding genes, yet remain poorly understood. In particular, little is known on whether and how smORF-encoding RNAs might need tightly regulated expression within a given tissue, at a given time during development. We addressed these questions through the analysis of Drosophila polished rice (pri, a.k.a. tarsal less or mille pattes), which encodes four smORF peptides (11-32 amino acids in length) required at several stages of development. Previous work has shown that the expression of pri during epidermal development is regulated in the response to ecdysone, the major steroid hormone in insects. Here, we show that pri transcription is strongly upregulated by ecdysone across a large panel of cell types, suggesting that pri is a core component of ecdysone response. Although pri is produced as an intron-less short transcript (1.5 kb), genetic assays reveal that the developmental functions of pri require an unexpectedly large array of enhancers (spanning over 50 kb), driving a variety of spatiotemporal patterns of pri expression across developing tissues. Furthermore, we found that separate pri enhancers are directly activated by the ecdysone nuclear receptor (EcR) and display distinct regulatory modes between developmental tissues and/or stages. Alike major developmental genes, the expression of pri in a given tissue often involves several enhancers driving apparently redundant (or shadow) expression, while individual pri enhancers can harbor pleiotropic functions across tissues. Taken together, these data reveal the broad role of Pri smORF peptides in ecdysone signaling and show that the cis-regulatory architecture of the pri gene contributes to shape distinct spatial and temporal patterns of ecdysone response throughout development.

Anatomy and evolution of a DNA replication origin

DNA amplification occurs at the DNA puff II/9A locus in the fungus fly Sciara coprophila. As a foundation to study the molecular mechanism for the initiating events of II/9A DNA re-replication, we have sequenced 14 kb spanning a DNase hypersensitive site (DHS) upstream of the 1 kb amplification origin and through transcription units II/9-1 and II/9-2 downstream of the origin. These elements are annotated as well as the ORC binding site at the origin and the transition point (TP) between continuous and discontinuous DNA syntheses that marks the origin of bidirectional replication at the nucleotide level. A 9 bp motif found at the TP is repeated near the other end of the 1 kb ORI and may identify a putative second TP. The steroid hormone ecdysone induces DNA amplification as well as transcription and puffing at locus II/9A. Within the 14 kb, several matches to the ecdysone response element (EcRE) consensus sequence were identified, including some in the amplification origin region. EcRE O-P is at a central axis of a remarkable symmetry, equidistant to the TPs that are themselves equidistant to EcRE O-1 and EcRE O-2. DNA sequence alterations have occurred throughout the II/9A region in a newly discovered polymorphism (#2). Polymorphism #2 is not specific to developmental stage, sex, or tissue, and it does not impair DNA amplification. The DHS, both 9 bp TP sequences, and EcREs O-1, O-P, and O-2 are conserved between the polymorphism #1 and #2 sequences, suggesting their functional importance and retention during evolutionary selection. Moreover, a 72 bp sequence in the Sciara DHS at DNA puff II/9A is conserved in DNA puff C-3 of Rhynchosciara americana. Comparisons are discussed between the Sciara II/9A amplicon and the chorion locus amplicon on the third chromosome of Drosophila.

Orphan nuclear receptor ftz-f1 (NR5A3) promotes egg chamber survival in the Drosophila ovary

Gamete production in mammals and insects is controlled by cell signaling pathways that facilitate communication between germ cells and somatic cells. Nuclear receptor signaling is a key mediator of many aspects of reproduction, including gametogenesis. For example, the NR5A subfamily of nuclear receptors is essential for gonad development and sex steroid production in mammals. Despite the original identification of the NR5A subfamily in the model insect Drosophila melanogaster, it has been unclear whether Drosophila NR5A receptors directly control oocyte production. Ftz-f1 is expressed throughout the ovary, including in germline stem cells, germline cysts, and several populations of somatic cells. We show that ftz-f1 is required in follicle cells prior to stage 10 to promote egg chamber survival at the mid-oogenesis checkpoint. Our data suggest that egg chamber death in the absence of ftz-f1 is due, at least in part, to failure of follicle cells to exit the mitotic cell cycle or failure to accumulate oocyte-specific factors in the germline. Taken together, these results show that, as in mammals, the NR5A subfamily promotes maximal reproductive output in Drosophila. Our data underscore the importance of nuclear receptors in the control of reproduction and highlight the utility of Drosophila oogenesis as a key model for unraveling the complexity of nuclear receptor signaling in gametogenesis.

Nuclear receptors linking physiology and germline stem cells in Drosophila

Maternal nutrition and physiology are intimately associated with reproductive success in diverse organisms. Despite decades of study, the molecular mechanisms linking maternal diet to the production and quality of oocytes remain poorly defined. Nuclear receptors (NRs) link nutritional signals to cellular responses and are essential for oocyte development. The fruit fly, Drosophila melanogaster, is an excellent genetically tractable model to study the relationship between NR signaling and oocyte production. In this review, we explore how NRs in Drosophila regulate the earliest stages of oocyte development. Long-recognized as an essential mediator of developmental transitions, we focus on the intrinsic roles of the Ecdysone Receptor and its ligand, ecdysone, in oogenesis. We also review recent studies suggesting broader roles for NRs as regulators of maternal physiology and their impact specifically on oocyte production. We propose that NRs form the molecular basis of a broad physiological surveillance network linking maternal diet with oocyte production. Given the functional conservation between Drosophila and humans, continued experimental investigation into the molecular mechanisms by which NRs promote oogenesis will likely aid our understanding of human fertility.