Transformation of meiotic drive into hybrid sterility in Drosophila.

Hybrid male sterility is one of the fastest evolving intrinsic reproductive barriers between recently isolated populations. A leading explanation for the evolution of hybrid male sterility involves genomic conflicts with meiotic drivers in the male germline. There are, however, few examples directly linking meiotic drive to hybrid sterility. Here, we report that the Sex-Ratio chromosome of Drosophila pseudoobscura, which causes X-chromosome drive within the USA subspecies, causes near complete male sterility when moved into the genetic background of the Bogota subspecies. In addition, we show that this new form of sterility is genetically distinct from the sterility of F1 hybrid males in crosses between USA males and Bogota females. Our observations provide a tractable study system where non-cryptic drive within species is transformed into strong hybrid sterility between very young subspecies.

Drosophila E93 promotes adult development and suppresses larval responses to ecdysone during metamorphosis.

Pulses of the steroid hormone ecdysone act through transcriptional cascades to direct the major developmental transitions during the Drosophila life cycle. These include the prepupal ecdysone pulse, which occurs 10 â€‹hours after pupariation and triggers the onset of adult morphogenesis and larval tissue destruction. E93 encodes a transcription factor that is specifically induced by the prepupal pulse of ecdysone, supporting a model proposed by earlier work that it specifies the onset of adult development. Although a number of studies have addressed these functions for E93, little is known about its roles in the salivary gland where the E93 locus was originally identified. Here we show that E93 is required for development through late pupal stages, with mutants displaying defects in adult differentiation and no detectable effect on the destruction of larval salivary glands. RNA-seq analysis demonstrates that E93 regulates genes involved in development and morphogenesis in the salivary glands, but has little effect on cell death gene expression. We also show that E93 is required to direct the proper timing of ecdysone-regulated gene expression in salivary glands, and that it suppresses earlier transcriptional programs that occur during larval and prepupal stages. These studies support the model that the stage-specific induction of E93 in late prepupae provides a critical signal that defines the end of larval development and the onset of adult differentiation.

Regulation of male fertility and accessory gland gene expression by the Drosophila HR39 nuclear receptor.

Successful reproduction is dependent on the transfer of male seminal proteins to females upon mating. These proteins arise from secretory tissues in the male reproductive tract, including the prostate and seminal vesicles in mammals and the accessory gland in insects. Although detailed functional studies have provided important insights into the mechanisms by which accessory gland proteins support reproduction, much less is known about the molecular mechanisms that regulate their expression within this tissue. Here we show that the Drosophila HR39 nuclear receptor is required for the proper expression of most genes that encode male accessory gland proteins. Consistent with this role, HR39 mutant males are infertile. In addition, tissue-specific RNAi and genetic rescue experiments indicate that HR39 acts within the accessory glands to regulate gene expression and male fertility. These results provide new directions for characterizing the mammalian orthologs of HR39, the SF-1 and LRH-1 nuclear receptors, both of which are required for glandular secretions and reproduction. In addition, our studies provide a molecular mechanism to explain how the accessory glands can maintain the abundant levels of seminal fluid production required to support fertility.

The Drosophila E78 nuclear receptor regulates dietary triglyceride uptake and systemic lipid levels.

BACKGROUND: Lipid levels are maintained by balancing lipid uptake, synthesis, and mobilization. Although many studies have focused on the control of lipid synthesis and mobilization, less is known about the regulation of lipid digestion and uptake. RESULTS: Here we show that the Drosophila E78A nuclear receptor plays a central role in intestinal lipid homeostasis through regulation of the CG17192 digestive lipase. E78A mutant adults fail to maintain proper systemic lipid levels following eclosion, with this effect largely restricted to the intestine. Transcriptional profiling by RNA-seq revealed a candidate gene for mediating this effect, encoding the predicted adult intestinal lipase CG17192. Intestine-specific disruption of CG17192 results in reduced lipid levels similar to that seen in E78A mutants. In addition, dietary supplementation with free fatty acids, or intestine-specific expression of either E78A or CG17192, is sufficient to restore lipid levels in E78A mutant adults. CONCLUSION: These studies support the model that E78A is a central regulator of adult lipid homeostasis through its effects on CG17192 expression and lipid digestion. This work also provides new insights into the control of intestinal lipid uptake and demonstrate that nuclear receptors can play an important role in these pathways.

Drosophila HNF4 Directs a Switch in Lipid Metabolism that Supports the Transition to Adulthood.

Animals must adjust their metabolism as they progress through development in order to meet the needs of each stage in the life cycle. Here, we show that the dHNF4 nuclear receptor acts at the onset of Drosophila adulthood to direct an essential switch in lipid metabolism. Lipid stores are consumed shortly after metamorphosis but contribute little to energy metabolism. Rather, dHNF4 directs their conversion to very long chain fatty acids and hydrocarbons, which waterproof the animal to preserve fluid homeostasis. Similarly, HNF4α is required in mouse hepatocytes for the expression of fatty acid elongases that contribute to a waterproof epidermis, suggesting that this pathway is conserved through evolution. This developmental switch in Drosophila lipid metabolism promotes lifespan and desiccation resistance in adults and suppresses hallmarks of diabetes, including elevated glucose levels and intolerance to dietary sugars. These studies establish dHNF4 as a regulator of the adult metabolic state.

Draft genome sequence of Gluconobacter morbifer G707T, a pathogenic gut bacterium isolated from Drosophila melanogaster intestine.

Gluconobacter morbifer G707(T), a minor member of gut microbiota, was isolated from fruit fly (Drosophila melanogaster). Here, the draft genome sequence of Gluconobacter morbifer G707(T) is reported.

Draft genome sequence of Commensalibacter intestini A911T, a symbiotic bacterium isolated from Drosophila melanogaster intestine.

Commensalibacter intestini A911(T), a predominant symbiotic bacterium capable of stably colonizing gut epithelia, was isolated from the fruit fly, Drosophila melanogaster. Here we report the draft genome sequence of Commensalibacter intestini A911(T).

Genetic evidence of a redox-dependent systemic wound response via Hayan protease-phenoloxidase system in Drosophila.

Systemic wound response (SWR) through intertissue communication in response to local wounds is an essential biological phenomenon that occurs in all multicellular organisms from plants to animals. However, our understanding of SWR has been greatly hampered by the complexity of wound signalling communication operating within the context of an entire organism. Here, we show genetic evidence of a redox-dependent SWR from the wound site to remote tissues by identifying critical genetic determinants of SWR. Local wounds in the integument rapidly induce activation of a novel circulating haemolymph serine protease, Hayan, which in turn converts pro-phenoloxidase (PPO) to phenoloxidase (PO), an active form of melanin-forming enzyme. The Haemolymph Hayan-PO cascade is required for redox-dependent activation of the c-Jun N-terminal kinase (JNK)-dependent cytoprotective program in neuronal tissues, thereby achieving organism level of homeostasis to resist local physical trauma. These results imply that the PO-activating enzyme cascade, which is a prominent defense system in humoral innate immunity, also mediates redox-dependent SWR, providing a novel link between wound response and the nervous system.

Regulation of DUOX by the Galphaq-phospholipase Cbeta-Ca2+ pathway in Drosophila gut immunity.

All metazoan guts are in constant contact with diverse food-borne microorganisms. The signaling mechanisms by which the host regulates gut-microbe interactions, however, are not yet clear. Here, we show that phospholipase C-beta (PLCbeta) signaling modulates dual oxidase (DUOX) activity to produce microbicidal reactive oxygen species (ROS) essential for normal host survival. Gut-microbe contact rapidly activates PLCbeta through Galphaq, which in turn mobilizes intracellular Ca(2+) through inositol 1,4,5-trisphosphate generation for DUOX-dependent ROS production. PLCbeta mutant flies had a short life span due to the uncontrolled propagation of an essential nutritional microbe, Saccharomyces cerevisiae, in the gut. Gut-specific reintroduction of the PLCbeta restored efficient DUOX-dependent microbe-eliminating capacity and normal host survival. These results demonstrate that the Galphaq-PLCbeta-Ca(2+)-DUOX-ROS signaling pathway acts as a bona fide first line of defense that enables gut epithelia to dynamically control yeast during the Drosophila life cycle.

Involvement of pro-phenoloxidase 3 in lamellocyte-mediated spontaneous melanization in Drosophila.

Phenoloxidase (PO), a melanin-forming enzyme around the foreign bodies, is an important component of the host defense system in invertebrates. Pro-PO is the enzymatically inactive zymogen form of PO. In the Drosophila genome, three Pro-PO isoforms have been identified to date. These include Pro-PO1 and 2, which are primarily expressed in crystal cells, and Pro-PO3, which is predominantly found in the lamellocytes. In this study, we demonstrated that Drosophila Pro-PO3, but not Pro-PO1 or 2, is enzymatically active in its zymogen form. These findings were evidenced by spectacular melanin forming capacities of various cells and tissues that overexpressed these proenzymes. Furthermore, the melanization phenotype observed in the lamellocyte-enriched hop(Tum-1) mutant was drastically reduced in the absence of PPO3, indicating that PPO3 plays a major role in the lamellocyte-mediated spontaneous melanization process. Taken together, these findings indicate that the biochemical properties, activation mode and in vivo role of Pro-PO3 are likely distinct from those of the other two Pro-PO enzymes involved in Drosophila physiology.

CLIP-domain serine proteases in Drosophila innate immunity.

Extracellular proteases play an important role in a wide range of host physiological events, such as food digestion, extracellular matrix degradation, coagulation and immunity. Among the large extracellular protease family, serine proteases that contain a "paper clip"-like domain and are therefore referred to as CLIP-domain serine protease (clip-SP), have been found to be involved in unique biological processes, such as immunity and development. Despite the increasing amount of biochemical information available regarding the structure and function of clip-SPs, their in vivo physiological significance is not well known due to a lack of genetic studies. Recently, Drosophila has been shown to be a powerful genetic model system for the dissection of biological functions of the clip-SPs at the organism level. Here, the current knowledge regarding Drosophila clip-SPs has been summarized and future research directions to evaluate the role that clip-SPs play in Drosophila immunity are discussed.

Drosophila immunity: a large-scale in vivo RNAi screen identifies five serine proteases required for Toll activation.

Unlike mammalian Toll-like Receptors, the Drosophila Toll receptor does not interact directly with microbial determinants but is rather activated upon binding a cleaved form of the cytokine-like molecule Spatzle (Spz). During the immune response, Spz is thought to be processed by secreted serine proteases (SPs) present in the hemolymph that are activated by the recognition of gram-positive bacteria or fungi . In the present study, we have used an in vivo RNAi strategy to inactivate 75 distinct Drosophila SP genes. We then screened this collection for SPs regulating the activation of the Toll pathway by gram-positive bacteria. Here, we report the identification of five novel SPs that function in an extracellular pathway linking the recognition proteins GNBP1 and PGRP-SA to Spz. Interestingly, four of these genes are also required for Toll activation by fungi, while one is specifically associated with signaling in response to gram-positive bacterial infections. These results demonstrate the existence of a common cascade of SPs upstream of Spz, integrating signals sent by various secreted recognition molecules via more specialized SPs.

A Spätzle-processing enzyme required for toll signaling activation in Drosophila innate immunity.

The Toll receptor was originally identified as an indispensable molecule for Drosophila embryonic development and subsequently as an essential component of innate immunity from insects to humans. Although in Drosophila the Easter protease processes the pro-Spätzle protein to generate the Toll ligand during development, the identification of the protease responsible for pro-Spätzle processing during the immune response has remained elusive for a decade. Here, we report a protease, called Spätzle-processing enzyme (SPE), required for Toll-dependent antimicrobial response. Flies with reduced SPE expression show no noticeable pro-Spätzle processing and become highly susceptible to microbial infection. Furthermore, activated SPE can rescue ventral and lateral development in embryos lacking Easter, showing the functional homology between SPE and Easter. These results imply that a single ligand/receptor-mediated signaling event can be utilized for different biological processes, such as immunity and development, by recruiting similar ligand-processing proteases with distinct activation modes.

The homeobox gene Caudal regulates constitutive local expression of antimicrobial peptide genes in Drosophila epithelia.

In Drosophila melanogaster, although the NF-kappaB transcription factors play a pivotal role in the inducible expression of innate immune genes, such as antimicrobial peptide genes, the exact regulatory mechanism of the tissue-specific constitutive expression of these genes in barrier epithelia is largely unknown. Here, we show that the Drosophila homeobox gene product Caudal functions as the innate immune transcription modulator that is responsible for the constitutive local expression of antimicrobial peptides cecropin and drosomycin in a tissue-specific manner. These results suggest that certain epithelial tissues have evolved a unique constitutive innate immune strategy by recruiting a developmental "master control" gene.