The ThioredoxinT and deadhead gene pair encode testis- and ovary-specific thioredoxins in Drosophila melanogaster

Three classes of epigenomic regulators converge to hyperactivate the essential maternal gene deadhead within a heterochromatin mini-domain

The formation of a diploid zygote is a highly complex cellular process that is entirely controlled by maternal gene products stored in the egg cytoplasm. This highly specialized transcriptional program is tightly controlled at the chromatin level in the female germline. As an extreme case in point, the massive and specific ovarian expression of the essential thioredoxin Deadhead (DHD) is critically regulated in Drosophila by the histone demethylase Lid and its partner, the histone deacetylase complex Sin3A/Rpd3, via yet unknown mechanisms. Here, we identified Snr1 and Mod(mdg4) as essential for dhd expression and investigated how these epigenomic effectors act with Lid and Sin3A to hyperactivate dhd. Using Cut&Run chromatin profiling with a dedicated data analysis procedure, we found that dhd is intriguingly embedded in an H3K27me3/H3K9me3-enriched mini-domain flanked by DNA regulatory elements, including a dhd promoter-proximal element essential for its expression. Surprisingly, Lid, Sin3a, Snr1 and Mod(mdg4) impact H3K27me3 and this regulatory element in distinct manners. However, we show that these effectors activate dhd independently of H3K27me3/H3K9me3, and that dhd remains silent in the absence of these marks. Together, our study demonstrates an atypical and critical role for chromatin regulators Lid, Sin3A, Snr1 and Mod(mdg4) to trigger tissue-specific hyperactivation within a unique heterochromatin mini-domain.

Multicellular development depends on a tight control of gene expression in each cell type. This relies on the coordinated activities of nuclear proteins that interact with DNA or its histone scaffold to promote or restrict gene transcription. For example, we previously showed that the histone modifying enzymes Lid and Sin3A/Rpd3 are required in Drosophila ovaries for the massive expression of deadhead (dhd), a gene encoding for a thioredoxin that is essential for fertility. In this paper, we have further identified two additional dhd regulators, Snr1 and Mod(mdg4) and dissected the mechanism behind hyperactivation of this gene. Using the epigenomic profiling method Cut&Run with a dedicated data analysis approach, we unexpectedly found that dhd is embedded in an unusual chromatin mini-domain featuring repressive histone modifications H3K27me3 and H3K9me3 and flanked by two regulatory elements. However, we further showed that Lid, Sin3A, Snr1 and Mod(mdg4) behave like obligatory activators of dhd independently of this mini-domain. Our study unveils how multiple broad-acting epigenomic effectors operate in non-canonical manners to ensure a critical and specialized gene activation event. These findings challenge our knowledge on these regulatory mechanisms and their roles in development and pathology.

Structures of the germline-specific Deadhead and thioredoxin T proteins from Drosophila melanogaster reveal unique features among thioredoxins

Thioredoxins (Trxs) are ubiquitous enzymes that regulate the redox state in cells. In Drosophila, there are two germline-specific Trxs, Deadhead (Dhd) and thioredoxin T (TrxT), that belong to the lethal(3)malignant brain tumor signature genes and to the 'survival network' of genes that mediate the cellular response to DNA damage. Dhd is a maternal protein required for early embryogenesis that promotes protamine-histone exchange in fertilized eggs and midblastula transition. TrxT is testis-specific and associates with the lampbrush loops of the Y chromosome. Here, the first structures of Dhd and TrxT are presented, unveiling new features of these two thioredoxins. Dhd has positively charged patches on its surface, in contrast to the negatively charged surfaces commonly found in most Trxs. This distinctive charge distribution helps to define initial encounter complexes with DNA/RNA that will lead to final specific interactions with cofactors to promote chromatin remodeling. TrxT contains a C-terminal extension, which is mostly unstructured and highly flexible, that wraps the conserved core through a closed conformation. It is believed that these new structures can guide future work aimed at understanding embryo development and redox homeostasis in Drosophila. Moreover, due to their restricted presence in Schizophora (a section of the true flies), these structures can help in the design of small-molecular binders to modulate native redox homeostasis, thereby providing new applications for the control of plagues that cause human diseases and/or bring about economic losses by damaging crop production.

Genomic signatures of globally enhanced gene duplicate accumulation in the megadiverse higher Diptera fueling intralocus sexual conflict resolution

Gene duplication is an important source of evolutionary innovation. To explore the relative impact of gene duplication during the diversification of major insect model system lineages, we performed a comparative analysis of lineage-specific gene duplications in the fruit fly Drosophila melanogaster (Diptera: Brachycera), the mosquito Anopheles gambiae (Diptera: Culicomorpha), the red flour beetle Tribolium castaneum (Coleoptera), and the honeybee Apis mellifera (Hymenoptera). Focusing on close to 6,000 insect core gene families containing maximally six paralogs, we detected a conspicuously higher number of lineage-specific duplications in Drosophila (689) compared to Anopheles (315), Tribolium (386), and Apis (223). Based on analyses of sequence divergence, phylogenetic distribution, and gene ontology information, we present evidence that an increased background rate of gene duplicate accumulation played an exceptional role during the diversification of the higher Diptera (Brachycera), in part by providing enriched opportunities for intralocus sexual conflict resolution, which may have boosted speciation rates during the early radiation of the megadiverse brachyceran subclade Schizophora.

Molecular Identification of Two Thioredoxin Genes From Grapholita molesta and Their Function in Resistance to Emamectin Benzoate

Thioredoxins (Trxs), a member of the thioredoxin system, play crucial roles in maintaining intracellular redox homeostasis and protecting organisms against oxidative stress. In this study, we cloned and characterized two genes, GmTrx2 and GmTrx-like1, from Grapholita molesta. Sequence analysis showed that GmTrx2 and GmTrx-like1 had highly conserved active sites CGPC and CXXC motif, respectively, and shared high sequence identity with selected insect species. The quantitative real-time polymerase chain reaction results revealed that GmTrx2 was mainly detected at first instar, whereas GmTrx-like1 was highly concentrated at prepupa day. The transcripts of GmTrx2 and GmTrx-like1 were both highly expressed in the head and salivary glands. The expression levels of GmTrx2 and GmTrx-like1 were induced by low or high temperature, E. coli, M. anisopliae, H2O2, and pesticides (emamectin benzoate). We further detected interference efficiency of GmTrx2 and GmTrx-like1 in G. molesta larvae and found that peroxidase capacity, hydrogen peroxide content, and ascorbate content all increased after knockdown of GmTrx2 or GmTrx-like1. Furthermore, the hydrogen peroxide concentration was increased by emamectin benzoate and the sensitivity for larvae to emamectin benzoate was improved after GmTrx2 or GmTrx-like1 was silenced. Our results indicated that GmTrx2 and GmTrx-like1 played vital roles in protecting G. molesta against oxidative damage and also provided the theoretical basis for understanding the antioxidant defense mechanisms of the Trx system in insects.

RNA Interference-Mediated Knockdown of Male Fertility Genes in the Queensland Fruit Fly Bactrocera tryoni (Diptera: Tephritidae)

The Queensland fruit fly, Bactrocera tryoni, is Australia’s most important horticultural pest. The Sterile Insect Technique (SIT) has been used to control this species for decades, using radiation to sterilize males before field-release. This method of sterilization can potentially reduce the insects’ abilities to compete for mates. In this study, RNA interference (RNAi) techniques were examined for their potential to sterilize male B. tryoni without adversely affecting mating competitiveness. B. tryoni adults were injected or fed double-stranded RNAs (dsRNAs) targeting spermatogenesis genes (tssk1, topi and trxt); quantitative reverse-transcriptase PCR analyses confirmed that transcript levels were reduced 60–80% for all three genes following injections. Feeding produced a significant gene knockdown for tssk1 and trxt after three days, but interestingly, two genes (trxt and topi) produced an excess of transcripts after 10 days of feeding. Despite these fluctuations in transcript levels, all three dsRNAs impacted the fecundity of treated males, with tssk1- and topi-dsRNA-treated males producing 75% fewer viable offspring than the negative controls. Mating competition assays demonstrated that dsRNA-treated males can actively compete with untreated males. These findings suggest that RNAi technology could serve as an alternative to radiation as a means of sterilizing these insects in an SIT program.

Dynamic redox balance directs the oocyte-to-embryo transition via developmentally controlled reactive cysteine changes

The metabolic and redox state changes during the transition from an arrested oocyte to a totipotent embryo remain uncharacterized. Here, we applied state-of-the-art, integrated methodologies to dissect these changes in Drosophila We demonstrate that early embryos have a more oxidized state than mature oocytes. We identified specific alterations in reactive cysteines at a proteome-wide scale as a result of this metabolic and developmental transition. Consistent with a requirement for redox change, we demonstrate a role for the ovary-specific thioredoxin Deadhead (DHD). dhd-mutant oocytes are prematurely oxidized and exhibit meiotic defects. Epistatic analyses with redox regulators link dhd function to the distinctive redox-state balance set at the oocyte-to-embryo transition. Crucially, global thiol-redox profiling identified proteins whose cysteines became differentially modified in the absence of DHD. We validated these potential DHD substrates by recovering DHD-interaction partners using multiple approaches. One such target, NO66, is a conserved protein that genetically interacts with DHD, revealing parallel functions. As redox changes also have been observed in mammalian oocytes, we hypothesize a link between developmental control of this cell-cycle transition and regulation by metabolic cues. This link likely operates both by general redox state and by changes in the redox state of specific proteins. The redox proteome defined here is a valuable resource for future investigation of the mechanisms of redox-modulated control at the oocyte-to-embryo transition.

An in vivo genetic screen in Drosophila identifies the orthologue of human cancer/testis gene SPO11 among a network of targets to inhibit lethal(3)malignant brain tumour growth

Using transgenic RNAi technology, we have screened over 4000 genes to identify targets to inhibit malignant growth caused by the loss of function of lethal(3)malignant brain tumour in Drosophila in vivo. We have identified 131 targets, which belong to a wide range of gene ontologies. Most of these target genes are not significantly overexpressed in mbt tumours hence showing that, rather counterintuitively, tumour-linked overexpression is not a good predictor of functional requirement. Moreover, we have found that most of the genes upregulated in mbt tumours remain overexpressed in tumour-suppressed double-mutant conditions, hence revealing that most of the tumour transcriptome signature is not necessarily correlated with malignant growth. One of the identified target genes is meiotic W68 (mei-W68), the Drosophila orthologue of the human cancer/testis gene Sporulation-specific protein 11 (SPO11), the enzyme that catalyses the formation of meiotic double-strand breaks. We show that Drosophila mei-W68/SPO11 drives oncogenesis by causing DNA damage in a somatic tissue, hence providing the first instance in which a SPO11 orthologue is unequivocally shown to have a pro-tumoural role. Altogether, the results from this screen point to the possibility of investigating the function of human cancer relevant genes in a tractable experimental model organism like Drosophila.

Unlocking sperm chromatin at fertilization requires a dedicated egg thioredoxin in Drosophila

In most animals, the extreme compaction of sperm DNA is achieved after the massive replacement of histones with sperm nuclear basic proteins (SNBPs), such as protamines. In some species, the ultracompact sperm chromatin is stabilized by a network of disulfide bonds connecting cysteine residues present in SNBPs. Studies in mammals have established that the reduction of these disulfide crosslinks at fertilization is required for sperm nuclear decondensation and the formation of the male pronucleus. Here, we show that the Drosophila maternal thioredoxin Deadhead (DHD) is specifically required to unlock sperm chromatin at fertilization. In dhd mutant eggs, the sperm nucleus fails to decondense and the replacement of SNBPs with maternally-provided histones is severely delayed, thus preventing the participation of paternal chromosomes in embryo development. We demonstrate that DHD localizes to the sperm nucleus to reduce its disulfide targets and is then rapidly degraded after fertilization.

An unregulated regulator: Vasa expression in the development of somatic cells and in tumorigenesis

Growing evidence in diverse organisms shows that genes originally thought to function uniquely in the germ line may also function in somatic cells, and in some cases even contribute to tumorigenesis. Here we review the somatic functions of Vasa, one of the most conserved "germ line" factors among metazoans. Vasa expression in somatic cells is tightly regulated and often transient during normal development, and appears to play essential roles in regulation of embryonic cells and regenerative tissues. Its dysregulation, however, is believed to be an important element of tumorigenic cell regulation. In this perspectives paper, we propose how some conserved functions of Vasa may be selected for somatic cell regulation, including its potential impact on efficient and localized translational activities and in some cases on cellular malfunctioning and tumorigenesis.

Sequence analysis, expression profiles and function of thioredoxin 2 and thioredoxin reductase 1 in resistance to nucleopolyhedrovirus in Helicoverpa armigera

The thioredoxin system, including NADPH, thioredoxin (Trx), and thioredoxin reductase (TrxR), plays significant roles in maintaining intracellular redox homeostasis and protecting organisms against oxidative damage. In this study, the characteristics and functions of H. armigera HaTrx2 and HaTrxR1 were identified. Sequence analysis showed that HaTrx2 and HaTrxR1 were both highly conserved and shared high sequence identity with other insect counterparts. The mRNA of HaTrx2 was expressed the highest in 5th instar 96 h and was mainly detected in heads and epidermis. The expression of HaTrxR1 was highly concentrated in 5th instar 72 h and 96 h, and higher in malpighian tube, midgut and hemocyte than other examined tissues. HaTrx2 and HaTrxR1 were markedly induced by various types of stress. HaTrx2- or HaTrxR1-knockdown increased ROS production in hemocytes and also increased the lipid damage in NPV infected H. armigera larvae. Furthermore, interference with expression of HaTrx2 or HaTrxR1 transcripts in H. armigera larvae resulted in increased sensitivity to NPV infection and shortened LT₅₀ values. Our findings indicated that HaTrx2 and HaTrxR1 contribute to the susceptibility of H. armigera to NPV and also provided the theoretical basis for the in-depth study of insect thioredoxin system.

Comparative study of two thioredoxins from common cutworm (Spodoptera litura): cloning, expression, and functional characterization

Thioredoxins (Trxs) are a ubiquitous family of antioxidant enzymes that are involved in protecting organisms against various oxidative stresses. Here, we cloned and characterized two thioredoxins, named SlTrx1 and SlTrx2, from the common cutworm Spodoptera litura. SlTrx1 and SlTrx2, respectively, consist of 988 and 606 bp full-length cDNA with 318 and 447 bp open reading frames encoding 106 and 149 amino acid residues. Furthermore, the N-terminal region of SlTrx2 contains a predicted mitochondrial localization signal (33 amino acids). A phylogenetic relationship analysis revealed that SlTrx1 is in the cytosolic thioredoxin Trx1 cluster, whereas SlTrx2 is in the mitochondrial thioredoxin Trx2 cluster. Recombinant SlTrx1 (14 kDa) and SlTrx2 (16 kDa), expressed in baculovirus-infected insect Sf9 cells, demonstrated insulin disulfide reductase activity at the same optimum temperature and pH value of 35 °C and 7.0, respectively, in vitro. During S. litura development, we found that SlTrx1 and SlTrx2 had similar transcript expression patterns and were constitutively expressed in the epidermis, fat body, and midgut, with the highest expression occurring in the sixth-instar larval stage in the epidermis and midgut. In addition, both SlTrx1 and SlTrx2 mRNA were up-regulated in S. litura after injection with H2O2, cumene hydroperoxide, indoxacarb, and metaflumizone. These results suggest that SlTrx1 and SlTrx2 function as potent antioxidant enzymes, and provide a molecular basis for the roles SlTrx1 and SlTrx2 during development and the oxidative stress response of S. litura.

Involvement of redox state in the aging of Drosophila melanogaster

SIGNIFICANCE

The main objective of this review was to provide an exposition of investigations, conducted in Drosophila melanogaster, on the role of reactive oxygen species and redox state in the aging process. While early transgenic studies did not clearly support the validity of the oxidative stress hypothesis of aging, predicated on the accumulation of structural damage, they spawned a broader search for redox-related effects that might impact the aging process.

RECENT ADVANCES

Initial evidence implicating the thiol redox state as a possible causative factor in aging has been obtained in Drosophila. Overexpression of genes, such as GCL, G6PD, Prx2, and Prx5, which are involved in the maintenance of thiol redox homeostasis, has strong positive effects on longevity. Further, the depletion of peroxiredoxin activity in the mitochondria through the double knockdown of Prx5 and Prx3 not only results in a redox crisis but also elicits a rapid aging phenotype.

CRITICAL ISSUES

Herein, we summarize the present status of knowledge about the main components of the machinery controlling thiol redox homeostasis and describe how age-related redox fluctuations might impact aging more acutely through disruption of the redox-sensitive signaling mechanisms rather than via the simple accumulation of structural damage.

FUTURE DIRECTIONS

Based on these initial insights into the plausible impact of redox fluctuations on redox signaling, future studies should focus on the pathways that have been explicitly implicated in aging, such as insulin signaling, TOR, and JNK/FOXO, with particular attention to elements that are redox sensitive.

Targeting of Painting of fourth to roX1 and roX2 proximal sites suggests evolutionary links between dosage compensation and the regulation of the fourth chromosome in Drosophila melanogaster

In Drosophila melanogaster, two chromosome-specific targeting and regulatory systems have been described. The male-specific lethal (MSL) complex supports dosage compensation by stimulating gene expression from the male X-chromosome, and the protein Painting of fourth (POF) specifically targets and stimulates expression from the heterochromatic 4(th) chromosome. The targeting sites of both systems are well characterized, but the principles underlying the targeting mechanisms have remained elusive. Here we present an original observation, namely that POF specifically targets two loci on the X-chromosome, PoX1 and PoX2 (POF-on-X). PoX1 and PoX2 are located close to the roX1 and roX2 genes, which encode noncoding RNAs important for the correct targeting and spreading of the MSL-complex. We also found that the targeting of POF to PoX1 and PoX2 is largely dependent on roX expression and identified a high-affinity target region that ectopically recruits POF. The results presented support a model linking the MSL-complex to POF and dosage compensation to regulation of heterochromatin.

Molecular cloning, expression and antioxidant characterisation of a typical thioredoxin gene (AccTrx2) in Apis cerana cerana

Thioredoxins (Trxs) are a family of small, highly conserved and ubiquitous proteins that are involved in protecting organisms against toxic reactive oxygen species (ROS). In this study, a typical thioredoxin 2 gene was isolated from Apis cerana cerana, AccTrx2. The full-length cDNA sequence of AccTrx2 was composed of 407 bp containing a 318 bp open reading frame (ORF) that encodes a predicted protein of 105 amino acids, 11.974 kDa and an isoelectric point of 4.45. Expression profile of AccTrx2 as determined by a quantitative real-time PCR (qRT-PCR) analysis was higher in brain than in other tissues, with its highest transcript occurring on the 15day post-emergence adult and upregulated by such abiotic stresses as 4 °C, 16 °C, 25 °C, H2O2, cyhalothrin, acaricide, paraquat, phoxime and mercury (HgCl2) treatments. However, AccTrx2 was slightly repressed when exposed to 42 °C treatment. Characterisation of the recombinant protein showed that the purified AccTrx2 had insulin disulfide reductase activity and could protect DNA from ROS damage. These results indicate that AccTrx2 functions as an antioxidant that plays an important role in response to oxidative stress.

Disruption of redox homeostasis leads to oxidative DNA damage in spermatocytes of Wolbachia-infected Drosophila simulans

Molecular interactions between symbiotic bacteria and their animal hosts are, as yet, poorly understood. The most widespread bacterial endosymbiont, Wolbachia pipientis, occurs in high density in testes of infected Drosophila simulans and causes cytoplasmic incompatibility (CI), a form of male-derived zygotic lethality. Wolbachia grow and divide within host vacuoles that generate reactive oxygen species (ROS), which in turn stimulate the up-regulation of antioxidant enzymes. These enzymes appear to protect the host from ROS-mediated damage, as there is no obvious fitness cost to Drosophila carrying Wolbachia infections. We have now determined that DNA from Wolbachia-infected mosquito Aedes albopictus (Aa23) cells shows a higher amount of the base 8-oxo-deoxyguanosine, a marker of oxidative DNA damage, than DNA from uninfected cells, and that Wolbachia infection in D. simulans is associated with an increase in DNA strand breaks in meiotic spermatocytes. Feeding exogenous antioxidants to male and female D. simulans dramatically increased Wolbachia numbers with no obvious effects on host fitness. These results suggest that ROS-induced DNA damage in sperm nuclei may contribute to the modification characteristic of CI expression in Wolbachia-infected males and that Wolbachia density is sensitive to redox balance in these flies.

Ectopic expression of germline genes drives malignant brain tumor growth in Drosophila

Model organisms such as the fruit fly Drosophila melanogaster can help to elucidate the molecular basis of complex diseases such as cancer. Mutations in the Drosophila gene lethal (3) malignant brain tumor cause malignant growth in the larval brain. Here we show that l(3)mbt tumors exhibited a soma-to-germline transformation through the ectopic expression of genes normally required for germline stemness, fitness, or longevity. Orthologs of some of these genes were also expressed in human somatic tumors. In addition, inactivation of any of the germline genes nanos, vasa, piwi, or aubergine suppressed l(3)mbt malignant growth. Our results demonstrate that germline traits are necessary for tumor growth in this Drosophila model and suggest that inactivation of germline genes might have tumor-suppressing effects in other species.

Reactive oxygen species: A radical role in development?

Reactive oxygen species (ROS), mostly derived from mitochondrial activity, can damage various macromolecules and consequently cause cell death. This ROS activity has been characterized in vitro, and correlative evidence suggests a role in various pathological conditions. In addition to this passive ROS activity, ROS also participate in cell signaling processes, though the relevance of this function in vivo is poorly understood. Throughout development, elevated cell activity is probably accompanied by highly active metabolism and, consequently, the production of large amounts of ROS. To allow proper development, cells must protect themselves from these potentially damaging ROS. However, to what degree ROS could participate as signaling molecules controlling fundamental and developmentally relevant cellular processes such as proliferation, differentiation, and death is an open question. Here we discuss why available data do not yet provide conclusive evidence on the role of ROS in development, and we review recent methods to detect ROS in vivo and genetic strategies that can be exploited specifically to resolve these uncertainties.

Loss of Trx-2 enhances oxidative stress-dependent phenotypes in Drosophila

Overexpression of thioredoxin (TRX) confers oxidative stress resistance and extends lifespan in mammals and insects. However, less is known about phenotypes associated with loss of TRX. We investigated loss-of-function phenotypes of Trx-2 in Drosophila, and found that the mutant flies are hyper-susceptible to paraquat, a free radical generator, but not to hydrogen peroxide. They contain a high amount of protein carbonyl, which dramatically increases with age. Trx-2 mutants express high levels of anti-oxidant genes, such as superoxide dismutase, catalase, and glutathione synthetase. This is the first demonstration of biochemical and physiological consequences caused by loss of Trx-2 in Drosophila.

Molecular mechanisms of gene regulation during Drosophila spermatogenesis

The differentiation of sperm from morphologically unremarkable cells into highly specialised free-living, motile cells requires the co-ordinated action of a very large number of gene products. The expression of these products must be regulated in a developmental context to ensure normal cellular differentiation. Many genes essential for spermatogenesis are not used elsewhere in the animal, or are expressed elsewhere, but using a different transcription regulation module. Spermatogenesis is thus a good system for elucidating the principles of tissue-specific gene expression, as well as being interesting in its own right. Here, I discuss the regulation of gene expression during spermatogenesis in Drosophila, focussing on the processes underlying the expression of testis-specific genes in the male germline.

Autosomal mutations affecting Y chromosome loops in Drosophila melanogaster

Background

The Y chromosome of Drosophila melanogaster harbors several genes required for male fertility. The genes for these fertility factors are very large in size and contain conspicuous amounts of repetitive DNA and transposons. Three of these loci (ks-1, kl-3 and kl-5) have the ability to develop giant lampbrush-like loops in primary spermatocytes, a cytological manifestation of their active state in these cells. Y-loops bind a number of non-Y encoded proteins, but the mechanisms regulating their development and their specific functions are still to be elucidated.

Results

Here we report the results of a screen of 726 male sterile lines to identify novel autosomal genes controlling Y-loop function. We analyzed mutant testis preparations both in vivo and by immunofluorescence using antibodies directed against Y-loop-associated proteins. This screen enabled us to isolate 17 mutations at 15 loci whose wild-type function is required for proper Y-loop morphogenesis. Six of these loci are likely to specifically control loop development, while the others display pleiotropic effects on both loops and meiotic processes such as spermiogenesis, sperm development and maturation. We also determined the map position of the mutations affecting exclusively Y-loop morphology.

Conclusion

Our cytological screening permitted us to identify novel genetic functions required for male spermatogenesis, some of which show pleiotropic effects. Analysis of these mutations also shows that loop development can be uncoupled from meiosis progression. These data represent a useful framework for the characterization of Y-loop development at a molecular level and for the study of the genetic control of heterochromatin.

Organization and regulation of sex-specific thioredoxin encoding genes in the genus Drosophila

Thioredoxins are small thiol proteins that have a conserved active site sequence, WCGPC, and reduce disulfide bonds in various proteins using the two active site cysteines, a reaction that oxidizes thioredoxin and renders it inactive. Thioredoxin reductase returns thioredoxin to its reduced, active form in a reaction that converts NADPH to NADP(+). The biological functions of thioredoxins vary widely; they have roles in oxidative stress protection, act as electron donors for ribonucleotide reductase, and form structural components of enzymes. To date, three thioredoxin genes have been characterized in Drosophila melanogaster: the generally expressed Thioredoxin-2 (Trx-2) and the two sex-specific genes ThioredoxinT (TrxT) and deadhead (dhd). The male-specific TrxT and the female-specific dhd are located as a gene pair, transcribed in opposite directions, with only 470 bp between their transcription start points. We show in this study that all three D. melanogaster thioredoxins are conserved in 11 other Drosophilid species, which are believed to have diverged up to 40 Ma ago and that Trx-2 is conserved all the way to Tribolium castaneum. We have found that the intriguing gene organization and regulation of TrxT and dhd is remarkably well conserved and identified potential conserved regulatory sequences. In addition, we show that the 50-70 C terminal amino acids of TrxT constitute a hyper-variable domain, which could play a role in sexual conflict and male-female co-evolution.

Thioredoxin-2 affects lifespan and oxidative stress in Drosophila

Thioredoxins are proteins that have thiol-reducing activity and a characteristic conserved active site (WCGPC). They have several documented functions, e.g. roles in defences against oxidative stress and as electron donors for ribonucleotide-reductase. In Drosophila melanogaster there are three "classical" thioredoxins with the conserved active site: deadhead, ThioredoxinT and Thioredoxin-2. Here, we report the creation of null-mutations in the Thioredoxin-2 (Trx-2) gene. Characterization of two Trx-2 mutants indicated that Trx-2 affects the lifespan of D. melanogaster, and is involved in the organism's oxidative stress protection system. We found that the mutants have a shorter lifespan than wild-type flies, and thioredoxin double mutant flies showed lower tolerance to oxidative stress than wild-type flies, while flies carrying multiple copies of a Trx-2 rescue construct showed higher tolerance. These findings suggest that Trx-2 has modest or redundant functions in Drosophila physiology under unstressed conditions, but could be important during times of environmental stress.

Thioredoxin Suppresses Parkin-associated Endothelin Receptor-like Receptor-induced Neurotoxicity and Extends Longevity in Drosophila

Parkin-associated endothelin receptor-like receptor (Pael-R) is a substrate of the E3 ubiquitin ligase Parkin, which has been implicated in the pathogenesis of Parkinson disease. Misexpression of human Pael-R in Drosophila has been shown to induce selective loss of dopaminergic neurons, a symptom of Parkinson disease. Using this model, we investigated whether thioredoxin (TRX), an evolutionarily conserved antioxidant and molecular chaperone, could suppress the neurotoxicity induced by Pael-R. The Drosophila genome contains three TRX-encoding genes, namely TrxT, Trx-2, and dhd. When each of the TRX genes was overexpressed together with Pael-R in all neurons, the number of dopaminergic neurons and level of locomotor activity were significantly increased compared with control flies. To assess the role of the antioxidant activity of TRX in this context, we generated redox-defective mutants, TrxT(C35A) and TrxT(D26A/K57I), and coexpressed each of them with Pael-R. The mutants suppressed the Pael-R neurotoxicity similarly to wild-type TrxT, although the extent of the rescue was slightly reduced for the locomotor activity. We confirmed that both mutants remained active as chaperones, suggesting that this activity may be the major cause of the suppression. In the absence of Pael-R, overexpression of TRX in all neurons increased the level of locomotor activity in aged flies and extended the mean longevity by 15%. Furthermore, overexpression of TRX suppressed neurotoxicity in a Drosophila model of Machado-Joseph disease expressing polyglutamine. These results establish that Drosophila TRX can function as an anti-aging agent and as a suppressor of Pael-R- and poly-glutamine-induced neurotoxicity.

Painting of fourth and chromosome-wide regulation of the 4th chromosome in Drosophila melanogaster

Drosophila melanogaster exhibits two expression-regulating systems that target whole, specific chromosomes: the dosage compensation system whereby the male-specific lethal complex doubles transcription of genes on the male X-chromosome and the chromosome 4-specific protein Painting of fourth, POF. POF is the first example of an autosome-specific protein and its presence raises the question of the universality of chromosome-specific regulation. Here we show that POF and heterochromatin protein 1 (HP1) are involved in the global regulation of the 4th chromosome. Contrary to previous conclusions, Pof is not essential for survival of diplo-4th karyotype flies. However, Pof is essential for survival of haplo-4th individuals and expression of chromosome 4 genes in diplo-4th individuals is decreased in the absence of Pof. Mapping of POF using chromatin immunoprecipitation suggested that it binds within genes. Furthermore, we show that POF binding is dependent on heterochromatin and that POF and HP1 bind interdependently to the 4th chromosome. We propose a balancing mechanism involving POF and HP1 that provides a feedback system for fine-tuning expression status of genes on the 4th chromosome.

Regulation of the activity of the tumor suppressor PTEN by thioredoxin in Drosophila melanogaster

Human Thioredoxin-1 (hTrx-1) is a small redox protein with a molecular weight of 12 kDa that contains two cysteine residues found in its catalytic site. HTrx-1 plays an important role in cell growth, apoptosis, and cancer patient prognosis. Recently, we have demonstrated that hTrx-1 binds to the C2 domain of the human tumor suppressor, PTEN, in a redox dependent manner. This binding leads to the inhibition of PTEN lipid phosphatase activity in mammalian tissue culture systems. In this study, we show that over-expression of hTrx-1 in Drosophila melanogaster promotes cell growth and proliferation during eye development as measured by eye size and ommatidia size. Furthermore, hTrx-1 rescues the small eye phenotype induced by the over-expression of PTEN. We demonstrate that this rescue of the PTEN-induced eye size phenotype requires cysteine-218 in the C2 domain of PTEN. We also show that hTrx-1 over-expression results in increased Akt phosphorylation in fly head extracts supporting our observations that the hTrx-1-induced eye size increase results from the inhibition of PTEN activity. Our study confirms the redox regulation of PTEN through disulfide bond formation with the hTrx-1 in Drosophila and suggests conserved mechanisms for thioredoxins and their interactions with the phosphatidylinositol-3-kinase signaling pathway in humans and fruit flies.

Genes of the antioxidant system of the honey bee: annotation and phylogeny

Antioxidant enzymes perform a variety of vital functions including the reduction of life-shortening oxidative damage. We used the honey bee genome sequence to identify the major components of the honey bee antioxidant system. A comparative analysis of honey bee with Drosophila melanogaster and Anopheles gambiae shows that although the basic components of the antioxidant system are conserved, there are important species differences in the number of paralogs. These include the duplication of thioredoxin reductase and the expansion of the thioredoxin family in fly; lack of expansion of the Theta, Delta and Omega GST classes in bee and no expansion of the Sigma class in dipteran species. The differential expansion of antioxidant gene families among honey bees and dipteran species might reflect the marked differences in life history and ecological niches between social and solitary species.

Lifespan decrease in a Caenorhabditis elegans mutant lacking TRX-1, a thioredoxin expressed in ASJ sensory neurons

Thioredoxins are a class of small proteins that play a key role in regulating many cellular redox processes. We report here the characterization of the first member of the thioredoxin family in metazoans that is mainly associated with neurons. The Caenorhabditis elegans gene B0228.5 encodes a thioredoxin (TRX-1) that is expressed in ASJ ciliated sensory neurons, and to some extent also in the posterior-most intestinal cells. TRX-1 is active at reducing protein disulfides in the presence of a heterologous thioredoxin reductase. A mutant worm strain carrying a null allele of the trx-1 gene displays a reproducible decrease in both mean and maximum lifespan when compared to wild-type. The identification and characterization of TRX-1 paves the way to use C. elegans as an in vivo model to study the role of thioredoxins in lifespan and nervous system physiology and pathology.

Cold hardening and transcriptional change in Drosophila melanogaster

Cold hardening treatment - a brief exposure to low temperatures - can protect certain insects against subsequent exposure to temperatures sufficiently low to cause damage or lethality. Microarray analysis to examine the changes in transcript abundance associated with cold hardening treatment (0 degrees C for 2 h followed by 30 min recovery at 25 degrees C) was undertaken in Drosophila melanogaster in order to gain insight into this phenomenon. Transcripts associated with 36 genes were identified, a subset of which appeared to be also differentially expressed after heat shock treatment. Quantitative RT-PCR was used to independently determine transcript abundance of a subset of these sequences. Taken together, these assays suggest that stress proteins, including Hsp23, Hsp26, Hsp83 and Frost as well as membrane-associated proteins may contribute to the cold hardening response.

Comparative structural analysis of oxidized and reduced thioredoxin from Drosophila melanogaster

Thioredoxins (Trx) participate in essential antioxidant and redox-regulatory processes via a pair of conserved cysteine residues. In dipteran insects like Drosophila and Anopheles, which lack a genuine glutathione reductase (GR), thioredoxins fuel the glutathione system with reducing equivalents. Thus, characterizing Trxs from these organisms contributes to our understanding of redox control in GR-free systems and provides information on novel targets for insect control. Cytosolic Trx of Drosophila melanogaster (DmTrx) is the first thioredoxin that was crystallized for X-ray diffraction analysis in the reduced and in the oxidized form. Comparison of the resulting structures shows rearrangements in the active-site regions. Formation of the C32-C35 disulfide bridge leads to a rotation of the side-chain of C32 away from C35 in the reduced form. This is similar to the situation in human Trx and Trx m from spinach chloroplasts but differs from Escherichia coli Trx, where it is C35 that moves upon change of the redox state. In all four crystal forms that were analysed, DmTrx molecules are engaged in a non-covalent dimer interaction. However, as demonstrated by gel-filtration analyses, DmTrx does not dimerize under quasi in vivo conditions and there is no redox control of a putative monomer/dimer equilibrium. The dimer dissociation constants K(d) were found to be 2.2mM for reduced DmTrx and above 10mM for oxidized DmTrx as well as for the protein in the presence of reduced glutathione. In human Trx, oxidative dimerization has been demonstrated in vitro. Therefore, this finding may indicate a difference in redox control of GR-free and GR-containing organisms.

Spermatocyte/Spermatid-specific Thioredoxin-3, a Novel Golgi Apparatus-associated Thioredoxin, Is a Specific Marker of Aberrant Spermatogenesis

Mammalian germ cells are endowed with a complete set of thioredoxins (Trx), a class of redox proteins located in specific structures of the spermatid and sperm tail. We report here the characterization, under normal and pathological conditions, of a novel thioredoxin with a germ line-restricted expression pattern, named spermatocyte/spermatid-specific thioredoxin-3 (SPTRX-3). The human SPTRX-3 gene maps at 9q32, only 50 kb downstream from the TRX-1 gene from which it probably originated as genomic duplication. Therefore, human SPTRX-3 protein comprises a unique thioredoxin domain displaying high homology with the ubiquitously expressed TRX-1. Among the tissues investigated, Sptrx-3 mRNA is found exclusively in the male germ cells at pachytene spermatocyte and round spermatid stages. Light and electron microscopy show SPTRX-3 protein to be predominately located in the Golgi apparatus of pachytene spermatocytes and round and elongated spermatids, with a transient localization in the developing acrosome of round spermatids. In addition, increased levels of SPTRX-3, possibly caused by overexpression, are observed in morphologically abnormal human spermatozoa from infertile men. In addition, SPTRX-3 is identified as a novel postobstruction autoantigen. In this report, we propose that SPTRX-3 can be used as a specific marker for diverse sperm and testis pathologies. SPTRX-3 is the first thioredoxin specific to the Golgi apparatus, and its function within this organelle might be related to the post-translational modification of proteins required for germ cell-specific functions, such as acrosomal biogenesis.

Painting of fourth in genus Drosophila suggests autosome-specific gene regulation

Painting of fourth (POF) is a chromosome-specific protein in Drosophila and represents the first example of an autosome-specific protein. POF binds to chromosome 4 in Drosophila melanogaster, initiating at the proximal region, followed by a spreading dependent on chromosome 4-specific sequences or structures. Chromosome-specific gene regulation is known thus far only as a mechanism to equalize the transcriptional activity of the single male X chromosome with that of the two female X chromosomes. In Drosophila, a complex including the male-specific lethal proteins, "paints" the male X chromosome, mediating its hypertranscription, explained to some extent by the acetylation of lysine 16 on histone H4. Here, we show that Pof is essential for viability in both sexes and for female fertility. POF binding to an autosome, the F element, is conserved in genus Drosophila, indicating functional conservation of the autosome specificity. In three of nine studied species, POF binds to the male X chromosome. When bound to the male X, it also colocalizes with the dosage compensation protein male-specific lethal 3, suggesting a relationship to dosage compensation. The chromosome specificity is determined at the species level and not by the amino acid sequence. We argue that POF is involved in a chromosome-specific regulatory function.

Regulation of transcription of meiotic cell cycle and terminal differentiation genes by the testis-specific Zn-finger protein matotopetli

A robust developmentally regulated and cell type specific transcriptional programme is activated in primary spermatocytes in preparation for differentiation of the male gametes during spermatogenesis. Work in Drosophila is beginning to reveal the genetic networks that regulate this gene expression. The Drosophila aly-class meiotic arrest loci are essential for activation of transcription of many differentiation-specific genes, as well as several genes important for meiotic cell cycle progression, thus linking meiotic cell cycle progression to cellular differentiation during spermatogenesis. The three previously described aly-class proteins (aly, comr and achi/vis) form a complex and are associated with chromatin in primary spermatocytes. We identify, clone and characterize a new aly-class meiotic arrest gene, matotopetli (topi), which encodes a testis-specific Zn-finger protein that physically interacts with Comr. The topi mutant phenotype is most like achi/vis in that topi function is not required for the nuclear localization of Aly or Comr, but is required for their accumulation on chromatin. Most target genes in the transcriptional programme depend on both topi and achi/vis; however, a small subset of target genes are differentially sensitive to loss of topi or achi/vis, suggesting that these aly-class predicted DNA binding proteins can act independently in some contexts.