Genomic deletions of the Drosophila melanogaster Hsp70 genes

Knockout of Hsp70 genes significantly affects locomotion speed and gene expression in leg skeletal muscles of Drosophila melanogaster

The functions of the heat shock protein 70 (Hsp70) genes were studied using a line of Drosophila melanogaster with a knockout of 6 of these genes out of 13. Namely, the effect of knockout of Hsp70 genes on negative geotaxis climbing (locomotor) speed and the ability to adapt to climbing training (0.5-1.5 h/day, 7 days/wk, 19 days) were examined. Seven- and 23-day-old Hsp70- flies demonstrated a comparable reduction (twofold) in locomotor speed and widespread changes in leg skeletal muscle transcriptome (RNA sequencing) compared with w1118 flies. To identify the functions of genes related to decreased locomotor speed, the overlapped differentially expressed genes at both time points were analyzed: the upregulated genes encoded extracellular proteins, regulators of drug metabolism, and the antioxidant response, whereas downregulated genes encoded regulators of carbohydrate metabolism and transmembrane proteins. In addition, in Hsp70- flies, activation of transcription factors related to disruption of the fibril structure and heat shock response (Hsf) was predicted, using the position weight matrix approach. In control flies, adaptation to chronic exercise training was associated mainly with gene response to a single exercise bout, whereas the predicted transcription factors were related to stress/immune (Hsf, NF-κB, etc.) and early gene response. In contrast, Hsp70- flies demonstrated no adaptation to training as well as a significantly impaired gene response to a single exercise bout. In conclusion, the knockout of Hsp70 genes not only reduced physical performance but also disrupted adaptation to chronic physical training, which is associated with changes in the leg skeletal muscle transcriptome and impaired gene response to a single exercise bout.NEW & NOTEWORTHY Knockout of six heat shock protein 70 (Hsp70) genes in Drosophila melanogaster reduced locomotion (climbing) speed that is associated with genotype-specific differences in leg skeletal muscle gene expression. Disrupted adaptation of Hsp70- flies to chronic exercise training is associated with impaired gene response to a single exercise bout.

Genome-wide identification of the HSP70 genes in Pacific oyster Magallana gigas and their response to heat stress

Heat shock protein 70 (HSP70), the most prominent and well-characterized stress protein in animals, plays an important role in assisting animals in responding to various adverse conditions. In the present study, a total of 113 HSP70 gene family members were identified in the updated genome of Magallana gigas (designated MgHSP70) (previously known as Crassostrea gigas). There were 75, 12, 11, and 8 HSP70s located in the cytoplasm, nucleus, mitochondria, and endoplasmic reticulum, respectively, and 7 HSP70s were located in both the nucleus and cytoplasm. Among 113 MgHSP70 genes, 107 were unevenly distributed in 8 chromosomes of M. gigas with the greatest number in chromosome 07 (61 genes, 57.01%). The MgHSP70 gene family members were mainly assigned into five clusters, among which the HSPa12 subfamily underwent lineage-specific expansion, consisting of 89 members. A total of 68 MgHSP70 genes (60.18%) were tandemly duplicated and formed 30 gene pairs, among which 14 gene pairs were under strong positive selection. In general, the expression of MgHSP70s was tissue-specific, with the highest expression in labial palp and gill and the lowest expression in adductor muscle and hemocytes. There were 35, 31, and 47 significantly upregulated genes at 6, 12, and 24 h after heat shock treatment (28 °C), respectively. The expression patterns of different tandemly duplicated genes exhibited distinct characteristics after shock treatment, indicating that these genes may have different functions. Nevertheless, genes within the same tandemly duplicated group exhibit similar expression patterns. Most of the tandemly duplicated HSP70 gene pairs showed the highest expression levels at 24 h. This study provides a comprehensive description of the MgHSP70 gene family in M. gigas and offers valuable insights into the functions of HSP70 in the mollusc adaptation of oysters to environmental stress.

CRISPR/Cas9-mediated tissue-specific knockout and cDNA rescue using sgRNAs that target exon-intron junctions in Drosophila melanogaster

In this protocol, we take CRISPR/Cas9 and Gal4/UAS approaches to achieve tissue-specific knockout in parallel with rescue of the knockout by cDNA expression in Drosophila. We demonstrate that guide RNAs targeting the exon-intron junction of target genes cleave the genomic locus of the genes, but not UAS-cDNA transgenes, in a tissue where Gal4 drives Cas9 expression. The efficiency of this approach enables the determination of pathogenicity of disease-associated variants in human genes in a tissue-specific manner in Drosophila. For complete details on the use and execution of this protocol, please refer to Yap et al. (2021).

The Role of GCN2 Kinase in Mediating the Effects of Amino Acids on Longevity and Feeding Behaviour in Drosophila

Restriction of amino acids in the diet can extend lifespan in diverse species ranging from flies to mammals. However, the role of individual amino acids and the underlying molecular mechanisms are only partially understood. The evolutionarily conserved serine/threonine kinase General Control Nonderepressible 2 (GCN2) is a key sensor of amino acid deficiency and has been implicated in the response of lifespan to dietary restriction (DR). Here, we generated a novel Drosophila GCN2 null mutant and analyzed its response to individual amino acid deficiency. We show that GCN2 function is essential for fly development, longevity and feeding behaviour under long-term, but not short-term, deprivation of all individual essential amino acids (EAAs) except for methionine. GCN2 mutants were longer-lived than control flies and showed normal feeding behaviour under methionine restriction. Thus, in flies at least two systems regulate these responses to amino acid deprivation. Methionine deprivation acts via a GCN2-independent mechanism, while all other EAA are sensed by GCN2. Combined deficiency of methionine and a second EAA blocked the response of GCN2 mutants to methionine, suggesting that these two pathways are interconnected. Wild type flies showed a short-term rejection of food lacking individual EAA, followed by a long-term compensatory increase in food uptake. GCN2 mutants also showed a short-term rejection of food deprived of individual EAA, but were unable to mount the compensatory long-term increase in food uptake. Over-expression of the downstream transcription factor ATF4 partially rescued the response of feeding behaviour in GCN2 mutants to amino acid deficiency. Phenotypes of GCN2 mutants induced by leucine and tryptophan, but not isoleucine, deficiency were partially rescued by ATF4 over-expression. The exact function of GCN2 as an amino acid sensor in vivo and the downstream action of its transcription factor effector ATF4 are thus context-specific with respect to the EAA involved.

Heat shock proteins: a history of study in Russia

This review describes a brief history of the discovery and studies in Russia and associated countries of the main stress protein (Hsp70) that plays important roles both in the normal function of the cell and body as well as under various stressful stimuli. Research on this protein at the Institute of Molecular Biology (Moscow) began with the elucidation of its adaptive functions at the cellular level and at the level of the whole organism. These studies examined the function of Hsp70 under normal and extreme conditions using a wide range of model and non-model animal species, from Leishmania and Drosophila to camels and humans. These analyses made it possible to elucidate the primary regulations in the evolution and function of heat shock (HS) genes in the studied organisms. Next, we studied the structure and characteristic features of heat shock genes and proteins in species with contrasting habitat temperatures. The systems of Hsp70 expression and isolation we developed using various research objects allowed us to proceed to study the protective properties of human recombinant Hsp70 in normal-aging animal models as well as animal models experiencing sepsis, Alzheimer's disease, and stroke. The results obtained open the prospects of using recombinant Hsp70 for the treatment of various neuropathologies in humans. This review describes the logic and history of investigation of Hsp70 performed by one group of scientists from Engelhardt Institute of Molecular Biology, Russian Academy of Sciences. It was not the goal of this paper to give a comprehensive general picture of other similar studies carried out in Russia during this period.

Hsp70 affects memory formation and behaviorally relevant gene expression in Drosophila melanogaster

Heat shock proteins, in particular Hsp70, play a central role in proteostasis in eukaryotic cells. Due to its chaperone properties, Hsp70 is involved in various processes after stress and under normal physiological conditions. In contrast to mammals and many Diptera species, inducible members of the Hsp70 family in Drosophila are constitutively synthesized at a low level and undergo dramatic induction after temperature elevation or other forms of stress. In the courtship suppression paradigm used in this study, Drosophila males that have been repeatedly rejected by mated females during courtship are less likely than naive males to court other females. Although numerous genes with known function were identified to play important roles in long-term memory, there is, to the best of our knowledge, no direct evidence implicating Hsp70 in this process. To elucidate a possible role of Hsp70 in memory formation, we used D. melanogaster strains containing different hsp70 copy numbers, including strains carrying a deletion of all six hsp70 genes. Our investigations exploring the memory of courtship rejection paradigm demonstrated that a low constitutive level of Hsp70 is apparently required for learning and the formation of short and long-term memories in males. The performed transcriptomic studies demonstrate that males with different hsp70 copy numbers differ significantly in the expression of a few definite groups of genes involved in mating, reproduction, and immunity in response to rejection. Specifically, our analysis reveals several major pathways that depend on the presence of hsp70 in the genome and participate in memory formation and consolidation, including the cAMP signaling cascade.

Expression of Heat Shock Protein 70 Is Insufficient To Extend Drosophila melanogaster Longevity

It has been known for over 20 years that Drosophila melanogaster flies with twelve additional copies of the hsp70 gene encoding the 70 kD heat shock protein lives longer after a non-lethal heat treatment. Since the heat treatment also induces the expression of additional heat shock proteins, the biological effect can be due either to HSP70 acting alone or in combination. This study used the UAS/GAL4 system to determine whether hsp70 is sufficient to affect the longevity and the resistance to thermal, oxidative or desiccation stresses of the whole organism. We observed that HSP70 expression in the nervous system or muscles has no effect on longevity or stress resistance but ubiquitous expression reduces the life span of males. We also observed that the down-regulation of hsp70 using RNAi did not affect longevity.

The Hsp70 chaperone is a major player in stress-induced transposable element activation

Previous studies have shown that heat shock stress may activate transposable elements (TEs) in Drosophila and other organisms. Such an effect depends on the disruption of a chaperone complex that is normally involved in biogenesis of Piwi-interacting RNAs (piRNAs), the largest class of germline-enriched small noncoding RNAs implicated in the epigenetic silencing of TEs. However, a satisfying picture of how chaperones could be involved in repressing TEs in germ cells is still unknown. Here we show that, in Drosophila, heat shock stress increases the expression of TEs at a posttranscriptional level by affecting piRNA biogenesis through the action of the inducible chaperone Hsp70. We found that stress-induced TE activation is triggered by an interaction of Hsp70 with the Hsc70-Hsp90 complex and other factors all involved in piRNA biogenesis in both ovaries and testes. Such interaction induces a displacement of all such factors to the lysosomes, resulting in a functional collapse of piRNA biogenesis. This mechanism has clear evolutionary implications. In the presence of drastic environmental changes, Hsp70 plays a key dual role in increasing both the survival probability of individuals and the genetic variability in their germ cells. The consequent increase of genetic variation in a population potentiates evolutionary plasticity and evolvability.

Harnessing model organisms to study insecticide resistance

The vinegar fly, Drosophila melanogaster, has made an enormous contribution to our understanding of insecticide targets, metabolism and transport. This contribution has been enabled by the unmatched capacity to manipulate genes in D. melanogaster and the fact that lessons learn in this system have been applicable to pests, because of the evolutionary conservation of key genes, particularly those encoding targets. With the advent of the CRISPR-Cas9 gene editing technology, genes can now be manipulated in pest species, but this review points to advantages that are likely to keep D. melanogaster at the forefront of insecticide research.

Efficient Expression of Genes in the Drosophila Germline Using a UAS Promoter Free of Interference by Hsp70 piRNAs

Using the yeast GAL4 transcription factor to control expression in Drosophila melanogaster has long been ineffective in female germ cells during oogenesis. Here, DeLuca and Spradling show that the expression problem of most Drosophila molecular tools...

Controlling the expression of genes using a binary system involving the yeast GAL4 transcription factor has been a mainstay of Drosophila developmental genetics for nearly 30 years. However, most existing GAL4 expression constructs only function effectively in somatic cells, but not in germ cells during oogenesis, for unknown reasons. A special upstream activation sequence (UAS) promoter, UASp was created that does express during oogenesis, but the need to use different constructs for somatic and female germline cells has remained a significant technical limitation. Here, we show that the expression problem of UASt and many other Drosophila molecular tools in germline cells is caused by their core Hsp70 promoter sequences, which are targeted in female germ cells by Hsp70-directed Piwi-interacting RNAs (piRNAs) generated from endogenous Hsp70 gene sequences. In a genetic background lacking genomic Hsp70 genes and associated piRNAs, UASt-based constructs function effectively during oogenesis. By reducing Hsp70 sequences targeted by piRNAs, we created UASz, which functions better than UASp in the germline and like UASt in somatic cells.

Heat shock protein 70 from a thermotolerant Diptera species provides higher thermoresistance to Drosophila larvae than correspondent endogenous gene

Heat shock proteins (Hsp70s) from two Diptera species that drastically differ in their heat shock response and longevity were investigated. Drosophila melanogaster is characterized by the absence of Hsp70 and other hsps under normal conditions and the dramatic induction of hsp synthesis after temperature elevation. The other Diptera species examined belongs to the Stratiomyidae family (Stratiomys singularior) and exhibits high levels of inducible Hsp70 under normal conditions coupled with a thermotolerant phenotype and much longer lifespan. To evaluate the impact of hsp70 genes on thermotolerance and longevity, we made use of a D. melanogaster strain that lacks all hsp70 genes. We introduced single copies of either S. singularior or D. melanogaster hsp70 into this strain and monitored the obtained transgenic flies in terms of thermotolerance and longevity. We developed transgenic strains containing the S. singularior hsp70 gene under control of a D. melanogaster hsp70 promoter. Although these adult flies did synthesize the corresponding mRNA after heat shock, they were not superior to the flies containing a single copy of D. melanogaster hsp70 in thermotolerance and longevity. By contrast, Stratiomyidae Hsp70 provided significantly higher thermotolerance at the larval stage in comparison with endogenous Hsp70.

Interplay between RNA interference and heat shock response systems in Drosophila melanogaster

The genome expression pattern is strongly modified during the heat shock response (HSR) to form an adaptive state. This may be partly achieved by modulating microRNA levels that control the expression of a great number of genes that are embedded within the gene circuitry. Here, we investigated the cross-talk between two highly conserved and universal house-keeping systems, the HSR and microRNA machinery, in Drosophila melanogaster We demonstrated that pronounced interstrain differences in the microRNA levels are alleviated after heat shock (HS) to form a uniform microRNA pattern. However, individual strains exhibit different patterns of microRNA expression during the course of recovery. Importantly, HS-regulated microRNAs may target functionally similar HS-responsive genes involved in the HSR. Despite the observed general downregulation of primary microRNA precursor expression as well as core microRNA pathway genes after HS, the levels of many mature microRNAs are upregulated. This indicates that the regulation of miRNA expression after HS occurs at transcriptional and post-transcriptional levels. It was also shown that deletion of all hsp70 genes had no significant effect on microRNA biogenesis but might influence the dynamics of microRNA expression during the HSR.

H2Av facilitates H3S10 phosphorylation but is not required for heat shock-induced chromatin decondensation or transcriptional elongation

A model has been proposed in which JIL-1 kinase-mediated H3S10 and H2Av phosphorylation is required for transcriptional elongation and heat shock-induced chromatin decondensation. However, here we show that although H3S10 phosphorylation is indeed compromised in the H2Av null mutant, chromatin decondensation at heat shock loci is unaffected in the absence of JIL-1 as well as of H2Av and that there is no discernable decrease in the elongating form of RNA polymerase II in either mutant. Furthermore, mRNA for the major heat shock protein Hsp70 is transcribed at robust levels in both H2Av and JIL-1 null mutants. Using a different chromatin remodeling paradigm that is JIL-1 dependent, we provide evidence that ectopic tethering of JIL-1 and subsequent H3S10 phosphorylation recruits PARP-1 to the remodeling site independently of H2Av phosphorylation. These data strongly suggest that H2Av or H3S10 phosphorylation by JIL-1 is not required for chromatin decondensation or transcriptional elongation in Drosophila.

Oligopeptide Transporters of the SLC15 Family Are Dispensable for Peptidoglycan Sensing and Transport in Drosophila

Peptidoglycan (PGN) detection by PGN recognition proteins (PGRP) is the main trigger of the antibacterial immune response in Drosophila. Depending on the type of immune cell, PGN can be sensed either at the cell membrane by PGRP-LC or inside the cell by PGRP-LE, which plays a role similar to that of Nod2 in mammals. Previous work, mainly in cell cultures, has shown that oligopeptide transporters of the SLC15 family are essential for the delivery of PGN for Nod2 detection inside of the cells, and that this function might be conserved in flies. By generating and analyzing the immune phenotypes of loss-of-function mutations in 3 SLC15 Drosophila family members, we tested their role in mediating PGRP-LE-dependent PGN activation. Our results show that Yin, CG2930, and CG9444 are required neither for PGRP-LE activation by PGN nor for PGN transport from the gut lumen to the insect blood. These data show that, while intracellular PGN detection is an essential step of the antibacterial response in both insects and mammals, the types of PGN transporters and sensors are different in these animals.

A Drosophila Model of Neuronopathic Gaucher Disease Demonstrates Lysosomal-Autophagic Defects and Altered mTOR Signalling and Is Functionally Rescued by Rapamycin

Glucocerebrosidase (GBA1) mutations are associated with Gaucher disease (GD), an autosomal recessive disorder caused by functional deficiency of glucocerebrosidase (GBA), a lysosomal enzyme that hydrolyzes glucosylceramide to ceramide and glucose. Neuronopathic forms of GD can be associated with rapid neurological decline (Type II) or manifest as a chronic form (Type III) with a wide spectrum of neurological signs. Furthermore, there is now a well-established link between GBA1 mutations and Parkinson's disease (PD), with heterozygote mutations in GBA1 considered the commonest genetic defect in PD. Here we describe a novel Drosophila model of GD that lacks the two fly GBA1 orthologs. This knock-out model recapitulates the main features of GD at the cellular level with severe lysosomal defects and accumulation of glucosylceramide in the fly brain. We also demonstrate a block in autophagy flux in association with reduced lifespan, age-dependent locomotor deficits and accumulation of autophagy substrates in dGBA-deficient fly brains. Furthermore, mechanistic target of rapamycin (mTOR) signaling is downregulated in dGBA knock-out flies, with a concomitant upregulation of Mitf gene expression, the fly ortholog of mammalian TFEB, likely as a compensatory response to the autophagy block. Moreover, the mTOR inhibitor rapamycin is able to partially ameliorate the lifespan, locomotor, and oxidative stress phenotypes. Together, our results demonstrate that this dGBA1-deficient fly model is a useful platform for the further study of the role of lysosomal-autophagic impairment and the potential therapeutic benefits of rapamycin in neuronopathic GD. These results also have important implications for the role of autophagy and mTOR signaling in GBA1-associated PD SIGNIFICANCE STATEMENT: We developed a Drosophila model of neuronopathic GD by knocking-out the fly orthologs of the GBA1 gene, demonstrating abnormal lysosomal pathology in the fly brain. Functioning lysosomes are required for autophagosome-lysosomal fusion in the autophagy pathway. We show in vivo that autophagy is impaired in dGBA-deficient fly brains. In response, mechanistic target of rapamycin (mTOR) activity is downregulated in dGBA-deficient flies and rapamycin ameliorates the lifespan, locomotor, and oxidative stress phenotypes. dGBA knock-out flies also display an upregulation of the Drosophila ortholog of mammalian TFEB, Mitf, a response that is unable to overcome the autophagy block. Together, our results suggest that rapamycin may have potential benefits in the treatment of GD, as well as PD linked to GBA1 mutations.

Alcohol-Induced Neuroadaptation Is Orchestrated by the Histone Acetyltransferase CBP

Homeostatic neural adaptations to alcohol underlie the production of alcohol tolerance and the associated symptoms of withdrawal. These adaptations have been shown to persist for relatively long periods of time and are believed to be of central importance in promoting the addictive state. In Drosophila, a single exposure to alcohol results in long-lasting alcohol tolerance and symptoms of withdrawal following alcohol clearance. These persistent adaptations involve mechanisms such as long-lasting changes in gene expression and perhaps epigenetic restructuring of chromosomal regions. Histone modifications have emerged as important modulators of gene expression and are thought to orchestrate and maintain the expression of multi-gene networks. Previously genes that contribute to tolerance were identified as those that show alcohol-induced changes in histone H4 acetylation following a single alcohol exposure. However, the molecular mediator of the acetylation process that orchestrates their expression remains unknown. Here we show that the Drosophila ortholog of mammalian CBP, nejire, is the histone acetyltransferase involved in regulatory changes producing tolerance—alcohol induces nejire expression, nejire mutations suppress tolerance, and transgenic nejire induction mimics tolerance in alcohol-naive animals. Moreover, we observed that a loss-of-function mutation in the alcohol tolerance gene slo epistatically suppresses the effects of CBP induction on alcohol resistance, linking nejire to a well-established alcohol tolerance gene network. We propose that CBP is a central regulator of the network of genes underlying an alcohol adaptation.

Inhibition of a NF-κB/Diap1 Pathway by PGRP-LF Is Required for Proper Apoptosis during Drosophila Development

NF-κB pathways are key signaling cascades of the Drosophila innate immune response. One of them, the Immune Deficiency (IMD) pathway, is under a very tight negative control. Although molecular brakes exist at each step of this signaling module from ligand availability to transcriptional regulation, it remains unknown whether repressors act in the same cells or tissues and if not, what is rationale behind this spatial specificity. We show here that the negative regulator of IMD pathway PGRP-LF is epressed in ectodermal derivatives. We provide evidence that, in the absence of any immune elicitor, PGRP-LF loss-of-function mutants, display a constitutive NF-κB/IMD activation specifically in ectodermal tissues leading to genitalia and tergite malformations. In agreement with previous data showing that proper development of these structures requires induction of apoptosis, we show that ectopic activation of NF-κB/IMD signaling leads to apoptosis inhibition in both genitalia and tergite primordia. We demonstrate that NF-κB/IMD signaling antagonizes apoptosis by up-regulating expression of the anti-apoptotic protein Diap1. Altogether these results show that, in the complete absence of infection, the negative regulation of NF-κB/IMD pathway by PGRP-LF is crucial to ensure proper induction of apoptosis and consequently normal fly development. These results highlight that IMD pathway regulation is controlled independently in different tissues, probably reflecting the different roles of this signaling cascade in both developmental and immune processes.

In multicellular organism such as mammals or insects, activation of innate immune responses occurs following detection of microbes by dedicated receptors called pattern recognition receptors. Such immune activation is taking place in immune competent tissue such as the skin, the digestive and respiratory epithelia and is under a tight negative control. Negative control is essential to finely adjust the duration and the intensity of the immune response to the level of infection. We found that the Drosophila innate immunity negative regulator PGRP-LF, is specifically expressed in non-immune tissues and plays an essential role during development, in absence of any infection. Lack of PGRP-LF function in these tissues inhibits apoptosis leading to incomplete genitalia rotation and tergite malformations. We show that such apoptosis inhibition results from the over expression of the negative regulator of apoptosis Diap1 specifically in PGRP-LF expressing cells. Our data highlight that proper negative regulation of immune signaling pathway in non-immune tissues is contributing to normal development and illustrate the growing evidence of the dual role of immune signaling pathway contribution to both immunity and in development processes.

Feeding-Related Traits Are Affected by Dosage of the foraging Gene in Drosophila melanogaster

Nutrient acquisition and energy storage are critical parts of achieving metabolic homeostasis. The foraging gene in Drosophila melanogaster has previously been implicated in multiple feeding-related and metabolic traits. Before foraging's functions can be further dissected, we need a precise genetic null mutant to definitively map its amorphic phenotypes. We used homologous recombination to precisely delete foraging, generating the for⁰ null allele, and used recombineering to reintegrate a full copy of the gene, generating the {for^BAC} rescue allele. We show that a total loss of foraging expression in larvae results in reduced larval path length and food intake behavior, while conversely showing an increase in triglyceride levels. Furthermore, varying foraging gene dosage demonstrates a linear dose-response on these phenotypes in relation to foraging gene expression levels. These experiments have unequivocally proven a causal, dose-dependent relationship between the foraging gene and its pleiotropic influence on these feeding-related traits. Our analysis of foraging's transcription start sites, termination sites, and splicing patterns using rapid amplification of cDNA ends (RACE) and full-length cDNA sequencing, revealed four independent promoters, pr1-4, that produce 21 transcripts with nine distinct open reading frames (ORFs). The use of alternative promoters and alternative splicing at the foraging locus creates diversity and flexibility in the regulation of gene expression, and ultimately function. Future studies will exploit these genetic tools to precisely dissect the isoform- and tissue-specific requirements of foraging's functions and shed light on the genetic control of feeding-related traits involved in energy homeostasis.

A Drosophila heat shock response represents an exception rather than a rule amongst Diptera species

Heat shock protein 70 (Hsp70) is the major player that underlies adaptive response to hyperthermia in all organisms studied to date. We investigated patterns of Hsp70 expression in larvae of dipteran species collected from natural populations of species belonging to four families from different evolutionary lineages of the order Diptera: Stratiomyidae, Tabanidae, Chironomidae and Ceratopogonidae. All investigated species showed a Hsp70 expression pattern that was different from the pattern in Drosophila. In contrast to Drosophila, all of the species in the families studied were characterized by high constitutive levels of Hsp70, which was more stable than that in Drosophila. When Stratiomyidae Hsp70 proteins were expressed in Drosophila cells, they became as short-lived as the endogenous Hsp70. Interestingly, three species of Ceratopogonidae and a cold-water species of Chironomidae exhibited high constitutive levels of Hsp70 mRNA and high basal levels of Hsp70. Furthermore, two species of Tabanidae were characterized by significant constitutive levels of Hsp70 and highly stable Hsp70 mRNA. In most cases, heat-resistant species were characterized by a higher basal level of Hsp70 than more thermosensitive species. These data suggest that different trends were realized during the evolution of the molecular mechanisms underlying the regulation of the responses of Hsp70 genes to temperature fluctuations in the studied families.

Polarized endosome dynamics by spindle asymmetry during asymmetric cell division

During asymmetric division, fate determinants at the cell cortex segregate unequally into the two daughter cells. It has recently been shown that Sara (Smad anchor for receptor activation) signalling endosomes in the cytoplasm also segregate asymmetrically during asymmetric division. Biased dispatch of Sara endosomes mediates asymmetric Notch/Delta signalling during the asymmetric division of sensory organ precursors in Drosophila. In flies, this has been generalized to stem cells in the gut and the central nervous system, and, in zebrafish, to neural precursors of the spinal cord. However, the mechanism of asymmetric endosome segregation is not understood. Here we show that the plus-end kinesin motor Klp98A targets Sara endosomes to the central spindle, where they move bidirectionally on an antiparallel array of microtubules. The microtubule depolymerizing kinesin Klp10A and its antagonist Patronin generate central spindle asymmetry. This asymmetric spindle, in turn, polarizes endosome motility, ultimately causing asymmetric endosome dispatch into one daughter cell. We demonstrate this mechanism by inverting the polarity of the central spindle by polar targeting of Patronin using nanobodies (single-domain antibodies). This spindle inversion targets the endosomes to the wrong cell. Our data uncover the molecular and physical mechanism by which organelles localized away from the cellular cortex can be dispatched asymmetrically during asymmetric division.

Tissue-Specific Regulation of Drosophila NF-x03BA;B Pathway Activation by Peptidoglycan Recognition Protein SC

In Drosophila, peptidoglycan (PGN) is detected by PGN recognition proteins (PGRPs) that act as pattern recognition receptors. Some PGRPs such as PGRP-LB or PGRP-SCs are able to cleave PGN, therefore reducing the amount of immune elicitors and dampening immune deficiency (IMD) pathway activation. The precise role of PGRP-SC is less well defined because the PGRP-SC genes (PGRP-SC1a, PGRP-SC1b and PGRP-SC2) lie very close on the chromosome and have been studied using a deletion encompassing the three genes. By generating PGRP-SC-specific mutants, we reevaluated the roles of PGRP-LB, PGRP-SC1 and PGRP-SC2, respectively, during immune responses. We showed that these genes are expressed in different gut domains and that they follow distinct transcriptional regulation. Loss-of-function mutant analysis indicates that PGRP-LB is playing a major role in IMD pathway activation and bacterial load regulation in the gut, although PGRP-SCs are expressed at high levels in this organ. We also demonstrated that PGRP-SC2 is the main negative regulator of IMD pathway activation in the fat body. Accordingly, we showed that mutants for either PGRP-LB or PGRP-SC2 displayed a distinct susceptibility to bacteria depending on the infection route. Lastly, we demonstrated that PGRP-SC1 and PGRP-SC2 are required in vivo for full Toll pathway activation by Gram-positive bacteria.

Genome engineering: Drosophila melanogaster and beyond

A central challenge in investigating biological phenomena is the development of techniques to modify genomic DNA with nucleotide precision that can be transmitted through the germ line. Recent years have brought a boon in these technologies, now collectively known as genome engineering. Defined genomic manipulations at the nucleotide level enable a variety of reverse engineering paradigms, providing new opportunities to interrogate diverse biological functions. These genetic modifications include controlled removal, insertion, and substitution of genetic fragments, both small and large. Small fragments up to a few kilobases (e.g., single nucleotide mutations, small deletions, or gene tagging at single or multiple gene loci) to large fragments up to megabase resolution can be manipulated at single loci to create deletions, duplications, inversions, or translocations of substantial sections of whole chromosome arms. A specialized substitution of chromosomal portions that presumably are functionally orthologous between different organisms through syntenic replacement, can provide proof of evolutionary conservation between regulatory sequences. Large transgenes containing endogenous or synthetic DNA can be integrated at defined genomic locations, permitting an alternative proof of evolutionary conservation, and sophisticated transgenes can be used to interrogate biological phenomena. Precision engineering can additionally be used to manipulate the genomes of organelles (e.g., mitochondria). Novel genome engineering paradigms are often accelerated in existing, easily genetically tractable model organisms, primarily because these paradigms can be integrated in a rigorous, existing technology foundation. The Drosophila melanogaster fly model is ideal for these types of studies. Due to its small genome size, having just four chromosomes, the vast amount of cutting-edge genetic technologies, and its short life-cycle and inexpensive maintenance requirements, the fly is exceptionally amenable to complex genetic analysis using advanced genome engineering. Thus, highly sophisticated methods developed in the fly model can be used in nearly any sequenced organism. Here, we summarize different ways to perform precise inheritable genome engineering using integrases, recombinases, and DNA nucleases in the D. melanogaster. For further resources related to this article, please visit the WIREs website.

The peculiarities of piRNA expression upon heat shock exposure in Drosophila melanogaster

Different types of stress including heat shock may induce genomic instability, due to the derepression and amplification of mobile elements (MEs). It remains unclear, however, whether piRNA-machinery regulating ME expression functions normally under stressful conditions. The aim of this study was to explore the features of piRNA expression after heat shock (HS) exposure in Drosophila melanogaster. We also evaluated functioning of piRNA-machinery in the absence of major stress protein Hsp70 in this species. We analyzed the deep sequence data of piRNA expression after HS treatment and demonstrated that it modulates the expression of certain double-stranded germinal piRNA-clusters. Notable, we demonstrated significant changes in piRNA levels targeting a group of MEs after HS only in the strain containing normal set of hsp70 genes. Surprisingly, we failed to detect any correlation between the levels of piRNAs and the transcription of complementary MEs in the studied strains. We propose that modulation of certain piRNA-clusters expression upon HS exposure in D. melanogaster occurs due to HS-induced altering of chromatin state at certain chromosome regions.

Two bromodomain proteins functionally interact to recapitulate an essential BRDT-like function in Drosophila spermatocytes

In mammals, the testis-specific bromodomain and extra terminal (BET) protein BRDT is essential for spermatogenesis. In Drosophila, it was recently reported that the tBRD-1 protein is similarly required for male fertility. Interestingly, however, tBRD-1 has two conserved bromodomains in its N-terminus but it lacks an extra terminal (ET) domain characteristic of BET proteins. Here, using proteomics approaches to search for tBRD-1 interactors, we identified tBRD-2 as a novel testis-specific bromodomain protein. In contrast to tBRD-1, tBRD-2 contains a single bromodomain, but which is associated with an ET domain in its C-terminus. Strikingly, we show that tbrd-2 knock-out males are sterile and display aberrant meiosis in a way highly similar to tbrd-1 mutants. Furthermore, these two factors co-localize and are interdependent in spermatocytes. We propose that Drosophila tBRD-1 and tBRD-2 associate into a functional BET complex in spermatocytes, which recapitulates the activity of the single mammalian BRDT-like protein.

The Role of Inducible Hsp70, and Other Heat Shock Proteins, in Adaptive Complex of Cold Tolerance of the Fruit Fly (Drosophila melanogaster)

Background

The ubiquitous occurrence of inducible Heat Shock Proteins (Hsps) up-regulation in response to cold-acclimation and/or to cold shock, including massive increase of Hsp70 mRNA levels, often led to hasty interpretations of its role in the repair of cold injury expressed as protein denaturation or misfolding. So far, direct functional analyses in Drosophila melanogaster and other insects brought either limited or no support for such interpretations. In this paper, we analyze the cold tolerance and the expression levels of 24 different mRNA transcripts of the Hsps complex and related genes in response to cold in two strains of D. melanogaster: the wild-type and the Hsp70^- null mutant lacking all six copies of Hsp70 gene.

Principal Findings

We found that larvae of both strains show similar patterns of Hsps complex gene expression in response to long-term cold-acclimation and during recovery from chronic cold exposures or acute cold shocks. No transcriptional compensation for missing Hsp70 gene was seen in Hsp70^- strain. The cold-induced Hsps gene expression is most probably regulated by alternative splice variants C and D of the Heat Shock Factor. The cold tolerance in Hsp70^- null mutants was clearly impaired only when the larvae were exposed to severe acute cold shock. No differences in mortality were found between two strains when the larvae were exposed to relatively mild doses of cold, either chronic exposures to 0°C or acute cold shocks at temperatures down to -4°C.

Conclusions

The up-regulated expression of a complex of inducible Hsps genes, and Hsp70 mRNA in particular, is tightly associated with cold-acclimation and cold exposure in D. melanogaster. Genetic elimination of Hsp70 up-regulation response has no effect on survival of chronic exposures to 0°C or mild acute cold shocks, while it negatively affects survival after severe acute cold shocks at temperaures below -8°C.

A histone modification identifies a DNA element controlling slo BK channel gene expression in muscle

The slo gene encodes the BK-type Ca(2+)-activated K(+) channels. In Drosophila, expression of slo is induced by organic solvent sedation (benzyl alcohol and ethanol), and this increase in neural slo expression contributes to the production of functional behavioral tolerance (inducible resistance) to these drugs. Within the slo promoter region, we observed that benzyl alcohol sedation produces a localized spike of histone acetylation over a 65-nucleotide (65-n) conserved DNA element called 55b. Changes in histone acetylation are commonly the consequence of transcription factor activity, and previously, a localized histone acetylation spike was used to successfully map a DNA element involved in benzyl alcohol-induced slo expression. To determine whether the 55b element was also involved in benzyl alcohol-induced neural expression of slo, we deleted it from the endogenous slo gene by homologous recombination. Flies lacking the 55b element were normal with respect to basal and benzyl alcohol-induced neural slo expression, the capacity to acquire and maintain functional tolerance, their threshold for electrically-induced seizures, and most slo-related behaviors. Removal of the 55b element did however increase the level of basal expression from the muscle/tracheal cell-specific slo core promoter and produced a slight increase in overall locomotor activity. We conclude that the 55b element is involved in control of slo expression from the muscle and tracheal-cell promoter but is not involved in the production of functional benzyl alcohol tolerance.

Activity of heat shock genes' promoters in thermally contrasting animal species

Heat shock gene promoters represent a highly conserved and universal system for the rapid induction of transcription after various stressful stimuli. We chose pairs of mammalian and insect species that significantly differ in their thermoresistance and constitutive levels of Hsp70 to compare hsp promoter strength under normal conditions and after heat shock (HS). The first pair includes the HSPA1 gene promoter of camel (Camelus dromedarius) and humans. It was demonstrated that the camel HSPA1A and HSPA1L promoters function normally in vitro in human cell cultures and exceed the strength of orthologous human promoters under basal conditions. We used the same in vitro assay for Drosophila melanogaster Schneider-2 (S2) cells to compare the activity of the hsp70 and hsp83 promoters of the second species pair represented by Diptera, i.e., Stratiomys singularior and D. melanogaster, which dramatically differ in thermoresistance and the pattern of Hsp70 accumulation. Promoter strength was also monitored in vivo in D. melanogaster strains transformed with constructs containing the S. singularior hsp70 ORF driven either by its own promoter or an orthologous promoter from the D. melanogaster hsp70Aa gene. Analysis revealed low S. singularior hsp70 promoter activity in vitro and in vivo under basal conditions and after HS in comparison with the endogenous promoter in D. melanogaster cells, which correlates with the absence of canonical GAGA elements in the promoters of the former species. Indeed, the insertion of GAGA elements into the S. singularior hsp70 regulatory region resulted in a dramatic increase in promoter activity in vitro but only modestly enhanced the promoter strength in the larvae of the transformed strains. In contrast with hsp70 promoters, hsp83 promoters from both of the studied Diptera species demonstrated high conservation and universality.

Drosophila protamine-like Mst35Ba and Mst35Bb are required for proper sperm nuclear morphology but are dispensable for male fertility

During spermiogenesis, histones are massively replaced with protamines. A previous report showed that Drosophila males homozygous for a genomic deletion covering several genes including the protamine-like genes Mst35Ba/b are surprisingly fertile. Here, we have precisely deleted the Mst35B locus by homologous recombination, and we confirm the dispensability of Mst35Ba/b for fertility.

miR-124 controls Drosophila behavior and is required for neural development

MicroRNA-124 (miR-124) is an evolutionarily conserved, small, noncoding RNA molecule that participates in the central nervous system (CNS) developmental control of gene expression. In the current study, we found that Drosophila embryos lacking the mir-124 gene did not exhibit detectable defects in axon growth or CNS development. On the other hand, adult mutants showed severe problems in locomotion, flight, and female fertility. Furthermore, the deficits that we observed in the adult stage could be marginally rescued with elav-GAL4 driven expression of miR-124, making elav-GAL4 an excellently simulated driver to induce entopic over-expression of miR-124. Further developmental assessment in the third instar larval neuromuscular junction (NMJ) and dendritic arborization (DA) neurons was performed with miR-124 knock outs, flies over-expressing miR-124, and rescue models. Typically, the absence and over-abundance of a molecular signal exerts opposite effects on development or phenotype. However, we determined that both miR-124 knock-outs and over-expressing flies displayed reduced NMJ 6/7 bouton number and branch length. Similarly, reduced ddaE branching numbers were observed between the two mutant lines. As to ddaF, we found that branching number was not influenced by mir-124 knock out, but was statistically reduced by miR-124 over-expression. While we were not able to determine any causal relationship between behavioral defects and dysplasia of NMJs or DA neurons, there were some accompanying relationships among behavioral phenotypes, NMJ abnormalities, and ddaE/ddaF dendritic branching which were all controlled by miR-124.

Prophenoloxidase activation is required for survival to microbial infections in Drosophila

The melanization reaction is a major immune response in Arthropods and involves the rapid synthesis of melanin at the site of infection and injury. A key enzyme in the melanization process is phenoloxidase (PO), which catalyzes the oxidation of phenols to quinones, which subsequently polymerize into melanin. The Drosophila genome encodes three POs, which are primarily produced as zymogens or prophenoloxidases (PPO). Two of them, PPO1 and PPO2, are produced by crystal cells. Here we have generated flies carrying deletions in PPO1 and PPO2. By analyzing these mutations alone and in combination, we clarify the functions of both PPOs in humoral melanization. Our study shows that PPO1 and PPO2 are responsible for all the PO activity in the hemolymph. While PPO1 is involved in the rapid early delivery of PO activity, PPO2 is accumulated in the crystals of crystal cells and provides a storage form that can be deployed in a later phase. Our study also reveals an important role for PPO1 and PPO2 in the survival to infection with Gram-positive bacteria and fungi, underlining the importance of melanization in insect host defense.

The melanization reaction is a major immune response in Arthropods and involves the rapid synthesis of a black pigment, melanin, at the site of infection and injury. Melanization requires the activation of proPhenoloxidase, an enzyme that catalyzes the oxidation of phenols to quinones, which polymerize to melanin. The Drosophila genome contains three genes encoding prophenoloxidases (PPO). In this paper, we have generated flies carrying deletions in the PPO1 and PPO2 genes. By analyzing these mutations alone and in combination, we clarify the functions of both prophenoloxidases in humoral melanization. We report that PPO2 composes most of the crystals found in crystal cells, a specific hemocyte cell type. Although PPO1 and PPO2 both contribute to phenoloxidase activity in the insect blood, these PPOs are not fully redundant. Our study shows that PPO1 is involved in the rapid delivery of phenoloxidase activity when required, while PPO2 provides a storage form that can be deployed in a second phase. Some controversy exists in the Drosophila field about the importance of melanization in the Drosophila host defense. Our study demonstrates the important role of PPO1 and PPO2 in the survival to infection with both Gram-positive bacteria and fungi, underlining the importance of melanization in insect immunity.

The Hmr and Lhr hybrid incompatibility genes suppress a broad range of heterochromatic repeats

Hybrid incompatibilities (HIs) cause reproductive isolation between species and thus contribute to speciation. Several HI genes encode adaptively evolving proteins that localize to or interact with heterochromatin, suggesting that HIs may result from co-evolution with rapidly evolving heterochromatic DNA. Little is known, however, about the intraspecific function of these HI genes, the specific sequences they interact with, or the evolutionary forces that drive their divergence. The genes Hmr and Lhr genetically interact to cause hybrid lethality between Drosophila melanogaster and D. simulans, yet mutations in both genes are viable. Here, we report that Hmr and Lhr encode proteins that form a heterochromatic complex with Heterochromatin Protein 1 (HP1a). Using RNA-Seq analyses we discovered that Hmr and Lhr are required to repress transcripts from satellite DNAs and many families of transposable elements (TEs). By comparing Hmr and Lhr function between D. melanogaster and D. simulans we identify several satellite DNAs and TEs that are differentially regulated between the species. Hmr and Lhr mutations also cause massive overexpression of telomeric TEs and significant telomere lengthening. Hmr and Lhr therefore regulate three types of heterochromatic sequences that are responsible for the significant differences in genome size and structure between D. melanogaster and D. simulans and have high potential to cause genetic conflicts with host fitness. We further find that many TEs are overexpressed in hybrids but that those specifically mis-expressed in lethal hybrids do not closely correlate with Hmr function. Our results therefore argue that adaptive divergence of heterochromatin proteins in response to repetitive DNAs is an important underlying force driving the evolution of hybrid incompatibility genes, but that hybrid lethality likely results from novel epistatic genetic interactions that are distinct to the hybrid background.

Sister species capable of mating often produce hybrids that are sterile or die during development. This reproductive isolation is caused by incompatibilities between the two sister species' genomes. Some hybrid incompatibilities involve genes that encode rapidly evolving proteins that localize to heterochromatin. Heterochromatin is largely made up of highly repetitive transposable elements and satellite DNAs. It has been hypothesized that rapid changes in heterochromatic DNA drives the changes in these HI genes and thus the evolution of reproductive isolation. In support of this model, we show that two rapidly evolving HI proteins, Lhr and Hmr, which reproductively isolate the fruit fly sister species D. melanogaster and D. simulans, repress transposable elements and satellite DNAs. These proteins also help regulate the length of the atypical Drosophila telomeres, which are themselves made of domesticated transposable elements. Our data suggest that these proteins are part of the adaptive machinery that allows the host to respond to changes and increases in heterochromatin and to maintain the activity of genes located within or adjacent to heterochromatin.

Suppression of polyglutamine protein toxicity by co-expression of a heat-shock protein 40 and a heat-shock protein 110

A network of heat-shock proteins mediates cellular protein homeostasis, and has a fundamental role in preventing aggregation-associated neurodegenerative diseases. In a Drosophila model of polyglutamine (polyQ) disease, the HSP40 family protein, DNAJ-1, is a superior suppressor of toxicity caused by the aggregation of polyQ containing proteins. Here, we demonstrate that one specific HSP110 protein, 70 kDa heat-shock cognate protein cb (HSC70cb), interacts physically and genetically with DNAJ-1 in vivo, and that HSC70cb is necessary for DNAJ-1 to suppress polyglutamine-induced cell death in Drosophila. Expression of HSC70cb together with DNAJ-1 significantly enhanced the suppressive effects of DNAJ-1 on polyQ-induced neurodegeneration, whereas expression of HSC70cb alone did not suppress neurodegeneration in Drosophila models of either general polyQ disease or Huntington's disease. Furthermore, expression of a human HSP40, DNAJB1, together with a human HSP110, APG-1, protected cells from polyQ-induced neural degeneration in flies, whereas expression of either component alone had little effect. Our data provide a functional link between HSP40 and HSP110 in suppressing the cytotoxicity of aggregation-prone proteins, and suggest that HSP40 and HSP110 function together in protein homeostasis control.

A DNA element regulates drug tolerance and withdrawal in Drosophila

Drug tolerance and withdrawal are insidious responses to drugs of abuse; the first increases drug consumption while the second punishes abstention. Drosophila generate functional tolerance to benzyl alcohol sedation by increasing neural expression of the slo BK-type Ca(2+) activated K(+) channel gene. After drug clearance this change produces a withdrawal phenotype-increased seizure susceptibility. The drug-induced histone modification profile identified the 6b element (60 nt) as a drug responsive element. Genomic deletion of 6b produces the allele, slo (Δ6b), that reacts more strongly to the drug with increased induction, a massive increase in the duration of tolerance, and an increase in the withdrawal phenotype yet does not alter other slo-dependent behaviors. The 6b element is a homeostatic regulator of BK channel gene expression and is the first cis-acting DNA element shown to specifically affect the duration of a drug action.

Genetic and biochemical tools for investigating sirtuin function in Drosophila melanogaster

Drosophila melanogaster is one of the most widely used genetic model systems in biology. The ease of working in an invertebrate model system allows the design and execution of many experiments that would be infeasible in a vertebrate model. Although the strength of the fly as a model system lies primarily in the ease of genetic manipulation, it is flexible enough that biochemical and proteomic approaches can also be used to build a more comprehensive study. Here we present a pair of complementary protocols that we have used to examine sirtuin biology in Drosophila. First, we describe our protocol for measuring lifespan in flies expressing a gene of interest under the inducible control of the Gene-Switch system. Finally, we describe a method for performing chromatin immunoprecipitation on adult flies, including some of the difficulties associated with using this technique in chitinous tissue.

Lissencephaly-1 promotes the recruitment of dynein and dynactin to transported mRNAs

Microtubule-based transport mediates the sorting and dispersal of many cellular components and pathogens. However, the mechanisms by which motor complexes are recruited to and regulated on different cargos remain poorly understood. Here we describe a large-scale biochemical screen for novel factors associated with RNA localization signals mediating minus end-directed mRNA transport during Drosophila development. We identified the protein Lissencephaly-1 (Lis1) and found that minus-end travel distances of localizing transcripts are dramatically reduced in lis1 mutant embryos. Surprisingly, given its well-documented role in regulating dynein mechanochemistry, we uncovered an important requirement for Lis1 in promoting the recruitment of dynein and its accessory complex dynactin to RNA localization complexes. Furthermore, we provide evidence that Lis1 levels regulate the overall association of dynein with dynactin. Our data therefore reveal a critical role for Lis1 within the mRNA localization machinery and suggest a model in which Lis1 facilitates motor complex association with cargos by promoting the interaction of dynein with dynactin.

A novel function for the Hox gene Abd-B in the male accessory gland regulates the long-term female post-mating response in Drosophila

In insects, products of the male reproductive tract are essential for initiating and maintaining the female post-mating response (PMR). The PMR includes changes in egg laying, receptivity to courting males, and sperm storage. In Drosophila, previous studies have determined that the main cells of the male accessory gland produce some of the products required for these processes. However, nothing was known about the contribution of the gland's other secretory cell type, the secondary cells. In the course of investigating the late functions of the homeotic gene, Abdominal-B (Abd-B), we discovered that Abd-B is specifically expressed in the secondary cells of the Drosophila male accessory gland. Using an Abd-B BAC reporter coupled with a collection of genetic deletions, we discovered an enhancer from the iab-6 regulatory domain that is responsible for Abd-B expression in these cells and that apparently works independently from the segmentally regulated chromatin domains of the bithorax complex. Removal of this enhancer results in visible morphological defects in the secondary cells. We determined that mates of iab-6 mutant males show defects in long-term egg laying and suppression of receptivity, and that products of the secondary cells are influential during sperm competition. Many of these phenotypes seem to be caused by a defect in the storage and gradual release of sex peptide in female mates of iab-6 mutant males. We also found that Abd-B expression in the secondary cells contributes to glycosylation of at least three accessory gland proteins: ovulin (Acp26Aa), CG1656, and CG1652. Our results demonstrate that long-term post-mating changes observed in mated females are not solely induced by main cell secretions, as previously believed, but that secondary cells also play an important role in male fertility by extending the female PMR. Overall, these discoveries provide new insights into how these two cell types cooperate to produce and maintain a robust female PMR.

Inducing extra copies of the Hsp70 gene in Drosophila melanogaster increases energetic demand

Background

Mutations that increase gene expression are predicted to increase energy allocation to transcription, translation and protein function. Despite an appreciation that energetic tradeoffs may constrain adaptation, the energetic costs of increased gene expression are challenging to quantify and thus easily ignored when modeling the evolution of gene expression, particularly for multicellular organisms. Here we use the well-characterized, inducible heat-shock response to test whether expressing additional copies of the Hsp70 gene increases energetic demand in Drosophila melanogaster.

Results

We measured metabolic rates of larvae with different copy numbers of the Hsp70 gene to quantify energy expenditure before, during, and after exposure to 36°C, a temperature known to induce robust expression of Hsp70. We observed a rise in metabolic rate within the first 30 minutes of 36°C exposure above and beyond the increase in routine metabolic rate at 36°C. The magnitude of this increase in metabolic rate was positively correlated with Hsp70 gene copy number and reflected an increase as great as 35% of the 22°C metabolic rate. Gene copy number also affected Hsp70 mRNA levels as early as 15 minutes after larvae were placed at 36°C, demonstrating that gene copy number affects transcript abundance on the same timescale as the metabolic effects that we observed. Inducing Hsp70 also had lasting physiological costs, as larvae had significantly depressed metabolic rate when returned to 22°C after induction.

Conclusions

Our results demonstrate both immediate and persistent energetic consequences of gene copy number in a multicellular organism. We discuss these consequences in the context of existing literature on the pleiotropic effects of variation in Hsp70 copy number, and argue that the increased energetic demand of expressing extra copies of Hsp70 may contribute to known tradeoffs in physiological performance of extra-copy larvae. Physiological costs of mutations that greatly increase gene expression, such as these, may constrain their utility for adaptive evolution.

A novel strategy for conditional gene knockout based on ΦC31 integrase and Gal4/UAS system in Drosophila

The Gal4/upstream activating sequences (UAS) system offers great advantages in target gene expression by separating the responder line and diverse tissue-specific expressed Gal4 driver lines in Drosophila. The bipartite system is commonly used in gain-of-function analysis, and by combining with the RNA interference technology, it can also be applied in loss-of-function analysis. However, the off-target effect caused by this strategy has not been well solved so far. Furthermore, it can only partially knockdown a specific gene expression. In this study, a novel conditional gene knockout method that combined the use of ϕC31 integrase and Gal4/UAS system was described. The target gene was preliminarily flanked by ϕC31 integrase recognition sites attB and attP, followed by conditional expressed Gal4 lines to drive the recombinase that were under UAS control to achieve spatial and temporal gene deletion. We found the strategy performed well in Drosophila, and the efficiency was higher than 82% in gene knockout by self-excision. Our strategy takes advantage of exiting Gal4 library to drive the recombinase, rather than conventionally used method which the recombinase was droved directly by specific promoters, thereby providing a more flexible and versatile tool for gene function analysis in Drosophila.

Invertebrate models of dystonia

The neurological movement disorder dystonia is an umbrella term for a heterogeneous group of related conditions where at least 20 monogenic forms have been identified. Despite the substantial advances resulting from the identification of these loci, the function of many DYT gene products remains unclear. Comparative genomics using simple animal models to examine the evolutionarily conserved functional relationships with monogenic dystonias represents a rapid route toward a comprehensive understanding of these movement disorders. Current studies using the invertebrate animal models Caenorhabditis elegans and Drosophila melanogaster are uncovering cellular functions and mechanisms associated with mutant forms of the well-conserved gene products corresponding to DYT1, DYT5a, DYT5b, and DYT12 dystonias. Here we review recent findings from the invertebrate literature pertaining to molecular mechanisms of these gene products, torsinA, GTP cyclohydrolase I, tyrosine hydroxylase, and the alpha subunit of Na+/K ATPase, respectively. In each study, the application of powerful genetic tools developed over decades of intensive work with both of these invertebrate systems has led to mechanistic insights into these human disorders. These models are particularly amenable to large-scale genetic screens for modifiers or additional alleles, which are bolstering our understanding of the molecular functions associated with these gene products. Moreover, the use of invertebrate models for the evaluation of DYT genetic loci and their genetic interaction networks has predictive value and can provide a path forward for therapeutic intervention.

Nucleosome-depleted chromatin gaps recruit assembly factors for the H3.3 histone variant

Most nucleosomes that package eukaryotic DNA are assembled during DNA replication, but chromatin structure is routinely disrupted in active regions of the genome. Replication-independent nucleosome replacement using the H3.3 histone variant efficiently repackages these regions, but how histones are recruited to these sites is unknown. Here, we use an inducible system that produces nucleosome-depleted chromatin at the Hsp70 genes in Drosophila to define steps in the mechanism of nucleosome replacement. We find that the Xnp chromatin remodeler and the Hira histone chaperone independently bind nucleosome-depleted chromatin. Surprisingly, these two factors are only displaced when new nucleosomes are assembled. H3.3 deposition assays reveal that Xnp and Hira are required for efficient nucleosome replacement, and double-mutants are lethal. We propose that Xnp and Hira recognize exposed DNA and serve as a binding platform for the efficient recruitment of H3.3 predeposition complexes to chromatin gaps. These results uncover the mechanisms by which eukaryotic cells actively prevent the exposure of DNA in the nucleus.

Using mutants, knockdowns, and transgenesis to investigate gene function in Drosophila

The sophisticated genetic techniques available in Drosophila are largely responsible for its success as a model organism. One of the most important of these is the ability to disrupt gene function in vivo and observe the resulting phenotypes. This review considers the ever-increasing repertoire of approaches for perturbing the functions of specific genes in flies, ranging from classical and transposon-mediated mutageneses to newer techniques, such as homologous recombination and RNA interference. Since most genes are used over and over again in different contexts during development, many important advances have depended on being able to interfere with gene function at specific times or places in the developing animal, and a variety of approaches are now available to do this. Most of these techniques rely on being able to create genetically modified strains of Drosophila and the different methods for generating lines carrying single copy transgenic constructs will be described, along with the advantages and disadvantages of each approach.

Metabolic and hormonal acclimation to heat stress in domesticated ruminants

Environmentally induced periods of heat stress decrease productivity with devastating economic consequences to global animal agriculture. Heat stress can be defined as a physiological condition when the core body temperature of a given species exceeds its range specified for normal activity, which results from a total heat load (internal production and environment) exceeding the capacity for heat dissipation and this prompts physiological and behavioral responses to reduce the strain. The ability of ruminants to regulate body temperature is species- and breed-dependent. Dairy breeds are typically more sensitive to heat stress than meat breeds, and higher-producing animals are more susceptible to heat stress because they generate more metabolic heat. During heat stress, ruminants, like other homeothermic animals, increase avenues of heat loss and reduce heat production in an attempt to maintain euthermia. The immediate responses to heat load are increased respiration rates, decreased feed intake and increased water intake. Acclimatization is a process by which animals adapt to environmental conditions and engage behavioral, hormonal and metabolic changes that are characteristics of either acclimatory homeostasis or homeorhetic mechanisms used by the animals to survive in a new 'physiological state'. For example, alterations in the hormonal profile are mainly characterized by a decline and increase in anabolic and catabolic hormones, respectively. The response to heat load and the heat-induced change in homeorhetic modifiers alters post-absorptive energy, lipid and protein metabolism, impairs liver function, causes oxidative stress, jeopardizes the immune response and decreases reproductive performance. These physiological modifications alter nutrient partitioning and may prevent heat-stressed lactating cows from recruiting glucose-sparing mechanisms (despite the reduced nutrient intake). This might explain, in large part, why decreased feed intake only accounts for a minor portion of the reduced milk yield from environmentally induced hyperthermic cows. How these metabolic changes are initiated and regulated is not known. It also remains unclear how these changes differ between short-term v. long-term heat acclimation to impact animal productivity and well-being. A better understanding of the adaptations enlisted by ruminants during heat stress is necessary to enhance the likelihood of developing strategies to simultaneously improve heat tolerance and increase productivity.

Type-I prenyl protease function is required in the male germline of Drosophila melanogaster

Many proteins require the addition of a hydrophobic prenyl anchor (prenylation) for proper trafficking and localization in the cell. Prenyl proteases play critical roles in modifying proteins for membrane anchorage. The type I prenyl protease has a defined function in yeast (Ste24p/Afc1p) where it modifies a mating pheromone, and in humans (Zmpste24) where it has been implicated in a disease of premature aging. Despite these apparently very different biological processes, the type I prenyl protease gene is highly conserved, encoded by a single gene in a wide range of animal and plant groups. A notable exception is Drosophila melanogaster, where the gene encoding the type I prenyl protease has undergone an unprecedented series of duplications in the genome, resulting in five distinct paralogs, three of which are organized in a tandem array, and demonstrate high conservation, particularly in the vicinity of the active site of the enzyme. We have undertaken targeted deletion to remove the three tandem paralogs from the genome. The result is a male fertility defect, manifesting late in spermatogenesis. Our results also show that the ancestral type I prenyl protease gene in Drosophila is under strong purifying selection, while the more recent replicates are evolving rapidly. Our rescue data support a role for the rapidly evolving tandem paralogs in the male germline. We propose that potential targets for the male-specific type I prenyl proteases include proteins involved in the very dramatic cytoskeletal remodeling events required for spermatid maturation.

Hsp70 protein levels and thermotolerance in Drosophila subobscura: a reassessment of the thermal co-adaptation hypothesis

Theory predicts that geographic variation in traits and genes associated with climatic adaptation may be initially driven by the correlated evolution of thermal preference and thermal sensitivity. This assumes that an organism's preferred body temperature corresponds with the thermal optimum in which performance is maximized; hence, shifts in thermal preferences affect the subsequent evolution of thermal-related traits. Drosophila subobscura evolved worldwide latitudinal clines in several traits including chromosome inversion frequencies, with some polymorphic inversions being apparently associated with thermal preference and thermal tolerance. Here we show that flies carrying the warm-climate chromosome arrangement O(3+4) have higher basal protein levels of Hsp70 than their cold-climate O(st) counterparts, but this difference disappears after heat hardening. O(3+4) carriers are also more heat tolerant, although it is difficult to conclude from our results that this is causally linked to their higher basal levels of Hsp70. The observed patterns are consistent with the thermal co-adaptation hypothesis and suggest that the interplay between behaviour and physiology underlies latitudinal and seasonal shifts in inversion frequencies.

Glial Hsp70 protects K+ homeostasis in the Drosophila brain during repetitive anoxic depolarization

Neural tissue is particularly vulnerable to metabolic stress and loss of ion homeostasis. Repetitive stress generally leads to more permanent dysfunction but the mechanisms underlying this progression are poorly understood. We investigated the effects of energetic compromise in Drosophila by targeting the Na(+)/K(+)-ATPase. Acute ouabain treatment of intact flies resulted in subsequent repetitive comas that led to death and were associated with transient loss of K(+) homeostasis in the brain. Heat shock pre-conditioned flies were resistant to ouabain treatment. To control the timing of repeated loss of ion homeostasis we subjected flies to repetitive anoxia while recording extracellular [K(+)] in the brain. We show that targeted expression of the chaperone protein Hsp70 in glial cells delays a permanent loss of ion homeostasis associated with repetitive anoxic stress and suggest that this is a useful model for investigating molecular mechanisms of neuroprotection.

Consequences of eukaryotic enhancer architecture for gene expression dynamics, development, and fitness

The regulatory logic of time- and tissue-specific gene expression has mostly been dissected in the context of the smallest DNA fragments that, when isolated, recapitulate native expression in reporter assays. It is not known if the genomic sequences surrounding such fragments, often evolutionarily conserved, have any biological function or not. Using an enhancer of the even-skipped gene of Drosophila as a model, we investigate the functional significance of the genomic sequences surrounding empirically identified enhancers. A 480 bp long "minimal stripe element" is able to drive even-skipped expression in the second of seven stripes but is embedded in a larger region of 800 bp containing evolutionarily conserved binding sites for required transcription factors. To assess the overall fitness contribution made by these binding sites in the native genomic context, we employed a gene-replacement strategy in which whole-locus transgenes, capable of rescuing even-skipped(-) lethality to adulthood, were substituted for the native gene. The molecular phenotypes were characterized by tagging Even-skipped with a fluorescent protein and monitoring gene expression dynamics in living embryos. We used recombineering to excise the sequences surrounding the minimal enhancer and site-specific transgenesis to create co-isogenic strains differing only in their stripe 2 sequences. Remarkably, the flanking sequences were dispensable for viability, proving the sufficiency of the minimal element for biological function under normal conditions. These sequences are required for robustness to genetic and environmental perturbation instead. The mutant enhancers had measurable sex- and dose-dependent effects on viability. At the molecular level, the mutants showed a destabilization of stripe placement and improper activation of downstream genes. Finally, we demonstrate through live measurements that the peripheral sequences are required for temperature compensation. These results imply that seemingly redundant regulatory sequences beyond the minimal enhancer are necessary for robust gene expression and that "robustness" itself must be an evolved characteristic of the wild-type enhancer.