Steroid regulation of autophagic programmed cell death during development

Steroid Signaling in Autophagy

Autophagy is a conserved cellular process essential for homeostasis and development that plays a central role in the degradation and recycling of cellular components. Recent studies reveal bidirectional interactions between autophagy and steroid-hormone signaling. Steroids are signaling molecules synthesized from cholesterol that regulate key physiological and developmental processes - including autophagic activity. Conversely, other work demonstrates that autophagy regulates steroid production by controlling the availability of precursor sterol substrate. Insights from Drosophila and mammalian models provide compelling evidence for the conservation of these mechanisms across species. In this review we explore how steroid hormones modulate autophagy in diverse tissues and contexts, such as metabolism and disease, and discuss advances in our understanding of autophagy's regulatory role in steroid hormone production. We examine the implications of these interactions for health and disease and offer perspectives on the potential for harnessing this functionality for addressing cholesterol-related disorders.

Activation of interleukin 33-NFκB axis in granulosa cells during atresia and its role in disposal of atretic follicles†

It has been previously shown that the cytokine interleukin 33 is required for two processes, i.e., autophagic digestion of granulosa cells and recruitment of macrophages into atretic follicles, for full disposal of atretic follicles. Now, this study shows that activation of interleukin 33-suppression of tumorigenicity 2-Nuclear Factor ĸB (NFκB) axis in granulosa in early atretic follicles may regulate those two events. Injection of human chorionic gonadotropin has been shown to induce a transient peak of interleukin 33 expression with synchronized atresia. In this model, interleukin 33-independent expression of suppression of tumorigenicity 2 in granulosa cells was detected in early atretic follicles before macrophage invasion. The activation of NFκB pathway in ovaries was further demonstrated in vivo in Tg mice with luciferase-reporter for NFκB activation; the activation was microscopically localized to granulosa cells in early atretic follicles. Importantly, antibody blockage of interleukin 33 or interleukin 33 Knock-out (KO) (Il33-/-) not only inhibited NFκB activity in ovaries, but it also altered expression of two key genes, i.e., reduction in proinflammatory interleukin6 (IL6) expression, and a surge of potential autophagy-inhibitory mammalian target of rapamycin (mTOR) expression in atretic follicles. By contrast, apoptosis and other genes, such as interleukin1β (IL1β) were not affected. In conclusion, in parallel to apoptosis, atresia signals also trigger activation of the interleukin 33-suppression of tumorigenicity 2-NFκB pathway in granulosa, which leads to (1) down-regulated expression of mTOR that is a negative regulator of autophagy and (2) up-regulated expression of proinflammatory IL6.

Understanding Developmental Cell Death Using Drosophila as a Model System

Cell death plays an essential function in organismal development, wellbeing, and ageing. Many types of cell deaths have been described in the past 30 years. Among these, apoptosis remains the most conserved type of cell death in metazoans and the most common mechanism for deleting unwanted cells. Other types of cell deaths that often play roles in specific contexts or upon pathological insults can be classed under variant forms of cell death and programmed necrosis. Studies in Drosophila have contributed significantly to the understanding and regulation of apoptosis pathways. In addition to this, Drosophila has also served as an essential model to study the genetic basis of autophagy-dependent cell death (ADCD) and other relatively rare types of context-dependent cell deaths. Here, we summarise what is known about apoptosis, ADCD, and other context-specific variant cell death pathways in Drosophila, with a focus on developmental cell death.

The appearance of cytoplasmic cytochrome C precedes apoptosis during Drosophila salivary gland degradation

Apoptosis is an important process for organism development that functions to eliminate cell damage, maintain homeostasis, and remove obsolete tissues during morphogenesis. In mammals, apoptosis is accompanied by the release of cytochrome C (Cyt-c) from mitochondria to the cytoplasm. However, whether this process is conserved in the fruit fly, Drosophila melanogaster, remains controversial. In this study, we discovered that during the degradation of Drosophila salivary gland, the transcription of mitochondria apoptosis factors (MAPFs), Cyt-c, and death-associated APAF1-related killer (Dark) encoding genes are all upregulated antecedent to initiator and effector caspases encoding genes. The proteins Cyt-c and the active caspase 3 appear gradually in the cytoplasm during salivary gland degradation. Meanwhile, the Cyt-c protein colocates with mito-GFP, the marker indicating cytoplasmic mitochondria, and the change in mitochondrial membrane potential coincides with the appearance of Cyt-c in the cytoplasm. Moreover, impeding or promoting 20E-induced transcription factor E93 suppresses or enhances the staining of Cyt-c and the active caspase 3 in the cytoplasm of salivary gland, and accordingly decreases or increases the mitochondrial membrane potential, respectively. Our research provides evidence that cytoplasmic Cyt-c appears before apoptosis during Drosophila salivary gland degradation, shedding light on partial conserved mechanism in apoptosis between insects and mammals.

Autophagy genes AMBRA1 and ATG8 play key roles in midgut remodeling of the yellow fever mosquito, Aedes aegypti

The function of two autophagy genes, an activating molecule BECN1 regulated autophagy (AMBRA1) and autophagy-related gene 8 (ATG8) in the midgut remodeling of Aedes aegypti was investigated. Real-time quantitative polymerase chain reaction (RT-qPCR) analysis of RNA samples collected from the last instar larvae and pupae showed that these two genes are predominantly expressed during the last 12 h and first 24 h of the last larval and pupal stages, respectively. Stable ecdysteroid analog induced and juvenile hormone (JH) analog suppressed these genes. RNA interference (RNAi) studies showed that the ecdysone-induced transcription factor E93 is required for the expression of these genes. JH-induced transcription factor krüppel homolog 1 (Kr-h1) suppressed the expression of these genes. RNAi-mediated silencing of AMBRA1 and ATG8 blocked midgut remodeling. Histological studies of midguts from insects at 48 h after ecdysis to the final larval stage and 12 h after ecdysis to the pupal stage showed that ATG gene knockdown blocked midgut remodeling. AMBRA1 and ATG8 double-stranded (dsRNA)-treated insects retained larval midgut cells and died during the pupal stage. Together, these results demonstrate that ecdysteroid induction of ATG genes initiates autophagy programmed cell death during midgut remodeling. JH inhibits midgut remodeling during metamorphosis by interfering with the expression of ATG genes.

Mblk-1/E93, an ecdysone related-transcription factor, targets synaptic plasticity-related genes in the honey bee mushroom bodies

Among hymenopteran insects, aculeate species such as bees, ants, and wasps have enlarged and morphologically elaborate mushroom bodies (MBs), a higher-order brain center in the insect, implying their relationship with the advanced behavioral traits of aculeate species. The molecular bases leading to the acquisition of complicated MB functions, however, remains unclear. We previously reported the constitutive and MB-preferential expression of an ecdysone-signaling related transcription factor, Mblk-1/E93, in the honey bee brain. Here, we searched for target genes of Mblk-1 in the worker honey bee MBs using chromatin immunoprecipitation sequence analyses and found that Mblk-1 targets several genes involved in synaptic plasticity, learning, and memory abilities. We also demonstrated that Mblk-1 expression is self-regulated via Mblk-1-binding sites, which are located upstream of Mblk-1. Furthermore, we showed that the number of the Mblk-1-binding motif located upstream of Mblk-1 homologs increased associated with evolution of hymenopteran insects. Our findings suggest that Mblk-1, which has been focused on as a developmental gene transiently induced by ecdysone, has acquired a novel expression pattern to play a role in synaptic plasticity in honey bee MBs, raising a possibility that molecular evolution of Mblk-1 may have partly contributed to the elaboration of MB function in insects.

Knockdown of Ecdysone-Induced Protein 93F Causes Abnormal Pupae and Adults in the Eggplant Lady Beetle

Ecdysone-induced protein 93F (E93) plays triple roles during post-embryonic development in insects whose juvenile instars are more than four. However, it only acts as a specifier of adult structures in Drosophila flies whose larval instars are fixed at three. In this study, we determined the functions of E93 in the eggplant lady beetle (Henosepilachna vigintioctopunctata), which has four larval instars. We uncovered that E93 was abundantly expressed at the prepupal and pupal stages. A precocious inhibition of the juvenile hormone signal by RNA interference (RNAi) of HvKr-h1 or HvHairy, two vital downstream developmental effectors, at the penultimate instar larval stage increased the expression of E93, Conversely, ingestion of JH by the third-instar larvae stimulated the expression of HvKr-h1 but repressed the transcription of either HvE93X1 or HvE93X2. However, disturbance of the JH signal neither drove premature metamorphosis nor caused supernumerary instars. In contrast, depletion of E93 at the third- and fourth-instar larval and prepupal stages severely impaired pupation and caused a larval-pupal mixed phenotype: pupal spines and larval scoli were simultaneously presented on the cuticle. RNAi of E93 at the pupal stage affected adult eclosion. When the beetles had suffered from a dsE93 injection at the fourth-instar larval and pupal stages, a few resultant adults emerged, with separated elytra, abnormally folded hindwings, a small body size and short appendages. Taken together, our results suggest the larval instars are fixed in H. vigintioctopunctata; E93 serves as a repressor of larval characters and a specifier of adult structures during the larval-pupal-adult transition.

Convergence of secretory, endosomal, and autophagic routes in trans-Golgi-associated lysosomes

At the trans-Golgi, complex traffic connections exist to the endolysosomal system additional to the main Golgi-to-plasma membrane secretory route. Here, we investigated three hits in a Drosophila screen displaying secretory cargo accumulation in autophagic vesicles: ESCRT-III component Vps20, SNARE-binding Rop, and lysosomal pump subunit VhaPPA1-1. We found that Vps20, Rop, and lysosomal markers localize near the trans-Golgi. Furthermore, we document that the vicinity of the trans-Golgi is the main cellular location for lysosomes and that early, late, and recycling endosomes associate as well with a trans-Golgi-associated degradative compartment where basal microautophagy of secretory cargo and other materials occurs. Disruption of this compartment causes cargo accumulation in our hits, including Munc18 homolog Rop, required with Syx1 and Syx4 for Rab11-mediated endosomal recycling. Finally, besides basal microautophagy, we show that the trans-Golgi-associated degradative compartment contributes to the growth of autophagic vesicles in developmental and starvation-induced macroautophagy. Our results argue that the fly trans-Golgi is the gravitational center of the whole endomembrane system.

Silencing of transcription factor E93 inhibits adult morphogenesis and disrupts cuticle, wing and ovary development in Locusta migratoria

Ecdysone-induced protein 93F (E93) plays important roles during the metamorphosis process in insects. In this study, a cDNA of the LmE93 gene was identified from the transcriptome of Locusta migratoria, which consists of the 3378-nucleotide open-reading frame (ORF) and encodes 1125 amino acids with helix-turn-helix (HTH) motifs. Reverse transcription quantitative polymerase chain reaction analysis revealed that LmE93 was highest expressed in ovary. The LmE93 expression level was markedly low from the 3rd to 4th instar nymphs, and greatly increased in 1-day-old 5th instar nymphs with a peak on middle nymphal days, then declined in the late nymphal days. Moreover, injected dsLmE93 into 4th and 5th instar nymphs greatly reduced LmE93 transcripts, respectively, and prevented the process of metamorphosis, causing supernumerary nymphal stages. Hematoxylin-eosin staining of the integument showed that the apolysis occurred in advance in 4th instar nymphs, and old cuticle degradation was decreased in dsLmE93-injected locusts of 5th instar nymphs. Smaller and no fully developed wings with reduced columns between the anterior and posterior regions were found in N6 and N7 supernumerary nymphs. In addition, the development of the ovary in dsLmE93-injected locusts was severely blocked, the yolk was almost not formed and there was no development of ovarioles. The results indicated that LmE93 play key roles in the metamorphosis, cuticle, wing and ovarian development of locusts.

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

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

Adaptation to hypoxia in Drosophila melanogaster requires autophagy

Macroautophagy/autophagy, a mechanism of degradation of intracellular material required to sustain cellular homeostasis, is exacerbated under stress conditions like nutrient deprivation, protein aggregation, organelle senescence, pathogen invasion, and hypoxia, among others. Detailed in vivo description of autophagic responses triggered by hypoxia is limited. We have characterized the autophagic response induced by hypoxia in Drosophila melanogaster. We found that this process is essential for Drosophila adaptation and survival because larvae with impaired autophagy are hypersensitive to low oxygen levels. Hypoxia triggers a bona fide autophagic response, as evaluated by several autophagy markers including Atg8, LysoTracker, Lamp1, Pi3K59F/Vps34 activity, transcriptional induction of Atg genes, as well as by transmission electron microscopy. Autophagy occurs in waves of autophagosome formation and maturation as hypoxia exposure is prolonged. Hypoxia-triggered autophagy is induced cell autonomously, and different tissues are sensitive to hypoxic treatments. We found that hypoxia-induced autophagy depends on the basic autophagy machinery but not on the hypoxia master regulator sima/HIF1A. Overall, our studies lay the foundation for using D. melanogaster as a model system for studying autophagy under hypoxic conditions, which, in combination with the potency of genetic manipulations available in this organism, provides a platform for studying the involvement of autophagy in hypoxia-associated pathologies and developmentally regulated processes.Abbreviations: Atg: autophagy-related; FYVE: zinc finger domain from Fab1 (yeast ortholog of PIKfyve); GFP: green fluorescent protein; HIF: hypoxia-inducible factor; hsf: heat shock factor; Hx: hypoxia; mCh: mCherry; PtdIns: phosphatidylinositol; PtdIns3P: phosphatidylinositol-3-phosphate; Rheb: Ras homolog enriched in brain; sima: similar; Stv: Starvation; TEM: transmission electron microscopy; Tor: target of rapamycin; UAS: upstream activating sequence; Vps: vacuolar protein sorting.

Epiblast and trophoblast morphogenesis in the pre-gastrulation blastocyst of the pig. A light- and electron-microscopical study

The epiblast of the amniote embryo is of paramount importance during early development as it gives rise to all tissues of the embryo proper. In mammals, it emerges through segregation of the hypoblast from the inner cell mass and subsequently undergoes transformation into an epithelial sheet to create the embryonic disc. In rodents and man, the epiblast cell layer is covered by the polar trophoblast which forms the placenta. In mammalian model organisms (rabbit, pig, several non-human primates), however, the placenta is formed by mural trophoblast whereas the polar trophoblast disintegrates prior to gastrulation and thus exposes the epiblast to the microenvironment of the uterine cavity. Both, polar trophoblast disintegration and epiblast epithelialization, thus pose special cell-biological requirements but these are still rather ill-understood when compared to those of gastrulation morphogenesis. This study therefore applied high-resolution light and transmission electron microscopy and three-dimensional (3D) reconstruction to 8- to 10-days-old pig embryos and defines the following steps of epiblast transformation: (1) rosette formation in the center of the ball-shaped epiblast, (2) extracellular cavity formation in the rosette center, (3) epiblast segregation into two subpopulations - addressed here as dorsal and ventral epiblast - separated by a "pro-amniotic" cavity. Ventral epiblast cells form between them a special type of desmosomes with a characteristic dense felt of microfilaments and are destined to generate the definitive epiblast. The dorsal epiblast remains a mass of non-polarized cells and closely associates with the disintegrating polar trophoblast, which shows morphological features of both apoptosis and autophagocytosis. Morphogenesis of the definitive epiblast in the pig may thus exclude a large portion of bona fide epiblast cells from contributing to the embryo proper and establishes contact de novo with the mural trophoblast at the junction between the two newly defined epiblast cell populations.

Autophagy in Drosophila and Zebrafish

Autophagy is a highly conserved cellular process that delivers cellular contents to the lysosome for degradation. It not only serves as a bulk degradation system for various cytoplasmic components but also functions selectively to clear damaged organelles, aggregated proteins, and invading pathogens (Feng et al., Cell Res 24:24-41, 2014; Galluzzi et al., EMBO J 36:1811-36, 2017; Klionsky et al., Autophagy 12:1-222, 2016). The malfunction of autophagy leads to multiple developmental defects and diseases (Mizushima et al., Nature 451:1069-75, 2008). Drosophila and zebrafish are higher metazoan model systems with sophisticated genetic tools readily available, which make it possible to dissect the autophagic processes and to understand the physiological functions of autophagy (Lorincz et al., Cells 6:22, 2017a; Mathai et al., Cells 6:21, 2017; Zhang and Baehrecke, Trends Cell Biol 25:376-87, 2015). In this chapter, we will discuss recent progress that has been made in the autophagic field by using these animal models. We will focus on the protein machineries required for autophagosome formation and maturation as well as the physiological roles of autophagy in both Drosophila and zebrafish.

E93-depleted adult insects preserve the prothoracic gland and molt again

Insect metamorphosis originated around the middle Devonian, associated with the innovation of the final molt; this occurs after histolysis of the prothoracic gland (PG; which produces the molting hormone) in the first days of adulthood. We previously hypothesized that transcription factor E93 is crucial in the emergence of metamorphosis, because it triggers metamorphosis in extant insects. This work on the cockroach Blattella germanica reveals that E93 also plays a crucial role in the histolysis of PG, which fits the above hypothesis. Previous studies have shown that the transcription factor FTZ-F1 is essential for PG histolysis. We have found that FTZ-F1 depletion towards the end of the final nymphal instar downregulates the expression of E93, whereas E93-depleted nymphs molt to adults that retain a functional PG. Interestingly, these adults are able to molt again, which is exceptional in insects. The study of insects able to molt again in the adult stage may reveal clues about how nymphal epidermal cells definitively become adult cells, and whether it is possible to reverse this process.

Cp1/cathepsin L is required for autolysosomal clearance in Drosophila

Macroautophagy/autophagy is a highly conserved lysosomal degradative pathway important for maintaining cellular homeostasis. Much of our current knowledge of autophagy is focused on the initiation steps in this process. Recently, an understanding of later steps, particularly lysosomal fusion leading to autolysosome formation and the subsequent role of lysosomal enzymes in degradation and recycling, is becoming evident. Autophagy can function in both cell survival and cell death, however, the mechanisms that distinguish adaptive/survival autophagy from autophagy-dependent cell death remain to be established. Here, using proteomic analysis of Drosophila larval midguts during degradation, we identify a group of proteins with peptidase activity, suggesting a role in autophagy-dependent cell death. We show that Cp1/cathepsin L-deficient larval midgut cells accumulate aberrant autophagic vesicles due to a block in autophagic flux, yet later stages of midgut degradation are not compromised. The accumulation of large aberrant autolysosomes in the absence of Cp1 appears to be the consequence of decreased degradative capacity as they contain undigested cytoplasmic material, rather than a defect in autophagosome-lysosome fusion. Finally, we find that other cathepsins may also contribute to proper autolysosomal degradation in Drosophila larval midgut cells. Our findings provide evidence that cathepsins play an essential role in the autolysosome to maintain basal autophagy flux by balancing autophagosome production and turnover.

The effect of E93 knockdown on female reproduction in the red flour beetle, Tribolium castaneum

The E93 transcription factor is a member of helix-turn-helix transcription factor family containing a Pip-squeak motif. This ecdysone primary response gene was identified as a regulator of cell death in Drosophila melanogaster where it is involved in ecdysone-induced autophagy and caspase activity that mediate degeneration of larval tissues during metamorphosis from larva to pupa. However, its function in adult insects is not well studied. To study E93 function in the red flour beetle, Tribolium castaneum, double-stranded RNA (dsRNA) targeting E93 (dsE93) was injected into newly emerged adults. Knockdown of E93 caused a decrease in the synthesis of vitellogenin (Vg), oocyte development, and egg-laying. Sequencing of RNA isolated from adults injected with dsE93 and control dsmalE (dsRNA targeting Escherichia coli malE gene) followed by differential gene expression analysis showed upregulation of genes involved in the metabolism of reserved nutrients. E93 knockdown induced changes in gene expression resulted in a decrease in Vg synthesis in the fat body and oocyte maturation in ovaries. Mating experiments showed that females injected with dsE93 did not lay eggs. Knockdown of E93 caused a reduction in the number and size of lipid droplets in the fat body when compared with that in control beetles injected with dsmalE. These data suggest that during the first 2-3 days after the emergence of adult females, E93 suppresses genes coding for enzymes that metabolize reserved nutrients until initiation of vitellogenesis and oogenesis.

Developmental stage-specific distribution and phosphorylation of Mblk-1, a transcription factor involved in ecdysteroid-signaling in the honey bee brain

In the honey bee, the mushroom bodies (MBs), a higher-order center in insect brain, comprise interneurons termed Kenyon cells (KCs). We previously reported that Mblk-1, which encodes a transcription factor involved in ecdysteroid-signaling, is expressed preferentially in the large-type KCs (lKCs) in the pupal and adult worker brain and that phosphorylation by the Ras/MAPK pathway enhances the transcriptional activity of Mblk-1 in vitro. In the present study, we performed immunoblotting and immunofluorescence studies using affinity-purified anti-Mblk-1 and anti-phosphorylated Mblk-1 antibodies to analyze the distribution and phosphorylation of Mblk-1 in the brains of pupal and adult workers. Mblk-1 was preferentially expressed in the lKCs in both pupal and adult worker brains. In contrast, some Mblk-1 was phosphorylated almost exclusively in the pupal stages, and phosphorylated Mblk-1 was preferentially expressed in the MB neuroblasts and lKCs in pupal brains. Immunofluorescence studies revealed that both Mblk-1 and phosphorylated Mblk-1 are located in both the cytoplasm and nuclei of the lKC somata in the pupal and adult worker brains. These findings suggest that Mblk-1 plays a role in the lKCs in both pupal and adult stages and that phosphorylated Mblk-1 has pupal stage-specific functions in the MB neuroblasts and lKCs in the honey bee brain.

E93 Integrates Neuroblast Intrinsic State with Developmental Time to Terminate MB Neurogenesis via Autophagy

Most neurogenesis occurs during development, driven by the cell divisions of neural stem cells (NSCs). We use Drosophila to understand how neurogenesis terminates once development is complete, a process critical for neural circuit formation. We identified E93, a steroid-hormone-induced transcription factor that downregulates phosphatidylinositol 3-kinase (PI3K) levels to activate autophagy for elimination of mushroom body (MB) neuroblasts. MB neuroblasts are a subset of Drosophila NSCs that generate neurons important for memory and learning. MB neurogenesis extends into adulthood when E93 is reduced and terminates prematurely when E93 is overexpressed. E93 is expressed in MB neuroblasts during later stages of pupal development only, which includes the time when MB neuroblasts normally terminate their divisions. Cell intrinsic Imp and Syp temporal factors regulate timing of E93 expression in MB neuroblasts, and extrinsic steroid hormone receptor (EcR) activation boosts E93 levels high for termination. Imp inhibits premature expression of E93 in a Syp-dependent manner, and Syp positively regulates E93 to promote neurogenesis termination. Imp and Syp together with E93 form a temporal cassette, which consequently links early developmental neurogenesis with termination. Altogether, E93 functions as a late-acting temporal factor integrating extrinsic hormonal cues linked to developmental timing with neuroblast intrinsic temporal cues to precisely time neurogenesis ending during development.

Ecdysteroid and juvenile hormone biosynthesis, receptors and their signaling in the freshwater microcrustacean Daphnia

The two essential insect hormones, ecdysteroids and juvenile hormones, are possessed not only by insects, but also widely by arthropods, and regulate various developmental and physiological processes. In contrast to the abundant information about molecular endocrine mechanisms in insects, the knowledge of non-insect arthropod endocrinology is still limited. In this review, we summarize recent reports about the molecular basis of these two major insect hormones in the freshwater microcrustacean Daphnia, a keystone taxon in limnetic ecology and a bioindicator in environmental studies. Comprehensive comparisons of endocrine signaling pathways between insects and daphnids may shed light on the regulatory mechanisms of various biological phenomena and, moreover, evolutionary processes of arthropod species.

Hedgehog and Wingless signaling are not essential for autophagy-dependent cell death

Autophagy-dependent cell death is a distinct mode of regulated cell death required in a context specific manner. One of the best validated genetic models of autophagy-dependent cell death is the removal of the Drosophila larval midgut during larval-pupal transition. We have previously shown that down-regulation of growth signaling is essential for autophagy induction and larval midgut degradation. Sustained growth signaling through Ras and PI3K blocks autophagy and consequently inhibits midgut degradation. In addition, the morphogen Dpp plays an important role in regulating the correct timing of midgut degradation. Here we explore the potential roles of Hh and Wg signaling in autophagy-dependent midgut cell death. We demonstrate that Hh and Wg signaling are not involved in the regulation of autophagy-dependent cell death. However, surprisingly we found that one key component of these pathways, the Drosophila Glycogen Synthase Kinase 3, Shaggy (Sgg), may regulate midgut cell size independent of Hh and Wg signaling.

Life, death and autophagy

Autophagy influences cell survival through maintenance of cell bioenergetics and clearance of protein aggregates and damaged organelles. Several lines of evidence indicate that autophagy is a multifaceted regulator of cell death, but controversy exists over whether autophagy alone can drive cell death under physiologically relevant circumstances. Here, we review the role of autophagy in cell death and examine how autophagy interfaces with other forms of cell death including apoptosis and necrosis.

Identification of Autophagy-Related Gene 7 and Autophagic Cell Death in the Planarian Dugesia japonica

Planarians undergo continuous body size remodeling under starvation or during regeneration. This process likely involves autophagy and autophagic cell death, but this hypothesis is supported by few studies. To test this hypothesis, we cloned and characterized autophagy-related gene 7 (Atg7) from the planarian Dugesia japonica (DjAtg7). The full-length cDNA of DjAtg7 measures 2272 bp and includes a 2082-bp open reading frame encoding 693 amino acids with a molecular weight of 79.06 kDa. The deduced amino acid sequence of DjAtg7 contains a conserved ATP-binding site and a catalytic active site of an E1-like enzyme belonging to the ATG7 superfamily. DjAtg7 transcripts are mainly expressed in intestinal tissues of the intact animals. After amputation, DjAtg7 was highly expressed at the newly regenerated intestinal branch on days 3-7 of regeneration and in the old tissue of the distal intestinal branch on day 10 of regeneration. However, knockdown of DjAtg7 by RNAi did not affect planarian regeneration and did not block autophagosome formation, which indicates that autophagy is more complex than previously expected. Interestingly, TEM clearly confirmed that autophagy and autophagic cell death occurred in the old tissues of the newly regenerated planarians and clearly revealed that the dying cell released vesicles containing cellular cytoplasmic contents into the extracellular space. Therefore, the autophagy and autophagic cell death that occurred in the old tissue not only met the demand for body remodeling but also met the demand for energy supply during planarian regeneration. Collectively, our work contributes to the understanding of autophagy and autophagic cell death in planarian regeneration and body remodeling.

Caspase-independent programmed cell death triggers Ca2PO4 deposition in an in vitro model of nephrocalcinosis

Nephrocalcinosis involves the deposition of microscopic crystals in the tubular lumen or interstitium. While the clinical, biochemical, and genetic aspects of the diseases causing nephrocalcinosis have been elucidated, little is known about the cellular events in this calcification process. We previously reported a phenomenon involving the spontaneous formation of Ca2PO4 nodules in primary papillary renal cells from a patient with medullary nephrocalcinosis harboring a rare glial cell-derived neurotrophic factor (GDNF) gene variant. We also demonstrated that cultivating GDNF-silenced human kidney-2 (HK-2) cells in osteogenic conditions for 15 days triggered Ca2PO4 deposits. Given the reportedly close relationship between cell death and pathological calcification, aim of the present study was to investigate whether apoptosis is involved in the calcification of GDNF-silenced HK-2 cells under osteogenic conditions. Silenced and control cells were cultured in standard and osteogenic medium for 1, 5, and 15 days, and any Ca2PO4 deposition was identified by means of von Kossa staining and environmental SEM (ESEM) analyses. Based on the results of annexin V and propidium iodide (PI) analysis, and terminal deoxynucleotidyl transferase dUTP-biotin nick end labeling (TUNEL) assay, the silenced cells in the osteogenic medium showed a significant increase in the percentage of cells in the late phase of apoptosis and an increased Ca2PO4 deposition at 15 days. The results of quantitative real-time PCR (qRT-PCR) of BAX and BCL2, and in-cell Western analysis of caspases indicated that the cell death process was independent of caspase-3, -6, -7, and -9 activation, however. Using this model, we provide evidence of caspase-independent cell death triggering the calcification process in GDNF-silenced HK-2 cells.

The Anti-Cancer Effects of Frondoside A

Frondoside A is a triterpenoid glycoside from the Atlantic Sea Cucumber, Cucumariafrondosa. Frondoside A has a broad spectrum of anti-cancer effects, including induction of cellular apoptosis, inhibition of cancer cell growth, migration, invasion, formation of metastases, and angiogenesis. In cell lines and animal models studied to date, the anti-cancer effects of the compound are seen in all solid cancers, lymphomas, and leukemias studied to date. These effects appear to be due to potent inhibition of p21-activated kinase 1 (PAK1), which is up-regulated in many cancers. In mouse models, frondoside A has synergistic effects with conventional chemotherapeutic agents, such as gemcitabine, paclitaxel, and cisplatin. Frondoside A administration is well-tolerated. No side effects have been reported and the compound has no significant effects on body weight, blood cells, or on hepatic and renal function tests after long-term administration. Frondoside A may be valuable in the treatment of malignancies, either as a single agent or in combination with other therapeutic modalities.

Atg2A/B deficiency switches cytoprotective autophagy to non-canonical caspase-8 activation and apoptosis

Autophagosomal membranes are emerging as platforms for various cell survival and death signaling networks beyond autophagy. While autophagy-dependent cell death has been reported in response to a variety of stimuli, the underlying molecular mechanisms remain far from clear. Here, we demonstrate that inhibition of autophagosome completion by Atg2A/B deletion accumulates immature autophagosomal membranes that promote non-canonical caspase-8 activation in response to nutrient starvation via an intracellular death-inducing signaling complex (iDISC). Importantly, iDISC-induced caspase-8 dimerization and activation occurs on accumulated autophagosomal membranes and requires the LC3 conjugation machinery but is independent from the extrinsic pathway of apoptosis. Moreover, we have identified NF-κB signaling and c-FLIP as negative regulators of iDISC-mediated caspase-8 activation and apoptosis. Collectively, these findings reveal autophagosomal membrane completion as a novel target to switch cytoprotective autophagy to apoptosis.

Complement-Related Regulates Autophagy in Neighboring Cells

Autophagy degrades cytoplasmic components and is important for development and human health. Although autophagy is known to be influenced by systemic intercellular signals, the proteins that control autophagy are largely thought to function within individual cells. Here, we report that Drosophila macroglobulin complement-related (Mcr), a complement ortholog, plays an essential role during developmental cell death and inflammation by influencing autophagy in neighboring cells. This function of Mcr involves the immune receptor Draper, suggesting a relationship between autophagy and the control of inflammation. Interestingly, Mcr function in epithelial cells is required for macrophage autophagy and migration to epithelial wounds, a Draper-dependent process. This study reveals, unexpectedly, that complement-related from one cell regulates autophagy in neighboring cells via an ancient immune signaling program.

Insecticidal Effects of Hemocoelic Delivery of Bacillus thuringiensis Cry Toxins in Achaea janata Larvae

Insecticidal effects of Bacillus thuringiensis Cry toxins in hemocoel of larvae have not been properly evaluated. In the present study, hemocoelic injection of four representative Cry toxins i.e., Cry1Aa, Cry1Ab, Cry1Ac, and DOR5 to an economically important lepidopteran insect pest Achaea janata, induced larval mortality, reduced larval growth rate and gave rise to smaller pupae, all in a dose-dependent manner. We observed extensive degeneration as well as the disintegration of larval tissues, most notably, fat body, and the possible involvement of lysosomal enzymes in tissue histolysis. The resultant “hypoproteinemia” and most relevantly, the drastic reduction of 80–85 kDa hexamerin proteins levels of hemolymph could be attributed to the pathological state of the fat body induced by Cry toxin injection. Formation of non-viable larval-pupal intermediates and emergence of defective adults also indicate toxicity effects of Cry toxins during metamorphosis. Thus, findings from our study suggest Cry toxins in larval hemocoel are also toxic to A. janata larval survival and subsequent development.

Mutants for Drosophila Isocitrate Dehydrogenase 3b Are Defective in Mitochondrial Function and Larval Cell Death

The death of larval salivary gland cells during metamorphosis in Drosophila melanogaster has been a key system for studying steroid controlled programmed cell death. This death is induced by a pulse of the steroid hormone ecdysone that takes place at the end of the prepupal period. For many years, it has been thought that the ecdysone direct response gene Eip93F (E93) plays a critical role in initiating salivary gland cell death. This conclusion was based largely on the finding that the three “type” alleles of E93 cause a near-complete block in salivary gland cell death. Here, we show that these three mutations are in fact allelic to Idh3b, a nearby gene that encodes the β subunit of isocitrate dehydrogenase 3, a mitochondrial enzyme of the tricarboxylic acid (TCA) cycle. The strongest of the Idh3b alleles appears to cause a near-complete block in oxidative phosphorylation, as mitochondria are depolarized in mutant larvae, and development arrests early during cleavage in embryos from homozygous-mutant germline mothers. Idh3b-mutant larval salivary gland cells fail to undergo mitochondrial fragmentation, which normally precedes the death of these cells, and do not initiate autophagy, an early step in the cell death program. These observations suggest a close relationship between the TCA cycle and the initiation of larval cell death. In normal development, tagged Idh3b is released from salivary gland mitochondria during their fragmentation, suggesting that Idh3b may be an apoptogenic factor that functions much like released cytochrome c in mammalian cells.

Non-apoptotic cell death in animal development

Programmed cell death (PCD) is an important process in the development of multicellular organisms. Apoptosis, a form of PCD characterized morphologically by chromatin condensation, membrane blebbing, and cytoplasm compaction, and molecularly by the activation of caspase proteases, has been extensively investigated. Studies in Caenorhabditis elegans, Drosophila, mice, and the developing chick have revealed, however, that developmental PCD also occurs through other mechanisms, morphologically and molecularly distinct from apoptosis. Some non-apoptotic PCD pathways, including those regulating germ cell death in Drosophila, still appear to employ caspases. However, another prominent cell death program, linker cell-type death (LCD), is morphologically conserved, and independent of the key genes that drive apoptosis, functioning, at least in part, through the ubiquitin proteasome system. These non-apoptotic processes may serve as backup programs when caspases are inactivated or unavailable, or, more likely, as freestanding cell culling programs. Non-apoptotic PCD has been documented extensively in the developing nervous system, and during the formation of germline and somatic gonadal structures, suggesting that preservation of these mechanisms is likely under strong selective pressure. Here, we discuss our current understanding of non-apoptotic PCD in animal development, and explore possible roles for LCD and other non-apoptotic developmental pathways in vertebrates. We raise the possibility that during vertebrate development, apoptosis may not be the major PCD mechanism.

Molecular mechanism underlying juvenile hormone-mediated repression of precocious larval-adult metamorphosis

Juvenile hormone (JH) represses precocious metamorphosis of larval to pupal and adult transitions in holometabolous insects. The early JH-inducible gene Krüppel homolog 1 (Kr-h1) plays a key role in the repression of metamorphosis as a mediator of JH action. Previous studies demonstrated that Kr-h1 inhibits precocious larval-pupal transition in immature larva via direct transcriptional repression of the pupal specifier Broad-Complex (BR-C). JH was recently reported to repress the adult specifier gene Ecdysone-induced protein 93F (E93); however, its mechanism of action remains unclear. Here, we found that JH suppressed ecdysone-inducible E93 expression in the epidermis of the silkworm Bombyx mori and in a B. mori cell line. Reporter assays in the cell line revealed that the JH-dependent suppression was mediated by Kr-h1. Genome-wide ChIP-seq analysis identified a consensus Kr-h1 binding site (KBS, 14 bp) located in the E93 promoter region, and EMSA confirmed that Kr-h1 directly binds to the KBS. Moreover, we identified a C-terminal conserved domain in Kr-h1 essential for the transcriptional repression of E93 Based on these results, we propose a mechanism in which JH-inducible Kr-h1 directly binds to the KBS site upstream of the E93 locus to repress its transcription in a cell-autonomous manner, thereby preventing larva from bypassing the pupal stage and progressing to precocious adult development. These findings help to elucidate the molecular mechanisms regulating the metamorphic genetic network, including the functional significance of Kr-h1, BR-C, and E93 in holometabolous insect metamorphosis.

Mobile-phone radiation-induced perturbation of gene-expression profiling, redox equilibrium and sporadic-apoptosis control in the ovary of Drosophila melanogaster

The daily use by people of wireless communication devices has increased exponentially in the last decade, begetting concerns regarding its potential health hazards. Drosophila melanogaster four days-old adult female flies were exposed for 30 min to radiation emitted by a commercial mobile phone at a SAR of 0.15 W/kg and a SAE of 270 J/kg. ROS levels and apoptotic follicles were assayed in parallel with a genome-wide microarrays analysis. ROS cellular contents were found to increase by 1.6-fold (x), immediately after the end of exposure, in follicles of pre-choriogenic stages (germarium - stage 10), while sporadically generated apoptotic follicles (germarium 2b and stages 7-9) presented with an averaged 2x upregulation in their sub-population mass, 4 h after fly's irradiation with mobile device. Microarray analysis revealed 168 genes being differentially expressed, 2 h post-exposure, in response to radiofrequency (RF) electromagnetic field-radiation exposure (≥1.25x, P < 0.05) and associated with multiple and critical biological processes, such as basic metabolism and cellular subroutines related to stress response and apoptotic death. Exposure of adult flies to mobile-phone radiation for 30 min has an immediate impact on ROS production in animal's ovary, which seems to cause a global, systemic and non-targeted transcriptional reprogramming of gene expression, 2 h post-exposure, being finally followed by induction of apoptosis 4 h after the end of exposure. Conclusively, this unique type of pulsed radiation, mainly being derived from daily used mobile phones, seems capable of mobilizing critical cytopathic mechanisms, and altering fundamental genetic programs and networks in D. melanogaster.

Vital staining for cell death identifies Atg9a-dependent necrosis in developmental bone formation in mouse

Programmed cell death has a crucial role in various biological events, including developmental morphogenesis. Recent evidence indicates that necrosis contributes to programmed cell death in addition to apoptosis, but it is unclear whether necrosis acts as a compensatory mechanism for failure of apoptosis or has an intrinsic role during development. In contrast to apoptosis, there have been no techniques for imaging physiological necrosis in vivo. Here we employ vital staining using propidium iodide to identify cells with plasma membrane disruption (necrotic cells) in mouse embryos. We discover a form of necrosis at the bone surface, which does not occur in embryos with deficiency of the autophagy-related gene Atg9a, although it is unaffected by Atg5 knockout. We also find abnormalities of the bone surface in Atg9a knockout mice, suggesting an important role of Atg9a-dependent necrosis in bone surface formation. These findings suggest that necrosis has an active role in developmental morphogenesis.

Apoptosis-related genes control autophagy and influence DENV-2 infection in the mosquito vector, Aedes aegypti

The mosquito Aedes aegypti is the primary urban vector for dengue virus (DENV) worldwide. Insight into interactions occurring between host and pathogen is important in understanding what factors contribute to vector competence. However, many of the molecular mechanisms for vector competence remain unknown. Our previous global transcriptional analysis suggested that differential expression of apoptotic proteins is involved in determining refractoriness vs susceptibility to DENV-2 infection in Ae. aegypti females following a DENV-infected blood meal. To determine whether DENV-refractory Ae. aegypti showed more robust apoptosis upon infection, we compared numbers of apoptotic cells from midguts of refractory and susceptible strains and observed increased numbers of apoptotic cells in only the refractory strain upon DENV-2 infection. Thereafter, we manipulated apoptosis through dsRNA interference of the initiator caspase, Aedronc. Unexpectedly, dsAedronc-treated females showed both decreased frequency of disseminated infection and decreased virus titer in infected individuals. Insect caspases have also previously been identified as regulators of the cellular recycling process known as autophagy. We observed activation of autophagy in midgut and fat body tissues following a blood meal, as well as programmed activation of several apoptosis-related genes, including the effector caspase, Casps7. To determine whether autophagy was affected by caspase knockdown, we silenced Aedronc and Casps7, and observed reduced activation of autophagy upon silencing. Our results provide evidence that apoptosis-related genes are also involved in regulating autophagy, and that Aedronc may play an important role in DENV-2 infection success in Ae. aegypti, possibly through its regulation of autophagy.

Reversible Toxic Effects of the Dietary Supplement Indole-3-Carbinol in an Immune Compromised Rodent Model: Intestine as the Main Target

Dietary supplements are widely used in the United States, but the safety issue remains unresolved. Immuno-deficient or immuno-compromised patients, estimated to exceed 10 million in the United States, are known to use dietary supplements. This population potentially may be susceptible to supplements' adverse effects. The cruciferous vegetable-derived indole-3-carbinol (I3C) is known for its possible protective effects against a number of chronic diseases and is commercially available as a dietary supplement. However, the safety of orally consumed I3C in the general population and particularly in immuno-compromised individuals remains unknown. In this study, rodent model of immune-deficient male BALB/c nu/nu athymic mice were given diets supplemented with 0-100 μmoles I3C/g diet for 4 weeks. We found that BALB/c nu/nu mice were not viable after three days on a 100 μmoles I3C/g supplemented diet. Switching to the control diet (without I3C) after first detection of stress resulted in a 75% recovery of mice. Mice fed with 10-50 μmoles I3C/g supplemented diet survived but showed concentration-dependent adverse effects. More importantly, the intestine appeared to be the target of I3C toxicity. Number and width of intestinal villi were significantly altered by I3C, which associated with a dose-dependent reduction in cell proliferation and increase in apoptosis. Other molecular effects observed for I3C include activation of multiple xenobiotic metabolism pathways. This is the first study to report hazardous effects of I3C supplementation that are specific to the gastrointestinal tract in an immuno-compromised model and should serve as a caution in using I3C as dietary supplements.

MOLECULAR CHARACTERIZATION OF AUTOPHAGY-RELATED GENE 5 FROM Spodoptera exigua AND EXPRESSION ANALYSIS UNDER VARIOUS STRESS CONDITIONS

Autophagy is not only involved in development, but also has been proved to attend immune response against invading pathogens. Autophagy protein 5 (ATG5) is an important autophagic protein, which plays a crucial role in autophagosome elongation. Although ATG5 has been well studied in mammal, yeast, and Drosophila, little is known about ATG5 in lepidopteran insects. We cloned putative SeAtg5 gene from Spodoptera exigua larvae by the rapid amplification of cDNA ends method, and its characteristics and the influences of multiple exogenous factors on its expression levels were then investigated. The results showed that the putative S. exigua SeATG5 protein is highly homologous to other insect ATG5 proteins, which has a conserved Pfm domain and multiple phosphorylation sites. Next, fluorescence microscope observation showed that mCherry-SeATG5 was distributed in both nucleus and cytoplasm of Spodoptera litura Sl-HP cells and partially co-localized with BmATG6-GFP, but it almost has no significant co-localization with GFP-HaATG8. Then, the Western blot analysis demonstrated that GFP-SeATG5 conjugated with ATG12. Moreover, real-time PCR revealed that its expression levels significantly increased at the initiation of pupation and the stage of adult. In addition, the expression levels of SeAtg5 can be enhanced by the starvation, UV radiation, and infection of baculovirus and bacterium. However, the expression levels of SeAtg5 decreased at 24 h post treatments in all these treatments except in starvation. These results suggested that SeATG5 might be involved in response of S. exigua under various stress conditions.

Beyond DNA puffs: What can we learn from studying sciarids?

Members of the Sciaridae family attracted the interest of researchers because of the demonstration that the DNA puff regions, which are formed in the salivary gland polytene chromosomes at the end of the fourth larval instar, constitute sites of developmentally regulated gene amplification. Besides contributing to a deeper understanding of the process of gene amplification, the study of sciarids has also provided important insights on other biological processes such as sex determination, programmed cell death, insect immunity, telomere maintenance, and nucleolar organizing regions (NOR) formation. Open questions in sciarids include among others, early development, the role of noncoding RNAs in gene amplification and the relationship between gene amplification and transcription in DNA puff forming regions. These and other questions can now be pursued with next generation sequencing techniques and experiments using RNAi experiments, since this latter technique has been shown to be feasible in sciarids. These new perspectives in the field of sciarid biology open the opportunity to consolidate sciarid species as important emerging models. genesis 54:361-378, 2016. © 2016 Wiley Periodicals, Inc.

Mechanisms and consequences of entosis

Multiple mechanisms have emerged where the engulfment of whole live cells, leading to the formation of what are called 'cell-in-cell' structures, induces cell death. Entosis is one such mechanism that drives cell-in-cell formation during carcinogenesis and development. Curiously, entotic cells participate actively in their own engulfment, by invading into their hosts, and are then killed non-cell-autonomously. Here we review the mechanisms of entosis and entotic cell death and the consequences of entosis on cell populations.

Prenatally administered dexamethasone impairs folliculogenesis in spiny mouse offspring

This study was designed to determine whether prenatal dexamethasone treatment has an effect on follicular development and atresia in the ovary of spiny mouse (Acomys cahirinus) offspring. Dexamethasone (125µg kg-1 bodyweight per day) was administered to pregnant spiny mice from Day 20 of gestation to parturition. The processes of follicle loss were analysed using classical markers of apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling reaction, active caspase-3) and autophagy (Lamp1). The present study indicated that dexamethasone reduced the pool of healthy primordial follicles. Moreover, the oocytes from these follicles showed intensive caspase-3 and Lamp1 staining. Surprisingly, dexamethasone caused an increase in the number of secondary follicles; however, most of these follicles were characterised by extensive degeneration of the oocyte and caspase-3 and Lamp1 labelling. Western-blot analysis indicated that the glucocorticoid receptor as well as apoptosis and autophagy markers were more strongly expressed in the DEX-treated group than in the control. On the basis of these findings, we have concluded that dexamethasone impairs spiny mouse folliculogenesis and enhances follicular atresia through induction of autophagy or combined autophagy and apoptosis.

Wildtype adult stem cells, unlike tumor cells, are resistant to cellular damages in Drosophila

Adult stem cells or residential progenitor cells are critical to maintain the structure and function of adult tissues (homeostasis) throughout the lifetime of an individual. Mis-regulation of stem cell proliferation and differentiation often leads to diseases including cancer, however, how wildtype adult stem cells and cancer cells respond to cellular damages remains unclear. We find that in the adult Drosophila midgut, intestinal stem cells (ISCs), unlike tumor intestinal cells, are resistant to various cellular damages. Tumor intestinal cells, unlike wildtype ISCs, are easily eliminated by apoptosis. Further, their proliferation is inhibited upon autophagy induction, and autophagy-mediated tumor inhibition is independent of caspase-dependent apoptosis. Interestingly, inhibition of tumorigenesis by autophagy is likely through the sequestration and degradation of mitochondria, as compromising mitochondria activity in these tumor models mimics the induction of autophagy and increasing the production of mitochondria alleviates the tumor-suppression capacity of autophagy. Together, these data demonstrate that wildtype adult stem cells and tumor cells show dramatic differences in sensitivity to cellular damages, thus providing potential therapeutic implications targeting tumorigenesis.

Cannabinoid-induced autophagy: Protective or death role?

Autophagy, the "self-digestion" mechanism of the cells, is an evolutionary conserved catabolic process that targets portions of cytoplasm, damaged organelles and proteins for lysosomal degradation, which plays a crucial role in development and disease. Cannabinoids are active compounds of Cannabis sativa and the most prevalent psychoactive substance is Δ(9)-tetrahydrocannabinol (THC). Cannabinoid compounds can be divided in three types: the plant-derived natural products (phytocannabinoids), the cannabinoids produced endogenously (endocannabinoids) and the synthesized compounds (synthetic cannabinoids). Various studies reported a cannabinoid-induced autophagy mechanism in cancer and non-cancer cells. In this review we focus on the recent advances in the cannabinoid-induced autophagy and highlight the molecular mechanisms involved in these processes.

Ral GTPase and the exocyst regulate autophagy in a tissue-specific manner

Autophagy traffics cellular components to the lysosome for degradation. Ral GTPase and the exocyst have been implicated in the regulation of stress-induced autophagy, but it is unclear whether they are global regulators of this process. Here, we investigate Ral function in different cellular contexts in Drosophila and find that it is required for autophagy during developmentally regulated cell death in salivary glands, but does not affect starvation-induced autophagy in the fat body. Furthermore, knockdown of exocyst subunits has a similar effect, preventing autophagy in dying cells but not in cells of starved animals. Notch activity is elevated in dying salivary glands, this change in Notch signaling is influenced by Ral, and decreased Notch function influences autophagy. These data indicate that Ral and the exocyst regulate autophagy in a context-dependent manner, and that in dying salivary glands, Ral mediates autophagy, at least in part, by regulation of Notch.

The Deubiquitinating Enzyme UBPY Is Required for Lysosomal Biogenesis and Productive Autophagy in Drosophila

Autophagy is a catabolic process that delivers cytoplasmic components to the lysosomes. Protein modification by ubiquitination is involved in this pathway: it regulates the stability of autophagy regulators such as BECLIN-1 and it also functions as a tag targeting specific substrates to autophagosomes. In order to identify deubiquitinating enzymes (DUBs) involved in autophagy, we have performed a genetic screen in the Drosophila larval fat body. This screen identified Uch-L3, Usp45, Usp12 and Ubpy. In this paper, we show that Ubpy loss of function results in the accumulation of autophagosomes due to a blockade of the autophagy flux. Furthermore, analysis by electron and confocal microscopy of Ubpy-depleted fat body cells revealed altered lysosomal morphology, indicating that Ubpy inactivation affects lysosomal maintenance and/or biogenesis. Lastly, we have shown that shRNA mediated inactivation of UBPY in HeLa cells affects autophagy in a different way: in UBPY-depleted HeLa cells autophagy is deregulated.

Alternative Splice in Alternative Lice

Genomic and transcriptomics analyses have revealed human head and body lice to be almost genetically identical; although con-specific, they nevertheless occupy distinct ecological niches and have differing feeding patterns. Most importantly, while head lice are not known to be vector competent, body lice can transmit three serious bacterial diseases; epidemictyphus, trench fever, and relapsing fever. In order to gain insights into the molecular bases for these differences, we analyzed alternative splicing (AS) using next-generation sequencing data for one strain of head lice and one strain of body lice. We identified a total of 3,598 AS events which were head or body lice specific. Exon skipping AS events were overrepresented among both head and body lice, whereas intron retention events were underrepresented in both. However, both the enrichment of exon skipping and the underrepresentation of intron retention are significantly stronger in body lice compared with head lice. Genes containing body louse-specific AS events were found to be significantly enriched for functions associated with development of the nervous system, salivary gland, trachea, and ovarian follicle cells, as well as regulation of transcription. In contrast, no functional categories were overrepresented among genes with head louse-specific AS events. Together, our results constitute the first evidence for transcript pool differences in head and body lice, providing insights into molecular adaptations that enabled human lice to adapt to clothing, and representing a powerful illustration of the pivotal role AS can play in functional adaptation.

20-Hydroxyecdysone (20E) Primary Response Gene E93 Modulates 20E Signaling to Promote Bombyx Larval-Pupal Metamorphosis

As revealed in a previous microarray study to identify genes regulated by 20-hydroxyecdysone (20E) and juvenile hormone (JH) in the silkworm, Bombyx mori, E93 expression in the fat body was markedly low prior to the wandering stage but abundant during larval-pupal metamorphosis. Induced by 20E and suppressed by JH, E93 expression follows this developmental profile in multiple silkworm alleles. The reduction of E93 expression by RNAi disrupted 20E signaling and the 20E-induced autophagy, caspase activity, and cell dissociation in the fat body. Reducing E93 expression also decreased the expression of the 20E-induced pupal-specific cuticle protein genes and prevented growth and differentiation of the wing discs. Importantly, the two HTH domains in E93 are critical for inducing the expression of a subset of 20E response genes, including EcR, USP, E74, Br-C, and Atg1. By contrast, the LLQHLL and PLDLSAK motifs in E93 inhibit its transcriptional activity. E93 binds to the EcR-USP complex via a physical association with USP through its LLQHLL motif; and this association is enhanced by 20E-induced EcR-USP interaction, which attenuates the transcriptional activity of E93. E93 acts through the two HTH domains to bind to GAGA-containing motifs present in the Atg1 promoter region for inducing gene expression. In conclusion, E93 transcriptionally modulates 20E signaling to promote Bombyx larval-pupal metamorphosis.

Autophagy in Cell Life and Cell Death

Macroautophagy (hereafter referred to as autophagy) is a process used by the cell to deliver cytoplasmic components to the lysosome for degradation. Autophagy is most often associated with cell survival, as it provides cells with molecular building blocks during periods of nutrient deprivation and also aids in the elimination of damaged organelles and protein aggregates. However, autophagy has also been implicated in cell death. Here, we review what is known about autophagy, its regulation, its role both in cell life and cell death, and what is known about autophagic cell death in vivo.

Ultrastructural analysis of apoptosis and autophagy in the midgut epithelium of Piscicola geometra (Annelida, Hirudinida) after blood feeding

Cell death in the endodermal region of the digestive tract of the blood-feeding leech Piscicola geometra was analyzed using light and transmission electron microscopes and the fluorescence method. Sexually mature specimens of P. geometra were bred under laboratory conditions and fed on Danio rerio. After copulation, the specimens laid cocoons. The material for our studies were non-feeding juveniles collected just after hatching, non-feeding adult specimens, and leeches that had been fed with fish blood (D. rerio) only once ad libitum. The fed leeches were prepared for our studies during feeding and after 1, 3, 7, and 14 days (not sexually mature specimens) and some weeks after feeding (the sexually mature). Autophagy in all regions of the endodermal part of the digestive system, including the esophagus, the crop, the posterior crop caecum (PCC), and the intestine was observed in the adult non-feeding and feeding specimens. In fed specimens, autophagy occurred at very high levels--in 80 to 90 % of epithelial cells in all four regions. In contrast, in adult specimens that did not feed, this process occurred at much lower levels--about 10 % (esophagus and intestine) and about 30 % (crop and PCC) of the midgut epithelial cells. Apoptosis occurred in the feeding adult specimens but only in the crop and PCC. However, it was absent in the non-feeding adult specimens and the specimens that were collected during feeding. Moreover, neither autophagy nor apoptosis were observed in the juvenile, non-feeding specimens. The appearance of autophagy and apoptosis was connected with feeding on toxic blood. We concluded that autophagy played the role of a survival factor and was involved in the protection of the epithelium against the products of blood digestion. Quantitative analysis was prepared to determine the number of autophagic and apoptotic cells.