Autophagy promotes caspase-dependent cell death during Drosophila development

The relationship between autophagic cell death and apoptosis is a poorly understood aspect of programmed cell death (PCD). We have examined this relationship by studying the elimination of an extra-embryonic tissue, known as the amnioserosa (AS), during Drosophila development. The AS becomes autophagic during the final stages of embryogenesis; ultimately, however, the elimination of the AS involves caspase-dependent nuclear fragmentation, tissue dissociation, and engulfment by phagocytic macrophages. Mutants that are defective in the activation or execution of caspase-dependent PCD fail to degrade and eliminate the AS but show no abatement in AS autophagy. Sustained autophagy does not, therefore, necessarily result in cell death. Surprisingly, the down-regulation of autophagy also results in a persistent AS phenotype and reduced cell death. Conversely, up-regulation of autophagy results in caspase-dependent premature AS dissociation. These observations are consistent with the interpretation that autophagy is a prerequisite for caspase-dependent cell death in the AS.     

Steroid regulation of programmed cell death during Drosophila development

Steroid hormones play an important role in the regulation of numerous physiological responses, but the mechanisms that enable these systemic signals to trigger specific cell changes remain poorly characterized. Recent studies of Drosophila illustrate several important features of steroid-regulated programmed cell death. A single steroid hormone activates both cell differentiation and cell death in different tissues and at multiple stages during development. While several steroid-regulated genes are required for cell execution, most of these genes function in both cell differentiation and cell death, and require more specific factors to kill cells. Genes that regulate apoptosis during Drosophila embryogenesis are induced by steroids in dying cells later in development. These apoptosis genes likely function downstream of hormone-induced factors to serve a more direct role in the death response. This article reviews the current knowledge of steroid signaling and the regulation of programmed cell death during development of Drosophila.     

Surviving Drosophila eye development: integrating cell death with differentiation during formation of a neural structure

Normal differentiation requires an appropriately orchestrated sequence of developmental events. Regulation of cell survival and cell death is integrated with these events to achieve proper cell number, cell type, and tissue structure. Here we review regulation of cell survival in the context of a precisely patterned neural structure: the Drosophila compound eye. Numerous mutations lead to altered differentiation and are frequently accompanied by altered patterns of cell death. We discuss various critical times of normal eye development, highlighting how inappropriate regulation of cell death contributes to different mutant phenotypes associated with genes that specify the entire eye primordia, others that pattern the retina, and those that eliminate extraneous cells to refine the precise pigment cell lattice. Finally, we address how the Drosophila eye may allow identification of additional mechanisms that contribute to the normal integration of cell survival with appropriate events of cellular differentiation.     

Inflated wings, tissue autolysis and early death in tissue inhibitor of metalloproteinases mutants of Drosophila

In vertebrates, tissue inhibitors of metalloproteinases (TIMPs) play key roles in extracellular matrix (ECM) homeostasis and growth control. Deletion of the recently cloned Timp gene of Drosophila results in a subviable phenotype. Adult flies display inflated wings similar to integrin mutants, suffer from a bloated gut and progressive dissolution of internal tissues, and die prematurely. Our results demonstrate that the Timp gene product controls selective aspects of ECM function in Drosophila, and suggest that it is involved in cell adhesion/cell signaling pathways. Hence, Drosophila Timp mutants may prove useful as a model system for a wide variety of pathological conditions related to ECM dysregulation.     

Wing reduction and cell death in Drosophila hydei: Analysis of the mutants Notch and Costal-nick

Cell death and its effect on wing size have been described in some wing mutants of Drosophila hydei. Dead cells in the imaginal discs were localized by Nile-bule and acridine-orange staining. Various Notch (N) alleles, the mutation Costal-nick (Cnk) and the compound N/Cnk show characteristic patterns of cell death in the imaginal wing disc. Some but not all of the structural features of the adult wing can be related to the site of cell death during larval stages. In N^Ax types, extensive cell death is followed by regenerative growth, invalidating a simple relation between size of the disk and size of the wing. In N^ts/Cnk cell death and wing morphology depend on the breeding temperature. From temperature experiments we conclude that cell death starts between day 4 and 5 after egg laying and can be induced by a shift to the restrictive temperature during the critical phase. Patterns of wing incisions and cell death in N^ts/Cnk genotypes seem not to be delimited by any of the known compartment boundaries.     

Drosophila cbl is essential for control of cell death and cell differentiation during eye development

Background

Activation of cell surface receptors transduces extracellular signals into cellular responses such as proliferation, differentiation and survival. However, as important as the activation of these receptors is their appropriate spatial and temporal down-regulation for normal development and tissue homeostasis. The Cbl family of E3-ubiquitin ligases plays a major role for the ligand-dependent inactivation of receptor tyrosine kinases (RTKs), most notably the Epidermal Growth Factor Receptor (EGFR) through ubiquitin-mediated endocytosis and lysosomal degradation.

Methodology/Principal Findings

Here, we report the mutant phenotypes of Drosophila cbl (D-cbl) during eye development. D-cbl mutants display overgrowth, inhibition of apoptosis, differentiation defects and increased ommatidial spacing. Using genetic interaction and molecular markers, we show that most of these phenotypes are caused by increased activity of the Drosophila EGFR. Our genetic data also indicate a critical role of ubiquitination for D-cbl function, consistent with biochemical models.

Conclusions/Significance

These data may provide a mechanistic model for the understanding of the oncogenic activity of mammalian cbl genes.     

Mutagen-sensitive mutants in Drosophila melanogaster: effects on premutational damage.

Drosophila melanogaster males from a Basc stock were mutagenized with either X-rays, ethyl methanesulfonate (EMS), or nitrogen mustard (HN2). Groups of identically treated males were crossed to different types of female. Sex-linked recessive lethals were scored as a genetic end point. The females used were homozygous for X-chromosomal mutations (mus(1)101D1, mus(1)104D1, mei-9 or mei-41D5) which lead to defective DNA repair and which increase the mutagen sensitivity of larvae. Females from a white stock with normal DNA repair capacities served as controls. The premutational lesions induced in mature sperm are only processed after insemination by the maternal enzyme systems present in the oocytes. Differences in the efficiency of the processing of lesions can lead to maternal effects on the frequency of mutations recovered from mutagenized sperm. It was found that, with the exception of mus(1)104D1, all mutants analysed significantly modify the mutation fixation of one or more types of premutational lesions. The most drastic effect is found with the mus(1)101D1 stock in which HN2-induced DNA cross-links do not lead to sex-linked recessive lethals. It is assumed that mus(1)101D1 is defective in an early step of DNA cross-link repair. Our first set of data clearly demonstrates that the study of maternal effects in Drosophila is an efficient tool to analyse the in vivo function of repair mutations on chemically induced mutagenesis.     

Eggs to die for: cell death during Drosophila oogenesis

Extensive programmed cell death occurs in the female germline of many species ranging from C. elegans to humans. One purpose for germline apoptosis is to remove defective cells unable to develop into fertile eggs. In addition, recent work suggests that the death of specific germline cells may also play a vital role by providing essential nutrients to the surviving oocytes. In Drosophila, the genetic control of germline apoptosis and the proteins that carry out the death sentences are beginning to emerge from studies of female sterile mutations. These studies suggest that the morphological changes that occur during the late stages of Drosophila oogenesis may be initiated and driven by a modified form of programmed cell death.     

Identification of factors that function in Drosophila salivary gland cell death during development using proteomics

Proteasome inhibitors induce cell death and are used in cancer therapy, but little is known about the relationship between proteasome impairment and cell death under normal physiological conditions. Here, we investigate the relationship between proteasome function and larval salivary gland cell death during development in Drosophila. Drosophila larval salivary gland cells undergo synchronized programmed cell death requiring both caspases and autophagy (Atg) genes during development. Here, we show that ubiquitin proteasome system (UPS) function is reduced during normal salivary gland cell death, and that ectopic proteasome impairment in salivary gland cells leads to early DNA fragmentation and salivary gland condensation in vivo. Shotgun proteomic analyses of purified dying salivary glands identified the UPS as the top category of proteins enriched, suggesting a possible compensatory induction of these factors to maintain proteolysis during cell death. We compared the proteome following ectopic proteasome impairment to the proteome during developmental cell death in salivary gland cells. Proteins that were enriched in both populations of cells were screened for their function in salivary gland degradation using RNAi knockdown. We identified several factors, including trol, a novel gene CG11880, and the cop9 signalsome component cop9 signalsome 6, as required for Drosophila larval salivary gland degradation.     

By design or by chance: cell death during Drosophila embryogenesis

Cell death plays an essential role during Drosophila embryogenesis. However, it remains an enigma as to what mechanisms determine (or select) the specific cells to be eliminated at a particular developmental stage. Is it mostly dependent on the lineage of the cell, signifying genetic predetermination, or is it due to the failure of a cell to compete for growth factors, which is more or less by chance? Recent developments in studying the molecular mechanism of cell death during Drosophila embryogenesis has provided much insight into our understanding of the relative importance of, and the interaction between, these two mechanisms in shaping the embryo.     

Melanotic mutants in Drosophila: pathways and phenotypes

Mutations in >30 genes that regulate different pathways and developmental processes are reported to cause a melanotic phenotype in larvae. The observed melanotic masses were generally linked to the hemocyte-mediated immune response. To investigate whether all black masses are associated with the cellular immune response, we characterized melanotic masses from mutants in 14 genes. We found that the melanotic masses can be subdivided into melanotic nodules engaging the hemocyte-mediated encapsulation and into melanizations that are not encapsulated by hemocytes. With rare exception, the encapsulation is carried out by lamellocytes. Encapsulated nodules are found in the hemocoel or in association with the lymph gland, while melanizations are located in the gut, salivary gland, and tracheae. In cactus mutants we found an additional kind of melanized mass containing various tissues. The development of these tissue agglomerates is dependent on the function of the dorsal gene. Our results show that the phenotype of each mutant not only reflects its connection to a particular genetic pathway but also points to the tissue-specific role of the individual gene.     

Taste perception: Drosophila - a model of good taste

Recent studies of taste receptors in Drosophila show remarkable parallels with the mammalian gustatory system, although the pathways are anatomically distinct. These parallels may reflect crucial constraints in the design of taste detection systems.     

Roles of myosin phosphatase during Drosophila development

Myosins are a superfamily of actin-dependent molecular motor proteins, among which the bipolar filament forming myosins II have been the most studied. The activity of smooth muscle/non-muscle myosin II is regulated by phosphorylation of the regulatory light chains, that in turn is modulated by the antagonistic activity of myosin light chain kinase and myosin light chain phosphatase. The phosphatase activity is mainly regulated through phosphorylation of its myosin binding subunit MYPT. To identify the function of these phosphorylation events, we have molecularly characterized the Drosophila homologue of MYPT, and analyzed its mutant phenotypes. We find that Drosophila MYPT is required for cell sheet movement during dorsal closure, morphogenesis of the eye, and ring canal growth during oogenesis. Our results indicate that the regulation of the phosphorylation of myosin regulatory light chains, or dynamic activation and inactivation of myosin II, is essential for its various functions during many developmental processes.     

The mutagenic effects of diepoxybutane in wild-type and mutagen-sensitive mutants of Drosophila melanogaster

Genetic tests reported here demonstrate that among the DEB-induced mutants on 2 X-chromosome loci, viz. y and w, at a minimum, one-third are chromosome deletions. Among 11 MMS-sensitive mutants tested, 9 are also somatically sensitive to DEB. In addition direct genetic tests established that the capacity to repair DEB damage induced in sperm is impaired in females homozygous for 2 mutagen-sensitive mutants. By inference the same is also the case in females homozygous for 3 other mutagen-sensitive mutants.