klumpfuss regulates cell death in the Drosophila retina

Programmed cell death (PCD) plays a central role in the sculpting and maturation of developing epithelia. In adult tissue, PCD plays a further role in the prevention of malignancy though removal of damaged cells. Here, we report that mutations in klumpfuss result in an excess of support cells during maturation of the developing Drosophila pupal retina. These ectopic cells are the result of a partial and specific failure of apoptotic death during normal cell fate selection. klumpfuss is required and differentially expressed in the cells that choose the life or death cell fate. We also provide genetic and biochemical evidence that klumpfuss regulates this process through down-regulation of the Epidermal Growth Factor Receptor/dRas1 signaling pathway. Based on its sequence Klumpfuss is an EGR-class nuclear factor, and our results suggest a mechanism by which mutations in EGR-class factors such as Wilms' Tumor Suppressor-1 may result in oncogenic events such as pediatric kidney tumors.     

A role for wingless in an early pupal cell death event that contributes to patterning the Drosophila eye

Programmed cell death (PCD) is utilized in a wide variety of tissues to refine structure in developing tissues and organs. However, little is understood about the mechanisms that, within a developing epithelium, combine signals to selectively remove some cells while sparing essential neighbors. One popular system for studying this question is the developing Drosophila pupal retina, where excess interommatidial support cells are removed to refine the patterned ommatidial array. In this paper, we present data indicating that PCD occurs earlier within the pupal retina than previously demonstrated. As with later PCD, this death is dependent on Notch activity. Surprisingly, altering Drosophila Epidermal Growth Factor Receptor or Ras pathway activity had no effect on this death. Instead, our evidence indicates a role for Wingless signaling to provoke this cell death. Together, these signals regulate an intermediate step in the selective removal of unneeded interommatidial cells that is necessary for a precise retinal pattern.     

TGF-beta modulates programmed cell death in the retina of the developing chick embryo

Programmed cell death (PCD) is a key phenomenon in the regulation of cell number in multicellular organisms. We have shown that reduction of endogenous transforming growth factor beta (TGF-beta) prevents apoptotic PCD of neurons in the developing peripheral and central nervous system, suggesting that TGF-beta is an important mediator of ontogenetic neuron death. Previous studies suggested that there are other pro-apoptotic molecules, nerve growth factor (NGF) and brain-derived neurotrophic factor, that induce cell death in the nervous system. In the developing chick retina, NGF induces PCD by activation of the p75 receptor. We have studied the role of TGF-beta and its putative interdependence with NGF-mediated PCD in the chick retina. We found that TGF-beta is present in the developing chick retina during the period of PCD and is essentially required to regulate PCD of retinal cells. TGF-beta 2, TGF-beta 3 and the ligand-binding TGF-beta receptor can be detected immunocytochemically in the central retina, a region where apoptosis is most prominent during the early period of PCD. Application of a TGF-beta-neutralizing antibody to chick embryos in ovo resulted in a decrease in the number of TUNEL-positive cells and a reduction of free nucleosome levels. In terms of magnitude, reduction of PCD caused by the neutralization of endogenous TGF-beta was equivalent to that seen after anti-NGF application. Neutralization of both factors did not result in a further decrease in apoptosis, indicating that NGF and TGF-beta may act on the same cell population. Furthermore, neutralization of TGF-beta did not affect the expression of NGF or the p75-receptor. Our results suggest that TGF-beta and NGF are both required to regulate cell death in the chick retina in vivo.     

Insect muscle as a model for programmed cell death

Programmed cell death (PCD) is a fundamental component of development in virtually all animals. Despite the ubiquity of this phenomenon, little is known about what tells a cell to die, and less still about the physiological and molecular mechanisms that bring about death. One system that has proven to be very amenable for the study of PCD is the intersegmental muscle (ISM) of the tobacco hawkmoth Manduca sexta. These giant muscle cells are used during the eclosion (emergence) behavior of the adult moth, and then die during the subsequent 30 h. This review uses the ISMs as a model system to address questions that are basic to any cell death system, including the following: (1) how do cells know when to die; (2) what physiological changes accompany death; (3) what are the molecular mechanisms that mediate death; and (4) do all cells die by the same process? For the ISMs, the trigger for PCD is a decline in the circulating titer of the insect molting hormone, 20-hydroxyecdysone (20-HE). During cell death there are rapid decreases in both the myofibrillar sensitivity to intracellular calcium and the resulting force of fiber contraction. The ability of the ISMs to under go PCD requires the repression and activation of specific genes. Two of the repressed genes encode actin and myosin. One of the upregulated presumptive cell-death genes encodes polyubiquitin, which appears to play a critical role in the rapid proteolysis that accompanies ISM death. One curious aspect of ISM death is that these cells display none of the features that are characteristic of apoptosis, suggesting that they may die by a fundamentally different mechanism. © 1992 John Wiley & Sons, Inc.     

Insect muscle as a model for programmed cell death.

Programmed cell death (PCD) is a fundamental component of development in virtually all animals. Despite the ubiquity of this phenomenon, little is known about what tells a cell to die, and less still about the physiological and molecular mechanisms that bring about death. One system that has proven to be very amenable for the study of PCD is the intersegmental muscle (ISM) of the tobacco hawkmoth Manduca sexta. These giant muscle cells are used during the eclosion (emergence) behavior of the adult moth, and then die during the subsequent 30 h. This review uses the ISMs as a model system to address questions that are basic to any cell death system, including the following: (1) how do cells know when to die; (2) what physiological changes accompany death; (3) what are the molecular mechanisms that mediate death; and (4) do all cells die by the same process? For the ISMs, the trigger for PCD is a decline in the circulating titer of the insect molting hormone, 20-hydroxyecdysone (20-HE). During cell death there are rapid decreases in both the myofibrillar sensitivity to intracellular calcium and the resulting force of fiber contraction. The ability of the ISMs to undergo PCD requires the repression and activation of specific genes. Two of the repressed genes encode actin and myosin. One of the upregulated presumptive cell-death genes encodes polyubiquitin, which appears to play a critical role in the rapid proteolysis that accompanies ISM death.(ABSTRACT TRUNCATED AT 250 WORDS)     

A screen for dominant modifiers of the irreC-rst cell death phenotype in the developing Drosophila retina

Programmed cell death (PCD) in the Drosophila retina requires activity of the irregular chiasmC-roughest (irreC-rst) gene. Loss-of-function mutations in irreC-rst block PCD during retinal development and lead to a rough eye phenotype in the adult. To identify genes that interact with irreC-rst and may be involved in PCD, we conducted a genetic screen for dominant enhancers and suppressors of the adult rough eye phenotype. We screened 150,000 mutagenized flies and recovered 170 dominant modifiers that localized primarily to the second and third chromosomes. At least two allelic groups correspond to previously identified death regulators, Delta and dRas1. Examination of retinae from homozygous viable mutants indicated two major phenotypic classes. One class exhibited pleiotropic defects while the other class exhibited defects specific to the cell population that normally undergoes PCD.     

Programmed cell death in the embryonic central nervous system of Drosophila melanogaster

Although programmed cell death (PCD) plays a crucial role throughout Drosophila CNS development, its pattern and incidence remain largely uninvestigated. We provide here a detailed analysis of the occurrence of PCD in the embryonic ventral nerve cord (VNC). We traced the spatio-temporal pattern of PCD and compared the appearance of, and total cell numbers in, thoracic and abdominal neuromeres of wild-type and PCD-deficient H99 mutant embryos. Furthermore, we have examined the clonal origin and fate of superfluous cells in H99 mutants by DiI labeling almost all neuroblasts, with special attention to segment-specific differences within the individually identified neuroblast lineages. Our data reveal that although PCD-deficient mutants appear morphologically well-structured, there is significant hyperplasia in the VNC. The majority of neuroblast lineages comprise superfluous cells, and a specific set of these lineages shows segment-specific characteristics. The superfluous cells can be specified as neurons with extended wild-type-like or abnormal axonal projections, but not as glia. The lineage data also provide indications towards the identities of neuroblasts that normally die in the late embryo and of those that become postembryonic and resume proliferation in the larva. Using cell-specific markers we were able to precisely identify some of the progeny cells, including the GW neuron, the U motoneurons and one of the RP motoneurons, all of which undergo segment-specific cell death. The data obtained in this analysis form the basis for further investigations into the mechanisms involved in the regulation of PCD and its role in segmental patterning in the embryonic CNS.     

Cell death in head and neck cancer pathogenesis and treatment

Many cancer therapies aim to trigger apoptosis in cancer cells. Nevertheless, the presence of oncogenic alterations in these cells and distorted composition of tumour microenvironment largely limit the clinical efficacy of this type of therapy. Luckily, scientific consensus describes about 10 different cell death subroutines with different regulatory pathways and cancer cells are probably not able to avoid all of cell death types at once. Therefore, a focused and individualised therapy is needed to address the specific advantages and disadvantages of individual tumours. Although much is known about apoptosis, therapeutic opportunities of other cell death pathways are often neglected. Molecular heterogeneity of head and neck squamous cell carcinomas (HNSCC) causing unpredictability of the clinical response represents a grave challenge for oncologists and seems to be a critical component of treatment response. The large proportion of this clinical heterogeneity probably lies in alterations of cell death pathways. How exactly cells die is very important because the predominant type of cell death can have multiple impacts on the therapeutic response as cell death itself acts as a second messenger. In this review, we discuss the different types of programmed cell death (PCD), their connection with HNSCC pathogenesis and possible therapeutic windows that result from specific sensitivity to some form of PCD in some clinically relevant subgroups of HNSCC.Subject terms: Oral cancer, Cell death, Oncogenesis     

Profiling drug-induced cell death pathways in the zebrafish lateral line

Programmed cell death (PCD) is an important process in development and disease, as it allows the body to rid itself of unwanted or damaged cells. However, PCD pathways can also be activated in otherwise healthy cells. One such case occurs in sensory hair cells of the inner ear following exposure to ototoxic drugs, resulting in hearing loss and/or balance disorders. The intracellular pathways that determine if hair cells die or survive following this or other ototoxic challenges are incompletely understood. We use the larval zebrafish lateral line, an external hair cell-bearing sensory system, as a platform for profiling cell death pathways activated in response to ototoxic stimuli. In this report the importance of each pathway was assessed by screening a custom cell death inhibitor library for instances when pathway inhibition protected hair cells from the aminoglycosides neomycin or gentamicin, or the chemotherapy agent cisplatin. This screen revealed that each ototoxin likely activated a distinct subset of possible cell death pathways. For example, the proteasome inhibitor Z-LLF-CHO protected hair cells from either aminoglycoside or from cisplatin, while d-methionine, an antioxidant, protected hair cells from gentamicin or cisplatin but not from neomycin toxicity. The calpain inhibitor leupeptin primarily protected hair cells from neomycin, as did a Bax channel blocker. Neither caspase inhibition nor protein synthesis inhibition altered the progression of hair cell death. Taken together, these results suggest that ototoxin-treated hair cells die via multiple processes that form an interactive network of cell death signaling cascades.     

Plant programmed cell death and the point of no return

The point of no return during programmed cell death (PCD) is defined as the step beyond which the cell is irreversibly committed to die. Some plant cells can be saved before this point by inducing the formation of functional chloroplasts. A visibly senescent tissue will then become green again and live for months or years. The mechanism of this reversal is only partially known. The point of no return in fungi and animals is often associated with lack of mitochondrial function. In plant cells that do not regreen, there is no evidence for PCD reversal that results in a long life. It is unclear why chloroplast-containing cells, in contrast to those with only mitochondria, have long lives after PCD reversal.     

Programmed cell death in the ovary: insights and future prospects using genetic technologies

Programmed cell death (PCD) plays a prominent role in development of the fetal ovaries and in the postnatal ovarian cycle. As is the case with other major organ systems, an evolutionarily conserved framework of genes and signaling pathways has been implicated in determining whether or not ovarian germ cells and somatic cells will die in response to either developmental cues or pathological insults. However, the identification of increasing numbers of potential ovarian cell death regulatory factors over the past several years has underscored the need for studies to now separate correlation (e.g. endogenous gene expression) from function (e.g. requirement of the gene product for the execution of PCD). In this regard, genetic technologies have recently been used to examine the functional significance of specific proteins and signaling molecules to the regulation of PCD in the female gonad in vivo. In addition to the more classic approaches, such as the use of genetic null and transgenic mice, methods that achieve cell lineage-selective and/or developmentally timed gene targeting are on the horizon for use by reproductive biologists to more accurately dissect the mechanisms by which PCD is controlled in the ovary. This minireview will highlight some of the advances that have already been made using gene knockout and transgenic mice, as well as provide an overview of the current and future status of cell lineage-selective gene disruption, in the context of PCD and ovarian function.     

Constitutive expression of the machinery for programmed cell death

In the presence of cycloheximide (CHX) to inhibit protein synthesis, a high concentration of staurosporine (STS) induces almost all cells in explant cultures of 8/8 types of newborn mouse organs and 3/3 types of adult mouse organs to die with the characteristic features of apoptosis. Eggs and blastomeres also die in this way when treated with STS and CHX, although they are less sensitive to this treatment than trophectoderm or inner cell mass cells whose sensitivity resembles that of other developing cells. Human red blood cells are exceptional in being completely resistant to treatment with STS and CHX. As (STS plus CHX)-induced cell deaths have been shown to display the characteristic features of programmed cell death (PCD), we conclude that all mammalian nucleated cells are capable of undergoing PCD and constitutively express all the proteins required to do so. It seems that the machinery for PCD is in place and ready to run, even though its activation often depends on new RNA and protein synthesis.     

Spatio-temporal pattern of programmed cell death in the developing Drosophila optic lobe

A large number of cells die via programmed cell death during the normal development of the Drosophila optic lobe. In this study, we report the precise spatial and temporal pattern of cell death in this organ. Cell death in the developing optic lobe occurs in two distinct phases. The first phase extends from the start of metamorphosis to the mid-pupal stage. During this phase, a large number of cells die in the optic lobe as a whole, with a peak of cell death at an early pupal stage in the lamina and medulla cortices and the region of the T2/T3/C neurons, and a smaller number of dead cells observed in the lobula plate cortex. The second phase extends from the mid-pupal stage to eclosion. Throughout this period, a small number of dying cells can be observed, with a small peak at a late pupal stage. Most of the dying cells are neurons. During the first phase, dying cells are distributed in specific patterns in cortices. The lamina cortex contains two distinct clusters of dying cells; the medulla cortex, four clusters; the lobula plate cortex, one cluster; and the region of the T2/T3/C neurons, one cluster. Many of the clusters maintain their distinct positions in the optic lobe but others extend the region they cover during development. The presence of distinct clusters of dying cells at different phases suggests that distinct mechanisms control cell death during different stages of optic lobe development in Drosophila.     

Cell death of barley aleurone protoplasts is mediated by reactive oxygen species

The barley aleurone layer is a terminally differentiated secretory tissue whose activity is hormonally controlled. The plant hormone gibberellic acid (GA) stimulates the secretion of hydrolytic enzymes and triggers the onset of programmed cell death (PCD). Abscisic acid (ABA) antagonizes the effects of GA and inhibits enzyme secretion and PCD. Reactive oxygen species (ROS) are key players in many types of PCD, and data presented here implicate ROS in hormonally regulated death of barley aleurone cells. Incubation of aleurone layers or protoplasts in H(2)O(2)-containing media results in death of GA-treated but not ABA-treated aleurone cells. Cells that are programmed to die are therefore less able to withstand ROS than cells that are programmed to remain alive. Illumination of barley aleurone protoplasts with blue or UV-A light results in a rapid increase in intracellular H(2)O(2) production. GA-treated protoplasts die rapidly in response to this increase in intracellular H(2)O(2) production, but ABA-treated protoplasts do not die. The rate of light-induced death could be slowed by antioxidants, and incubating protoplasts in the dark with the antioxidant butylated hydroxy toluene reduces the rate of hormonally induced death. Taken together, these data demonstrate that GA-treated aleurone protoplasts are less able than ABA-treated protoplasts to tolerate internally generated or exogenously applied H(2)O(2), and strongly suggest that ROS are components of the hormonally regulated cell death pathway in barley aleurone cells.     

Patterning the fly eye: the role of apoptosis

Early development in many tissues is characterized by a rapid expansion in cell number. Excess cells are removed through activation of their intrinsic apoptotic machinery. This over-expansion followed by selective removal is important for the sculpting of these tissues, and how specific cells are selected to die is one of the central questions in development. The Drosophila eye is a unique example of such patterning through cell death. Because of its remarkable reiterative design, the fly eye lends itself to studies of mutants with increased or decreased apoptosis. We know that the process of elimination of lattice cells is highly regulated. And we have learned that each ommatidial unit is involved in the life-death decision of lattice cells through cell-cell signaling. But, we have yet to understand how this signaling is regulated spatially to result in such precision. In this article, we describe and speculate on the role of selective cell death during maturation of the fly eye.     

Another way to die: autophagic programmed cell death

Programmed cell death (PCD) is one of the important terminal paths for the cells of metazoans, and is involved in a variety of biological events that include morphogenesis, maintenance of tissue homeostasis, and elimination of harmful cells. Dysfunction of PCD leads to various diseases in humans, including cancer and several degenerative diseases. Apoptosis is not the only form of PCD. Recent studies have provided evidence that there is another mechanism of PCD, which is associated with the appearance of autophagosomes and depends on autophagy proteins. This form of cell death most likely corresponds to a process that has been morphologically defined as autophagic PCD. The present review summarizes recent experimental evidence about autophagic PCD and discusses some aspects of this form of cell death, including the mechanisms that may distinguish autophagic death from the process of autophagy involved in cell survival.     

Noncanonical cell death pathways act during Drosophila oogenesis

Programmed cell death (PCD) is a highly conserved process that occurs during development and in response to adverse conditions. In Drosophila, most PCDs require the genes within the H99 deficiency, the adaptor molecule Ark, and caspases. Here we investigate 10 cell death genes for their potential roles in two distinct types of PCD that occur in oogenesis: developmental nurse cell PCD and starvation-induced PCD. Most of the genes investigated were found to have little effect on late stage developmental PCD in oogenesis, although ark mutants showed a partial inhibition. Mid-stage starvation-induced germline PCD was found to be independent of the upstream activators and ark although it requires caspases, suggesting an apoptosome-independent mechanism of caspase activation in mid-oogenesis. These results indicate that novel pathways must control PCD in the ovary.     

Apoptotic-like programmed cell death in plants

Programmed cell death (PCD) is now accepted as a fundamental cellular process in plants. It is involved in defence, development and response to stress, and our understanding of these processes would be greatly improved through a greater knowledge of the regulation of plant PCD. However, there may be several types of PCD that operate in plants, and PCD research findings can be confusing if they are not assigned to a specific type of PCD. The various cell-death mechanisms need therefore to be carefully described and defined. This review describes one of these plant cell death processes, namely the apoptotic-like PCD (AL-PCD). We begin by examining the hallmark 'apoptotic-like' features (protoplast condensation, DNA degradation) of the cell's destruction that are characteristic of AL-PCD, and include examples of AL-PCD during the plant life cycle. The review explores the possible cellular 'executioners' (caspase-like molecules; mitochondria; de novo protein synthesis) that are responsible for the hallmark features of the cellular destruction. Finally, senescence is used as a case study to show that a rigorous definition of cell-death processes in plant cells can help to resolve arguments that occur in the scientific literature regarding the timing and control of plant cell death.     

Eggs over easy: cell death in the Drosophila ovary

Programmed cell death is the most common fate of female germ cells in Drosophila and many animals. In Drosophila, oocytes form in individual egg chambers that are supported by germline nurse cells and surrounded by somatic follicle cells. As oogenesis proceeds, 15 nurse cells die for every oocyte that is produced. In addition to this developmentally regulated cell death, groups of germ cells or entire egg chambers may be induced to undergo apoptosis in response to starvation or other insults. Recent findings suggest that these different types of cell death involve distinct genetic pathways. This review focuses on progress towards elucidating the molecular mechanisms acting during programmed cell death in Drosophila oogenesis.