The control of apoptosis in Drosophila

Patterns of cell death in the embryonic antenna of the grasshopper Schistocerca gregaria

We have investigated the pattern of apoptosis in the antennal epithelium during embryonic development of the grasshopper Schistocerca gregaria. The molecular labels lachesin and annulin reveal that the antennal epithelium becomes subdivided into segment-like meristal annuli within which sensory cell clusters later differentiate. To determine whether apoptosis is involved in the development of such sensory cell clusters, we examined the expression pattern of the cell death labels acridine orange and TUNEL in the epithelium. We found stereotypic, age-dependent, wave-like patterns of cell death in the antenna. Early in embryogenesis, apoptosis is restricted to the most basal meristal annuli but subsequently spreads to encompass almost the entire antenna. Cell death then declines in more basal annuli and is only found in the tip region later in embryogenesis. Apoptosis is restricted throughout to the midregion of a given annulus and away from its border with neighboring annuli, arguing against a causal role in annular formation. Double-labeling for cell death and sensory cell differentiation reveals apoptosis occurring within bands of differentiating sensory cell clusters, matching the meristal organization of the apical antenna. Examination of the individual epithelial lineages which generate sensory cells reveals that apoptosis begins peripherally within a lineage and with age expands to encompass the differentiated sensory cell at the base. We conclude that complete lineages can undergo apoptosis and that the youngest cells in these lineages appear to die first, with the sensory neuron dying last. Lineage-based death in combination with cell death patterns in different regions of the antenna may contribute to odor-mediated behaviors in the grasshopper.

CpG ODN 1668 induce innate and adaptive immune responses in rock bream (Oplegnathus fasciatus) against rock bream iridovirus (RBIV) infection

Rock bream iridovirus (RBIV) causes severe mass mortalities in rock bream in Korea. CpG ODN 1668 showed promise as immunoprotective agents against RBIV infection in rock bream. In this study, we assessed innate/adaptive-related gene expression patterns in RBIV-infected rock bream with and without CpG ODN 1668 administration to determine important immune defense related factors that may affect fish survival. In the CpG ODN 1668+virus-injected group, virus copies were more than 7.4- to 790591-fold lower than in the virus-injected group at 4 d (8.79 × 10⁴ and 6.58 × 10⁵/μl, respectively), 7 d (5.30 × 10² and 2.29 × 10⁷/μl, respectively) and 10 dpi (7.79 × 10¹ and 6.16 × 10⁷/μl, respectively). Furthermore, in the CpG ODN 1668+virus-injected group, significantly higher levels of MyD88 (6 h, 1 d, 4 d and 7 dpi), IL1β (1 d, 2 d and 7 dpi) and perforin/granzyme (1 dpi) expression were observed, whereas these genes were not significantly expressed in the virus-injected group at that time points. Mx, ISG15 and PKR were significantly highly expressed at 4 d and 7 dpi and reduced when low viral loads at 10 dpi in the CpG ODN 1668+virus-injected group. Conversely, in the virus-injected group, Mx, ISG15 and PKR expression were significantly higher than the control group until 10 dpi. However, MHC class I, CD8, Fas, Fas ligand and caspases (3, 8 and 9) expression levels showed no statistically significant differences between virus- and CpG ODN 1668+virus-injected group. In summary, CpG ODN 1668 administration in fish induces innate immune response or cell death pathway, which could be a major contributing factor to effective fish control over viral transcription on 4 d to 10 dpi. Expression of MyD88, IL1β, perforin and granzyme-related immune gene response is critical factor for inhibition of RBIV replication.

Caffeine Taste Signaling in Drosophila Larvae

The Drosophila larva has a simple peripheral nervous system with a comparably small number of sensory neurons located externally at the head or internally along the pharynx to assess its chemical environment. It is assumed that larval taste coding occurs mainly via external organs (the dorsal, terminal, and ventral organ). However, the contribution of the internal pharyngeal sensory organs has not been explored. Here we find that larvae require a single pharyngeal gustatory receptor neuron pair called D1, which is located in the dorsal pharyngeal sensilla, in order to avoid caffeine and to associate an odor with caffeine punishment. In contrast, caffeine-driven reduction in feeding in non-choice situations does not require D1. Hence, this work provides data on taste coding via different receptor neurons, depending on the behavioral context. Furthermore, we show that the larval pharyngeal system is involved in bitter tasting. Using ectopic expressions, we show that the caffeine receptor in neuron D1 requires the function of at least four receptor genes: the putative co-receptors Gr33a, Gr66a, the putative caffeine-specific receptor Gr93a, and yet unknown additional molecular component(s). This suggests that larval taste perception is more complex than previously assumed already at the sensory level. Taste information from different sensory organs located outside at the head or inside along the pharynx of the larva is assembled to trigger taste guided behaviors.

Analysis of Phagocytosis in the Drosophila Ovary

Programmed cell death (PCD) is essential for health and development. Generally, the last step of PCD is clearance, or engulfment, by phagocytes. Engulfment can be broken down into five basic steps: attraction of the phagocyte, recognition of the dying cell, internalization, phagosome maturation, and acidification of the engulfed material. The Drosophila melanogaster ovary serves as an excellent model to study diverse types of PCD and engulfment by epithelial cells. Here, we describe several methods to detect and analyze multiple steps of engulfment in the Drosophila ovary: recognition, vesicle uptake, phagosome maturation, and acidification. Annexin V detects phosphatidylserine, which is flipped to the outer leaflet of the plasma membrane of apoptotic cells, serving as an "eat me" signal. Several germline markers including tral-GFP, Orb, and cleaved Dcp-1 can all be used to label the germline and visualize its uptake into engulfing follicle cells. Drosophila strains expressing GFP and mCherry protein fusions can enable a detailed analysis of phagosome maturation. LysoTracker labels highly acidified compartments, marking phagolysosomes. Together these labels can be used to mark the progression of engulfment in Drosophila follicle cells.

First report on the gastropod proapoptotic AIF3 counterpart from disk abalone (Haliotis discus discus) deciphering its transcriptional modulation by induced pathogenic stress

Apoptosis inducing factor (AIF) is a flavoprotein that is involved in oxidative phosphorylation and induces apoptosis in eukaryotic cells. There are three isozymes of AIF that have been identified to date, designated as AIF1, AIF2, and AIF3; the human AIF3 is also known as an AIF-like protein (AIFL). This study aimed to identify and characterize a homologue of AIF3 from disk abalone (AbAIF3) that belongs to the phylum Mollusca. The open reading frame (ORF) of AbAIF3 is 1749 base pairs (bp) in length and encodes a protein of 583 amino acids, with a predicted molecular mass of 63.14 kDa. Based on our in-silico analysis, the AbAIF3 protein harbored the typical domain architecture as that of the known AIF family proteins, consisting of N-terminal Rieske and pyridine nucleotide-disulphide oxidoreductase domain. Comparative protein sequence analysis confirmed that AbAIF3 is a homolog of AIF3. Moreover, our phylogenetic analysis revealed that AbAIF3 had a close evolutionary relationship with the molluscan counterparts. Interestingly, AbAIF3 was shown to induce apoptosis in HEK293T cells using transfection assays followed by flow cytometric analysis. In addition, we found that AbAIF3 mRNA expression was ubiquitous in physiologically important tissues, and significantly modulated upon experimental immune stimulations in hemocytes. Collectively, our study illustrates the indispensable role of AbAIF3 in inducing apoptosis in disk abalones, which in turn might be involved in hosts' immune defense mechanisms against microbial infections.

Drosophila model for studying phagocytosis following neuronal cell death

During central nervous system (CNS ) development, a large number of neurons die by apoptosis and are efficiently removed through phagocytosis. Since apoptosis and apoptotic cell clearance are highly conserved in evolution, relatively simple and easily accessible Drosophila embryonic CNS provides a good model to study molecular and cellular mechanisms of these processes. Here, we describe how to assess neuronal apoptosis and glial phagocytosis of apoptotic neurons using immunohistochemistry of whole fixed embryos and live imaging of developing embryonic CNS. Combination of these different strategies allows a comprehensive analysis of neuronal cell death in vivo.

Gene expression of pro- and anti-apoptotic proteins in rock bream (Oplegnathus fasciatus) infected with megalocytivirus (family Iridoviridae)

Viruses belonging to the genus Megalocytivirus cause diseases in marine fishes primarily in East and Southeast Asian countries. Rock bream iridovirus (RBIV), which is a member of the Megalocytivirus genus, causes severe mass mortalities in rock beam (Oplegnathus fasciatus) in Korea. In this study, we assessed apoptosis-related gene expression patterns in Megalocytivirus-infected rock bream in high mortality and low mortality conditions to determine important apoptosis-related factors, which may affect fish survival/or death. In the high mortality group (100% mortality at 15 dpi), significantly high levels of perforin, granzyme, Fas ligand and caspase 9 expression (5.6-, 10.2-, 13.4- and 4.2-fold, respectively) were observed in the kidney at 8 dpi. Basal expression levels of Fas and caspase 3 were observed at 8 d (1.5-/0.7-fold) and 10 dpi (1.3-/0.6-fold), accompanied by heavy viral loads (8.12 × 10(6)-2.21 × 10(7)/μl). Inhibitor of apoptosis 1 (IAP1) was highly expressed (3.5- to 4.8-fold) at 1 d and 4 dpi; however, IAP1 was reduced when fish died at 8 d and 10 dpi (1.7- to 2.0-fold), which was not significantly different from that of the control group. A similar expression pattern was observed in the low mortality group (18% expected mortality at 30 dpi), which was characterised by a delayed lower magnitude of expression with lower viral loads than the high mortality group. Perforin, granzyme and Fas ligand expression was significantly higher in the low mortality group than in the control group at several sampling points until 30 dpi. Fas and caspases 8, 9 and 3 expression levels showed no statistical significance until 30 dpi. In the low mortality group, significantly higher IAP1 expression compared with the control was observed at 10 d (2.2-fold), 20 d (3.6-fold) and 22 dpi (2.0-fold). In summary, perforin- and granzyme-related apoptosis initiation signals were activated; however, the Fas-induced apoptosis pathway did not efficiently respond. Upregulated IAP1 in RBIV-infected rock bream, which was reported for the first time in this study, exhibited inhibited apoptotic responses in RBIV-infected fish. Although it remains unclear whether apoptosis inhibition aids or impedes fish survival, our data clearly show that the apoptotic response is inhibited in RBIV-infected rock bream.

E4orf4 induces PP2A- and Src-dependent cell death in Drosophila melanogaster and at the same time inhibits classic apoptosis pathways

The adenovirus E4orf4 protein regulates the progression of viral infection, and when expressed alone in mammalian tissue culture cells it induces protein phosphatase 2A (PP2A)-B55- and Src-dependent cell death, which is more efficient in oncogene-transformed cells than in normal cells. This form of cell death is caspase-independent, although it interacts with classic caspase-dependent apoptosis. PP2A-B55-dependent E4orf4-induced toxicity is highly conserved in evolution from yeast to mammalian cells. In this work we investigated E4orf4-induced cell death in a whole multicellular organism, Drosophila melanogaster. We show that E4orf4 induced low levels of cell killing, caused by both caspase-dependent and -independent mechanisms. Drosophila PP2A-B55 (twins/abnormal anaphase resolution) and Src64B contributed additively to this form of cell death. Our results provide insight into E4orf4-induced cell death, demonstrating that in parallel to activating caspase-dependent apoptosis, E4orf4 also inhibited this form of cell death induced by the proapoptotic genes reaper, head involution defective, and grim. The combination of both induction and inhibition of caspase-dependent cell death resulted in low levels of tissue damage that may explain the inefficient cell killing induced by E4orf4 in normal cells in tissue culture. Furthermore, E4orf4 inhibited JNK-dependent cell killing as well. However, JNK inhibition did not impede E4orf4-induced toxicity and even enhanced it, indicating that E4orf4-induced cell killing is a distinctive form of cell death that differs from both JNK- and Rpr/Hid/Grim-induced forms of cell death.

Embryonic development of the insect central complex: insights from lineages in the grasshopper and Drosophila

The neurons of the insect brain derive from neuroblasts which delaminate from the neuroectoderm at stereotypic locations during early embryogenesis. In both grasshopper and Drosophila, each developing neuroblast acquires an intrinsic capacity for neuronal proliferation in a cell autonomous manner and generates a specific lineage of neural progeny which is nearly invariant and unique. Maps revealing numbers and distributions of brain neuroblasts now exist for various species, and in both grasshopper and Drosophila four putatively homologous neuroblasts have been identified whose progeny direct axons to the protocerebral bridge and then to the central body via an equivalent set of tracts. Lineage analysis in the grasshopper nervous system reveals that the progeny of a neuroblast maintain their topological position within the lineage throughout embryogenesis. We have taken advantage of this to study the pioneering of the so-called w, x, y, z tracts, to show how fascicle switching generates central body neuroarchitecture, and to evaluate the roles of so-called intermediate progenitors as well as programmed cell death in shaping lineage structure. The novel form of neurogenesis involving intermediate progenitors has been demonstrated in grasshopper, Drosophila and mammalian cortical development and may represent a general strategy for increasing brain size and complexity. An analysis of gap junctional communication involving serotonergic cells reveals an intrinsic cellular organization which may relate to the presence of such transient progenitors in central complex lineages.

Cell death shapes embryonic lineages of the central complex in the grasshopper Schistocerca gregaria

We have investigated cell death in identified lineages of the central complex in the embryonic brain of the grasshopper Schistocerca gregaria. Progeny from these lineages lie in the pars intercerebralis and direct projections to the protocerebral bridge and then the central body via the w, x, y, z tracts. Osmium-ethyl gallate staining reveals pycnotic cells exclusively in cortical regions, and concentrated specifically within the lineages of the W, X, Y, Z neuroblasts. Minimal cell death occurs in a sporadic, nonpatterned manner, in other protocerebral regions. Immunohistochemistry reveals pycnotic cells express the enzyme cleaved Caspase-3 in their cytoplasm and are therefore undergoing programmed cell death (apoptosis). The number of pycnotic bodies in lineages of the pars intercerebralis varies with age: small numbers are present in the Y, Z lineages early in embryogenesis (42%), the number peaks at 67-80%, and then declines and disappears late in embryogenesis. Cell death may encompass up to 20% of a lineage at mid-embryogenesis. Peak cell death occurs shortly after maximum neurogenesis in the Y, Z lineages, and is maintained after neurogenesis has ceased in these lineages. Cell death within a lineage is patterned. Apoptosis is more pronounced among older cells and almost absent among younger cells. This suggests that specific subsets of progeny will be culled from these lineages, and we speculate about the effect of apoptosis on the biochemical profile of such lineages.

Differential potencies of effector genes in adult Drosophila

The GAL4/UAS gene expression system in Drosophila has been crucial in revealing the behavioral significance of neural circuits. Transgene products that block neurotransmitter release and induce cell death have been proved to inhibit neural function powerfully. Here we compare the action of the five effector genes shibire(ts1), Tetanus toxin light chain (TNT), reaper, Diphtheria toxin A-chain (DTA), and inwardly rectifying potassium channel (Kir2.1) and show differences in their efficiency depending on the target cells and the timing of induction. Specifically, effectors blocking neuronal transmission or excitability led to adult-induced paralysis more efficiently than those causing cell ablation. We contrasted these differential potencies in adult to their actions during development. Furthermore, we induced TNT expression in the adult mushroom bodies. In contrast to the successful impairment in short-term olfactory memory by shibire(ts1), adult TNT expression in the same set of cells did not lead to any obvious impairment. Altogether, the efficiency of effector genes depends on properties of the targeted neurons. Thus, we conclude that the selection of the appropriate effector gene is critical for evaluating the function of neural circuits.

An ultrastructural analysis of cellular death in the CA1 field in the rat hippocampus after transient forebrain ischemia followed by 2, 4 and 10 days of reperfusion

An ultrastructural study was performed to investigate the type of cellular death that occurs in hippocampal CA1 field pyramidal neurons after 10 and 20 min of transient cerebral ischemia in the male adult Wistar rats, followed by 2, 4 and 10 days of reperfusion. The four-vessel occlusion method was used to induce ischemic insult for either 10 or 20 min, following which the animals were submitted to either 2, 4 or 10 days of reperfusion. The animals were then anaesthetised, and their brains removed, dehydrated, embedded, sectioned and examined under a transmission electron microscope. After ischemic insult, neurons from the CA1 field presented alterations, corresponding to the initial, intermediate and final stages of the degenerative process. The only difference observed between the 10 and 20 min ischemic groups was the degree of damage; the reaction was stronger in 20 min groups than in the 10 min groups. While neurons were found in the different stages of oncotic necrosis in all groups, differences were found between the groups in relation to prevalent stages. In both ischemic groups, after 2 days of reperfusion, the initial stage of oncotic necrosis was prevalent and large numbers of neurons appeared normal. In both groups, after 4 days of reperfusion, most of the neurons showed more advanced alterations, typical of an intermediate stage. In both groups, after 10 days of reperfusion, alterations corresponding to the intermediate and final stages of oncotic necrosis were also predominant. However, few intact neurons were identified and the neuropile appeared more organised, with numerous glial cells. In summary, the pyramidal neurons of the CA1 field displayed selective vulnerability and exhibited a morphological death pattern corresponding exclusively to an oncotic necrotic pathway.

Genetic and biochemical strategies for identifying Drosophila genes that function in circadian control

Explicit biochemical models have been elaborated for the circadian oscillators of cyanobacterial, fungal, insect, and mammalian species. In contrast, much remains to be learned about how such circadian oscillators regulate rhythmic physiological processes. This article summarizes contemporary genetic and biochemical strategies that are useful for identifying gene products that have a role in circadian control.

Caspase inhibition during apoptosis causes abnormal signalling and developmental aberrations inDrosophila

Programmed cell death or apoptosis plays an important role in the development of multicellular organisms and can also be induced by various stress events. In the Drosophila wing imaginal disc there is little apoptosis in normal development but X-rays can induce high apoptotic levels,which eliminate a large fraction of the disc cells. Nevertheless, irradiated discs form adult patterns of normal size, indicating the existence of compensatory mechanisms. We have characterised the apoptotic response of the wing disc to X-rays and heat shock and also the developmental consequences of compromising apoptosis. We have used the caspase inhibitor P35 to prevent the death of apoptotic cells and found that it causes increased non-autonomous cell proliferation, invasion of compartments and persistent misexpression of the wingless (wg) and decapentaplegic(dpp) signalling genes. We propose that a feature of cells undergoing apoptosis is to activate wg and dpp, probably as part of the mechanism to compensate for cell loss. If apoptotic cells are not eliminated,they continuously emit Wg and Dpp signals, which results in developmental aberrations. We suggest that a similar process of uncoupling apoptosis initiation and cell death may occur during tumour formation in mammalian cells.

The Drosophila Hox gene deformed sculpts head morphology via direct regulation of the apoptosis activator reaper

Hox proteins control morphological diversity along the anterior-posterior body axis of animals, but the cellular processes they directly regulate are poorly understood. We show that during early Drosophila development, the Hox protein Deformed (Dfd) maintains the boundary between the maxillary and mandibular head lobes by activating localized apoptosis. Dfd accomplishes this by directly activating the cell death promoting gene reaper (rpr). One other Hox gene, Abdominal-B (Abd-B), also regulates segment boundaries through the regional activation of apoptosis. Thus, one mechanism used by Drosophila Hox genes to modulate segmental morphology is to regulate programmed cell death, which literally sculpts segments into distinct shapes. This and other emerging evidence suggests that Hox proteins may often regulate the maintenance of segment boundaries.

Ectopic overexpression of Drosophila lamin C is stage-specific lethal

To gain insight into the function of the developmentally regulated A-type lamins we transformed Drosophila melanogaster with a construct containing the hsp70 promoter followed by the Drosophila lamin C (an analog of vertebrate A-type lamins) cDNA. Lamin C was expressed ectopically after heat shock of embryos and localized to the nucleus. No phenotypic change was observed after lamin C expression in embryos that normally do not contain lamin C. However, ectopic expression of lamin C during most larval (but not pupal) stages stalled growth, inhibited ecdysteroid signaling (in particular during the larval-prepupal transition), resulted in development of melanotic tumors, and finally caused death. During pupation in control animals, when massive apoptosis of larval tissues takes place, lamin C is proteolyzed into a fragment with a size similar to that predicted by caspase cleavage. The ectopically expressed lamin C is identically cleaved, resulting in a large increase of the steady-state level of the lamin C fragment. A null mutation of the dcp-1 gene, one of the two known Drosophila caspase genes, also results in development of melanotic tumors and larval death, suggesting that the ectopically expressed lamin C inhibits apoptosis through competitive inhibition of caspase activity.

Multiple functions of the EGF receptor in Drosophila eye development

BACKGROUND

During animal development, cells need to make spatially and temporally regulated fate decisions. These decisions are largely controlled by intercellular signalling, often through receptor tyrosine kinases. One of these, the epidermal growth factor receptor (EGFR), regulates multiple cell fate decisions. Its importance in the recruitment of photoreceptors in the developing fly eye, a useful model for neural development, has already been reported. Other EGFR functions in the eye have not been characterised.

RESULTS

We have examined the consequences of removing or activating the EGFR at different stages of eye development. The earliest stages of assembly occurred normally within EGFR- clones--the morphogenetic furrow was unimpeded and the R8 photoreceptor was specified. All subsequent photoreceptor recruitment was blocked. EGFR- clones had a characteristic shape indicating that they had undergone substantial cell death posterior to the furrow, where the differentiation program is normally activated; consistent with this, excess apoptosis was detected. We found that the receptor also regulates cell proliferation in the disc, has an early function at the disc margin (where the morphogenetic furrow initiates) and contributes to the regulation of spacing of the R8 precursors. Finally, we found that activation of the receptor is sufficient to trigger non-R8 photoreceptor development, even in cells in front of the furrow or in the absence of the proneural gene atonal.

CONCLUSION

At least five distinct functions of EGFR signalling need to be integrated during fly eye development. These include roles in cell proliferation, survival and differentiation.

Developmental changes in teratocytes of the braconid wasp Cotesia congregata in larvae of the tobacco hornworm, Manduca sexta

The endoparasitic wasp Cotesia congregata develops in the hemocoel of larval stages of the tobacco hornworm, Manduca sexta. Teratocytes were released from the serosal membrane during hatching of the first instar wasp larva at 2-3days after oviposition; about 160 cells were released per embryo. The cells increased in diameter from about 10 to >200&mgr;m prior to wasp emergence. Nascent microvilli, visible on the cell surface before hatching of the first instar larva, rapidly increased in length and number following release of the cells. Irrespective of when the wasps were due to emerge, or how many parasitoids were present in the host, dramatic cytological changes occurred in the cells during the last instar of the host's development. Many of these morphological and ultrastructural changes were symptomatic of the cytological features of degenerating or apoptotic cells, and large numbers of vesicles appeared interspersed amongst the microvilli. The nucleus developed extensive dentritic ramifications, and the chromatin condensed in large clumps on the inner nuclear membrane. At the final stages of the wasps' development, the nucleus occupied the bulk of the interior of the cell. The cytoplasm gradually grew dramatically more electronluscent and less granular, as did the nucleoplasm, which is also indicative of impending cell death. Following the parasites' emergence, many of the cells underwent extensive blebbing of the cell surface. Teratocytes within a host appeared heterogeneous with respect to their morphological appearance. Analysis of the proteins secreted by teratocytes in vitro following labelling with (35)S-methionine showed that many (>30) polypeptides were synthesized de novo and secreted by the cells; some proteins were clearly targeted for secretion. We presume that the cells likely secrete a large number of proteins in vivo as well as in vitro.

Steroid hormones act directly to trigger segment-specific programmed cell death of identified motoneurons in vitro

In larvae of the hawkmoth, Manduca sexta, accessory planta retractor (APR) motoneurons undergo a segment-specific pattern of programmed cell death at pupation. APR death is triggered hormonally by the prepupal peak of the ecdysteroid, 20-hydroxyecdysone (20-HE). Previous studies found no evidence that cellular interactions regulate the segmental pattern of APR death in vivo. To test the hypothesis that 20-HE acts directly on APRs to trigger a cell-autonomous, segment-specific pattern of death, APRs were labeled with the fluorescent dyes DiI or DiA, removed from the nervous system before the prepupal peak, and placed in low-density cell culture. Physiological levels of 20-HE triggered the same segment-specific pattern of APR death in vitro as seen in vivo, both in cultures containing a single APR and in cultures containing two APRs removed from the same donor animal. The presence or absence of contact with other cells did not influence the APRs' responses to 20-HE. The death of APRs in culture was characterized by fragmentation or rounding up of the cell body and fragmentation of the neurites. These findings suggest that intrinsic segmental identity regulates whether these motoneurons live or die when exposed to a steroid hormone during development.

Final checkpoint in the drug-promoted and poliovirus-promoted apoptosis is under post-translational control by growth factors

The treatment of HeLa subline (HeLa-B) cells with cycloheximide or Actinomycin D resulted in a rapid (approximately 1.5 h and approximately 2.5 h, respectively) development of morphological and biochemical signs of apoptosis. The addition of fetal bovine serum to the cycloheximide-treated or Actinomycin D-treated cells suppressed the apoptotic reaction, as evidenced by the postponement of the DNA fragmentation for at least 9 and 5 h, respectively. A similar suppressive effect was observed upon the serum addition to cells undergoing abortive infection with poliovirus, which died of apoptosis in the absence of the serum. The serum appeared to exert its anti-apoptotic effect without any appreciable lag and even immediately blocked further progress of ongoing DNA fragmentation. The epidermal growth factor also suppressed, although less efficiently and more transiently, the apoptotic reaction promoted by the metabolic inhibitors. It is concluded that growth factors may affect, without modulating either transcription or translation, the balance of pro-apoptotic and anti-apoptotic activities at a final checkpoint, just preceding the irreversible effector step of apoptosis.

Cell killing by the Drosophila gene reaper

The reaper gene (rpr) is important for the activation of apoptosis in Drosophila. To investigate whether rpr expression is sufficient to induce apoptosis, transgenic flies were generated that express rpr complementary DNA or the rpr open reading frame in cells that normally live. Transcription of rpr from a heat-inducible promoter rapidly caused wide-spread ectopic apoptosis and organismal death. Ectopic overexpression of rpr in the developing retina resulted in eye ablation. The occurrence of cell death was highly sensitive to the dosage of the transgene. Because cell death induced by the protein encoded by rpr (RPR) could be blocked by the baculovirus p35 protein, RPR appears to activate a death program mediated by a ced-3/ICE (interleukin-1 converting enzyme)-like protease.