Methods for Studying Programmed Cell Death in C. elegans

Physiological Effects of Oxidative Stress Caused by Saxitoxin in the Nematode Caenorhabditis elegans

Saxitoxin (STX) causes high toxicity by blocking voltage-gated sodium channels, and it poses a major threat to marine ecosystems and human health worldwide. Our work evaluated the neurotoxicity and chronic toxicology of STX to Caenorhabditis elegans by an analysis of lifespan, brood size, growth ability, reactive oxygen species (ROS) and adenosine triphosphate (ATP) levels, and the overexpression of green fluorescent protein (GFP). After exposure to a series of concentrations of STX for 24 h, worms showed paralysis symptoms and fully recovered within 6 h; less than 5% of worms died at the highest concentration of 1000 ng/mL for first larval stage (L1) worms and 10,000 ng/mL for fourth larval stage (L4) worms. Declines in lifespan, productivity, and body size of C. elegans were observed under the stress of 1, 10, and 100 ng/mL STX, and the lifespan was shorter than that in controls. With STX exposure, the productivity declined by 32-49%; the body size, including body length and body area, declined by 13-18% and 25-27%, respectively. The levels of ROS exhibited a gradual increase over time, accompanied by a positive concentration effect of STX resulting in 1.14-1.86 times higher levels compared to the control group in L4 worms. Conversely, no statistically significant differences were observed between L1 worms. Finally, after exposure to STX for 48 h, ATP levels and GFP expression in C. elegans showed a significant dose-dependent increase. Our study reports the first evidence that STX is not lethal but imposes substantial oxidative stress on C. elegans, with a dose-responsive relationship. Our results indicated that C. elegans is an ideal model to further study the mechanisms underlying the fitness of organisms under the stress caused by paralytic shellfish toxins including STX.

Intertwined Functions of Separase and Caspase in Cell Division and Programmed Cell Death

Timely sister chromatid separation, promoted by separase, is essential for faithful chromosome segregation. Separase is a member of the CD clan of cysteine proteases, which also includes the pro-apoptotic enzymes known as caspases. We report a role for the C. elegans separase SEP-1, primarily known for its essential activity in cell division and cortical granule exocytosis, in developmentally programmed cell death when the predominant pro-apoptotic caspase CED-3 is compromised. Loss of SEP-1 results in extra surviving cells in a weak ced-3(-) mutant, and suppresses the embryonic lethality of a mutant defective for the apoptotic suppressor ced-9/Bcl-2 implicating SEP-1 in execution of apoptosis. We also report apparent non-apoptotic roles for CED-3 in promoting germ cell proliferation, meiotic chromosome disjunction, egg shell formation, and the normal rate of embryonic development. Moreover, loss of the soma-specific (CSP-3) and germline-specific (CSP-2) caspase inhibitors result in CED-3-dependent suppression of embryonic lethality and meiotic chromosome non-disjunction respectively, when separase function is compromised. Thus, while caspases and separases have evolved different substrate specificities associated with their specialized functions in apoptosis and cell division respectively, they appear to have retained the residual ability to participate in both processes, supporting the view that co-option of components in cell division may have led to the innovation of programmed cell suicide early in metazoan evolution.

STRATEGY OF PROGRAMMED CELL DEATH IN PROKARYOTES

Programmed cell death (PCD) was first studied in eukaryotic organisms. This system also operates in the development life cycle of prokaryotes. The system PCD in microorganisms is activated a wide range of signals in response to the stresses associated with adverse environmental conditions or exposure to antibacterial agents. The results of numerous studies in the past decade allow considering the system PCD in prokaryotes as an evolutionary conservation of the species. These results significantly expanded understanding of the role of PCD in microorganisms and opened a number of important areas of research of the morphological and molecular genetic approaches to the study of death strategies for the survival in bacterial populations. The purpose of the review is to summarize the morphological and molecular genetic characteristics of PCD in prokaryotes which are real manifestations of the mechanisms of this phenomenon. 

Trypanosoma cruzi cell death induced by the Morita-Baylis-Hillman adduct 3-Hydroxy-2-methylene-3-(4-nitrophenylpropanenitrile)

Chagas disease, caused by the protozoan Trypanosoma cruzi, remains a serious health concern due to the lack of effective vaccines or satisfactory treatment. In the search for new compounds against this neglected disease, we have previously demonstrated that the compound 3-Hydroxy-2-methylene-3-(4-nitrophenylpropanenitrile) (MBHA3), derived from the Morita-Baylis-Hillman reaction, effectively caused a loss of viability in both the epimastigote and trypomastigote forms. However, the mechanisms of parasite death elicited by MBHA3 remain unknown. The aim of this study was to better understand the morphophysiological changes and the mechanism of cell death induced by MBHA3 treatment on T. cruzi. To perform this analysis, we used confocal microscopy and flow cytometry to monitor the fluorescent probes such as annexin-V/propidium iodide (AV/PI), calcein-AM/ethidium homodimer (CA/EH), acridine orange (AO) and rhodamine 123 (Rho 123). Lower concentrations of MBHA3 led to alterations in the mitochondrial membrane potential and AO labeling, but did not decrease the viability of the epimastiogote forms, as determined by the CA/EH and AV/PI assays. Conversely, treatment with higher concentrations of MBHA3 led to extensive plasma membrane damage, loss of mitochondrion membrane potential, DNA fragmentation and acidification of the cytoplasm. Our findings suggest that at higher concentrations, MBHA3 induces T. cruzi epimastigote death by necrosis in a mitochondrion-dependent manner.

Methods for detection and analysis of apoptosis signaling in the C. elegans germline

This review assesses current and emerging methods for the detection, and analysis of apoptosis in the Caenorhabditis elegans germline. The nematode worm C. elegans is highly tractable to genetic manipulation, making it an excellent model for elucidating mechanisms of apoptosis signaling in a multicellular setting. Here we profile the most efficacious fluorescent tools to visualize and quantify germline apoptosis. We focus specifically on the application of fluorescent markers to screen by RNAi for genes and pathways that regulate germline apoptosis under normal conditions or in response to genotoxic stress. We also present the limitations of these methods, and suggest complimentary techniques in order that researchers new to the field can comprehensively assess apoptosis phenotypes in the C. elegans germline.

Anti-apoptotic signaling as a cytoprotective mechanism in mammalian hibernation

In the context of normal cell turnover, apoptosis is a natural phenomenon involved in making essential life and death decisions. Apoptotic pathways balance signals which promote cell death (pro-apoptotic pathways) or counteract these signals (anti-apoptotic pathways). We proposed that changes in anti-apoptotic proteins would occur during mammalian hibernation to aid cell preservation during prolonged torpor under cellular conditions that are highly injurious to most mammals (e.g. low body temperatures, ischemia). Immunoblotting was used to analyze the expression of proteins associated with pro-survival in six tissues of thirteen-lined ground squirrels, Ictidomys tridecemlineatus. The brain showed a concerted response to torpor with significant increases in the levels of all anti-apoptotic targets analyzed (Bcl-2, Bcl-xL, BI-1, Mcl-1, cIAP1/2, xIAP) as well as enhanced phosphorylation of Bcl-2 at S70 and T56. Heart responded similarly with most anti-apoptotic proteins elevated significantly during torpor except for Bcl-xL and xIAP that decreased and Mcl-1 that was unaltered. In liver, BI-1 increased whereas cIAP1/2 decreased. In kidney, there was an increase in BI-1, cIAP and xIAP but decreases in Bcl-xL and p-Bcl-2(T56) content. In brown adipose tissue, protein levels of BI-1, cIAP1/2, and xIAP decreased significantly during torpor (compared with euthermia) whereas Bcl-2, Bcl-xL, Mcl-1 were unaltered; however, Bcl-2 showed enhanced phosphorylation at Thr56 but not at Ser70. In skeletal muscle, only xIAP levels changed significantly during torpor (an increase). The data show that anti-apoptotic pathways have organ-specific responses in hibernators with a prominent potential role in heart and brain where coordinated enhancement of anti-apoptotic proteins occurred in response to torpor.