Michael D. Jacobson

Programmed Cell Death in Animal Development

We thank P. Golstein, R. Horvitz, A. Mudge, and R. Parnaik for helpful comments on the manuscript; J. Scholes for providing the drawings for Figure 2Figure 2; and J.-C. Ameisen, J. Burne, P. Golstein, R. Horvitz, K. Plasleitt, K. Roberts, and G. Stanfield for providing electron micrographs. Because of the limited number of references allowed, we were unable to cite many important papers; we apologize to their authors.

Programmed cell death and Bcl-2 protection in the absence of a nucleus.

The molecular basis of programmed cell death (PCD) is unknown. An important clue is provided by the Bcl‐2 protein, which can protect many cell types from PCD, although it is not known where or how it acts. Nuclear condensation, DNA fragmentation and a requirement for new RNA and protein synthesis are often considered hallmarks of PCD. We show here, however, that anucleate cytoplasts can undergo PCD and that Bcl‐2 and extracellular survival signals can protect them, indicating that, in some cases at least, the nucleus is not required for PCD or for Bcl‐2 or survival factor protection. We propose that PCD, like the cell cycle, is orchestrated by a cytoplasmic regulator that has multiple intracellular targets.

Does oligodendrocyte survival depend on axons

BACKGROUND We have shown previously that oligodendrocytes and their precursors require signals from other cells in order to survive in culture. In addition, we have shown that about 50% of the oligodendrocytes produced in the developing rat optic nerve normally die, apparently in a competition for the limiting amounts of survival factors. We have hypothesized that axons may control the levels of such oligodendrocyte survival factors and that the competition-dependent death of oligodendrocytes serves to match their numbers to the number of axons that they myelinate. Here we test one prediction of this hypothesis - that the survival of developing oligodendrocytes depends on axons. RESULTS We show that oligodendrocyte death occurs selectively in transected nerves in which the axons degenerate. This cell death is prevented by the delivery of exogenous ciliary neurotrophic factor (CNTF) or insulin-like growth factor I (IGF-1), both of which have been shown to promote oligodendrocyte survival in vitro. We also show that purified neurons promote the survival of purified oligodendrocytes in vitro. CONCLUSION These results strongly suggest that oligodendrocyte survival depends upon the presence of axons; they also support the hypothesis that a competition for axon-dependent survival signals normally helps adjust the number of oligodendrocytes to the number of axons that require myelination. The identities of these signals remain to be determined.

Is programmed cell death required for neural tube closure

Programmed cell death (PCD) plays an important part in animal development. It is responsible for eliminating the cells between developing digits, for example, and is involved in hollowing out solid structures to create cavities (reviewed in [1] [2]). There are many cases, however, where PCD occurs in developing tissues but its function is unknown. Important examples are seen during the folding, pinching off, and fusion of epithelial sheets during vertebrate morphogenesis, as in the formation of the neural tube and lens vesicle [2]; PCD is an invariable accompaniment to these processes, but it is unclear whether it is required for the processes to occur or is just an unavoidable consequence of them. There is increasing evidence that PCD in animals is mediated by a family of cysteine proteases, known as caspases, which are thought to act in a proteolytic cascade, cleaving one another and key intracellular proteins to kill the cell in a controlled way [3] [4]. Inhibitors of caspases are, therefore, potential tools for studying the roles of PCD during animal development [5] [6]. Here, we show that peptide caspase inhibitors block neural tube closure in explanted chick embryos, suggesting that PCD is required for this crucial developmental process.

Apoptosis: Bcl-2-related proteins get connected

Bcl-2 family proteins are key intracellular regulators of programmed cell death. Several recent discoveries demonstrate how these proteins interact with the molecular machinery that controls and executes the cell-death programme, and how they can themselves be regulated by extracellular survival signals.

Apoptosis: Breaking the ICE

Structural and functional similarities have been discovered between two mammalian proteins. Bcl-2 ang interleukin 1 beta-converting enzyme, and proteins encoded by nematode cell-death genes.

Programmed cell death: a missing link is found

Two families of proteins have advanced our understanding of the molecular basis of programmed cell death (PCD) in animal cells - the caspases and Bcl-2-related proteins. While caspases lie at the heart of the death programme, Bcl-2-related proteins act as key intracellular regulators. Although there has been considerable progress in elucidating the biochemical functions of caspases, how Bcl-2-related proteins regulate caspase activation and thereby PCD, has remained a mystery. One key to resolving this mystery seems to lie with a new third family of proteins related to the Caenorhabditis elegans cell-death protein CED-4, which connects Bcl-2-related proteins to caspases. An important step in defining this new family has been made by the identification of a human CED-4 homologue.

Ceramide changes during FAS (CD95/APO-1) mediated programmed cell death are blocked with the ICE protease inhibitor zVAD.FMK

We sought to investigate whether the changes in ceramide that occur duing FAS mediated programmed cell death (PCD) are upstream or downstream of the activation of ICE-like proteases. Changes in ceramide have been studied after challenge with the anti-FAS antibody, anti APO-1 in SKW 6.4 and U937 cells. Challenge with anti APO-1 leads to a 50% drop in cell survival as judged by nuclear morphology after 4 hours of incubation. In both U937 and SKW 6.4 cultures labelled for 48 hours with 14C acetate, the amount of ceramide approximately doubled after 24h incubation with anti APO-1 but the time course of ceramide changes was slower than the time course of anti APO-1 induced cell death. Complete inhibition of the effects of anti APO-1 on cell death and on ceramide production was observed when the ICE protease inhibitor zVAD.fmk but not zFA.fmk (a structurally similar but inactive peptide) were added together with anti-APO-1. These results suggests that the activation of sphingomyelin hydrolysis occurs downstream of the receptor-linked activation of members of the ICE protease family. Moreover, these results suggest that ceramide is not an upstream messenger in apoptosis and may instead be produced as a consequence of cell death.