Morphology of Apoptosis

Using conventional histology, it is not always easy to distinguish apoptosis from necrosis they can occur simultaneously, depending on the intensity and duration of the stimulus, the extent of ATP depletion, and so on. Table 16.2 compares some of the major morphological features of apoptosis and necrosis. 

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Telomerase Ribonucleoprotein Suppression of telomerase activity inhibition of cell proliferation change in morphology induction of apoptosis... 

Active caspases 8, 9 and 10 can convert caspase-3, the most abundant effector caspase from its pro-form to its active cleaved form. Cleavage of a number of different substrates by caspase-3 and also by caspase-6 and -7 which are two other executioner caspases besides caspase-3 then results in the typical morphology which is characteristic of apoptosis. Yet, the activation of caspase-3 and also of caspase-9 can be counteracted by IAPs, so called inhibitor of apoptosis proteins. However, concomitantly with cytochrome C also other proteins are released from mitochondria, including Smac/DIABLO. Smac/DIABLO and potentially other factors can interact with IAPs and thereby neutralize their caspase-inhibitory activity. This releases the breaks on the cell death program and allows apoptosis to ensue. 

Another morphological assay of apoptosis is done with acridine orange, a nuclear staining that reveals chromatin condensation under light and fluorescent microscope. 

Annexin V PT UOS staining is another procedure which allows to label the cells by allowing the observation of the morphological features of apoptosis. 

When embryos treated as described above were left to develop, they reached the onset of gastrulation with no visible changes in morphology compared to untreated embryos. However, as they reached stage 10.5, the embryos underwent rapid and synchronous apoptosis. This rapid cell death had striking morphological characteristics individual cells from the embryo lost their cohesion and adhesiveness and rapidly lysed so that few or no intact cells were found in each embryo 20 minutes following the onset of apoptosis (Fig. IB). 

The morphological and biochemical characteristics of apoptosis are not always manifest in cells undergoing programmed cell death 612... 

Tepper, A.D., Ruurs, P., Wiedmer, T, Sims, PJ., Borst, J. and van Bhtterswijk, W.J., 2000, Sphingomyelin hydrolysis to ceramide during the execution phase of apoptosis results from phospholipid scrambling and alters cell-surface morphology. J. Cell Biol., 150 F5-7. 

In the previous paragraph changes occurring at the level of chromatin structure have been described. All these events cannot be considered from those taking place in the cytoplasm. Indeed, it is very likely that, albeit classical definition of apoptosis is based upon morphological criteria involving mainly the nucleus, cytoplasmic events are pivotal in determining the cellular fate after inadiation. 

Although taxanes bind to p-tubulin promoting microtubule polymerization and stabilization of the spindle complex, they serve to cause a sustained mitotic block at the metaphase/anaphase boundary. This block will occur at a lower concentration than that which is required to increase the microtubule mass (10). However, it is not completely clear how this interaction with microtubules translates into cell death. Morphologic features and the characteristic DNA fragmentation patterns seen in the setting of apoptosis have been documented in tumor cells after therapy with taxanes (10). These observations are accompanied by the phosphorylation of Bcl-2, an anti-apoptotic protein, changing the cellular balance between Bax and Bcl-2 to a status that favors apoptosis (11). 

During the process of apoptosis, several mitochondrial proteins are released into the cytoplasm, including AIF and cytochrome C for the activation of proteases (L4). AIF, a tlavoprotein, can induce apoptotic morphological changes of the nucleus in a caspase-independent manner (M7, S8). Cytochrome C probably executes apoptosis by interaction with cytoplasmic protein Apaf-1 and direct activation of caspases (L2). Since the release of AIF and cytochrome C is regulated by the proteins of the Bcl-2 family, Bcl-2 can inhibit apoptosis by retention of cytochrome C in the mitochondria (T6). 

Many biochemical methods have been developed for the assessment of apoptosis. They are based on the analysis of cellular morphology, DNA fragmentation, or... 

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