Cell and Molecular Biology

Behrouz Mahmoudi

The Apoptosis

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Figure 17-37. Cell death. These electron micrographs show cells that have died by (A) necrosis or (B and C) apoptosis. The cells in (A) and (B) died in a culture dish, whereas the cell in (C) died in a developing tissue and has been engulfed by a neighboring cell. Note that the cell in (A) seems to have exploded, whereas those in (B) and (C) have condensed but seem relatively intact. The large vacuoles visible in the cytoplasm of the cell in (B) are a variable feature of apoptosis. (Courtesy of Julia Burne.)

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Figure 17-35. Sculpting the digits in the developing mouse paw by apoptosis. (A) The paw in this mouse embryo has been stained with a dye that specifically labels cells that have undergone apoptosis. The apoptotic cells appear as bright green dots between the developing digits. (B) This interdigital cell death eliminates the tissue between the developing digits, as seen one day later, when few, if any, apoptotic cells can be seen. (From W. Wood et al., Development 127:5245 5252, 2000. © The Company of Biologists.)

Prenatal Development

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5x10e7 T-cells/day in thymus, 2-4% escape apoptosis.

T-cell Development

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Bcl-2 translocation to Ig promoter region

B-cell Development

Lymphoma

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Figure 22-19. Renewal of the gut lining. (A) The pattern of cell turnover and the proliferation of stem cells in the epithelium that forms the lining of the small intestine. The arrow shows the general upward direction of cell movement onto the villi, but some cells, including a proportion of the goblet and enteroendocrine cells, stay behind and differentiate while still in the crypts. The nondividing differentiated cells (Paneth cells) at the very bottom of the crypts also have a finite lifetime, and are continually replaced by progeny of the stem cells. (B) Photograph of a section of part of the lining of the small intestine, showing the villi and crypts. Note how mucus-secreting goblet cells (stained red) are interspersed among other cell types. Enteroendocrine cells are less numerous and less easy to identify without special stains. for the structure of these cells.

Maintenance of epithelial tissues

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Mitochondria-independent apoptosis

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T-cell lytic granules: perforin (pores in plasma membrane) Granzyme B (protease, Caspase-3 ICAD degradation)

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Apaf-1

Pro-caspase-9

Cytochrome C

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cH

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Anti-Apoptotic

Apoptotic (Multidomain)

(BH3 only)

(BH3 only activators)

(BH3 only sensitizers)

Mitochondria-dependent apoptosis (Bcl-2 family proteins)

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A) MEFs from various genetic backgrounds infected with tBid retrovirus and measured for apoptosis after 24hours.

Annexin-V: Phosphatidylserine (PS) externalization.

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bax

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ubiquitin ligase

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Cell death summary

Survival Signals Damage or Stress

Bcl-2 proteins

Mitochondrial dysfunction

Caspase cascade

Morphological changesDNA fragmentationNuclear condensationPS externalizationMembrane blebbing

Death receptors / T-cells

Initiation

Execution

Commitment point