Devo Lect 19 - Apoptosis Flashcards
Critical roles of Apoptosis
Amphibian metamorphosis; circulatory system; CNS; immune system; limb development
Apoptosis in Circulatory
Pharyngeal arches break down
Apoptosis in CNS
Forms the ventricles in the brains for fluid
Apoptosis in Immune system
Neutrophils undergo apoptosis after it is done its job
Steps (from video)
Cytochrome C released from mito.; Lipid asymmetry (phosphotidyl serine expressed on outside rather than inside); plamsa membranes become more permeable
Characteristics of apoptosis
Blebbing of plasma membrane; nucleus and cytoplasm condense; chromatin degrades (nucleases); cytochrome C released from mito membrane, interacts with other molecules, increases intracellular Ca; PS exposed on plasma membrane; membrane is more permeable; cell fragmentation
PS
Phosphotidyl serine; usually involved in cell signaling. When exposed on outside it acts as a marker for macrophages
TUNEL stain
stain that binds to cut up DNA, adds a labeled nucleotide to the end of the fragments; more fragments results in more colour
Why is apoptosis a good way to die?
Doesn’t release DNA and lysosomes (although they don’t work at normal pH), less inflammation; DNA is foreign to immune system, could cause autoimmune response
C. elegans
1090 cells in fate map, only 959 survive - apoptosis; tested with mutagens, see if cells undergo apoptosis more or less (by number of mutant cells)
CED-3 gene
CED-3 in C. elegans: mutant, 1090 cells (no apoptosis), overexpressed = apoptosis; inducer; mammal homologue = caspase
CED-9 gene
in C. elegans; mutant increase apoptosis, overexpression = less apoptosis; inhibitor of CED-3
Why have inhibitors and activators in apoptosis?
More precise control of the process. Very important!
Activating apoptosis in C elegans
EGL-1 (death signals) inhibit CED-9, so CED-9 can not inhibit CED-3 and apoptosis starts
BCL2 signaling
CED-9 homologue in mammals; in intracellular membranes (eg mito.). Inhibits Apaf1 which activates Caspase 9; BCL2 inhibited by Bax and Bik, which also form a pore in the mito to release cytochrome C; cyto C binds to Apaf1 and initiates apoptotic pathway
Triggers of Apoptosis
Killer T cells; kill infected cells. Steps: 1. recognize viral antigen, 2. Release of cytolytic granules from T cell (proteases, nucleases, perforin (pores)), 3. Fas ligand (on T cell) and receptor trigger apoptotic cascade (caspases)
Knockouts in T cells
FasL -/- : decrease effectiveness of apoptosis initiation by 50%; FasL and Perforin -/- : cannot kill cells at all
Define ischemia
Lack of oxygen in a tissue due to a block of a blood vessel, resulting in cell death - necrotic
Confusing part of stroke
Initial cell death due to ischemia, but then other cells around it continue to die around it after the stroke.
Apoptosis vs Necrosis
Apoptosis is programmed, good because you don’t release materials out; necrosis is death in response to damage or chemicals etc., spills contents all over
Caspases functions
Many involved in apoptosis, some involved in inflammation
ICE
Interleukin converting enzyme: aka caspase1, cuts part of IL to activate it. Interleukins stimulate inflammation
Inflammation in stroke
Increased inflammation in brain due to initial stroke, some cells die in response to this
Inhibiting caspase 1
Induce stroke and use Caspase 1 inhibitor; much less cell damage, and much less IL present; lots of drug research to treat with these w/o direct injection to brain
