You are working in a laboratory investigating the effects of new chemicals calle

Question

You are working in a laboratory investigating the effects of new chemicals called X and Y that kill cells. To test whether X and Y cause necrosis or apoptosis, you briefly treat cultured cells with each chemical and perform several assays.

Without making the cells permeable in any way, you stain them with Annexin V linked to a green fluorophore, which binds phosphatidylserine, and propidium iodide, which fluoresces red when it binds DNA. Neither of these compounds can travel across intact plasma membranes. Again during sample preparation you mixed up the samples. Assign a likely identity to the samples in Figure C. Annexin V staining is shown as \ hatching, propidium iodide staining is shown as // hatching, and staining with both in the same region appears as crosshatching.

Explanation / Answer

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Annexin V is able to bind with phosphatidylserine (PS) which is located in the inner membrane, but in an early apoptotic cell this PS will be flipped towards outer membrane that able to bind with Annexin V.

Propidium iodide (PI) can bind with dead cells DNA due to their increased membrane permeability, PI+ mostly indicates the necrotic cells, but at the late apoptosis stage DNA fragmentation would take place that also give a positive result for PI stain along with Annexin V. Whereas, necrotic cells only give PI positivity.

Simply,

Only PI+ is necrosis

Only Annexin V+ is early apoptosis

Both Annexin V+ and PI+ (double positive) is late apoptosis

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