- Which of the following methods can be used to selectively lyse newly dividing cells?
(1) MTT (3-(4,5-Dimethylthiazol- 2-yl) – 2,5- diphenyltetrazolium bromide) treatment of dividing cells followed by UVB irradiation
(2) Treatment of dividing cells with caspase inducers
(3) Bromodeoxyuridine (BrdU) labelling of dividing cells followed by exposure to light
(4) Treatment of dividing cells with 51Cr and measuring its release over a period of time.
The correct method is (3) Bromodeoxyuridine (BrdU) labelling of dividing cells followed by exposure to light.
Why option (3) works
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BrdU is a thymidine analog that is incorporated into DNA only in cells undergoing DNA synthesis (S phase).
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When BrdU‑labelled cells are exposed to appropriate light (typically UV‑A), BrdU makes DNA highly photosensitive, leading to strand breaks and lethal photochemical damage in those cells.
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Non‑dividing cells, which do not incorporate BrdU, are much less affected, so lysis is selective for newly dividing cells.
Why the other options are not appropriate
(1) MTT treatment followed by UVB irradiation
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MTT is a tetrazolium dye used to measure cell viability/metabolic activity; cells reduce it to formazan crystals for colorimetric assays.
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It is not designed to sensitize DNA or membranes for selective killing, and UVB would damage all cells, not just newly dividing ones.
(2) Treatment with caspase inducers
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Caspase activators trigger apoptosis broadly in cells that receive the signal.
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They generally do not discriminate between recently divided and quiescent cells unless tied to a very specific promoter or signal, which is not indicated here.
(4) Treatment with ⁵¹Cr and measuring its release
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Chromium‑51 is used to label cells (e.g., in cytotoxicity assays) so that lysis can be quantified by released radioactivity.
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It is a readout of cell death, not a method to selectively induce lysis of only newly dividing cells.
Thus, the method that specifically exploits DNA incorporation during S phase to lyse newly dividing cells is BrdU labelling followed by light exposure (option 3).
