Hoechst 33342 is a membrane-permeant dye that fluoresces when it binds to DNA. W

Question

Hoechst 33342 is a membrane-permeant dye that fluoresces when it binds to DNA. When a population

of cells is incubated briefly with Hoechst dye and then sorted in a flow cytometer, the cells display various level

of fluorescence as shown. A flow cytometer measures the DNA fluorescence levels of the cells and plots them

on the X-axis of the graph. You use this technique to measure the DNA content of three samples: a cell

preparation from a mouse testis with all the testis cell types, isolated cells arrested in prophase, and a

mammalian cell culture of normally growing cells. Unfortunately you forgot to label the tubes. Explain which

of the three FACS profiles below is most likely to correspond to each of the three samples?

I know the diagram is a little rough but im sure you get the idea... im really stuck on this one

Explanation / Answer

The mouse testis has many cell types so we can safely say that sample I corresponds to the mouse testis. The testis contains germ cells, sertoli cells and leydig cells corresponding to the 3 peaks in the first graph. The second graph belongs to the cells arrested in prophase. as the DNA is doubled in prophase, there will be two equal peaks, which is seen in sample II. the third graph belongs to the mammalian cell culture. as cell culture is always made up of one type of cell, the sample III corresponds to mammalian cell culture.

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