You are studying a cell line that responds to a peptide ligand called Fge1 by ac

Question

You are studying a cell line that responds to a peptide ligand called Fge1 by

activating a MAP kinase pathway. In these cells, activation of the MAP kinase

pathway ultimately leads to phosphorylation of a transcription factor, Goh1, and

the transcription of several genes, including the Suf1 gene. You treat cells with

Fge1 and measure Suf1 mRNA production and are very excited to see that cells

seem to respond to Fge1 in a graded fashion such that an increasing concentration

of Fge1 seems to increase Suf1 mRNA production, as illustrated in Figure 1.

You also raise an antibody that specifically recognizes the phosphorylated form of

Goh1. Using this antibody for immunofluorescence studies, you examine the

phosphorylation state of Goh1 in cells that have been treated with varying

concentrations of Fge1. You see that cells seem to either stain with the antibody

or not, with no difference in the intensity of staining between the cells that stain.

Furthermore, the percentage of cells that stain seems to vary with Fge1

concentration, as seen in Table 1.

Are your immunofluorescence results more consistent with the possibility that

phosphorylated Goh1 increases progressively in individual cells as the

concentration of Fge1 increases, or are they more consistent with the possibility

that individual cells respond in an all-or-nothing fashion? Propose an explanation

for how cells respond to Fge1 that is consistent with both your observations.

URL to figure.table

http://tinypic.com/r/29o4js5/9

Explanation / Answer

The individual cells respond in an all-or-nothing fashion. Once Goh1 is phosphorylated, it will start the transcription of Suf1 gene. So, more is the Fge1 , more is Suf1 in the cells.

Anti-Phospho Goh1 antibody stains phosphorylated Goh1 cells and intensity of staining in cells is same. This means that the number of phosphorylated Goh1 transcription factors in all cells is same.

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