bis_104_pq_12_ans_spring_08 - was observed When...

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BIS 104 Practice Question #12 12. When PECAM-1 positive / EphrinB2 negative undifferentiated ECs were treated with 2.5 pM pure VEGF protein, approximately 50% of the ECs responded by differentiating (they began expressing EphrinB2). His treatment with VEGF did not lead to any net change in the total number of ECs. What may be concluded from these results? CONCLUSION: The differentiation of ECs following exposure to VEGF is a true inductive process mediated by the ligand. It is not achieved by VEGF mediated stimulation of clonal expansion of a previously existing EC subpopulation. (i.e., no net increase in EC cells number
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Unformatted text preview: was observed) When undifferentiated ECs were treated with higher concentrations of VEGF (25 and 250 pM) under the same conditions as above, there was no further increase in the number of EphrinB2 positive cells beyond that achieved with 2.5 pM VEGF. What is a possible explanation for this result? Low levels of VEGF were sufficient to saturate all existing VEGF receptors on responding ECs. The remaining 40 - 50% of non-responding ECs may lack functional receptors for VEGF, so no matter how much VEGF is added they will never respond....
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