You are investigating the activity of different cadherins in cells. You use recombinant DNA technology to express GFP-E-cadherin (green) in some L-cells (which do not normally contain cadherin) and YFP-P-cadherin (yellow) in other L-cells
Explain results you expect in three cultures containing: (1) only cells expressing GFP-E-cadherin, (2) only cells expressing YFP-P-cadherin, and (3) a mixture of GFP-E-cadherin-expressing and YFP-P-cadherin-expressing cells. Also predict how (a) knocking down the ability of the cells to synthesize fibronectin (FN) or (b) adding EGTA, which depletes free Ca2+ concentration in the culture medium, might affect the results.
What will be an ideal response?
Answer:
1) The GFP-E-cadherin-expressing cells would form adherens junctions (labeled green) with one or more cells, possibly forming a sheet of cells.
2) The YFP-E-cadherin-expressing cells would form adherens junctions (labeled yellow) with one or more cells, possibly forming a sheet of cells.
3) Both cell types would form adherens junctions but only with cells expressing the same type of cadherin, because cadherin extracellular interactions are cadherin-type specific.
a) Cells expressing either labeled cadherin would be expected to form adherens junctions regardless of whether they can synthesize FN or not, but they may not adhere and spread on the substrate as well without FN.
b) Medium lacking Ca2+ will not support the formation of cadherin-dependent adherens junctions, because cadherin–cadherin interaction depends on the presence of extracellular Ca2+.
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