Analyze The Data

Researchers have isolated two E-cadherin mutant isoforms that are hypothesized to function differently from that of the wild-type E-cadherin. An E-cadherin negative mammary carcinoma cell line was transfected with the mutant E-cadherin genes A (part a in the figure) and B (part b) (diamonds) and the wild-type E-cadherin gene (black circles) and compared to untransfected cells (open circles) in an aggregation assay. In this assay, cells are first dissociated by trypsin treatment and then allowed to aggregate in solution over a period of minutes. Aggregating cells from mutants A and B are presented in panels a and b respectively. To demonstrate that the observed adhesion was cadherin-mediated, the cells were pretreated with a nonspecific antibody (left panel) or a function-blocking anti-E-cadherin monoclonal antibody (right panel).

a. Why do cells transfected with the wild-type E-cadherin gene have greater aggregation than control, nontransfected cells?

b. From these data, what can be said about the function of mutants A and B?

HAT medium 238 hyaluronan 217 hybridoma 238 immunoglobulin cell-adhesion molecule (IgCAM) 227 integrin 199 laminin 211

monoclonal antibody 237 multiadhesive matrix protein 209 paracellular pathway 208 plasmodesma 233 proteoglycan 209 RGD sequence 221 selectin 199 syndecan 214 tight junction 202

(a) Nonspecific Anti-E-cadherin

c. Why does the addition of the anti-E-cadherin monoclonal antibody, but not the nonspecific antibody, block aggregation?

d. What would happen to the aggregation ability of the cells transfected with the wild-type E-cadherin gene if the assay were performed in media low in Ca2+?

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