APC is a tumor suppressor and acts in the Wnt signaling pathway to prevent the TCF complex from turning on Wnt-responsive genes
Mice that lack the gene encoding TCF4 do not have the ability to maintain the pool of proliferating gut stem cells needed to renew the gut lining. What do you predict will happen in mice that lack the APC gene?
(a) Mice lacking the APC gene will be like the mice lacking TCF4 and not be able to renew the gut lining.
(b) Mice lacking the APC gene will have inappropriate proliferation of gut stem cells.
(c) Mice lacking the APC gene will have a hyperactive Wnt receptor even though there is no Wnt signal.
(d) Mice lacking the APC gene will be like normal healthy mice, since APC is a tumor suppressor and thus not needed unless there is a tumor present.
Choice (b) is correct. Mice lacking the APC gene have a phenotype that is the opposite to what is seen in mice lacking TCF4, since APC inhibits TCF [choice (a)]. APC acts downstream of the Wnt signal and should not affect the Wnt receptor [choice (c)]. Tumor suppressor genes are genes that can cause tumors when both copies are inactivated in a diploid cell; these tumor suppressor genes typically have other normal functions in the cell [choice (d)].
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