Patterning of Mesenchyme - Secondary Mesenchyme

In order to test the idea that SMCs respond to the animal pole as a specific "target" site, Hardin and McClay (1990) performed several experiments. If the basic "rule" SMCs use is to continue their transient attachment behavior until they strike this target, then we would expect several things. First, allowing them to touch this region earlier than they would normally should cause them to make stable attachments earlier than usual. Second, delaying their contact with this region should delay the dramatic change in their behavior. Fortunately, we can test these ideas by changing the shape of the embryo, as shown above. In each case, the results support the conclusion that physical contact with the animal pole target region induces the change in their behavior. The next page shows pictures of actual embryos on which these experiments have been performed.