Before revision:  In some circumstances, two species of motors that are directed oppositely (e.g. kinesin, dynein) can be attached to the same cargo . The resulting net motion is known to be bidirectional , but the mechanism of switching remains unclear.
After revision:  In some circumstances, two species of motors that are directed oppositely (e.g. kinesin, dynein) can be attached to the same cargo , which is known to be bidirectional , but the mechanism of switching remains unclear.