Amazing Cell Tricks: Contour Map Navigation

Watch a cell divide, and if things go well, it always divides in the middle.  How does a cell figure out where its middle is?  It follows its contour map.  PhysOrg titled its entry, “Dividing cells find their middle by following a protein ‘contour map’.”
    Cell division, or cytokinesis, is a precisely-controlled operation that is vital to all of life (see 12/28/2007).  Each molecule in the cell has to know its proper position during each stage, and how to get there.  For some molecules, crossing a cell is like navigating a countryside over a long distance.  Human navigators, we know, need a topo map printed out or software or GPS.  They also have to know where they are trying to go, and have sensory equipment (eyes, kinesthetic sense) to gauge contour lines on a hill or valley.  How can a cell pull off this feat?  They use periodically-placed signaling molecules that act like beacons.
    The team measured all over the cell the positions of important sensory molecules involved in cell division.  They detected a gradient – like the slope of a hill – that was greatest at the center, where the site of cleavage must be located.  The proteins and enzymes that create the cleavage furrow are thus able to sense the contours and arrive at the right spot to begin cleaving the cell in two.

Wonderful stuff, that molecules are so precisely choreographed that they can arrive in formation like band players on a football field.  The explanation was duly marvelous, but… it seems to beg the question.  What tells the signalling molecules where to go and where the center is?  If Dan found the mountaintop because Bob hollered to him from the summit, how did Bob find it?  Clearly more is going on than scientists have thus far been able to figure out.