Cells detect subtle guidance

[See ref 5 ]

Guidance is not chemical in nature

It has been known for decades that scratches or ridges on a surface cause cells to line up alongside and follow them. Any surface material can guide cells. No special chemicals are required. In fact, glass, plastic, gold and other typical surface materials are chemically completely inert. The cells cannot have specific receptors for such materials on their surface. Also, it is not necessary for such guiding lines to be chemically different from the rest of the surface. Besides, the necessary serum in the fluid medium around the cells instantly coats all surfaces with proteins. So, all surfaces are practically made of serum proteins. Yet, the cells detect the presence of guiding lines.

Cells are not forced mechanically to accept guidance

Are these guiding lines mechanical obstacles that force the cells to move in certain directions?.In order to answer this question I put cells on a glass surface which was very thinly coated with gold. Then I wiped scratces into the gold film exposing the glass underneath. Cells like to walk on glass and gold alike. Furthermore, the gold was much thinner (300 A) than the thickness of a cell (30,000 -60,000 A). In other word there was not much of a step height between the glass and the gold surfaces. Yet, as shown by the straightness of the track below, the cells were guided quite well by these very subtle guiding lines.

(The illustration is animated.Click here for a minimal strip of frames.)
Looking at the same cell in phase contrast microscopy advance along the track as shown in the sequence below, shows that the cell was by no means confined to the glass-'road' it followed. Many times it extended its body well into the gold surface. Eventually, it walked out at a point where the 'road' was no different than anyplace else. In short, the cells was certainly not forced into the guiding line. Following it,therefore, meant that it detected and followed clues, not forces.

(The illustration is animated.Click here for a minimal strip of frames.)

Significance for cell intelligence:

Cells process clues from the surroundings and can re-program a new heading.
Most startling, however, is the unknown nature of these clues. In order to follow a line the cell must detect and process the signals from at least 2 points on the line. The signals cannot be chemical in nature. Thus, the cells seem to be able to process spatial data. Subsequently, they override their earlier movement program and follow the guidance. The term 'follow' can be applied only in a global sense. Locally speaking, the cells move in and out of guiding roads at will. In other words, their long term movement has been re-programmed for a new heading while their minute-to-minute movements seem to remain quite free.