Lecture notes for October 14 and 16



Accumulation of cells in a specific place can be either by selective adhesiveness ("haptotaxis") or by chemotaxis.

Scientists tend to think of chemotaxis as ONE mechanism, But bacterial chemotaxis is by an increase in random turning when the attractant concentration decreases.

Leucocyte & Dictyostelium chemotaxis is by turning of locomotion toward the side where there is a higher concentration of attractant.



Two mechanisms of chemotaxis


Two videos of computer simulations of mechanisms of chemotaxis, with narration.

    first video: demonstration of behavioral rules that can produce the effects of chemotaxis

    second video: user's choice of different rules


Chemotaxis of a chick dorsal root axon toward a pipette containing nerve growth factor;
based on a classic paper by Gundersen and Barrett, 1979



Unanswered questions about artery and vein geometry Guidance of "GROWING" ends of capillaries:

Does it work by chemotaxis? Which kind of chemotaxis?

Do we mean the kind in which the crawling ("growing") tip of a capillary turns toward whichever direction has the higher concentration of the attractant substance? I suspect that is what most biologists assume is meant.

A different version of chemotaxis works by cells extending along straight lines when the attractant concentration is increasing, butthen changing direction (randomly) whenever the attractant concentration decreases

Capillary diameter control mechanism(s); and flow rates

Arteries and veins, diameter

Richard Thoma "Histomechanical Laws"
German, late 1800s; paper published in 1901, Optimum branching angles of arteries

Also see the optional reading on arterial branching


The class on October 16 started with two videos on chemotaxis in Dictyostelium, from John Tyler Bonner. On October 19th, another video was shown of a Dictyostelium cell responding to a pipette containing the chemoattractant cyclic AMP. These aren't my videos, but you can find similar ones by searching for "Dictyostelium chemotaxis" on the web.

Optional reading: review article on axon guidance