The next topic for Unsolved Problems:

H. V. Wilson discovered that sponge cells can re-aggregate after totally random rearrangement. Researchers have spent a century trying to figure out what is means!

Please take a look at each of the following papers, and decide which one you are most interested in reporting to the class about (as part of a group of 2 or 3 students per scientific paper).


(I)   TAKEN by Birgel, Noone and Anuma

Jeremy Green, "Sophistications of cell sorting," Nature Cell Biology 10, 375 - 377 (2008)

This is a short review paper about new developments and histories of some old arguments about what force causes randomly dissociated cells to sort out: the phenomenon discovered by H.V. Wilson at UNC


(II)   TAKEN by Wheeler and Oliver

Krieg et al., Tensile forces govern germ-layer organization in zebrafish, Nature Cell Biology 10, 429-436 (2008)

A review & research paper that takes sides in the dispute about what force causes cell sorting.


(III)   TAKEN by Patel and Burkholz

Discher et al., "Tissue Cells Feel and Respond to the Stiffness of Their Substrate," Science 310, 1139-1143 (2005)

Do cell forces control cell differentiation, in addition to the reverse?



(This is the single greatest paper ever written about cell sorting.

Nine years of research by Johannes Holtfreter and an MD/PhD student, Journal of Experimental Zoology 128 (2005)

It is long (67 pages); but you don't need to report on every detail.



Stopak and Harris, Connective tissue morphogenesis by fibroblast traction: I. Tissue culture observations, Developmental Biology 90, 383-398 (1982) David Stopak took this course! Then did wonderful research.

Are muscles and tendons created by cell traction forces? How can it be proved conclusively whether David and I proposed the correct explanation? We need to know.



Only one student is needed to report on this web site. The most interesting aspect is what they have failed to understand. They do make an honest effort, which should be respected.


(VII) "A video tour of cell motility"   TAKEN by Desai and Chuang

Note, although this is not a research paper, but a web site, it is a good subject for a course report. It has lots of beautiful movies, plus Prof. Vic Small's ideas about how cell movement is related to changes in geometric arrangement of cytoplasmic proteins.


(VIII)   TAKEN by Cremer

Another web page, about science&politics&money&ego & tensegrity, not to be confused with INtegrity.



Let's experiment with one student making an oral report on a professor's youtube report.

Please also comment on the comments people made, linked to this youtube video.



"Sorting out of normal and virus-transformed cells in cellular aggregates"

Howard Gershman's wonderful paper in Journal of Cell Biology 1976, Volume 68, pages 276-286. What change in properties of cancer cells causes them to sort out from normal cells, to an exterior position? Is it because they are less adhesive or is their contractility weaker? It could be really important to know which? Or both!


(XI)  TAKEN by KulA and Yang

Vasioukhin et al. (2000) Directed Actin Polymerization Is the Driving Force for Epithelial Cell-Cell Adhesion. Cell Volume 100, Issue 2, 21 January 2000, Pages 209-219

If you report on this paper, please consider the possibility that what they thought were filopodia were really previously-existing "retraction fibers" (hollow tubes of membrane and cytoplasm that had been left behind when cells retracted away from each other because of low calcium concentrations) and when these re-inflated with cytoplasm they became big enough for their microscopes to resolve, and were misinterpreted as protrusions. Is it a blooper? Or did they correctly understand what they were seeing?

Either way, such protrusion could sometimes happen:

Hurtley, Science 287 (5454), 769


(XII)  TAKEN by Min and Fan

"Cell Movement Is Guided by the Rigidity of the Substrate", as of July 2000. Lo et al. Biophysical Journal Volume 79, Issue 1, July 2000, Pages 144-152

Now called "durotaxis," nobody yet knows how the locations and directions of stiffness in a sheet of material causes cells to orient and move preferentially from less still to more stiff locations.

This could be an extremely important phenomenon; for example one scientist has proposed a positive feedback cycle in which stiffness in the walls of arteries attracts more cells, etc. causing hardening of the arteries. Several more papers on this subject can be quickly found.


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