CM THEORY SEMINAR<br>On the Nature of Shape in Biology: From Cerebral Cortex Folding to Cell Crawling

The cerebral cortex of the brain, the outer grey matter, eventually develops folds to presumably enhance its surface area. Scientists have proposed two different physical mechanisms for generating such folds, an axon-pulling mechanism and a buckling-due-to-growth mechanism. Which of these two mechanisms is more relevant for determining the shape of the brain?  Cells typically assume a fan-like shape when crawling along a prepared surface but can assume an elongated shape when crawling in the more native three-dimensional fibrous environment known as the extracellular matrix. What physical mechanisms for cell crawling persist (and do not persist) when going from two dimensions to three dimensions to drive the cellular shape change?

Finally, the shape of a cell membrane in mammalian cells during endocytosis (the process by cells engulf external molecules to "eat" them) is typically spherical, while in yeast cells it is typically tubular.  What is the reason behind this difference in shape? Given my background as a condensed matter theorist, I will present simple, yet insightful models, that begin to answer the above questions.