Additional Class Notes for November 9th This class was mostly a continuation of the discussion of regulative and mosaic development, begun on October 21. All citations are strictly optional reading, not required. The class began with some photographs from a special issue of The International Journal of Developmental Biology, Volume 50, numbers 2/3, published in 2006, specifically the following paper: Beloussov, Lev (2006). An interview with Albert Harris. Direct physical formation of anatomical structures by cell traction forces. Int. J. Dev. Biol. 50: 93-101. Unfortunately this journal isn't available in the UNC library. Duke has it, but we were unable to access it from home. If anyone is interested in reading this article, we will be happy to send you a pdf file. More on Regulative vs. Mosaic Development Some insects have regulative development, but Drosophila, the most frequently used insect model organism, does not. The nematode Caenorhabditis elegans is the classic example of mosaic development. Yet people continue to use these model organisms to study patterns of embryonic development. "When confronted with a problem you can't explain, choose an organism that doesn't have it." Hans Meinhardt proposed a mathematical model for generating patterns in embryos. Richard Gordon and Lev Beloussov published an interview with him in the same journal issue cited above. The title is "From observations to paradigms; the importance of theories and models." It includes a photograph of Meinhardt with Lewis Wolpert, who has been mentioned several times in this course, and Jonathan Cooke, whose work is mentioned at the beginning of the notes on pattern formation. There was also a discussion of embryonic induction experiments by Hans Spemann, and by Johannes Holtfreter. For more on this (optional, not required reading), see these notes from Biology 441. Scroll down to "Experimental Embryology with Amphibians". Discher et al. reported that cells can differentiate in response to stiffness of the material they are cultured on. link to this paper. Planaria (flatworms) have regulation that is comparable to Driesch's sea urchin embryos separated at the 4-cell stage. Some other figures were also shown.