11-07 - BIO 5099 Molecular Biology for Computer...

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BIO 5099: Molecular Biology for Computer Scientists (et al) Lecture 21: More developmental biology http://compbio.uchsc.edu/hunter/bio5099 [email protected] How long does the human cleavage phase last? Question from last week about the timing of developmental stages in humans First cell division is about 24 hours after fertilization. Compaction to form blastocyst at about day 4; implantation Gastrulation begins about day 14 and takes about a week A few more items about mammalian cleavage Not only are cleavage divisions relatively slow (12-24 hours each), but there are several other differences in mammalian cleavage Rotational orientation of cleavage planes Asynchronous division of blastomeres (odd cell counts) Switch from maternal to genomic control of gene expression happens much earlier At 8/16 cell phase, compaction happens, where half of the cells separate from the other half, forming a chorion, the embryonic part of the placenta.
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Maternal gradients Axis formation in drosophila depends on maternal gradients (not just a/p, but also dorsal/ventral and probably lateral, too). Nurse cells surrounding the unfertilized egg (oocyte) in the ovary export mRNA and ribosomes into the egg. The pattern of nurse cells around the egg is asymmetric, making gradients possible. Morphogenesis Cellular differentiation is only part of embryogenesis. How do cells get organized into complexly structured organs? How do cells segregate by type to make tissues? How are tissues ordered into organs? How are organs spatially arranged? How do cells know where to go, how to get there, and when to stop? Much of the answer is due to differential affinity among cells . Cells can recognize their neighbors, and most importantly, adhere to them. Cell Adhesion Differential ability to adhere to other cells is the mechanism by which cells segregate. A thermodynamic model minimizing interfacial free energy
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11-07 - BIO 5099 Molecular Biology for Computer...

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