Geraldine Seydoux talked about how embryos determine body axis. She used the C.elegans as the model organism. Newly fertilized cell has two pronuclei -maternal and paternal – that fuse to one nucleus and cell division ensues to create a ball of cells. At one point the cell becomes asymmetrical – the smaller cell always ends up on the side of the posterior side and bigger cell on anterior side. But this had to be proven and linked to the adult cell. This research is shown by John Sulston who traced cell lineage of C.elegans and found that posterior side ended up being represented by the smaller cell. To dig in deeper – Professor Seydoux showed the gonads of the C.elegans (hermaphrodites) – oocytes had the maternal pronucleus and the sperms had the paternal – sperm fertilized the oocyte and the smaller cell ended up being at the posterior side, so the hypotheses were 1) the sperm determined the posterior side 2) that the oocyte directed the axis determination. They tested the first hypothesis: sperm induces posterior? They changed the position of sperm entry and the result was that that the embryo polarity was reversed. How did this work? They looked at the molecules involved in the oocyte cytoplasm. Genetic screening of wild types and mutants with symmetric cells and cloning those cells allowed them to identify the protein and their genes.
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