Totipotent cell count in human zygotes
Category: Science > Biology
Asked by: silentbobdude-ga
List Price: $5.00
15 Jan 2006 21:47 PST
Expires: 14 Feb 2006 21:47 PST
Question ID: 433849
In human development, how many totipotent cells are created in the zygote? What is the inhibiting agent that prevents the other totipotent cells from becoming complete human beings? (i.e. why is the earth NOT full of conjoined twins)? When performing embryo cryopreservation, how many cells does the embryo consist of?
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Re: Totipotent cell count in human zygotes
From: pforcelli-ga on 16 Jan 2006 09:49 PST
This is somewhat of a tricky question. At approximately the 16 cell stage there is a differentiation event, in which some cells are directed to become the trophectoderm which produces the chorion and the cells of the inner cell mass which will give rise to the embryo. This is the first differentiation event. So, at this point, no cells are left totipotent. However the ICM cells are pluripotent and able to form ever cell in the body. the ICM consists of approximately 13 cells by the 64 cell stage. The cells in the ICM move down differentiation pathways guided by Notch/Wnt/Frz/Oct signaling which serves to inhibit and excite certain characteristics in neighboring cells. This sort of lateral inhibition is common in differentiation. If memory serves embryo cryopreservation typically occurs 1-3 days after fertilization so you'd be looking at maybe 4-8 cells. I'm not an embryologist, so thats the best I can do. Good Luck. PForcelli.
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