Central Enigma – Embryology

by John McLachlan, PhD

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    00:01 So there are three components to the central enigma. The first is the cells will increase in number from one cell to billions of cell. Now cell division is extremely important particularly if you are studying cancer, but it is largely outside the scope of these lectures on embryology. And then cells will increase in kind. They go from one kind of cell, the fertilized egg to many kinds of cells.

    00:27 It rather depends on how you counted, but there are probably hundreds of different cell types and these cell types are then divided into subtypes. So looking at a very wide range of sorts of cells or kinds of cells which arise during the course of development.

    00:46 So obviously one of our key questions is how do those cells become different from each other? But that is not the only question. There is another question about how cells become arranged in space with respect to each other. So your arm and leg are recognizably different and yet they are made of very much the same kinds of cells just arranged differently with respect to each other, they are deployed with respect to each other.

    01:15 So that is another thing they were going to have to solve in another part of the central enigma that we are going to have to address. Now you might be thinking that the answer is DNA and it is certainly true that DNA is absolutely essential to developmental processes and I am not suggesting it is not. But there is something you should think about which is the fact that the DNA in all of your cells is identical and therefore when cells become different from each other, those differences cannot arise from the DNA. They reflect different patterns of DNA expression, but something has to make different parts of the DNA switch on or switch off at particular times. So there must be some other kind of information signal that is coming into the genome to allow it to specialize in particular ways. And the best evidence for this is Dolly, the sheep, the first cloned organism. And what happened with Dolly was that the scientists involved took a nucleus from a differentiated cell that was, in fact, mammary gland cell and they showed that DNA could turn into all of the different kinds of DNA in an adult sheep. Now once there was no irreversible specialization have taken place in the DNA at all, the best estimate is that any DNA from any of your cells is capable of giving rise to a complete organism, the DNA itself is not specialized.

    About the Lecture

    The lecture Central Enigma – Embryology by John McLachlan, PhD is from the course Embryology: Early Stages with John McLachlan.

    Author of lecture Central Enigma – Embryology

     John McLachlan, PhD

    John McLachlan, PhD

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