The Incredible egg: part 2

Contunued from The Incredile Egg: Part 1

Every cell in your body has the DNA that makes you uniquely you.  Every gene that is need for every cell is in all of them, regardless of the kind of cell.  So what makes heart cells differ from neurons?  Not all cells express the same genes.  So, while a heart cell has the genes to make it function like a neuron, it expresses the genes that make it a heart cell.

Which brings us to some stem cell terminology.  Each stem cell has different genes expressed that make them fall in one of these categories:

Totipotent stem cells can become all cell types in the body, plus other tissue like placenta cells.

Pluripotent stem cells can become most or all of the over 200 cell types in the human body. Embryonic stem cells are pluripotent.

Multipotent stem cells can become multiple cell types. Most adult stem cells are multipotent.

Unipotent stem cells can only become one cell type.   

So, in theory, any cell could become a pluripotent stem cell, if we could figure out which genes need to be expressed. 

So what does this have to do with an egg?  Well, the egg has the magic formula. 

In SCNT, the egg takes DNA from a fully differentiated skin cell and turns on and off the right genes to make it pluripotent again.  Actually, in SCNT the egg makes a totipotent cell (able to make all cell types including a placenta) which means it makes a zygote, a one-celled embryo.  After a weeks growth, the zygote becomes a blastocyst with about 200 cells.  The inner cells mass is then pluripotent and researchers break open the embryo to get to the pluripotent cells inside.

So, as of now, the only way to reprogram one of your unipotent cells back to pluripotency, whether through SCNT or ANT, is to use an egg.  Unfortunately, in doing so, SCNT creates a cloned human embryo in the process.

Women, you feeling at all special yet?

More on the ethical and theological implications of the incredible egg later...