Expert: Dana Krempels, Ph.D. - 12/4/2009

Question
Good Evening :-)  
I am trying to understand the general principle of somatic stem cell transfer.  I understand this was the method used to clone 'Dolly' the sheep.  I think I understand that nucleic material is put into an enucleated oocyte #?#. But assuming this method was used to produce human tissue;
1) where would the oocyte come from?  
b) would the DNA come from the person requiring the tissue? and..
c) Assuming the cell 'takes' the nucleic material how does it know what type of cell to differentiate into and proliferate?

I'm quite confused but would welcome any feedback.  This is a great site!.  Thank you kindly in anticipation.

With regards.

Answer
Dear Cher,

Yes, somatic stem cell transfer involves the insertion of a donor cell nucleus into an enucleated oocyte (which has cellular components necessary for proliferation of the cell, once it has a nucleus, though the many processes involved are not completely understood, nor are they reliably "harnessed" yet).

1) where would the oocyte come from?  

In most cases, from a member of the same species as the nucleus donor.  If that's not possible, then as closely related a species as possible, to avoid cytoplasm/nucleus incompatibility problems.

b) would the DNA come from the person requiring the tissue? and..

Yes.

c) Assuming the cell 'takes' the nucleic material how does it know what type of cell to differentiate into and proliferate?

This is one of the great mysteries of cloning, and it is not fully understood.  For every successful mammal clone that makes it to birth, thousands are aborted or never fully form.  But the main idea is for the nucleus of the stem cell to behave as if it were a zygote nucleus, and to start the cell dividing "from scratch", activating the proper genes for embryo development and morphogenesis.

The exact mechanisms of this activation are still under study, and more is known every day.

Hope this helps.

Dana