A LEARNED ESSAY ON STEM CELLS

Daughters Karen and Kristen will re-visit this country with me next month

Sure wish this lady could be with us

 I have mentioned stem cells 47 times in this blog.  It is time to determine if I really know what they are and what they do.  (The smart money is on:  probably not.)  I am going to write this “learned essay” off the top of my head; not even Wikipedia will be involved.  I expect biologically sophisticated readers (e.g., daughter Kristen Beck, niece Rebecca Hunsinger, great friend and benefactor Dr. Joanne Ingwall, paleontology colleague and occasional social critic Dr. Sharron Sussman) to comment, correct, and even chastise, if appropriate.  Failing that I will continue to muddy the waters and roll science back on its haunches – and it will be your fault, not mine.

So, what’nhell is a stem cell?  Well, it is an “undifferentiated” cell that has the capacity to turn into one or more types of specialized cells – liver, muscle, skin, etc.  You read a lot about “embryonic stem cells”.  These little buggers are derived from embryos, natch, and seem to occupy a realm of constant warfare between science and (some flavors of) religion.  This is because they have the capacity to develop into a whole and complete human being.  (There also are murine embryonic stem cells, but nobody worries much about the immortal souls of mice.  Other mammals have ESCs too, of course.)  As I understand it, there are two kinds of ESCs: “omnipotent ESCs, which can give rise to an embryo plus a placenta to nourish it, and “pluripotent ESCs” which can’t do the placenta thing.  I am far from certain about this, but it doesn’t’ matter anyway.  The overriding problem is that there are lots and lots of well-meaning, intelligent people who regard using ESCs in experiments as murder.  I see their point, but disregard it.

Question:  Is a human zygote also an omnipotent ESC? 

There also exist many other kinds of less “potent” stem cells.  These are specialized stem cells (SSC) which can turn into only a single type of cell: liver, say, or blood, muscle, etc.  Actually, they don’t “turn into” anything; rather, they divide, with one daughter being the specialized, working cell in question and the other an exact (it is hoped) copy of the original SSC.  In this way the SSC is essentially immortal and hangs around doing its thing indefinitely.

Question:  I had always thought that ordinary somatic cells divide to replenish its organ.  For instance, if an old liver cell with tattered telomeres received orders (from where?) to croak, its near neighbor, another somatic liver cell, would receive orders to divide, thereby filling the gap.  That must be wrong, right?

Question:  Cancer is said to result from unlucky mutations or groups of such mutations.  Does this mean that the SSC itself is mutated, or its sister the specialized cell?  Or both?

So, I am vaguely aware that it has proved possible to take an SSC and, using almost magical biological sleight of hand, induce it to climb back up the developmental ladder and become equivalent to am ESC.  They call these things iESCs, which codes for “induced embryonic stem cells”, although maybe they should be called induced pluripotent stem cells (iPSC) because they have little to nothing to do with embryos. 

An aside:  If iPSCs are ever used to generate a human being – in effect, a human clone - expect all hell to break loose.

OK, I think that’s all I know about stem cells.  You are to be praised if you read this far.  Thank you.  BUT WAIT:

Overriding big picture question.  When, for instance, a liver SSC divides to make a functional liver cell and a duplicate of itself, if mitosis does its job correctly both daughter cells have identical DNA – although they have profoundly different roles to play.  The difference must be epigenetic. Different genes are silenced in the two sibling cells.  What in Heaven’s name controls this?