Writing about the topic of stem cells is like walking through a minefield with a blindfold on after being spun around thirty times. So, before I continue on, I must emphasize my sincerest apologies to anyone I might offend beforehand, and assure readers that I believe human life to be sacred. That being said, continue reading at your own risk.
Firstly I would like to express my immeasurable excitement and enthusiasm from having read articles like this one: http://m.usatoday.com/article/news/2123881 ; or this one: http://www.frc.org/insight/adult-stem-cell-sucess-stories-2008-jan-june. These kinds of stories are unquestionably revolutionary. These people had vital tissues they needed to survive grown from their very own stem cells; no use of ethically questionable embryonic stem cells required. Adult stem cells are even being used in more recent trials to grow entire organs: livers, kidneys, pancreas’, etc. The kinds of possibilities being opened up by the use of adult stem cells is no doubt one of the cutting edge treatments of medicine.
Some might be wondering just what exactly an adult stem cell is since so much media attention is focused mostly, if not entirely, on the controversial use of embryonic stem cells. I sometimes wonder myself on whether it is a widespread misconception that embryonic stem cells are the only kinds of stem cells. To clear the air, allow me to give readers a quick biology lesson.
Stem cells are cells that can be programmed into reproducing into a variety of different, specialized cell types. Basically, stem cells are “blank slates” that can grow into many different types of tissue. The way stem cells differentiate themselves and assume what particular tissue or organ they are supposed to become is determined by the stem cell’s position relative to other, already existing tissues. A stem cell’s unique position can influence its initial differentiation based on the nearby obstructions, and also receive certain chemical signals from neighboring developed cells so the stem cell itself can determine its current location within the organism. For example, a stem cell that has the capacity to differentiate and develop into a trachea will only do so after it has been oriented anteriorly (in front of) an esophagus (or esophagus like structure) and after it has received chemical messages from nearby already developed cells, such as cells of the voicebox or the larynx. The DNA of the stem cell is programmed to begin a particular line of reproduction and development only after ingesting the correlating chemical signal from neighboring cells. As another example, placing stem cells at the end of lung capillaries will induce the stem cells to grow into bronchioles. The stem cells have “figured” out where they are and act accordingly. Fetal and embryonic development follows a very similar mechanism of growth. As the embryo begins to divide, grow, and cleave, a large array of preset chemical messengers within the original cell disperse in the relative directions that their correlating tissue will be in some later stage of embryonic growth. To illustrate, chemical signals that induce stem cells to grow into feet and leg muscles will be concentrated towards the bottom end of the first embryonic cell. As the embryo grows, the intra-cellular chemical signals begin to separate and disperse further and further, taking their place for when stem cells are to begin growing in their (the chemical signaling molecules’) direction.
TLDR: Stem cells figure out what kind of tissue to grow into by determining the surrounding structures. Stem cells placed near a brain will not spontaneously grow into a leg. They know they are near the brain.
The problem with adult stem cells is that they are not capable of differentiating into every kind of tissue in the body. They have a much smaller range of possible differentiation options than embryonic stem cells. Fortunately, most tissues in the body are being proven to have small stores of “specialized stem cells”: bone marrow can differentiate into blood vessels, blood, and some transport organs/tissues. Skin stem cells can be used to grow epidermal tissue, sebaceous and sweat glands, as well as hair follicles. Hematopoietic, mammary, intestinal, mesenchymal, olfactory, and testicular adult stem cells have been discovered so far, each kind with the capacity to regenerate their correlating nearby tissues. Two big sets of important kinds of tissue are not in this list: muscular and neural. Hence, then, why embryonic stem cell research is often conjoined with aiding paraplegic treatment or those with other kinds of neural disorders.
Embryonic stem cells are, to date, the only kind of stem cells that can effectively grow into functional neural and muscular tissue. These two tissues lack any known sufficient reservoir of system-specific stem cells, and have not been found to appreciably regenerate on their own. It is this characteristic of embryonic stem cells that has made them so readily used by scientists and researchers who some citizens would dub as unethical and immoral. It is this characteristic that, once again, brings into question where the arbitrary line of when human life begins.
There is some good news. Small amounts of neural stem cells have been found in both rats and humans. One set of neural stem cells is responsible for neurogenesis: the process of new neuron generation in the hippocampus, the brain structure related to memory function. It is not conclusive as to the differentiating potential of these neural stem cells, as these cells do not act as stem cells when transplanted back into the brain, but this may not be a dead end. Neural crest cells that are remnants of the embryonic neural crest have been found in hair follicles, showing the capacity to differentiate into key neural tissues such as neurons, Schwann cells, myofibroblasts (technically muscular tissue), chondrocytes (technically cartilage), and melanocytes (melanin producing cells in the skin). The latter three cell types are not neural tissue, but are often associated with and usually in direct contact with neural tissue. Bearing in mind that the first tissues to develop in an embryo are muscular and neural, remnant neural stem cells from the embryonic stage of the adult in question will have a very wide variety of potential neural/muscular cell types that they can differentiate into. Still even more hopeful are testicular stem cells. These stem cells are the only adult human stem cells to date which show promise of regenerating and developing into muscular tissue.
For female muscular tissue in particular, however, there remains little option for muscular stem cell treatment outside of using embryonic stem cells. Astrocytes, an important ganglia cell type of males and females, also remain (to my knowledge) without any known predeceasing adult stem cell. Unless there are discoveries of stem cell types that can differentiate into the above kinds of tissue, the embryonic stem cell controversy may very well be here to stay.
(Note that, in this video, female olfactory stem cells were cultured into neural cells. In this case it worked for her, but olfactory stem cells used to culture neural cells is not yet an absolute avenue of treatment for all women suffering neural damage. Let’s just hope this woman’s case is not the last.)
Earlier in the article I mentioned the boundary line of where human life begins as being arbitrary. Let there be no negative connotation to the word “arbitrary”. It merely means that the boundary line is drawn by us, the people, and then cemented into law.
My personal opinion on the matter is, I warn you, a rather liberal outtake. The more and more I understand of the fields of biology and biochemistry, the more I realize that nature has not set this boundary line so clearly for us. For some, fertilization is the point of no return that makes the most sense. For others, me included, fertilization means the DNA of the male and the female reproductive cells have begun merging. I know better than to try to convince myself a fertilized egg is suddenly equivalent to human life. A fertilized egg is just a non-sentient human cell, like a skin cell or a blood cell. Sure, it has all the precursors to lead up to an undeniably human fetus, but so do sperm cells and egg cells. Both sperm cells and egg cells die off all the time. Like crazy, really. For fertilization/conception to even take place, sperm cells have to cross an obstacle course of chemical and pH deterrents in the female reproductive tract; in order to make life, life has to die by the millions! Plus, it takes about two weeks for any hopefuls to actually reach the final destination. So, as a fun side note, remember that you were the only one that could cross the long, arduous traverse. Even though the sperm cell itself really has little to do with the DNA inside…uh, carrying on…
Personally, I place the starting point of human life at the point the embryo develops a functioning nervous system (usually about five weeks after intercourse, and three weeks after fertilization), even to a very small degree: at this point it can both feel and react to what it feels, and the basic mechanisms from which human conscience and sentience are derived begin to take place.
When it comes to law, I also know better. I know that different individuals will feel that the line is best drawn at different points, and that one should trust one’s own heart on the matter rather than what some liberal scientist or right-wing nut tells you. Human life really shouldn’t be defined by anyone else but you anyways. It is giving someone else a lot of power to define the limits of morality by entrusting the very definition of human life into their hands. In my opinion (I emphasize this, as I’m sure there will be those who disagree), it is also dangerous to trust someone else’s interpretation of God’s will on the matter: that is also an awful lot of power of the definition of morality to be handing over to someone else. God will speak to you and you alone on the matter, let nobody else drown that out with their own ideas. As previously stated, this is all just my opinion.
All in all, since the point where human life begins is something we all consider inescapably important yet differ in opinion towards its placement, and given the implications of morality being determined by politicians, I’ve always been politically Pro-Choice on the matter. In day-to-day practice and feelings, I’m very Pro-Life. I’d rather pursue the investigation of alternative stem cell sources from an adult body than to jade my worldview by pushing the limits and regularly using cloned embryonic stem cells.
Besides, who knows, that discarded cloned embryo might have had a mutation or genetic discrepancy that set it apart from its “donor”. Cloning is not exactly perfect 100% of the time, after all. I’ll let the reader extrapolate from here.