a little slice

An analysis of the following: stem cells and gametogenesis.

For those of you unfamiliar with the world of biology- gametogenesis is the process by which haploid or diploid cells develop into mature gametes. Two familiar forms of gametogeneis in humans are spermatogenesis and oogenesis. Spermatogenesis occurs throughout life in the post-pubertal male. Oogenesis- is less understood. The declaration by Zuckerman et al. in 1951, that the number oocytes in the mature mammalian female is finite after birth, remained unquestioned until about 2004. Many articles have been published about the possibility of progenitor oocyte cells existing in the postnatal mammalian female. However, this information is still inconclusive (A general overview of the status circa 2004 of germline oocytes can be found here).

There are many pitfalls to this system of germ cell generation. Primarly, women undergoing radiation treatments or chemotherapy are at a tremendous risk of harming their germcells- putting their future progeny at risk of significant birth defects. Males suffer the same consequences, however, as spermatogenesis occurs throughout adulthood- it is possible to intercept undamaged sperm for the purposes of reproduction. You can imagine other problems with infertility that arise from gametogenesis (i.e. miscarriages).

So what am I rambling on about may you ask? Well, mostly this post is to address general inquiry. Challenging dogma is something I view as important. So here let me discuss gametogenesis and the stem cell.

A good review of the current status on germ cell derivation from stem cells can be found here

Of great interest is the derivation of either sex germ cell- from female origins: (Main conclusion of the paper: We have characterised the ability of PGCs from female embryos to respond to the masculinising signal that emanates from the somatic cells in a male genital ridge. Furthermore, we have identified molecular differences between PGCs in male and female embryos that reveal how PGCs may not only respond to the masculinising environment of the developing testis, but may also contribute to it.)

the entire article by McLaren et al. 2002 is quite good, one main point:

A small proportion (7%) of the 11.5 dpc female donor PGCs developed as prospermatogonia when aggregated with 12.5 dpc female urogenital ridges

This is fantastic news. Although the proportion is small, they effectively generated male gametes from female donors. This is in 2002, mind you.

Additional evidence provided by Hubner et al., 2003, showed that they effectively could derive oocytes from male and female stem cell lines of mice. Not only did they develop oocytes, they also “conclude that mouse ES cells are capable of differentiating into oocytes and form structures very similar, if not identical, to blastocysts, thereby demonstrating that these cells are actually totipotent even in vitro.” They were basically one step away from making a baby.

So what’s the current status? Well, as we all know, trials from mice to humans can take anywhere from 10-??? years. But it is good to know that the potential is there. It is good to know that maintain the right to reproduce won’t be restricted to the most traditional sense. This diagram(from the review article mentioned earlier) sums up the potential promises of stem cells:

as you can see the path to primordial germ cells can come from many directions. so long as some parts of your body are healthy- even one single cell- the possibilities of preserving your germline exist.