Yes - stem cells are down there too!

Some of you might be surprised to learn that stem cells are also found in the testicles. These are adult stem cells known as spermatogenic stem cells. (Embryonic stem cells are cells that are so new that they can still grow into any tissue) Spermatogenic stem cells eventually become the sperm cells that fertilize eggs. It takes several stages to reach the final stage. Spermatogenic stem cells are shaped like regular cells then divide several times until they divide into cells with only one set of chromosomes. After that, these cells continue to develop and begin to take on the more familiar shape of spermatozoa – head, midpiece and tail. In the human male this entire process takes about 64 days.

Most interestingly, is that this process of maturation does not occur by itself but actually occurs inside of another cell that is acting as a "nurse" cell. These nurse cells are known as Sertoli cells and are one of the most interesting cells to me. The testicles are filled with seminiferous tubules which are lined with millions and millions of these Sertoli cells.

In the electron micrograph above, you can see the bottom half of a cross section of a single seminiferous tubule. In green are the strangely shaped Sertoli cells and the spermatogenic stem cells are in purple. The red cells with tails (closer to what would be the center of the tubule) are the mature sperm cells that will flow through the tubule and then pass into the vas deferens for ejaculation.

Who knew males could be so complicated?

- Just a peasant


Photo from the University of Delaware