Stem cells, are sometimes called imortal cells because they have the hability to generate an infinite number of daughter cells...so what about their Telomers? Theorically, these cells have their enzimes active while indiferenciated, or there is some other mechanism involved ?

Again, what stem cells are you talking about? May I suggest that when talking about stem cells, people specify what stem cells they are talking about (/rant).

ES cells and many other stem cells do express telomerase. However, even with the expression of telomerase in hematopoietic stem cells and progenitors, these cells still lose telomere length with age. These stem cells are known to exhaust, you can't just keep transplanting them. Thus, it looks like telomere shortining is one aspect contributing to the aging of the hematopoietic system.

Peter Lansdorp has done many of these studies if your interested in looking his work up.

Well, i didint know that different lineages of SCs have different molecular mechanisms when we talk about the telomerases, that was why I didint especified what type of cell.
But thanks for the explanation !!!

Sorry for my rant on stem cell terminology, but I really believe people need to specify what types of cells they are talking about. I just came back from a meeting on "stem cells" and even among many of the presenters the words 'stem cells' were tossed about much too freely. It really helps to narrow down the conversation when you know if the conversation is about embryonic stem cells, hematopoietic stem cells, mesenchymal stem cells, neural stem cells etc.

I'm not picking on you, I'm just taking this opportunity voice a frustration in the hopes that conversations on these boards can be a little bit more informative.