ABSTRACT

INTRODUCTION Stem cells (SCs) are undifferentiated cells that have the potential to self-replicate and give rise to specialized cells. SCs can be obtained not only from the embryo at cleavage or blastocyst stages [embryonic stem cells (ESCs)] but also from extraembryonic tissues such as the umbilical cord obtained at birth (1), the placenta (2), and the amniotic fluid (3). SCs can also be obtained in the adult mammals from specific niches. These somatic stem cells (SSCs) can be found in a wide range of tissues including bone marrow (BM), blood, fat, skin, and also the testis (4-6).