[Current views on the biology of the stem cell]

Stem cells (SC) represent a unique cell population capable of self renewing and differentiation. Embryonal SC, represented in the internal cell mass blastocyst, give rise to cells of all three germ leaves. SC are also represented in many tissues of the adult organism. Their physiological function consists in renewing or restoration of the differentiated cells pool during the life span of the organism. The majority of regional SC of the adults differentiate into the limited number of cell types though some regional SC have a wider differential potential. Perfection of SC investigation methods at the molecular genetic level will help to reveal subtle mechanisms of these cells functioning.