Medical Sciences

ABSTRACT Mammalian embryonic stem cells (ESC) have a number of specific properties that make them a unique object of fundamental and applied studies. In culture, ESC can remain in an infinitely undifferentiated state and dif-ferentiate into descendants of all three germ layers – ectoderm, endoderm, and mesoderm – that is, they can poten-tially produce more than 200 cell types comprising the body of an adult mammal. These properties of ESC are refered to as self-renewal and pluripotency. In this review, the basic signal pathways implicated in the maintenance of ESC pluripotency are considered. The major genes comprising a subsystem of “internal regulators of pluripotency, ” their protein products and regulators, are characterized, and interaction with other factors is described as well. The role of epigenetic mechanisms and microRNAs in the system of ESC self-renewal and pluripotency, as well as the relationship between pluripotency and X-chromosome inactivation in female mammals, is discussed