Embryonic stem cells (ESC) are the origin of all kind of cells of the different animal tissues including human tissues.

They divide herself repeatedly during the first embryonic phase (proliferative phase) resulting in new ESC and adult stem cells (ASC), maintaining both of them the differentiation capability.

However, once the differentiation process is running every new kind of cell only will create cells of the same tissue, despite of the available of the same genes as the original stem cells. So, for example, appear haematopoietic stem cell (HSC) in the marrow, originating long-term haematopoietic stem cells (LT-HSC) and short-term haemotopoietic stem cells (ST-HSC).

This is because the genetic material remains off by the relationship between OCT4, SOX2 and Nanog genes, that are important in the differentiation process of embryonic stem cells. These genes produce different proteins from PCG group that inhibit the DNA chromosomic transcription into RNA messenger by acetylation of the histones. These proteins are produced in a determined sequence, for every adult stem cell, for this reason the off process is sequencial too and it can be reversible resulting in a process of physiological regeneration like in the case of ephitelium or in a pathological degeneration as in the tumors.

However this off process is not finished at all, in the bone marrow, in the fat tissue and in the ephitelium, exists already, even in adult tissues, an adult stem cells percentage (ASC) with the capability to move to other tissues and regenerate it.