Differentiating Systems and Their Methylation Patterns

Abstract

The hemoglobin gene Clusters provided the first examples of correlations between DNA methylation and gene function at specific loci. The hemopoietic system consists of populations of several types of cells that are derived by the division of hemopoietic stem cells. The time of differentiation of the stem cells during development is difficult to determine because they have few known distinguishing phenotypes except their potential for seif reproduction and the generation of cells that can differentiate into most, if not all, of the cells which reside in the myloid tissues, primarily bone marrow, and the lymphoid tissues in lymph nodes, spieen and the thymus gland (Till 1981, Siminowitch etal. 1963, Curry and Trentin 1967). The cells of the myloid tissues include three major types of precursor cells: 1. proerythroblasts which divide and differentiate into erythroblasts and ultimately the erythrocytes, 2. myeloblasts which divide and form myelocytes (these continue to divide and differentiate into granulocytes), and 3. megakaryoblasts which divide and differentiate into megakaryocytes (when mature the megakaryocytes fragment into the small blood platelets which lack a nucleus and survive a relatively short time).