HISTONE H1(0) EXPRESSION IS RESTRICTED TO PROGENITOR CELLS DURING HUMAN HEMATOPOIESIS

The histone H1(0) accumulates in cells with little or no proliferative activity during the terminal phase of differentiation in adult tissue s. The hematopoietic cell system is an interesting in vivo model to st udy the relationship between H1(0) and both the proliferative capacity and differentiation state of cells. Using immunofluorescence techniqu es, we have analyzed the distribution of histone H1(0) during human he matopoietic differentiation, in normal bone marrow cells and in cell l ines representative of cells blocked at early stages of differentiatio n. In enriched bone marrow cell suspensions, H1(0) was not expressed i n any cell population highly engaged into a differentiation pathway. H owever, more than 50 % of cells from blastic population (CD34-positive cells) were expressing H1(0), whereas only 5% of CD34-negative cell p opulation expressed H1(0). We show that H1(0) was also detected in alm ost all the cell lines studied. These results indicate that histone H1 (0) is expressed in immature cells which, although committed, still re tain several differentiation potentialities. For normal human hematopo iesis, cells expressing H1(0) belong to a population of cells that are largely quiescent, although having a high proliferative capacity. H1( 0) is no longer present in terminally differentiating or differentiate d cells with limited or no proliferative potential. Thus, we suggest t hat H1(0) accumulates in cells with little or no proliferative activit y but which are able to resume cell proliferation if required. These r esults are in keeping with the hypothesis that H1(0) contributes to st abilize a chromatin structure in cells for which integrity and/or long evity are essential.