Use of somatic cell fusion to reprogram globin genes

Abstract Somatic cell fusion@21S omatic cell fusion , pioneered by Henry Harris and Nils Ringertz over three decades ago, 1–5 has been used to illuminate many interesting cellular processes involving cytoplasmic-nuclear interactions. 6 Cell fusion creates a multinucleated cell surrounded by a single membrane, termed a heterokaryon if the fused cells originate from two or more tissues or species. If heterokaryons are maintained in culture for several days, some will form hybrids, which result when the chromosomes from both nuclei coalesce into one metaphase plate during mitosis, creating hybrid nuclei in the daughter cells. Heterokaryons and cell hybrids have been used to detect gene regulatory factors, 7 to show the extinction of one cellular phenotype and dominance of another, 8,9 and to confer a new or added property on a recipient cell. 10 It is for the very daunting task of understanding development, with all its cell-specific gene activations and repressions, that cell fusion has been especially useful, particularly for understanding whether gene programming is plastic or irreversible. 11 @91Developmental hemoglobin switching@21During ontogeny, vertebrates of all classes undergo one or more hemoglobin (Hb) switches, typically an early switch from embryonic to fetal or larval Hbs, and a subsequent switch from fetal/larval to adult Hb. 12,13 By investigating these switches, in addition to understanding the mechanisms for gene regulation that lead to the orderly emergence of phenotypic characters, we may reap medical benefits from being able to partially or wholly reverse the fetal-to-adult Hb switch in humans with sickle cell disease or beta-thalassemias. Fetal hemoglobin (HbF), composed of alpha- and gamma-globin chains, when present in sufficient quantities, prevents sickling; and in the beta-thalassemias, the gamma chains replace the absent or markedly reduced beta-globin chains. 14 However, manipulation of a Hb switch may require knowing the correct combination of trans-acting factors and how they interact, problems yet to be elucidated.