Differentiation in the Presence of Bromodeoxyuridine is “All-or-none”

Abstract

HAEMOGLOBIN (Hb) synthesis is initiated in immature, primitive erythroblasts of the chick at 35 h incubation^1–4. If bromodeoxyuridine (BUdR) is introduced into eggs about a cell cycle earlier, at 25 h, Hb does not appear⁴. In contrast, dividing erythroblasts that have just begun to synthesize Hb are resistant to the analogue^3–6. Together with observations on many other systems, results with red blood cells have led to the proposal that BUdR inhibits “switching loci” for most types of differentiation and so the initiation of new synthetic programmes⁴. For most cell types, BUdR inhibition is readily reversible and therefore not a consequence of mutagenesis; also, BUdR suppression leads to only slight alterations in the general synthetic capacity of the affected cells^4–9. Our results show that BUdR alters the fraction of individual precursor cells that differentiate into clones of Hb producing red blood cells.