During the perinatal period the switchover from fetal (HbF) to adult hemoglobin (HbA) synthesis in humans, γ-globin levels decline as the proportion of β-globin increases under the influence of a developmental clock. In order to examine if a quantitative relationship existed between the mRNAs encoding globins and their translation into proteins during the period of switchover, the relative amounts of the mRNAs and the relative amounts ofα, β, γ-globin synthesis in cord blood samples were measured and compared. The synthesis of globins in reticulocytes was measured by the incorporation of [3H]-leucine followed by the separation and quantitation of the polypeptides on a C4-reverse phase HPLC equipped with an integrator. The relative proportions of the mRNAs of globins were determined by RNase protection assay. Total RNA isolated from cord blood was incubated with [32P]-labelled cRNA probes (of equivalent specific activity) of α, β, γ-globins overnight at 50°C, followed by RNAse A (10 μg/ml) /T1 (200 U/ml) digestion at 25°C, separation of the protected fragments on 6% urea-polyacrylamide gels and densitometry of the radioactive bands by phosphorimaging. A comparison cord blood samples from 18 newborn infants of different gestational ages (27-40 weeks; birth weight: 850-4035 g) with no congenital anomalies, revealed a strong and significant correlation (r2= 0.934) between the ratio of mRNAs encoding HbF and HbA and the ratio of de novo synthesis of HbF and HbA. There was a linear relationship between the proportions of mRNAs encoding HbF and HbA with the proportional synthesis of HbF and HbA throughout the gestational age studied. This information can be useful for studies furthering the understanding of the mechanisms regulating globin gene expression.
