Hemoglobin production during the perinatal period is characterized by several switches in hemoglobin composition of the red cell. There is the transition from fetal to adult hemoglobin (γ to β globin), the changes in the relative proportion of the 2 types of γ globin chains which switch from a Gγ-Aγ ratio of 3:1 in the fetus to 2:3 in the adult and the increase in the dominance of α2/α1 mRNA. In order to document these switches at the globin mRNA levels postnatally, 21 preterm infants (gestational range: 24-30wk) and 6 term infants were followed and sampled at different postconceptional ages (30-55wk). The relative proportions of the mRNAs of globins were determined by RNase protection assay. Total RNA isolated from blood (50μl) was incubated with [32P]-labelled cRNA probes ofα, β, and γ-globins, followed by RNase A/T1 digestion, separation of the protected fragments and densitometry of the radioactive bands by phosphorimaging. RT/PCR was used to determine the relative amounts of the transcripts from the 2 individual γ genes. The data obtained in this study was correlated with postconceptional age and compared with that of a previous study which used cord blood from infants of 24 to 41 wk of gestation. The preterm infants included in this study when they reached the age of term(37-42wk) the percent of globin mRNAs encoding HbF,[γ/(γ+β)]-mRNAs was similar to that of newborn term infants(68.7±10 vs 72.5±9). Similarly, there was a normal increase in the dominance of α2/α1 mRNA in relation to postconceptional age. Also in these infants, the proportion of Gγ-mRNAs to total γ-mRNA(62.9±3.0%) remained stable until the postconceptional age of term was reached, the values were similar to that obtained in term newborn infant cord blood. In the infants sampled post term (42-55 wk), the levels of globin mRNAs corresponded to the proportions of globin synthesis previously documented at the same postconceptional age. The proportion of Gγ-mRNAs to totalγ-mRNA decreased only after 44 wk of postconceptional age. The known switches in hemoglobin composition described at the mRNA level in this study appear to be developpementally regulated and unrelated to the birth process.
