Hemoglobin production in humans is characterized by two major switches, from embryonic to fetal, during the transition from yolk sax to the liver stage of hematopoiesis and from fetal to adult hemoglobin around the perinatal period. Any disturbance in these switching controls may result in abnormalities of globin gene expression and hemoglobin disorders (i.e., thalassemia, HPFH). The specific pattern of globin gene expression during development has been characterized. It has been generally assumed that the switches from embryonic to fetal globin protein synthesis accurately reflects as corresponding switch in mRNA, and the lack of embryonic globin in adult life ins due to a complete turn off of embryonic gene transcription. Recently, we used a two- phase liquid human adult erythroid (HAE) cell culture procedure, coupled with RT-PCR mRNA quantitative method, to set up a new system, for characterizing the pattern of embryonic epsilon globin gene expression at the mRNA level. Based on the trial experiments in RNA's from normal individuals, K562 cells and the mix RNA of normal individual + K562 cell, primers for specific amplification of epsilon gene were designed and screened so that the whole three exon sequences could be amplified with a high sensitivity, accuracy and reproducibility. We found, unexpectedly, that; (1) The expression of epsilon gene was assessed at the level of steady-state mRNA in HAE cells: (2) With the cell life-age, the levels of gamma and beta mRNA were increased, peaking at day 5-7 and 11-13, respectively; while the ratio of gamma/beta mRNA was gradually reduced, from 1.03 at day 5 to 0.29 at day 11; (3) The epsilon mRNA was also present in a relatively abundant amount in adult peripheral blood erythroid cells. The expression of epsilon mRNA in adult reticulocytes and HAE cells appears to be erythroid specific, s it was not detected in nonerythroid hematopoietic cells (B-cell Raji, T-cell Jurkat). In general, these data appear to be in accordance with the timed changes of globin gene expression during development. The result also indicates a significant discrepancy between the embryonic epsilon mRNA and the absence of the epsilon globin chain in adult blood. The presence of embryonic epsilon mRNA in adults raises the possibility that basal expression may increase in response to erythroid stress in a fashion similar too that seen in fetal hemoglobin. Therefore, the methodology we developed provides a powerful tool for further studies of globin gene switches and the function of the epsilon globin silencer, as well as the mechanism of HU effects on the globin gene expression. Current work is in progress aimed at studying the action of pharmacological induction of the expression of gamma globin gene, and possibly epsilon gene using this newly developed methodology.
