Allele-specific transcription of fetal genes in primary erythroid cell cultures from lepore and δβ° thalassemia patients

Objective Autonomous gene silencing and gene competition by globin promoters for locus control region (LCR) function have been proposed as mechanisms in developmental regulation of β-like genes. δβ° thalassemias are syndromes presenting an increased production of fetal hemoglobin in adult life; the majority of them are due to various deletions in β-globin gene cluster. We studied samples from double heterozygotes for β-thalassemia and for Lepore or Sicilian δβ° deletions, both lacking β-promoter sequence. Our goal was to address the question of whether the allele carrying the δβ° deletion is responsible for high level of fetal hemoglobin (HbF) production. Patients and Methods We analyzed the globin gene transcription in human erythroid cell cultures from peripheral blood stem cells, using primary transcript in situ hybridization. We performed primary erythroid cultures from patients with the following genotypes: Lepore/β°39, Sicilian δβ°/β°39, and, as controls, two thalassemia patients with nondeletional mutations (IVS1,6/IVS1,6; IVS1,6/β°39), and one normal individual. Results The cells where it is possible to unambiguously assign γ genes transcription in cis with the deletion (γ:β) are strongly represented with respect to the nine other combinations of γ and β hybridization signals. These cells are at least nine times more represented than those expressing the γ allele in trans to the deletion. Conclusion The allele-specific transcription of fetal genes in cis with the deletion is favored in both deletional genotypes. The absence of the adult promoter may influence LCR recruitment by fetal promoter, supporting the hypothesis that competition mechanism and gene silencing can coexist in regulating human globin gene transcription.