A 2.7-kb portion of the 5' flanking region of the murine glycoprotein α(IIb) gene is transcriptionally active in primitive hematopoietic progenitor cells

Abstract

The continuous generation of mature blood cells from primitive multipotent progenitor cell requires a highly complex series of cellular events that are still largely unknown. To examine the molecular events associated with the commitment of these hematopoietic progenitor cells to the megakaryocytic lineage, the α subunit of the platelet integrin {IIb)β3 was used as marker. Despite an abundance of information regarding the role of this integrin in platelet adhesion and aggregation, the mechanisms that control the expression of the genes that code for these proteins are poorly understood and the earliest hematopoietic cell capable of expressing them has not been clearly identified. Thus, a strategy was developed to eradicate, using a conditional toxigene, all the hematopoietic cells capable of expressing the α(IIb) gene in mice. This was achieved by targeting the expression of the gene encoding the herpes simplex virus thymidine kinase (tk), specifically to these cell types, using a 2.7-kb fragment of the 5'- flanking region of the murine α(IIb) gene. Three transgenic lines having 1, 3, and 4 copies of the transgene, respectively were produced and analyzed. Administration of ganciclovir (GCV) to these mice induced a severe thrombocytopenia, which was due to the depletion of the entire megakaryocytic lineage, as shown by bone marrow (BM) culture and electron microscopy analysis. The time required to attain a severe was dependent on the level of the expression of the transgene and varied from 7 to 11 days. This condition was completely reversed when GCV treatment was discontinued. Progenitor cell assays showed that the α(IIb) promoter was active in primitive hematopoietic progenitor cells possessing myeloid, erythroid, and megakaryocytic potential and that the transcriptional activity of the promoter decreased progressively are differentiation proceeded towards the erythroid and myeloid lineages.