Thrombasthenic mice generated by replacement of the integrin αIIb gene: demonstration that transcriptional activation of this megakaryocytic locus precedes lineage commitment

Abstract

AbstractTo analyze the transcriptional activity of the gene encoding the α subunit of the platelet integrin αIIbβ3during the hematopoietic differentiation, mice were produced in which the herpes virus thymidine kinase (tk) was introduced in this megakaryocytic specific locus using homologous recombination technology. This provided a convenient manner in which to induce the eradication of particular hematopoietic cells expressing the targeted gene. Results of progenitor cell cultures and long-term bone marrow (BM) assays showed that the growth of a subset of stem cells was reduced in the presence of the antiherpetic drug ganciclovir, demonstrating that the activation of the toxic gene occurs before the commitment to the megakaryocytic lineage. Furthermore theknock-in of the tk gene into the αIIb locus resulted in the knock-out of the αIIb gene in homozygous mice. Cultures of BM cells of these animals, combined with ultrastructural analysis, established that the αIIbglycoprotein is dispensable for lineage commitment and megakaryocytic maturation. Platelets collected from αIIb-deficient mice failed to bind fibrinogen, to aggregate, and to retract a fibrin clot. Moreover, platelet α-granules did not contain fibrinogen. Consistent with these characteristics, the mice displayed bleeding disorders similar to those in humans with Glanzmann thrombasthenia.