ULTRASTRUCTURAL ANALYSIS OF BONE-MARROW HEMATOPOIESIS IN MICE TRANSGENIC FOR THE THYMIDINE KINASE GENE DRIVEN BY THE ALPHA(IIB) PROMOTER

Transgenic mice have been generated with expression of the herpes viru s thymidine kinase gene directed by a 2.7-kb fragment of the alpha(III b) murine promoter of the gene encoding the alpha(IIb)-subunit of the platelet integrin alpha(IIb)beta(3) (Tropel et al, Blood 90:2995, 1997 ). Administration of ganciclovir (GCV) to these mice resulted not only in an acute cessation of platelet production due to the depletion of the megakaryocytic lineage, but also a decrease in erythrocyte and leu kocyte numbers. Immunogold staining on ultrathin frozen sections and e lectron microscopy has now shown that the remaining population of imma ture hematopoietic cells contain a high proportion of Sca-1(+) and CD3 4(+) cells, with CD45R(+) cells of the lymphopoietic lineage being mai ntained. Stromal cells were also preserved. Blood thrombopoietin level s were high. At 4 days of the recovery phase, Sca-1 and CD34 antigen e xpression decreased with intense proliferation of cells of the three l ineages, with megakaryocyte (MK) progenitors being identified by their positivity for glycoprotein Ilb-IIIa. These results suggest that tran scriptional activity for the alpha(IIb) gene promoter was present on p luripotent hematopoietic stem cells. At 6 to 8 days after cessation of GCV, numerous mature MK were observed, some of them with deformed sha pes crossing the endothelial barrier through thin apertures. Proplatel et production was visualized in the vascular sinus. After 15 days, cir culating platelet levels had increased to approximately 65% of normal. Transgenic alpha IIb-tk mice constitute a valuable model to study in vivo megakaryocytopoiesis. (C) 1998 by The American Society of Hematol ogy.