K. Ravid et al., TARGETED EXPRESSION OF A CONDITIONAL ONCOGENE IN HEMATOPOIETIC-CELLS OF TRANSGENIC MICE, The Journal of cell biology, 123(6), 1993, pp. 1545-1553
We have produced two lines of transgenic mice in which the expression
of temperature-sensitive SV-40 large T antigen is targeted to bone mar
row megakaryocytes via the platelet factor 4 (PF4) tissue-specific pro
moter. The progeny of these transgenic mice were observed for about 3
mo, and no malignancies were detected over this period of time. The of
fspring of these transgenic mice, 6- to 12-wk of age, served as a sour
ce of bone marrow cells, which upon in vitro cultivation at the permis
sive temperature yielded immortalized cell lines (MegT). At the permis
sive temperature, MegT cells exhibit the characteristics of early 2N a
nd 4N megakaryocytes which include the presence of specific gene produ
cts such as PF4, glycoprotein IIb, acetylcholinesterase, and CD45 as w
ell as absence of molecular markers of other cell lineages such as the
macrophage marker Mac-1, the helper cell marker CD4, the mast cell ma
rker IgE, the cell marker CD2 or the erythroid cell marker alpha-globi
n. rhe inactivation of the oncogene by a shift of temperature from 34-
degrees to 39.5-degrees-C produces a reduction in the frequency of the
2N cells, in conjunction with the appearance of 8N and 16N cells, con
sisting of 27 and 3% of total cells, respectively. Thus, we have gener
ated hematopoietic cell lines that are trapped in the early stages of
megakaryocyte commitment, but able to undergo part of the normal progr
am of terminal differentiation.