0 10 Unexpected unexpecte VBN 11 14 and and CC 15 26 coordinated coordinate VBN 27 37 expression expression NN 38 40 of of IN 41 46 Spi-1 Spi-1 NNP 46 47 , , , 48 53 Fli-1 Fli-1 NNP 53 54 , , , 55 58 and and CC 59 73 megakaryocytic megakaryocytic JJ 74 79 genes gene NNS 80 82 in in IN 83 87 four four CD 88 101 Epo-dependent epo-dependent JJ 102 106 cell cell NN 107 112 lines line NNS 113 124 established establish VBN 125 129 from from IN 130 140 transgenic transgenic JJ 141 145 mice mouse NNS 146 156 displaying display VBG 157 175 erythroid-specific erythroid-specific JJ 176 186 expression expression NN 187 189 of of IN 190 191 a a DT 192 207 thermosensitive thermosensitive JJ 208 212 SV40 sv40 NN 213 214 T t NN 215 222 antigen antigen NN 222 223 . . . 225 229 Most most RBS 230 245 erythroleukemic erythroleukemic JJ 246 250 cell cell NN 251 256 lines line NNS 257 268 established establish VBN 269 271 in in FW 272 277 vitro vitro FW 278 287 coexpress coexpres VBP 288 300 erythrocytic erythrocytic JJ 301 304 and and CC 305 319 megakaryocytic megakaryocytic JJ 320 327 markers marker NNS 328 332 that that WDT 333 338 often often RB 339 342 are be VBP 343 353 associated associate VBN 354 358 with with IN 359 369 expression expression NN 370 372 of of IN 373 378 Spi-1 spi-1 NN 379 385 and/or and/or CC 386 391 Fli-1 fli-1 NN 392 405 transcription transcription NN 406 413 factors factor NNS 414 419 known know VBN 420 422 as as IN 423 438 transactivators transactivator NNS 439 441 of of IN 442 464 megakaryocyte-specific megakaryocyte-specific JJ 465 474 promoters promoter NNS 474 475 . . . 476 478 In in IN 479 482 the the DT 483 490 present present JJ 491 496 study study NN 496 497 , , , 498 500 we we PRP 501 509 examined examine VBD 510 513 the the DT 514 525 possibility possibility NN 526 528 of of IN 529 541 establishing establish VBG 542 545 new new JJ 546 550 cell cell NN 551 556 lines line NNS 557 564 keeping keep VBG 565 573 strictly strictly RB 574 592 erythroid-specific erythroid-specific JJ 593 603 properties property NNS 604 606 in in FW 607 612 vitro vitro FW 613 620 through through IN 621 624 the the DT 625 633 targeted target VBN 634 637 and and CC 638 649 conditional conditional JJ 650 665 immortalization immortalization NN 666 668 of of IN 669 681 erythrocytic erythrocytic JJ 682 693 progenitors progenitor NNS 693 694 . . . 695 698 For for IN 699 703 that that DT 704 711 purpose purpose NN 711 712 , , , 713 715 we we PRP 716 727 established establish VBD 728 735 several several JJ 736 741 lines line NNS 742 744 of of IN 745 755 transgenic transgenic JJ 756 760 mice mouse NNS 761 771 displaying display VBG 772 790 erythroid-specific erythroid-specific JJ 791 801 expression expression NN 802 804 of of IN 805 806 a a DT 807 822 thermosensitive thermosensitive JJ 823 827 SV40 sv40 NN 828 829 T t NN 830 837 antigen antigen NN 837 838 . . . 839 841 As as IN 842 850 expected expect VBN 850 851 , , , 852 857 these these DT 858 868 transgenic transgenic JJ 869 873 mice mouse NNS 874 883 developed develop VBD 884 896 splenomegaly splenomegaly NN 897 900 due due JJ 901 903 to to TO 904 907 the the DT 908 915 massive massive JJ 916 929 amplification amplification NN 930 932 of of IN 933 936 Ter Ter NNP 937 940 119 119 CD 941 949 positive positive JJ 950 959 erythroid erythroid JJ 960 969 nucleated nucleated JJ 970 975 cells cell NNS 976 986 expressing express VBG 987 988 T t NN 989 996 antigen antigen NN 996 997 . . . 998 1005 Despite despite IN 1006 1010 this this DT 1011 1018 drastic drastic JJ 1019 1025 effect effect NN 1026 1028 in in FW 1029 1033 vivo vivo FW 1033 1034 , , , 1035 1038 the the DT 1039 1041 in in FW 1042 1047 vitro vitro FW 1048 1063 immortalization immortalization NN 1064 1066 of of IN 1067 1091 erythropoietin-dependent erythropoietin-dependent JJ 1092 1101 erythroid erythroid JJ 1102 1113 progenitors progenitor NNS 1114 1126 unexpectedly unexpectedly RB 1127 1135 occurred occur VBD 1136 1138 at at IN 1139 1142 low low JJ 1143 1152 frequency frequency NN 1152 1153 , , , 1154 1157 and and CC 1158 1161 all all DT 1162 1166 four four CD 1167 1171 cell cell NN 1172 1177 lines line NNS 1178 1189 established establish VBN 1190 1199 expressed express VBD 1200 1204 both both CC 1205 1217 erythrocytic erythrocytic JJ 1218 1219 ( ( ( 1219 1226 globins globin NNS 1226 1227 ) ) ) 1228 1231 and and CC 1232 1246 megakaryocytic megakaryocytic JJ 1247 1254 markers marker NNS 1255 1256 ( ( ( 1256 1268 glycoprotein glycoprotein NN 1269 1272 IIb IIb NNP 1272 1273 , , , 1274 1282 platelet platelet NN 1283 1289 factor factor NN 1290 1291 4 4 CD 1291 1292 ) ) ) 1293 1295 as as RB 1296 1300 well well RB 1301 1303 as as IN 1304 1309 Spi-1 spi-1 NN 1310 1313 and and CC 1314 1319 Fli-1 fli-1 NN 1320 1331 transcripts transcript NNS 1332 1334 at at IN 1335 1345 permissive permissive JJ 1346 1357 temperature temperature NN 1357 1358 . . . 1359 1368 Switching switch VBG 1369 1372 the the DT 1373 1378 cells cell NNS 1379 1381 to to TO 1382 1385 the the DT 1386 1399 nonpermissive nonpermissive JJ 1400 1411 temperature temperature NN 1412 1415 led lead VBD 1416 1418 to to TO 1419 1420 a a DT 1421 1427 marked marked JJ 1428 1436 increase increase NN 1437 1439 in in IN 1440 1446 globin globin NN 1447 1451 gene gene NN 1452 1462 expression expression NN 1463 1466 and and CC 1467 1478 concomitant concomitant JJ 1479 1487 decrease decrease NN 1488 1490 in in IN 1491 1501 expression expression NN 1502 1504 of of IN 1505 1510 Spi-1 Spi-1 NNP 1510 1511 , , , 1512 1517 Fli-1 Fli-1 NNP 1517 1518 , , , 1519 1522 and and CC 1523 1537 megakaryocytic megakaryocytic JJ 1538 1543 genes gene NNS 1544 1546 in in IN 1547 1549 an an DT 1550 1574 erythropoietin-dependent erythropoietin-dependent JJ 1575 1581 manner manner NN 1581 1582 . . . 1583 1596 Interestingly interestingly RB 1596 1597 , , , 1598 1606 enhanced enhance VBN 1607 1617 expression expression NN 1618 1620 of of IN 1621 1626 Spi-1 spi-1 NN 1627 1630 and and CC 1631 1636 Fli-1 fli-1 NN 1637 1642 genes gene NNS 1643 1650 already already RB 1651 1654 was be VBD 1655 1663 detected detect VBN 1664 1666 in in IN 1667 1670 the the DT 1671 1674 Ter Ter NNP 1675 1678 119 119 CD 1679 1687 positive positive JJ 1688 1692 cell cell NN 1693 1703 population population NN 1704 1706 of of IN 1707 1717 transgenic transgenic JJ 1718 1722 mice mouse NNS 1723 1729 spleen spleen NN 1730 1732 in in FW 1733 1737 vivo vivo FW 1737 1738 . . . 1739 1746 However however RB 1746 1747 , , , 1748 1752 like like IN 1753 1759 normal normal JJ 1760 1763 Ter Ter NNP 1764 1767 119 119 CD 1768 1777 erythroid erythroid JJ 1778 1783 cells cell NNS 1783 1784 , , , 1785 1790 these these DT 1791 1794 Ter Ter NNP 1795 1798 119 119 CD 1799 1807 positive positive JJ 1808 1813 cells cell NNS 1814 1818 from from IN 1819 1829 transgenic transgenic JJ 1830 1834 mice mouse NNS 1835 1840 still still RB 1841 1850 expressed express VBD 1851 1855 high high JJ 1856 1862 levels level NNS 1863 1865 of of IN 1866 1877 beta-globin beta-globin NN 1878 1881 and and CC 1882 1886 very very RB 1887 1890 low low JJ 1891 1893 or or CC 1894 1906 undetectable undetectable JJ 1907 1919 glycoprotein glycoprotein NN 1920 1923 IIb IIb NNP 1924 1927 and and CC 1928 1936 platelet platelet NN 1937 1943 factor factor NN 1944 1945 4 4 CD 1946 1960 megakaryocytic megakaryocytic JJ 1961 1972 transcripts transcript NNS 1972 1973 . . . 1974 1979 Taken take VBN 1980 1988 together together RB 1988 1989 , , , 1990 1995 these these DT 1996 2000 data datum NNS 2001 2009 indicate indicate VBP 2010 2014 that that IN 2015 2018 the the DT 2019 2029 unexpected unexpected JJ 2030 2040 expression expression NN 2041 2043 of of IN 2044 2058 megakaryocytic megakaryocytic JJ 2059 2064 genes gene NNS 2065 2067 is be VBZ 2068 2069 a a DT 2070 2078 specific specific JJ 2079 2087 property property NN 2088 2090 of of IN 2091 2103 immortalized immortalize VBN 2104 2109 cells cell NNS 2110 2114 that that WDT 2115 2121 cannot cannot MD 2122 2124 be be VB 2125 2134 explained explain VBN 2135 2139 only only RB 2140 2142 by by IN 2143 2151 enhanced enhance VBN 2152 2162 expression expression NN 2163 2165 of of IN 2166 2171 Spi-1 spi-1 NN 2172 2178 and/or and/or CC 2179 2184 Fli-1 fli-1 NN 2185 2190 genes gene NNS 2190 2191 . . .