0 4 Cell cell NN 5 20 cycle-dependent cycle-dependent JJ 21 31 initiation initiation NN 32 35 and and CC 36 53 lineage-dependent lineage-dependent JJ 54 64 abrogation abrogation NN 65 67 of of IN 68 74 GATA-1 gata-1 NN 75 85 expression expression NN 86 88 in in IN 89 93 pure pure JJ 94 109 differentiating differentiate VBG 110 123 hematopoietic hematopoietic JJ 124 135 progenitors progenitor NNS 135 136 . . . 138 141 The the DT 142 152 programmed program VBN 153 174 activation/repression activation/repression NN 175 177 of of IN 178 191 transcription transcription NN 192 199 factors factor NNS 200 202 in in IN 203 208 early early JJ 209 222 hematopoietic hematopoietic JJ 223 238 differentiation differentiation NN 239 242 has have VBZ 243 246 not not RB 247 250 yet yet RB 251 255 been be VBN 256 264 explored explore VBN 264 265 . . . 266 269 The the DT 270 281 DNA-binding dna-binding JJ 282 289 protein protein NN 290 296 GATA-1 gata-1 NN 297 299 is be VBZ 300 308 required require VBN 309 312 for for IN 313 319 normal normal JJ 320 329 erythroid erythroid JJ 330 341 development development NN 342 345 and and CC 346 355 regulates regulate VBZ 356 375 erythroid-expressed erythroid-expressed JJ 376 381 genes gene NNS 382 384 in in IN 385 393 maturing mature VBG 394 407 erythroblasts erythroblast NNS 407 408 . . . 409 411 We we PRP 412 420 analyzed analyze VBD 421 427 GATA-1 gata-1 NN 428 438 expression expression NN 439 441 in in IN 442 447 early early JJ 448 453 human human JJ 454 459 adult adult JJ 460 473 hematopoiesis hematopoiesis NN 474 476 by by IN 477 482 using use VBG 483 485 an an DT 486 488 in in FW 489 494 vitro vitro FW 495 501 system system NN 502 504 in in IN 505 510 which which WDT 511 512 “ `` `` 512 516 pure pure JJ 516 517 ” '' '' 518 523 early early JJ 524 537 hematopoietic hematopoietic JJ 538 549 progenitors progenitor NNS 550 553 are be VBP 554 561 induced induce VBN 562 564 to to TO 565 572 gradual gradual JJ 573 576 and and CC 577 589 synchronized synchronize VBN 590 605 differentiation differentiation NN 606 617 selectively selectively RB 618 623 along along IN 624 627 the the DT 628 637 erythroid erythroid JJ 638 640 or or CC 641 663 granulocyte-macrophage granulocyte-macrophage JJ 664 671 pathway pathway NN 672 674 by by IN 675 687 differential differential JJ 688 697 treatment treatment NN 698 702 with with IN 703 716 hematopoietic hematopoietic JJ 717 723 growth growth NN 724 731 factors factor NNS 731 732 . . . 733 736 The the DT 737 743 GATA-1 gata-1 NN 744 748 gene gene NN 748 749 , , , 750 756 though though IN 757 766 virtually virtually RB 767 773 silent silent JJ 774 776 in in IN 777 786 quiescent quiescent JJ 787 798 progenitors progenitor NNS 798 799 , , , 800 802 is be VBZ 803 812 activated activate VBN 813 818 after after IN 819 827 entrance entrance NN 828 832 into into IN 833 836 the the DT 837 841 cell cell NN 842 847 cycle cycle NN 848 852 upon upon IN 853 864 stimulation stimulation NN 865 869 with with IN 870 883 hematopoietic hematopoietic JJ 884 890 growth growth NN 891 898 factors factor NNS 898 899 . . . 900 912 Subsequently subsequently RB 912 913 , , , 914 924 increasing increase VBG 925 935 expression expression NN 936 941 along along IN 942 945 the the DT 946 955 erythroid erythroid JJ 956 963 pathway pathway NN 964 973 contrasts contrast VBZ 974 978 with with IN 979 981 an an DT 982 988 abrupt abrupt JJ 989 1003 downregulation downregulation NN 1004 1006 in in IN 1007 1010 the the DT 1011 1033 granulocyte-macrophage granulocyte-macrophage JJ 1034 1041 lineage lineage NN 1041 1042 . . . 1043 1048 These these DT 1049 1056 results result NNS 1057 1064 suggest suggest VBP 1065 1066 a a DT 1067 1092 microenvironment-directed microenvironment-directed JJ 1092 1093 , , , 1094 1102 two-step two-step JJ 1103 1108 model model NN 1109 1112 for for IN 1113 1119 GATA-1 gata-1 NN 1120 1130 expression expression NN 1131 1133 in in IN 1134 1149 differentiating differentiate VBG 1150 1163 hematopoietic hematopoietic JJ 1164 1175 progenitors progenitor NNS 1176 1180 that that WDT 1181 1189 involves involve VBZ 1190 1191 ( ( ( 1191 1192 i i LS 1192 1193 ) ) ) 1194 1209 cycle-dependent cycle-dependent JJ 1210 1220 initiation initiation NN 1221 1224 and and CC 1225 1226 ( ( ( 1226 1228 ii ii LS 1228 1229 ) ) ) 1230 1247 lineage-dependent lineage-dependent JJ 1248 1259 maintenance maintenance NN 1260 1262 or or CC 1263 1274 suppression suppression NN 1274 1275 . . . 1276 1290 Hypothetically hypothetically RB 1290 1291 , , , 1292 1298 on/off on/off JJ 1299 1307 switches switch NNS 1308 1310 of of IN 1311 1329 lineage-restricted lineage-restricted JJ 1330 1345 transactivators transactivator NNS 1346 1349 may may MD 1350 1358 underlie underlie VB 1359 1362 the the DT 1363 1369 binary binary JJ 1370 1374 fate fate NN 1375 1384 decisions decision NNS 1385 1387 of of IN 1388 1401 hematopoietic hematopoietic JJ 1402 1413 progenitors progenitor NNS 1413 1414 . . .