Dc. Ma et al., CD34+ cells derived from fetal liver contained a high proportion of immature megakaryocytic progenitor cells, EUR J HAEMA, 64(5), 2000, pp. 304-314
Endoreplication and maturation of the megakaryocyte (MK) may be retarded or
delayed during ontogenesis. In this study, CD34+ cells were isolated from
both human fetal liver and adult bone marrow and incubated with thrombopoie
tin (TPO). The cell number, morphological characteristics, platelet-associa
ted antigen phenotype, maturation stage and DNA ploidy of CD41+ cells were
examined from day 0 to day 12 in culture. 1) TPO stimulated the proliferati
on of fetal liver (FL)-derived CD34+ cells with a mean 73.14-fold increase
of CD41+ cells after 12 d in culture. Adult BM-derived CD34+ cells increase
d only slightly, with a mean 8.18-fold increase of CD41+ cells. 2) Although
the membrane phenotype of both FL CD34+ -derived MKs and BM CD34+ -derived
MKs analyzed with CD41a, CD42a, CD61 and CD34 were similar, all FL CD34+-d
erived MKs were in maturation stage I and II and in low ploidy (<4N) class.
By comparison, BM CD34+ MKs possessed 15% MKs in maturation stage III and
IV and with 23% MKs in high ploidy class (>4N). 3) Most of cultured FL-deri
ved CD34+ cells did not have a well developed demarcation system (DM) and n
umerous alpha-granules after 12 d incubation. von Willebrand factor (vWF) a
ppeared earlier on the cultured BM-derived CD34+ cells than on FL-derived C
D34+ cells. 3) The expression of both cyclin E and cyclin B-1 progressively
increased in FL CD34+ cells induced by TPO during 12 d in culture. 5) The
expression of cyclin D-1 gradually decreased in FL CD34+ cells induced by T
PO over 12 d incubation. 6) Immunocytochemical analysis showed that cyclin
D-3 was detected only in cytoplasm of cultured FL-derived CD34+ cells, wher
eas in both cytoplasm and nuclei of cultured BM-derived CD34+ cells. These
data suggest that FL-derived CD34+ cells contain a high proportion of immat
ure megakaryocytic progenitor cells. It further suggests that TPO can push
these progenitor cells into proliferation by upregulating the expression of
cyclins B-1 and E, and drive a high proportion of cells into megakaryocyti
c lineage.