Multipotent hematopoietic progenitors divide asymmetrically to create progenitors of the lymphomyeloid and erythromyeloid lineages

Abstract

Hematopoietic stem and progenitor cells (HSPCs) can self-renew and create committed progenitors, a process supposed to involve asymmetric cell divisions (ACDs). Previously, we had linked the kinetics of CD133 expression with ACDs but failed to detect asymmetric segregation of classical CD133 epitopes on fixed, mitotic HSPCs. Now, by using a novel anti-CD133 antibody (HC7), we confirmed the occurrence of asymmetric CD133 segregation on paraformaldehyde-fixed and living HSPCs. After showing that HC7 binding does not recognizably affect biological features of human HSPCs, we studied ACDs in different HSPC subtypes and determined the developmental potential of arising daughter cells at the single-cell level. Approximately 70% of the HSPCs of the multipotent progenitor (MPP) fraction studied performed ACDs, and about 25% generated lymphoid-primed multipotent progenitor (LMPP) as wells as erythromyeloid progenitor (EMP) daughter cells. Since MPPs hardly created daughter cells maintaining MPP characteristics, our data suggest that under conventional culture conditions, ACDs are lineage instructive rather than self-renewing.

Graphical abstract

Figure 1

Subcellular Distribution Analyses of HC7, but Not AC133, Epitopes Allow Detection of Asymmetrically Dividing Cells within Paraformaldehyde-Fixed HSPC Samples (A) Subcellular localization of AC133 and HC7 epitopes on 50–60 hr cultured, morphologically polarized CD133⁺CD34⁺ cells. (B) Epitope localization on mitotic cells with symmetric (upper row) or asymmetric distribution (lower row) of the HC7 epitopes. Scale bars, 10 μm. See also Figure S1 and Table S2 for a summary of observed frequencies of asymmetric versus symmetric HC7 epitope distributions.

Figure 2

AC133 and HC7 Antibodies Allow Tracking of ACDs in Living HSPCs over Time (A) AC133 and HC7 epitope expression on either freshly isolated CD34⁺ cells (left panel) or CD34⁺ cells that had been cultured for 50–60 hr in the presence of early-acting cytokines before (right panel). Cells were stained simultaneously with anti-AC133, anti-HC7, anti-CD34, anti-CD38, and anti-CD45RA antibodies. To analyze the expression of AC133 and HC7 epitopes on different HSPC subpopulations, obtained expression levels were plotted to those of CD34, CD38, and CD45RA and compared to each other. (B) Time-lapse images (extracted from Movie S1) showing asymmetric segregation of HC7 epitopes of a mitotic CD133⁺CD34⁺ cell. (C) Time-lapse images showing asymmetric segregation of AC133 epitopes of a mitotic CD133⁺CD34⁺ cell. Scale bars, 10 μm. See also Figure S2 and Movie S1.

Figure 3

Binding of Neither AC133 nor HC7 Antibodies Recognizably Affects Cell Biological Properties of CD133⁺CD34⁺ Cells The impact of AC133 and HC7 antibody binding on cell biological properties of cultured CD133⁺CD34⁺ cells was analyzed in different settings: on the establishment of morphological cell polarity (antibodies were added before cultivation) (A and B), on the maintenance of morphological cell polarity (antibodies were added following cultivation) (C), on their in vitro migratory activity measured in the transwell assay (D), on their in vitro motility measured by tracking their movements via time-lapse microscopy (E), and on their cell adhesion capabilities measured as the frequency of cells that tightly adhered to AFT024 stromal cells (F). In all settings, nontreated (control) or isotype-treated CD34⁺ cells (isotype) were used as controls. Pictures to the right of the bar graphs show images of cultured HSPCs at specified time points (A–C), on the microporous membrane (3 μm pore size) of a transwell insert (D), a center-corrected plot of the migration patterns of individually tracked HSPCs (E), and of PKH2-stained CD34⁺ cells that adhered to AFT024 stromal cells (F). n, number of independent experiments; arrow bars are given as SD of the mean; scale bars, 10 μm.

Figure 4

AC133- and HC7-Stained CD34⁺ Cells Reveal Comparable In Vitro and In Vivo Differentiation Potentials (A) CD34⁺ cells cultured for 50–60 hr were stained with either AC133 or HC7 and anti-CD34 antibodies and flow cytometrically analyzed before (presort) or after fluorescent cell sorting of CD133⁺CD34⁺ cells (postsort). (B) Experimental strategy for in vitro and in vivo analysis of sorted cell fractions using either AC133 or HC7 antibodies. (C and D) Total CFC frequencies of AC133- and HC7-stained CD133⁺CD34⁺ and CD133⁻CD34⁺ cells (C) as well as the total frequencies of the obtained colony subtypes (D). (E and F) CD34⁺ cells cultured for 50–60 hr were purified by fluorescent cell sorting according to the gating strategy shown in (A). Aliquots of 50,000 CD133⁺CD34⁺ cells were transplanted in four independent experiments to a total of 23 NOD/SCID mice. The total human cell engraftment was determined upon measuring the content of human CD45⁺ cells in the mice’s bone marrow 8 weeks after transplantation (E) and plotted in comparison to each other (F). (G) The content of hematopoietic subpopulations within the human CD45⁺ cell fractions was determined by using markers specific for the detection of B cells (CD19/20), natural killer cells (CD56), erythroid cells (CD71), myeloid cells (CD13), monocytes/macrophages (CD14), and granulocytes (CD15). (H) Obtained results were plotted in comparison to each other. n, number of independent experiments; N, number of mice; arrow bars are given as SD of the mean.

Figure 5

Most Mitotic HSPCs of the MPP-Enriched, but Not LMPP- and GMP-Enriched, Cell Fractions Reveal Asymmetric Segregation of HC7 Epitopes (A) Recently, we proposed a revised version of the hematopoietic tree predicting different lineage relationships (Görgens et al., 2013b). Accordingly, MPPs can be enriched as CD133⁺CD34⁺CD45RA⁻CD38^lowCD10⁻CD7⁻, LMPPs as CD133⁺CD34⁺CD45RA⁺CD38^lowCD10⁻CD7^+/−, and GMPs as CD133⁺CD34⁺CD45RA⁺CD38⁺CD10⁻CD7⁻ cells. (B) Experimentally, MPP-, LMPP-, and GMP-enriched fractions were sort purified from freshly isolated CD34⁺ cells (Figure S3) and cultured for 50–60 hr in the presence of early acting cytokines. After staining with PE-conjugated HC7 antibodies, cells were tracked via time-lapse microscopy (90 s time intervals) and discriminated regarding their HC7 epitope segregation behavior, either as asymmetrically or symmetrically dividing cells. (C and D) Example of an asymmetrically dividing cell of the MPP fraction (C) and a symmetrically dividing cell of the GMP fraction (D). (E) Comparison of the ACD rates within the MPP-, LMPP-, and GMP-enriched fractions obtained in two independent experiments. (F) The embedded table summarizes the data. n, number of independent experiments; arrow bars are given as SD of the mean. See also Figure S3.

Figure 6

Cells of the MPP Fraction Create CD133⁺Lymphomyeloid as well as CD133^low Erythromyeloid Daughter Cells (A) Model proposing that MPPs (CD133⁺CD45RA⁻) divide asymmetrically to create lymphomyeloid (LMPP; CD133⁺CD45RA⁺) and erythromyeloid (EMP; CD133^low) daughter cells. The dot plot of purified cells of the MPP fraction indicates the classification of MPPs, LMPPs, and EMPs according to their expression levels of CD133 and CD45RA, and arrows indicate proposed shifts of MPP daughter cells into either the LMPP or EMP fraction, respectively. (B) Experimental strategy to analyze progeny fractions received from 100 (upper row) or 10 (lower row) sorted cells of MPP fractions, respectively. In two independent experiments, cells of the MPP fraction (Figure S3) were deposited by fluorescent cell sorting into individual wells of U-bottom 96-well plates, cultured for 6 days, and stained with anti-CD34, anti-CD133, and anti-CD45RA antibodies. Dead cells were excluded from the analyses via DAPI staining; doublets were discriminated by forward scatter area versus forward scatter height gating. Scale bars, 50 μm. (C) Experimental strategy to analyze progeny fractions received from individually sorted cells of MPP fractions. Following deposition of single cells into individual wells of a 96 well U-bottom plates, the plating efficiency was determined by bright-field microscopy. Cells were cultured for 6 days. Arising progeny were enumerated by bright-field microscopy and analyzed like the progeny of the bulk cultures described in (C). Scale bars represent 50 μm (4) and 200 μm (6). (D) Distribution reflecting the enumeration of the progeny fraction sizes of 339 individually deposited cells of MPP fractions. (E) Distribution of the immunophenotypes of progeny fractions obtained from 95 individually deposited cells of MPP fractions. (F) Representative examples of flow cytometric analyses of progeny fractions obtained from individually deposited cells of MPP fractions. See also Figure S4.

Figure 7

Large Proportions of Asymmetrically Dividing Cells of the MPP Fraction Create LMPP- and EMP-like Daughter Cells (A) Experimental strategy for the separation and functional analysis of individual daughter cells arising from cells of the MPP fraction that were deposited as single, HC7-stained cells and tracked for 16 hr via time-lapse microscopy with 8–12 min time intervals. The content of the wells was analyzed by bright-field microscopy. Movies of the wells containing two daughter cells were analyzed for the occurrence of ACDs or SCDs. The whole media content of wells whose daughter cells clearly arose from an ACD or SCD were mixed and aspirated with a standard pipette to separate the daughter cells and distributed to three new wells. Successful separations were confirmed by bright-field microscopy. Siblings of ACD were discriminated as CD133⁺ and CD133⁻ by fluorescence microscopy. Wells with successfully separated daughter cells were overlaid with CFC assay medium and cultured for 14 days. Arising CFC colonies were scored according to their phenotype and analyzed by flow cytometry (Figure S5) according to our previous description (Görgens et al., 2013b). (B) Cumulative statistical overview of three independent separation experiments. In total, 39 or 25 cells of the MPP fraction performed confirmed ACDs or SCDs, respectively, and created daughter cells, both of which formed colonies (details are given in Table S3). (C) Example of the prevailing colonies types that were formed (either a CD133⁺ daughter cell-derived CFU-GM colony or a CD133⁻ daughter cell-derived CFU-MIX colony). Scale bars, 200 μm. (D and E) Combined output of the colony assays of the siblings resulting from ACDs (D) or SCDs (E), respectively (details are given in Table S4). See also Figures S5 and S6, Tables S3 and S4, and Movies S2 and S3.