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One of the objectives within the European research project CoRePaSol (supported within the CEDR Transnational Program) was to summarize assessment and research of stiffness modulus of cold recycled mixes determined according to repeated indirect tensile stress test (IT-CY). In most cases the stiffness modulus values were compared to the values of indirect tensile strength (ITS), which is currently the most commonly used characteristic for proving the quality of a cold recycled mix. The first part of experimental measurements was focused on the standard cold recycled mixes, thus mixes whose aggregate skeleton is formed entirely by RAP and which contain either just the bituminous binder (bituminous emulsion or foamed bitumen), or a combination of one of these binders and a hydraulic binder (cement). Later also combinations with other types of recyclable materials were done and tested. Stiffness modulus and in most cases also the indirect tensile strength values were investigated from many points of view, e.g. the effect of different bituminous / hydraulic binder content on these characteristics, time-dependent progress in change of these characteristics, effect of testing temperature or the influence of fines addition on the stiffness modulus value. This paper therefore brings some summarization of the gained experience.

No abstract.

Flow cytometric analysis of ten bulked seeds is proposed to quantify particular embryo ploidy classes in Hieracium. The method is recommended 1) for the detection and quantification of residual sexuality in facultative apomicts, which can generate progeny from heteroploid crosses, 2) for the quantitative screening of pollen donors with different ploidy levels, based on the fertilization success of the maternal plant, and 3) for the screening of parents producing a high proportion of polyhaploids.Flow cytometric analysis of ten bulked seeds is proposed to quantify particular embryo ploidy classes in Hieracium. The method is recommended 1) for the detection and quantification of residual sexuality in facultative apomicts, which can generate progeny from heteroploid crosses, 2) for the quantitative screening of pollen donors with different ploidy levels, based on the fertilization success of the maternal plant, and 3) for the screening of parents producing a high proportion of polyhaploids.

The structure and dynamics of poly(N-isopropylacrylamide) (PNIPA)−clay nanocomposite (NC) gels have been investigated by small-angle neutron scattering and dynamic light scattering in order to account for their high strength and high deformability. The structure of clay dispersion in water was an assembly of clay platelets 300 Å in diameter and 10 Å thick. The structure factors of the clay dispersions were reduced to a master curve by normalizing with the clay concentration, Cclay, even across its sol−gel transition. On the other hand, the structure factors of the NC gels cannot be represented with a simple addition of the structure factors of the components, but with a sum of Lorentz (L) and squared-Lorentz (SL) functions. It was found that the SL term, indicating the gel inhomogeneities, becomes dominant by increasing Cclay. The chain dynamics of the gels was found to be similar to the conventional PNIPA gels chemically cross-linked with bis-acrylamide.

Growth of GaN on sapphire (0001) substrates by metalorganic molecular beam epitaxy (MOMBE) was studied using triethyl gallium (TEGa) and rf-plasma excited active nitrogen. A series of samples were grown under various TEGa flow rates while growth temperature (800 °C) and nitrogen supply were fixed. At a very low TEGa flow rate, the grown layer was polycrystalline. With increasing TEGa flow rate, the dominant polytype of the grown layer changed from hexagonal GaN (h-GaN) to cubic GaN (c-GaN). From the dependence of growth rate on TEGa flow rates, it was revealed that a Ga-stabilized growth condition results in the growth of c-GaN. By increasing growth time, the c-GaN composition became larger, indicating preferential growth of c-GaN.

Using a clonal culture system, we investigated the lymphohematopoietic effects of recombinant interleukin-7 (IL-7) obtained from conditioned media of transfected COS 1 cells. IL-7 alone acted on murine bone marrow cells and supported the formation of B-cell colonies. These colony cells were positive for B220, and some of them were also found to have either IgM or Thy-1. B220+, IgM- cells, but not B220- cells sorted from fresh bone marrow cells were able to form B cell colonies in the presence of IL-7. Thus, IL-7 supported the differentiation of B220+, IgM- cells to B220+, IgM+ cells. B220+, IgM+ cells did not proliferate in the presence of IL-7. IL-7 did not affect the myeloid colony formation supported by IL-3, IL-5, IL-6, granulocyte macrophage colony stimulating factor (GM-CSF), and G-CSF. On the other hand, lymphocyte colony formation was not affected by IL-2, IL-3, IL-4, IL-5, IL-6, GM-CSF, or G-CSF. Interestingly, IL-1 alpha inhibited IL-7- induced B cell colony formation in a dose-dependent manner, while the same concentration of IL-1 alpha enhanced the myeloid colony formation by IL-3. This reciprocal effect of IL-1 alpha may act on hematopoietic progenitor cells without accessory cells. These data show that IL-7 is a B cell growth factor and that IL-1 alpha may play an important role in differentiation of myeloid and lymphoid lineages.

We studied the effect of purified interleukin-3 (IL-3) and erythropoietin on colony formation by hemopoietic progenitors in serum- free cultures of spleen cells from 5-fluorouracil (5-FU)-treated mice. In the presence of IL-3 alone, most of the multilineage (three or more lineages) colonies did not contain erythroid cells. However, in the presence of IL-3 and erythropoietin, most of the multilineage colonies contained various numbers of erythroid cells. Replating experiments suggest that IL-3 maintains the growth of the progenitor cells, which could differentiate into erythroid cells. Erythropoietin facilitated the terminal differentiation and amplification of erythroid cells, although it did not sustain the growth of multipotential stem cells. Single-cell transfer experiments demonstrate that IL-3 supported the late stages of differentiation of neutrophils, macrophages, eosinophils, and megakaryocytes in the absence of lineage-specific factors. Therefore, IL-3 supports the differentiation of multilineage hemopoietic progenitors, and the terminal differentiation of most hemopoietic lineages, with the exception of the erythroid lineage.

The radiative emission in nitrogen doped ZnSe grown by molecular beam epitaxy (MBE) and metalorganic molecular beam epitaxy (MOMBE) has been studied by means of time-resolved spectroscopy at 18 K. The lifetime of the free exciton emission and the oscillator strength of the acceptor bound exciton transition decreases with increased nitrogen incorporation. ZnSe:N MOMBE grown samples show different or additional compensation mechanism compared with MBE grown ZnSe:N due to higher defect concentration. The characteristic lifetime of the donor-acceptor pair emission is found to increase with increased incorporation of nitrogen as longer radiative lifetime of more localized carriers is expected as the carriers are trapped in deeper potential wells.

To characterize and clarify the function of CD34 antigen experimentally, we isolated two types of CD34 mRNA from a cDNA library of murine stromal cell line, PA-6 stimulated with lipopolysaccharide (LPS) and 12-o-tetra-decanoylphorbol 13-acetate (TPA) using a human CD34 probe. In addition to the clone (open reading frame [ORF]:1149bp) reported by Brown et al, a novel clone (ORF:978 bp) was obtained. The difference between the two clones was in the cytoplasmic portion of CD34; the former has 73 amino acids, while the latter has 16. We investigated the genomic sequence of cytoplasmic portion and found conserved nucleotide sequences at the exon-intron junction (GT ... AG). Thus, it was concluded that alternative splicing gave two types of CD34 mRNA. A novel clone contains the longer cDNA, including a insert of 156 bp, but results in a shorter predicted coding sequence because of the introduction of an inframe stop codon. Northern blot analysis using a murine cDNA probe (HindIII fragment, 900 bp) showed that CD34 was highly expressed in the brain and testis, and moderately in the thymus, spleen, and bone marrow, but not in adult liver. However, day 12 to 14 fetal liver cells showed significant expression of CD34. Quantitative reverse transcription polymerase chain reaction showed that spleen, thymus, bone marrow, and testis RNA gave two bands of almost equal intensity, but in the brain a novel clone was expressed three times more than the other clone. Furthermore, Northern blot analysis using a probe (156 bp) specific for the spliced intracellular region confirmed the significant mRNA expression of a novel clone. Although the biologic significance of alternative splicing remains to be elucidated, it is suggested that a different carboxyterminal tail causes a change in signal transduction.

A male neonate with Down's syndrome and congenital myeloproliferative disorder was studied. His blood picture showed the unique coexistence of leukocytosis with matured cells and a large number of blast cells. The in vitro proliferation and differentiation of blast cells into various lineages in the presence of phytohemagglutinin-stimulated leukocyte conditioned medium (PHA-LCM) was examined by using a liquid culture and a methylcellulose culture system. The differentiation of blast cells into myeloid cells was confirmed by specific cytochemical stainings, electron microscopy, and an immunologic study. No specific factors in the plasma of the patient promoted the proliferation or differentiation of blast cells. The cellular composition of colonies grown in methylcellulose culture from single blast cells was studied by a micromanipulation technique. High plating efficiency was observed. Of 136 cultures, 78 showed colony growth. Half of the blast cells were colony-forming cells that could proliferate and differentiate into basophils, neutrophils, eosinophils, macrophages, and erythrocytes in the presence of PHA-LCM. Using the blast cells with a high differentiation capacity to the basophil pathway, we studied the effect of recombinant granulocyte-macrophage colony-stimulating factor (GM- CSF). Recombinant GM-CSF support neutrophils, eosinophils, and macrophages but not typical basophils. These findings of the cell differentiation of blast cells into various kinds of cells in vitro were in agreement with the finding of neutrophilia, eosinophilia, basophilia, and thrombocythemia in this patient.

Blast cell colonies seen in cultures of spleen cells from 5- fluorouracil-treated mice provide a highly enriched population of primitive hemopoietic progenitors. Our recent studies of the differentiation potentials of the paired daughter cells of these progenitors showed different patterns of differentiation in the colonies produced by the separated daughter cells. In this study, we carried out sequential micromanipulation of paired progenitors followed by cytologic examinations of the colonies derived from these progenitors. Of the total 94 evaluable cultures, consisting of three or more colonies, 52 consisted of macrophage colonies and one consisted of megakaryocyte colonies. In the remaining 41 cultures, diverse combinations of colonies revealing heterogeneous compositions of cell lineages were identified. Presumptive genealogic trees of the differentiation of hemopoietic progenitors constructed for the latter group of cultures suggested that monopotent progenitors may be derived from pluripotent progenitors in two ways: (1) directly during one cell division of pluripotent cells or (2) as a result of progressive lineage restriction during successive division of the pluripotent progenitors. The results also suggested that some of the oligopotent progenitors are capable of limited self-renewal.

The cDNA for the murine granulocyte/macrophage colony-stimulating factor (GM-CSF) was cloned from a cDNA library obtained from a murine T cell line, IH5.5, by using two synthetic probes that encoded two parts of the GM-CSF from murine lung. The cDNA inserted into the plasmid vector pcDV1 was transfected into monkey COS-1 cells and the conditioned medium was used to investigate the hemopoietic activities of the resultant product, recombinant GM-CSF (rGM-CSF), by means of various colony assays. rGM-CSF stimulated only neutrophil/macrophage colonies in the cultures of murine normal bone marrow and fetal liver cells. No other colony stimulating activities (CSA) were seen in the preparation including burst-promoting activity, eosinophil-CSA, megakaryocyte-CSA and mast cell-CSA. rGM-CSF could not support colony formation of 5-fluorouracil-treated mouse spleen cells, in which only the primitive population of stem cells survived. However, after culture of these cells with PWM-spleen cell-conditioned medium (PWM-SCM), the colonies consisting of blast cells were formed. These blast cells could now be induced to form neutrophil/macrophage colonies in the presence of rGM-CSF. Pure neutrophil colonies, pure macrophage colonies, as well as mixed neutrophil/macrophage colonies, were formed from these single blast cells in the presence of rGM-CSF by micromanipulation. rGM-CSF did not act on pluripotent hemopoietic stem cells, but did act directly and selectively on neutrophil/macrophage progenitors. Moreover, striking heterogeneities were noted in the size of the colonies and the proportion of components. GM-CSF is, therefore, considered to play a noninstructive role in the differentiation of the GM pathway.

The treatment of mice with high doses of 5-fluorouracil (5-FU) results in an enrichment of primitive hematopoietic progenitors. Using this procedure, we obtained a new class of murine hematopoietic colonies that had very high secondary plating efficiencies in vitro and could differentiate into not only myeloid cells but also into lymphoid lineage cells. The phenotypes of interleukin-3 (IL-3) induced blast colony cells were Thy-1-positive and lineage-marker-negative. We examined whether these blast colony cells contained primitive hematopoietic stem cells in vivo and could reconstitute hematopoietic tissues in lethally irradiated mice. Blast colony cells could generate macroscopic visible spleen colonies on days 8 and 12, and 5 x 10(3) blast cells were sufficient to protect them from lethally irradiation. It was shown that 6 or 8 weeks after transplantation of 5 x 10(3) blast cells, donor male cells were detected in the spleen and thymus of the female recipients but not in the bone marrow by Southern blot analysis using Y-encoded DNA probe. After 10 weeks, bone marrow cells were partially repopulated from donor cells. In a congenic mouse system, donor-derived cells (Ly5.2) were detected in the thymus and spleen 6 weeks after transplantation. Fluorescence-activated cell sorter analyses showed that B cells and macrophages developed from donor cells in the spleen. In the thymus, donor-derived cells were found in CD4, CD8 double-positive, single-positive, and double-negative populations. Reconstitution of bone marrow was delayed and myeloid and lymphoid cells were detected 10 weeks after transplantation. These results indicate that IL-3-induced blast cells contain the primitive hematopoietic stem cells capable of reconstituting hematopoietic organs in lethally irradiated mice.

We compared the development of B-cell progenitors with that of myeloid progenitors in fetal liver cells at various gestational ages. Day 12 to 14 fetal liver cells did not form pre-B-cell colonies. Pre-B-cell colonies were developed from day 15 fetal liver cells. The incidence of colonies increased with increases in gestational age and reached a maximum on days 18 to 19. In contrast, the incidence of myeloid colonies formed in the presence of interleukin-3 (IL-3) and erythropoietin did not change significantly during days 13 to 21 of gestation. After coculturing day 13 fetal liver cells with IL-7- producing stromal cell line ST-2, they could respond to IL-7 and proliferate. Analysis of the phenotypes showed that day 13 fetal liver cells were B220-, IgM-, while culturing day 13 fetal liver cells with ST-2 and untreated day 18 fetal liver cells contained the population of B220+ cells. Even in the presence of IL-7-defective stromal cell line FLS-3, IL-7-responsive cells could be induced from day 13 fetal liver cells. IL-7 acted on B220+ cells and induced pre-B-cell colonies that contained IgM+ cells in the methylcellulose culture. IL-7 mRNA was expressed in days 13 and 18 fetal liver cells but not in pre-B cells or adult liver cells. From these findings, it is suggested that stromal cells or stromal-derived factors but not IL-7 were required for the differentiation from B220- cells to B220+ cells. In the second stage, B220+, IgM- cells proliferated and some of them differentiated to IgM+ cells in the presence of IL-7 alone. The two-step model can apply to in vivo early B lymphopoiesis.

Granulocyte colony-stimulating factor (G-CSF) was reported to increase the number of colony-forming units-spleen (CFU-S) and multilineage colonies as well as myeloid-committed cells. We investigated the effects of G-CSF on myeloid progenitors and primitive stem cells in a mouse bone marrow transplantation (BMT) system. Lethally irradiated mice received BM cells from untreated or 5-fluorouracil-treated mice, and then were administered G-CSF or carrier buffer (control) for 5 days from immediately after BMT. A pre-CFU-S assay was performed by the repeated transplantation of BM cells from the first BMT recipients to other mice. By the method of polymerase chain reaction, most of the spleen colonies in the secondary recipients were confirmed to be derived from the first donors. G-CSF did not increase the peripheral white blood cell count significantly, but did increase the number of immature myeloid cells and granulocyte-macrophage colony-forming cells in the BM. The number of erythroid cells in the BM was initially suppressed and then increased by G-CSF treatment. In addition, the pre- CFU-S assay showed an increase in pre-CFU-S cells due to G-CSF administration. The number of spleen colonies of first BMT recipients did not increase, but a higher percentage of them were committed to a certain lineage by G-CSF treatment. These findings suggest that G-CSF has important roles in the early stages of hematopoiesis.

We present the in vitro differentiation of marrow cells from a patient with Down's syndrome accompanied by megakaryoblastic leukemia into basophils in the presence of phytohemagglutinin-stimulated leukocyte conditioned medium, using a liquid culture and methylcellulose culture system. Identification of basophils was established by metachromatic staining with toluidine blue, transmission electron microscopy, and the presence of histamine. However, these basophils did not release histamine in response to calcium ionophore or chemotactic peptide. Samples from suspension cultures that contained 90% basophils showed chromosomal markers characteristic of leukemic cells (48, XY, +11, +21, t(1;15)) in all examined mitoses. The cellular composition of leukemic colonies grown in methylcellulose culture from single cells was studied using the micromanipulation technique. High plating efficiency and extreme predominance of basophil colonies were observed. In a total 137 cultures, 79 revealed colony growth. Of 59 colonies that were analyzed by cytologic examination, 46 were pure basophil colonies. These basophil colonies showed disperse morphology, similar to that of a normal basophil colony. The clonality of the basophil colonies and skewing of lineage expression were documented from leukemic single-cell cultures. These data showed that leukemic cells have the capacity for differentiation into some lineages that are not expressed in vivo.

Colloidal gold-labeled soybean agglutinin (SBA), Helix pomatia agglutinin (HPA), Dolichos biflorus agglutinin (DBA), and Griffonia simplicifolia lectin (GS-1) were used for electron microscopic observation of blood cells. Colloidal gold-labeled SBA, HPA, and DBA showed marked deposition on eosinophil granules at all stages of maturation. Gold particles were not deposited on basophils, neutrophils, monocytes, lymphocytes, or other blood cells. Only a few colloidal gold-labeled GS-1 were deposited on eosinophil granules. Eosinophil granules are rich in N-acetyl-D-galactosamine compounds, and the colloidal gold-labeled SBA, HPA, and DBA are useful for electron microscopic detection of eosinophil granules.

Using a clonal culture system, we investigated the hemopoietic effects of purified recombinant IL-5 obtained from conditioned media of transfected Xenopus oocytes. IL-5 alone acted on untreated bone marrow cells and supported the formation of a small number of colonies, all of which were predominantly eosinophilic. However, it did not support colony formation by spleen cells from 5-FU-treated mice, in which only primitive stem cells had survived, while IL-3 and G-CSF did. Eosinophil-containing colonies were formed from these cells in the presence of IL-5 and G-CSF together. In contrast, G-CSF alone did not support any eosinophil colonies. The eosinophilopoietic effect of IL-5 was dose-dependent, and was neutralized specifically by anti-IL-5 antibody. To exclude the possibility of interactions with accessory cells in the same culture dish, we replated a small number (200 cells/dish) of enriched hemopoietic progenitors, obtained from blast cell colonies, which were formed by cultivation of spleen cells from 5-FU-treated mice in the presence of IL-3 or G-CSF. From these replated blast cells, eosinophil colonies were induced in dishes containing IL-5 but not in those containing G-CSF alone. From these findings, it was concluded that IL-5 did not act on primitive hemopoietic cells, but on blast cells induced by IL-3 or G-CSF. IL-5 specifically facilitated the terminal differentiation and proliferation of eosinophils. In this respect, the role of IL-5 in eosinophilopoiesis seems to be analogous to erythropoietin, which promotes the terminal differentiation and amplification of erythroid cells. Moreover, IL-5 maintained the viability of mature eosinophils obtained from peritoneal exudate cells of the mice infected with parasites, indicating mature functional eosinophils carried IL-5 receptors. The synergistic effects of IL-5 and colony-stimulating factors on the expansion of eosinophils is supposed to contribute to the urgent mobilization of eosinophils at the time of helminthic infections and allergic responses.

By using a micromanipulator, single cells from blast cell colonies were individually transferred to 35-mm culture dishes for secondary colony formation. When individual colonies appeared to be mature, they were examined for cellular composition by May-Grunwald-Giemsa staining and were replated for determination of unexpressed hemopoietic potentials. We describe here a total of 50 mixed hemopoietic colonies. Seven types of colonies consisting of cells in two different lineages were seen--i.e., neutrophil-macrophage, neutrophil-eosinophil, macrophage-eosinophil, macrophage-mast cell, macrophage-megakaryocyte, macrophage-erythrocyte, and erythrocyte-megakaryocyte. Six types of colonies revealed three cell lineages--i.e., neutrophil-macrophage-eosinophil, neutrophil-macrophage-mast cell, neutrophil-macrophage-erythrocyte, macrophage-mast cell-erythrocyte, neutrophil-macrophage-megakaryocyte, and neutrophil-erythrocyte-megakaryocyte lineages. In addition, multilineage colonies expressing terminal differentiation in varying combinations of more than three lineages were present. Replating studies confirmed that the progenitors for many of these colonies are terminally committed to differentiation only in the lineages disclosed by staining. This study, thus, provides a proof for the single-cell origin of mouse hemopoietic colonies expressing various combinations of cell lineages. It also supports the hypothesis that the differentiation of multipotential hemopoietic progenitors is through progressive and stochastic restriction in cell lineages.

Blast colonies were developed by rIL-3 from the spleen cells of mice pretreated with 5-fluorouracil (5-FU) in the methylcellulose cultures. When such IL-3-induced blast colonies were individually lifted up and recultured in the presence of rIL-3 and recombinant erythropoietin (rEpo), a variety of hematopoietic colonies developed from every single colony, including neutrophils, macrophages, eosinophils, megakaryocytes, mast cells, and erythroblasts. The results indicated that IL-3-induced blast colonies consisted of multipotential hematopoietic progenitor cells. By culturing individual IL-3-induced blast colonies in the presence of rIL-2 and irradiated peritoneal macrophages, on the other hand, the proliferation of homogeneous lymphoid cells was observed in 5 of 24 wells, each of which received a single blast colony. Morphologically, they were typical large granular lymphocytes (LGL), and thus it was indicated that LGL could be differentiated directly from the hematopoietic progenitor cells utterly in vitro by rIL-2 and accessory macrophages. From one of these culture wells, a continuous LGL line, IL3B1, was successfully obtained. The proliferation of IL3B1 was dependent on IL-2 in the presence of accessory macrophages, but they no longer responded to IL-3, nor to another T cell growth factor, IL-4. Flow cytometric analysis indicated that the phenotype of IL3B1 was Thy-1+,T3+,L3T4-,Lyt-2-,T200+ Asialo GM1+, whereas that of original IL-3-induced blast cells was Thy-1+,T3-,L3T4-,Lyt-2-,B220-. The results suggested that the expression of T3 molecules was induced in the process of LGL differentiation from the hematopoietic progenitor cells in vitro. Conforming to this, it was revealed that both gamma and beta chain genes of the TCR were rearranged in IL3B1. Northern blot analysis indicated that IL3B1 had abundant mRNA for gamma chain, while mRNA for beta chain was rather faint. Functionally, IL3B1 exhibited typical NK-patterned cytotoxic activity against a panel of tumor cell targets. In addition, they showed significant cytotoxic activity against normal bone marrow cells, as well as various factor-dependent myelogenous progenitor cell lines, all of which were resistant to endogenous NK activity of the fresh spleen cells. These results indicated that at least a set of T3+ LGL with rearranged TCR genes could be directly differentiated from isolated hematopoietic progenitor cells in vitro. Results also suggested that such a prethymically differentiated subset of T-lineage lymphocytes, namely T3+ double-negative LGL, had particular cytotoxic activity in addition to conventional NK activity, which might well contribute to feedback regulation of hematopoiesis.

We analyzed the differentiation of murine hemopoietic colonies derived from paired progenitors in culture. Single progenitors were isolated by use of a micromanipulation technique from blast cell colonies cultured from the spleens of 5-fluorouracil-treated mice. Eighteen to 24 hr later, the paired progenitors were separated with a micromanipulator and cultured in methylcellulose medium containing erythropoietin and pokeweed-mitogen spleen cell conditioned medium. Six to nine days later, the two colonies derived from the paired progenitors were individually picked and differential counts were performed by using May-Grunwald-Giemsa stain. The abbreviations used here are n, neutrophil; m, macrophage; e, eosinophil; mast, mast cell; M, megakaryocyte; E, erythrocyte. Of a total of 387 pairs that could be evaluated, 68 were pairs of colonies consisting of dissimilar combinations of cell lineages such as m-nmmastEM, M-nmmastEM, nm-nmmastEM, nmmastM-nmmastEM, M-nmmastM, nmmast-nmmastM, nm-nmmastE, M-nmM, n-nmM, mM-nmM, m-nmmast, nm-nme, me-nm, mM-nm, n-ne, m-mmast, m-mM, M-nm, M-mM, E-nm, m-nm, M-m, etc. Thirty-nine were homologous pairs revealing identical lineage combinations such as nmmastEM, nmmastM, nmmast, mmastEM, nmEM, nme, nmM, mM, and nm lineages. However, in members of some of these pairs, the proportions of the individual cell lineages were significantly different. The remainder were pairs of single lineage colonies. Paired progenitors obtained from the stem cell colonies of normal mice also revealed homologous and nonhomologous expression of the cell lineages. Comparison of lineage expression in colonies derived from single progenitors with the sum of lineages expressed in pairs of colonies derived from single progenitors indicated that the diversity was not due to injury inflicted by micromanipulation. These observations provide experimental data in support of stochastic mechanisms of stem cell differentiation.