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At least 433 records · Page 24Linked to original sources
PubMed2001

Progression of T cell lineage restriction in the earliest subpopulation of murine adult thymus visualized by the expression of lck proximal promoter activity.

The proximal promoter of lck directs gene expression exclusively in T cells. To investigate the developmental regulation of the lck proximal promoter activity and its relationship to T cell lineage commitment, a green fluorescence protein (GFP) transgenic (Tg) mouse in which the GFP expression is under the control of the proximal promoter of lck was created. In the adult GFP-Tg mice, >90% of CD4(+)CD8(+) and CD4(+)CD8(-) thymocytes, and the majority of CD4(-)CD8(+) and CD4(-)CD8(-) [double-negative (DN)] thymocytes were highly positive for GFP. Slightly lower but substantial levels of expression of GFP was also observed in mature splenic T cells. No GFP(+) cells was detected in non-T lineage subsets, including mature and immature B cells, CD5(+) B cells, and NK cells, indicating a preserved tissue specificity of the promoter. The earliest GFP(+) cells detected were found in the CD44(+)CD25(-) DN thymocyte subpopulation. The developmental potential of GFP(-) and GFP(+) cells in the CD44(+)CD25(-) DN fraction was examined using in vitro culture systems. The generation of substantial numbers of alphabeta and gammadelta T cells as well as NK cells was demonstrated from both GFP(-) and GFP(+) cells. However, no development of B cells or dendritic cells was detected from GFP(+) CD44(+)CD25(-) DN thymocytes. These results suggest that the progenitors expressing lck proximal promoter activity in the CD44(+)CD25(-) DN thymocyte subset have lost most of the progenitor potential for the B and dendritic cell lineage. Thus, progression of T cell lineage restriction in the earliest thymic population can be visualized by lck proximal promoter activity, suggesting a potential role of Lck in the T cell lineage commitment.

Animals↗
PubMed2006

Proceedings of the SMBE Tri-National Young Investigators' Workshop 2005. Lineage-specific expansions and contractions of the bitter taste receptor gene repertoire in vertebrates.

The sense of bitter taste plays a critical role in how organisms avoid generally bitter toxic and harmful substances. Previous studies revealed that there were 25 intact bitter taste receptor (T2R) genes in humans and 34 in mice. However, because the recent chicken genome project reported only three T2R genes, it appears that extensive gene expansions occurred in the lineage leading to mammals or extensive gene contractions occurred in the lineage leading to birds. Here, I examined the T2R gene repertoire in placental mammals (dogs, Canis familiaris; and cows, Bos taurus), marsupials (opossums, Monodelphis domestica), amphibians (frogs, Xenopus tropicalis), and fishes (zebrafishes, Danio rerio; and pufferfishes, Takifugu rubripes) to investigate the birth-and-death process of T2R genes throughout vertebrate evolution. I show that (1) the first extensive gene expansions occurred before the divergence of mammals from reptiles/birds but after the divergence of amniotes (reptiles/birds/mammals) from amphibians, (2) subsequent gene expansions continuously took place in the ancestral mammalian lineage and the lineage leading to amphibians, as evidenced by the presence of 15, 18, 26, and 49 intact T2R genes in the dog, cow, opossum, and frog genome, respectively, and (3) contractions of the gene repertoire happened in the lineage leading to chickens. Thus, continuous gene expansions have shaped the T2R repertoire in mammals, but the contractions subsequent to the first round of expansions have made the chicken T2R repertoire narrow. These dramatic changes in the repertoire size might reflect the daily intake of foods from an external environment as a driving force of evolution.

Animals↗
PubMed2005

Marking cell lineages in living tissues.

We have generated a novel genetic system to visualize cell lineages in living tissues at high resolution. Heat shock was used to trigger the excision of a specific transposon and activation of a fluorescent marker gene. A histone-YFP marker was used to allow identification of cell lineages and easy counting of cells. Constitutive expression of a green fluorescent membrane protein was used to provide a precise outline of all surrounding cells. Marked lineages can be induced from specific cells within the organism by targeted laser irradiation, and the fate of the marked cells can be followed non-invasively. We have used the system to map cell lineages originating from the initials of primary and lateral roots in Arabidopsis. The lineage marking technique enabled us to measure the differential contribution of primary root pericycle cell files to developing lateral root primordia. The majority of cells in an emerging lateral root primordium derive from the central file of pericycle founder cells while off-centre founder cells contribute only a minor proliferation of tissue near the base of the root. The system shows great promise for the detailed study of cell division during morphogenesis.

Arabidopsis↗
PubMed1998

Distribution of macrophage lineage cells in rat gingival tissue after topical application of lipopolysaccharide: an immunohistochemical study using monoclonal antibodies: OX6, ED1 and ED2.

To discuss the role of macrophage lineage cells on the periodontal tissue destruction, we immunohistochemically examined the phenotype and the dynamics of macrophage lineage cells 1 or 3 h or 1, 2, 3 or 7 d after topical application of LPS (5 mg/ml in physiological saline) from the rat gingival sulcus using 3 monoclonal antibodies: OX6 (antigen-presenting cells), ED1 (monocytes, macrophages and dendritic cells) and ED2 (resident macrophages). We could detect at least 3 different types of macrophage lineage cells, namely OX6+/ED1+/ED2- dendritic cells and exudate macrophages and ED2+ resident macrophages. After LPS application the majority of macrophage lineage cells accumulated in the subjunctional epithelial area were newly extravasated OX6+/ED1+/ED2- dendritic cells or macrophages. The number of these cells increased progressively with time and reached a maximum level at d 2. On the other hand, number and tissue distribution of ED2+ resident macrophages did not change. These results indicate that several types of macrophage lineage cells exist in rat gingival tissue and suggest that dendritic cells and exudate macrophages transiently accumulated after LPS application are responsible for various host immune response and tissue destruction caused by LPS.

Administration, Topical↗
PubMed2026

Near-Whole-Genome Sequencing of Peste Des Petits Ruminants Virus Lineage IV From the Savannah District, Northern Côte d'Ivoire in 2023.

Peste des petits ruminants (PPR) is a highly contagious viral disease affecting sheep and goats, causing substantial economic losses in endemic countries. In the Savannah district of Côte d'Ivoire, knowledge of the genetic diversity and molecular epidemiology of the PPR virus (PPRV) remains limited. This study investigated the genetic diversity and phylogenetic relationships of PPRV circulating in this region using whole-genome sequencing (WGS). A cross-sectional survey was conducted between September and December 2023. Nasal swabs collected from sheep and goats were screened for PPRV ribonucleic acid (RNA) using real-time reverse transcription polymerase chain reaction (RT-qPCR). Samples with low quantification cycle (Cq) values of less than 35 and successful multiplex PCR amplification profiles were selected for sequencing using the Oxford Nanopore MinION platform. Near-complete consensus genomes were generated through reference-based assembly and analysed alongside representative strains from all recognised PPRV lineages. Of the 355 samples analysed, 25 (7.0%) tested positive for PPRV RNA, with positive detections in all three surveyed regions (Poro, Tchologo and Bagoué). The four samples with the lowest Cq values, originating from all three administrative regions, were successfully sequenced, generating genomes that covered 82.0%-86.2% of the reference genome at a depth of ≥ 10 ×. The missing regions were mainly located at the 5' and 3' genomic termini, as well as in limited internal regions associated with amplicon dropout. Phylogenetic analysis revealed that all four sequences belonged to lineage IV and exhibited high nucleotide similarity (98.1%-99.9%). The Ivorian strains clustered with recent lineage IV viruses from West, North and Central Africa, whereas historical Ivorian lineages I and II formed distinct clades. These findings confirm the predominance of lineage IV in northern Côte d'Ivoire and provide baseline genomic data to support molecular epidemiological surveillance in the region.

PPRV↗
PubMed2004

Rosiglitazone facilitates angiogenic progenitor cell differentiation toward endothelial lineage: a new paradigm in glitazone pleiotropy.

BACKGROUND: Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists inhibit vascular smooth muscle proliferation and migration and improve endothelial function. It is unknown whether PPAR-gamma agonists favorably modulate bone marrow (BM)-derived angiogenic progenitor cells (APCs) to promote endothelial lineage differentiation and early reendothelialization after vascular intervention. METHODS AND RESULTS: C57/BL6 mice, treated with or without rosiglitazone (8 mg/kg per day), a PPAR-gamma agonist, underwent femoral angioplasty. Rosiglitazone treatment attenuated neointimal formation (intima/media ratio: 0.98+/-0.12 [rosiglitazone] versus 3.1+/-0.5 [control]; P<0.001; n=10 per group). Using a BM transplantation model, we identified that 58+/-12% of the cells within the neointima at 4 weeks were derived from the BM. Pure endothelial marker-positive, pure alpha-smooth muscle actin (alphaSMA)-positive, or double-positive APCs could be found both in mouse BM and in human peripheral blood after culture in conditional medium enriched with vascular endothelial growth factor. Rosiglitazone caused a 6-fold (P<0.001) increase in colony formation by human endothelial progenitor cells, promoted the differentiation of APCs toward the endothelial lineage in mouse BM in vivo (0.66+/-0.06% [control] to 0.95+/-0.08% [rosiglitazone]; P<0.05) and in human peripheral blood in vitro (13.2+/-1.5% [control] to 28.4+/-3.3% [rosiglitazone]; P<0.05), and inhibited the differentiation toward the smooth muscle cell lineage. Within the neointima, rosiglitazone also stimulated APCs to differentiate into mature endothelial cells and caused earlier reendothelialization compared with controls (31+/-5 versus 8+/-2 CD31-positive cells per millimeter of neointimal surface on day 14; P<0.01). CONCLUSIONS: Similar to embryonic stem cell-derived progenitors, the adult BM and peripheral blood harbor APCs that are at least bipotential and able to differentiate into endothelial and smooth muscle lineages. The PPAR-gamma agonist rosiglitazone promotes the differentiation of these APCs toward the endothelial lineage and attenuates restenosis after angioplasty.

Angioplasty↗
PubMed2002

Relationships between early B- and NK-lineage lymphocyte precursors in bone marrow.

Recent studies have demonstrated that lineage marker-negative (Lin(-)) c-kit(Lo) Flk-2/Flt3(+) IL-7R(+) Sca-1(Lo) CD27(+) Ly-6C(-) Thy-1(-)CD43(+) CD16/32(Lo/-) terminal deoxynucleotidyl transferase (TdT)(+) cells in murine bone marrow are functional lymphocyte precursors. However, it has not been clear if this is an obligate intermediate step for transit of multipotential hematopoietic stem cells to natural killer (NK) cells. We have now used serum-free, stromal cell-free cultures to determine that NK progenitors are enriched among an estrogen-regulated, c-kit(Lo) subset of the Lin(-) fraction. However, several experimental approaches suggested that this population is heterogeneous and likely represents a stage where B and NK lineages diverge. Although most B-cell precursors were directly sensitive to estrogen in culture, much of the NK-cell precursor activity in that fraction was hormone resistant. B-lineage potential was largely associated with interleukin 7 receptor alpha (IL-7R(alpha)) expression and was selectively driven in culture by IL-7. In contrast, many NK precursors did not display detectable amounts of this receptor and their maturation was selectively supported by IL-15. Finally, single-cell experiments showed that the Lin(-) c-kit(Lo) fraction contains a mixture of B/NK, B-restricted, and NK-restricted progenitors. Two-step culture experiments revealed that NK precursors become hormone resistant on or before acquisition of CD122, signaling commitment to the NK lineage. CD45R is preferentially, but not exclusively, expressed on maturing B-lineage cells. Production of these 2 blood cell types is regulated in bone marrow by common and then independent mechanisms that can now be studied with greater precision.

Animals↗
PubMed2005

T/B lineage choice occurs prior to intrathymic Notch signaling.

Commitment of hemopoietic progenitors to the T-cell lineage is a crucial requirement for T-cell development, yet the timing and developmental cues regulating this process remain controversial. Here we have devised a technique to analyze the T-cell/B-cell lineage potential of precursors that have been recruited to the fetal mouse thymus but which have yet to contact the thymic epithelial microenvironment. We show that lymphoid progenitors arriving at the thymus are not bipotent T/B precursors, and provide evidence that intrathymic Notch signaling is not the mechanism determining T/B lineage choice in migrant precursors. Rather, we provide evidence that Notch signaling influences T/B lineage choice in lymphoid precursors through interactions with defined stromal components within the fetal liver. Collectively, our data redefine our understanding of the role and timing of Notch signaling in relation to lineage choices in lymphoid precursors.

Animals↗
PubMed2003

Myogenic cells fates are antagonized by Notch only in asymmetric lineages of the Drosophila heart, with or without cell division.

During the formation of the Drosophila heart, a combinatorial network that integrates signaling pathways and tissue-specific transcription factors specifies cardiac progenitors, which then undergo symmetric or asymmetric cell divisions to generate the final population of diversified cardiac cell types. Much has been learned concerning the combinatorial genetic network that initiates cardiogenesis, whereas little is known about how exactly these cardiac progenitors divide and generate the diverse population of cardiac cells. In this study, we examined the cell lineages and cell fate determination in the heart by using various cell cycle modifications. By arresting the cardiac progenitor cell divisions at different developing stages, we determined the exact cell lineages for most cardiac cell types. We found that once cardiac progenitors are specified, they can differentiate without further divisions. Interestingly, the progenitors of asymmetric cell lineages adopt a myocardial cell fate as opposed to a pericardial fate when they are unable to divide. These progenitors adopt a pericardial cell fate, however, when cell division is blocked in numb mutants or in embryos with constitutive Notch activity. These results suggest that a numb/Notch-dependent cell fate decision can take place even in undivided progenitors of asymmetric cell divisions. By contrast, in symmetric lineages, which give rise to a single type of myocardial-only or pericardial-only progeny, repression or constitutive activation of the Notch pathway has no apparent effect on progenitor or progeny fate. Thus, inhibition of Notch activity is crucial for specifying a myogenic cell fate only in asymmetric lineages. In addition, we provide evidence that whether or not Suppressor-of-Hairless can become a transcriptional activator is the key switch for the Numb/Notch activity in determining a myocardial versus pericardial cell fate.

Animals↗
PubMed2005

The homeodomain protein PAL-1 specifies a lineage-specific regulatory network in the C. elegans embryo.

Maternal and zygotic activities of the homeodomain protein PAL-1 specify the identity and maintain the development of the multipotent C blastomere lineage in the C. elegans embryo. To identify PAL-1 regulatory target genes, we used microarrays to compare transcript abundance in wild-type embryos with mutant embryos lacking a C blastomere and to mutant embryos with extra C blastomeres. pal-1-dependent C-lineage expression was verified for select candidate target genes by reporter gene analysis, though many of the target genes are expressed in additional lineages as well. The set of validated target genes includes 12 transcription factors, an uncharacterized wingless ligand and five uncharacterized genes. Phenotypic analysis demonstrates that the identified PAL-1 target genes affect specification, differentiation and morphogenesis of C-lineage cells. In particular, we show that cell fate-specific genes (or tissue identity genes) and a posterior HOX gene are activated in lineage-specific fashion. Transcription of targets is initiated in four temporal phases, which together with their spatial expression patterns leads to a model of the regulatory network specified by PAL-1.

Analysis of Variance↗
PubMed1999

Prospero distinguishes sibling cell fate without asymmetric localization in the Drosophila adult external sense organ lineage.

The adult external sense organ precursor (SOP) lineage is a model system for studying asymmetric cell division. Adult SOPs divide asymmetrically to produce IIa and IIb daughter cells; IIa generates the external socket (tormogen) and hair (trichogen) cells, while IIb generates the internal neuron and sheath (thecogen) cells. Here we investigate the expression and function of prospero in the adult SOP lineage. Although Prospero is asymmetrically localized in embryonic SOP lineage, this is not observed in the adult SOP lineage: Prospero is first detected in the IIb nucleus and, during IIb division, it is cytoplasmic and inherited by both neuron and sheath cells. Subsequently, Prospero is downregulated in the neuron but maintained in the sheath cell. Loss of prospero function leads to 'double bristle' sense organs (reflecting a IIb-to-IIa transformation) or 'single bristle' sense organs with abnormal neuronal differentiation (reflecting defective IIb development). Conversely, ectopic prospero expression results in duplicate neurons and sheath cells and a complete absence of hair/socket cells (reflecting a IIa-to-IIb transformation). We conclude that (1) despite the absence of asymmetric protein localization, prospero expression is restricted to the IIb cell but not its IIa sibling, (2) prospero promotes IIb cell fate and inhibits IIa cell fate, and (3) prospero is required for proper axon and dendrite morphology of the neuron derived from the IIb cell. Thus, prospero plays a fundamental role in establishing binary IIa/IIb sibling cell fates without being asymmetrically localized during SOP division. Finally, in contrast to previous studies, we find that the IIb cell divides prior to the IIa cell in the SOP lineage.

Animals↗
PubMed2006

Detection of platelet-derived growth factor-alpha (PDGF-A) protein in cells of Leydig lineage in the postnatal rat testis.

Platelet-derived growth factor-A (PDGF-A) is a locally produced growth factor in the rat testis secreted by both Sertoli cells and Leydig cells. It has been suggested that PDGF-A may be involved in modulation of testosterone production and may be essential to Leydig cell differentiation, however it is not known at what stage of differentiation PDGF-A begins to be expressed in the cells of Leydig lineage in the postnatal rat testis. Therefore, the objectives of this research were to determine at what postnatal age and in which cell type is PDGF-A first expressed in cells of the adult Leydig cell lineage, and does PDGF-A expression coincide with expression of 3beta-hydroxysteroid dehydrogenase (3beta-HSD), an indicator of steroid hormone synthesis. Male Sprague Dawley rats of postnatal day 1, 7, 9-14, 21, 28, 40, 60, and 90 were used (n=6). Animals were euthanized and their testicles removed, fixed in Bouin's solution, embedded in paraffin, and 5 micrometers sections were prepared. Immunolocalization of PDGF-A and 3beta-HSD was carried out using a peroxidase-streptavidin-biotin method. PDGF-A was first detected in cells of the Leydig cell lineage at postnatal day 10 in progenitor cells, which were surrounding the seminiferous tubules (peritubular). These cells were confirmed to be the progenitor cells and not the mesenchymal or any other spindle-shaped cells in the testis interstitium by immunolocalization of 3beta-HSD and PDGF-A in the cells in adjacent sections of testis tissue from rats of postnatal days 10-14. After postnatal day 10, PDGF-A was continued to be expressed in subsequent cells of the Leydig lineage through day 90 (adult), however, was not present in peritubular mesenchymal precursor cells of the Leydig cell lineage or any other spindle-shaped cells in the testis interstitium at any tested age. These results revealed that PDGF-A first appears in Leydig progenitor cells in the postnatal rat testis at the onset of mesenchymal cell differentiation into progenitor cells at postnatal day 10 and suggest that a functional role(s) of PDGF-A in postnatally differentiated Leydig cells in the rat testis is established at the time of the onset of postnatal Leydig stem cell differentiation. It is suggested that the significance of the first expression of PDGF-A in the Leydig progenitor cells may be associated with inducing cell proliferation and migration of this cell away from the peritubular region during Leydig cell differentiation.

Animals↗
PubMed1998

Cell lineage relationship in the stomach of normal and genetically manipulated mice.

The oxyntic mucosa of the mouse stomach is lined with a heterogeneous population of cells that form numerous short pits continuous with long tubular glands. Tritiated thymidine radioautography has made it possible to pinpoint the origin of all cell types and to follow the differentiation/migration of different cell lineages along the pit-gland unit. The proliferating multipotent stem cells functionally anchored in the upper glandular region, the isthmus, give rise to three main lineage precursors: 1) pre-pit cells, which migrate upward to the pit while differentiating into mucus-producing pit cells; 2) pre-neck cells, which migrate downward to the glandular neck while differentiating into mucus-producing neck cells that, by approaching the glandular base, gradually change their phenotype into pepsinogen- and intrinsic factor-producing zymogenic cells; 3) pre-parietal cells, which differentiate into acid-producing parietal cells in the isthmus and then undergo bipolar migration towards the pit and the glandular base. Thus, parietal cells are the only cells that complete their differentiation in the isthmus and then migrate to be scattered throughout the pit-gland unit. To determine whether parietal cells play a role in controlling decisions about cell fate within the pit-gland unit, the gastric epithelium has been examined in transgenic mice expressing the H,K-ATPase beta-subunit-1035 to +24/simian virus 40 large T antigen fusion gene. The blockade in parietal cell differentiation in these mice produces an amplification of lineage precursors, a marked depletion of zymogenic cells and an increase in pit cell census. Ablation of parietal cells in another transgenic mouse model expressing the H,K-ATPase beta-subunit-1035 to +24/diphtheria toxin fragment A fusion gene also produces amplification of lineage precursors, and similar effects on zymogenic and pit cell census. These findings strongly suggest that parietal cells produce regulatory signals that control the cellular differentiation program of both pit and zymogenic cell lineages, and would hopefully improve our ability to identify the cellular pathways leading to malignant transformation.

Animals↗
PubMed2000

MHC recognition in thymic development: distinct, parallel pathways for survival and lineage commitment.

The molecular events triggered by MHC recognition and how they lead to the emergence of mature CD4 and CD8 lineage thymocytes are not yet understood. To address these questions, we have examined what signals are necessary to drive the development of CD8 lineage thymocytes in TCRalpha(-) mice in which TCR/MHC engagement cannot occur. We find that the combination of constitutive Notch activity and constitutive Bcl-2 expression are necessary and sufficient to allow the appearance of mature CD8 lineage thymocytes in TCRalpha(-) mice. In addition, Notch activity alone in TCRalpha(-) mice can induce the up-regulation of HES1, suggesting that thymocytes are competent to respond to Notch signaling in the absence of MHC recognition. These data indicate that survival and lineage commitment represent distinct, parallel pathways that occur as a consequence of MHC recognition, both of which are necessary for the development of mature CD8 lineage T cells.

Animals↗
PubMed2005

Enforced expression of Spi-B reverses T lineage commitment and blocks beta-selection.

The molecular changes that restrict multipotent murine thymocytes to the T cell lineage and render them responsive to Ag receptor signals remain poorly understood. In this study, we report our analysis of the role of the Ets transcription factor, Spi-B, in this process. Spi-B expression is acutely induced coincident with T cell lineage commitment at the CD4(-)CD8(-)CD44(-)CD25(+) (DN3) stage of thymocyte development and is then down-regulated as thymocytes respond to pre-TCR signals and develop beyond the beta-selection checkpoint to the CD4(-)CD8(-)CD44(-)CD25(-) (DN4) stage. We found that dysregulation of Spi-B expression in DN3 thymocytes resulted in a dose-dependent perturbation of thymocyte development. Indeed, DN3 thymocytes expressing approximately five times the endogenous level of Spi-B were arrested at the beta-selection checkpoint, due to impaired induction of Egr proteins, which are important molecular effectors of the beta-selection checkpoint. T lineage-committed DN3 thymocytes expressing even higher levels of Spi-B were diverted to the dendritic cell lineage. Thus, we demonstrate that the prescribed modulation of Spi-B expression is important for T lineage commitment and differentiation beyond the beta-selection checkpoint; and we provide insight into the mechanism underlying perturbation of development when that expression pattern is disrupted.

Animals↗
PubMed2006

Stem cells primed for action: polycomb repressive complexes restrain the expression of lineage-specific regulators in embryonic stem cells.

Stem cells are characterised by a capacity to self renew and generate progeny capable of differentiating along several defined lineage paths. Embryonic Stem (ES) cells are derived from the inner cell mass (ICM) of early-stage embryos and can contribute to all tissues of the developing embryo. Discovering how ES cell pluripotency and lineage induction is achieved is important for understanding normal development and for successfully applying stem cell-based therapies. A series of recent studies have shown that the chromatin profile of ES cells is unusual and have revealed a critical role for the Polycomb Repressive Complexes (PRCs) in maintaining pluripotency. In human and mouse ES cells many genes that encode transcription factors that are required for lineage specification bind PRC2 and carry bivalent (or opposing) histone signatures, being enriched for conventional indicators of active chromatin such as acetylated H3K9 and methylated H3K4, while lying within domains of repressive trimethylated H3K27. Mutant ES cells that lack H3K27 methylation inappropriately expressed these genes showing that PRC2 represses lineage-specific gene programs in ES cells. Here we discuss the implications of these new discoveries and explore the interdependence of PRC1 and PRC2 in regulating lineage-specific gene expression in ES cells.

Animals↗
PubMed1999

Loss of c-kit accompanies B-lineage commitment and acquisition of CD45R by most murine B-lymphocyte precursors.

Using surface markers, we identified two bone marrow (BM) subsets enriched for TdT+ cells on the brink of CD45R acquisition. These two populations, Lin-c-kitLo and Lin-c-kit-, consisting of 35.4% and 7. 4%, respectively, TdT+ cells, generated B-lineage cells in overnight cultures. Approximately half of the c-kitLo B-lineage precursors were bipotential, yielding myeloid and lymphoid progeny, whereas most that were c-kit- gave rise only to lymphocytes. Analysis of B-lineage progression during a finite culture period showed that the most mature precursors were concentrated in the Lin-c-kit- population. Moreover, a majority of the earliest CD45R+ pro-B cells in BM, identified as CD45R+ CD43(+) BP-1(-) CD25(-) natural killer (NK)1.1(-) sIgM-, were also c-kit-. These c-kit- cells, like their c-kitLo counterparts, expressed TdT, proliferated in response to interleukin (IL)-7, and generated sIgM+ cells. These data suggest that TdT expression is initiated as c-kit downregulation begins in Lin- cells, with progressive loss of c-kit during B-lineage differentiation. CD45R expression is initiated during the transition from c-kitLo to c-kit- with many cells losing c-kit before acquiring CD45R. The ability to isolate highly enriched populations of viable CD45R- precursors will be instrumental in characterizing the earliest B-lineage cells.

Animals↗
PubMed2000

Fidelity and infidelity in commitment to B-lymphocyte lineage development.

During B-lymphocyte development in mouse fetal liver and bone marrow, a pre-B I cell stage is reached in which the cells express B-lineage-specific genes, such as CD19, Ig alpha and Igbeta and VpreB and lambda5, which encode the surrogate light (SL) chain. In these pre-B I cells both alleles of the immunoglobulin heavy (IgH) chain locus are D(H)J(H) rearranged. Transplantation of pre-B I cells from wild-type (e.g. C57Bl/6) mice in histocompatible RAG-deficient hosts leads to long-term reconstitution of some of the mature B-cell compartments and to the establishment of normal IgM levels, a third of the normal serum IgA levels, and IgG levels below the detection limit. Neither T-lineage nor myeloid cells of donor origin can be detected in the transplanted hosts, indicating that the pre-B I cells are committed to B-lineage differentiation. Consequently, the B-cell-reconstituted hosts respond to T-cell-independent antigens but not to T-cell-dependent antigens. Responses to T-cell-dependent antigens can be restored in the pre-B I-cell-transplanted, RAG-deficient hosts by the concomitant transplantation of mature CD4+ T cells. The transplanted wild-type pre-B I cells do not home back to the bone marrow and become undetectable shortly after transplantation. B-lymphocyte development in Pax-5-deficient mice becomes arrested at the transition of pre-B I to pre-B II cells i.e. at the stage when V(H) to D(H)J(H) rearrangements occur and when the pre-B-cell receptor, complete with muH chains and SL chains, is normally formed. T-lineage and myeloid cell development in these mice is normal. Pre-B I cells of Pax-5-deficient mice have a wild-type pre-B I-cell-like phenotype: while they do not express Pax-5-controlled CD19 gene, and express Ig alpha to a lesser extent, they express Igbeta, VpreB and lambda5, and proliferate normally in vitro on stromal cells in the presence of interleukin (IL)-7. Clones of these pre-B I cells carry characteristic D(H)J(H) rearrangements on both IgH chain alleles. However, removal of IL-7 from the tissue cultures, unlike wild-type pre-B I cells, does not induce B-cell differentiation to surface IgM-expressing B cells, but induces macrophage differentiation. This differentiation into macrophages requires either the presence of stromal cells or addition of macrophage colony-stimulating factor (M-CSF). Addition of M-CSF followed by granulocyte-macrophage colony-stimulating factor induces the differentiation to MHC class II-expressing, antigen-presenting dendritic cells. In vitro differentiation to granulocytes and osteoclasts can also be observed in the presence of the appropriate cytokines. Moreover, transplantation of Pax-5-deficient pre-B I clones into RAG-deficient hosts, while not allowing B-cell differentiation, leads to the full reconstitution of the thymus with all stages of CD4-CD8- and CD4+CD8+ thymocytes, to normal positive and negative selection of thymocytes in the thymus, and to the development of normal, reactive mature CD4+ and CD8+ T-cell compartments in the peripheral lymphoid tissues, all carrying the clone-specific D(H)J(H) rearrangements. On the other hand, Ig alpha, Igbeta, VpreB and lambda5 are turned off in the thymocytes, demonstrating that the expression of these genes does not commit cells irreversibly to the B lineage. Further more, Pax-5-deficient pre-B I cells are long-term reconstituting cells. They home back to the bone marrow of the RAG-deficient host, can be reisolated and regrown in tissue culture, and can be retransplanted into a secondary RAG-deficient host. This again develops thymocytes and mature T cells and allows the transplanted clonal pre-B I cells to home to the bone marrow.

Animals↗