Characterization and retroviral transduction of an early human lymphomyeloid precursor assayed in nonswitched long-term culture on murine stroma

In the hierarchy of human hematopoietic progenitors, long-term culture-initiating cells (LTC-IC) and extended LTC-IC belong to the earliest cell populations that can be assayed in vitro. We report the identification of a multipotential lymphomyeloid progenitor detected in a nonswitch culture system. We observed the emergence of CD33+ myeloid and CD19+ B-lymphoid cells following plating of lineage-depleted (Lin-) CD34 -enriched or purified CD34+ CD38- cord blood cells on MS-5 stroma in the absence of exogenous cytokines. Both CD19+ CD20- pro-B and CD19+ CD20+ pre-B lymphocytes coexist with myeloid cells in long-term culture. A limiting dilution approach was used to show that a single CD34+ CD38- cell can generate lymphomyeloid progeny in conventional (5-week) and extended (10-week) cultures. Most of the clones in long-term culture or extended long-term culture contained not only lymphoid and myeloid cells, but also myeloid clonogenic progenitors. A high proportion of CD34+ CD38- cells gave rise to lymphomyeloid clones after 5 and 10 weeks of culturing (up to 48% and 16%, respectively), which distinguishes the assay reported here from those using switch culture conditions. We performed retroviral gene transfer experiments involving 1-3 days of exposure of Lin CD34+ -enriched cells to virus encoding enhanced green fluorescent protein. Monitoring of gene transfer efficiency into LTC-IC by enhanced green fluorescent protein fluorescence showed that it is possible to achieve marking of lymphomyeloid LTC-IC, albeit to a lesser extent than myeloid-restricted LTC-IC.

Retroviral transduction of TLS-ERG initiates a leukemogenic program in normal human hematopoietic cells

Many chimeric oncogenes have been identified by virtue of the association between chromosomal translocation and specific human leukemias. However, the biological mechanism by which these oncogenes disrupt the developmental program of normal human hematopoietic cells during the initiation of the leukemogenic process is poorly understood due to the absence of an appropriate experimental system to study their function. Here, we report that retroviral transduction of TLS-ERG, a myeloid leukemia-associated fusion gene, to human cord blood cells results in altered myeloid and arrested erythroid differentiation and a dramatic increase in the proliferative and self-renewal capacity of transduced myeloid progenitors. Thus, TLS-ERG expression alone induced a leukemogenic program that exhibited similarities to the human disease associated with this translocation. These results provide an experimental examination of the early stages of the human leukemogenic process induced by a single oncogene and establish a paradigm to functionally assay putative leukemogenic genes in normal human hematopoietic cells.

Structure and evolution of the human IKBA gene

IkappaBalpha belongs to a gene family whose members are characterized by their 6-7 Ankyrin repeats, which allow them to interact with members of the Rel family of transcription factors. We have sequenced a human IkappaBalpha genomic clone to determine its gene structure. The human IkappaBalpha gene (IKBA) has six exons and five introns that span approximately 3.5 kb. This genomic organization is similar to that of other members of the Ankyrin gene family. The human IKBA gene shares similar intron/exon boundaries with the human BCL3 and NFKB2 genes, which is consistent with their conserved Ankyrin repeats. To examine further the evolutionary relationship between human IkappaBalpha and other members of its gene family, we performed a phylogenetic analysis. Although the resulting phylogenetic tree does not identify a common ancestor of the IkappaBalpha and other members of its gene family, it indicates that this family diverges into two groups based on structure and function.

Three NF-kappa B sites in the I kappa B-alpha promoter are required for induction of gene expression by TNF alpha

NF-kappa B was first identified as a postive regulator which bound to a 10 bp sequence in the first intron of the Ig kappa light chain gene. Further characterization of this transcription factor has revealed that NF-kappa B is kept from binding to its consensus sequence by its inhibitor, IkB-alpha, which retains NF-kappa B in the cytoplasm. Upon receiving various extra- and intracellular signals, I kappa B-alpha is rapidly degraded and NF-kappa B is induced to translocate into the nucleus. This process precedes the rapid induction of I kappa B-alpha mRNA and protein. To understand how I kappa B-alpha is replenished, we have cloned and sequenced the 5' flanking region of the I kappa B-alpha gene and have identified the transcription start site and three NF-kappa B sites in this region. Further characterization of these NF-kappa B sites show that they have different affinities for three specific protein complexes which we identify here to consist of various members of the Rel family. In transient assays, cotransfection with a p65 expression vector is able to activate an I kappa B-alpha promoter-CAT reporter construct and all three NF-kappa B sites are required for full activation of the I kappa B-alpha gene following stimulation with TNF-alpha. Our data confirm a transcriptional autoregulatory loop involved in maintaining appropriate NF-kappa B and I kappa B-alpha levels in the cell.

Mapping and characterization of 129 cosmids on human chromosome 11p

We constructed cosmid libraries from human-hamster somatic cell hybrids that possess all or part of the short arm of chromosome 11 as their only human complement and isolated 129 human 11p clones. These cosmids map to 22 of 25 intervals distinguished by a hybrid panel for chromosome 11p. Forty-eight single-copy sequences were subcloned from 25 cosmids. Six of 17 (35%) single-copy sequences tested identify 11 new polymorphisms. Restriction endonuclease analysis identified CpG islands in 16 of 68 cosmids (23.5%). Analysis of the distribution of restriction endonuclease sites recognizing CpG dinucleotides showed that clusters of these sites, including those associated with the 5' region of an 11p13 Wilms' tumor gene, WT1, can span greater distances than generally recognized. The cosmids reported here should contribute to the construction of long-range physical maps and the isolation of additional genes on the short arm of chromosome 11.

Isolation and characterization of a zinc finger polypeptide gene at the human chromosome 11 Wilms' tumor locus

We have isolated a series of genomic and cDNA clones mapping within the boundaries of constitutional and tumor deletions that define the Wilms' tumor locus on human chromosome 11 (band p13). The transcription unit corresponding to these clones spans approximately 50 kb and encodes an mRNA approximately 3 kb long. This mRNA is expressed in a limited range of cell types, predominantly in the kidney and a subset of hematopoietic cells. The polypeptide encoded by this locus has a number of features suggesting a potential role in transcriptional regulation. These include the presence of four zinc finger domains and a region rich in proline and glutamine. The amino acid sequence of the predicted polypeptide shows significant homology to two growth regulated mammalian polypeptides, EGR1 and EGR2. The genetic localization of this gene, its tissue-specific expression, and the function predicted from its sequence lead us to suggest that it represents the 11p13 Wilms' tumor gene.

A genetic linkage map of 27 loci from PND to FY on the short arm of human chromosome I

A genetic linkage map of 27 loci on the short arm of human chromosome 1 has been developed by analysis of the 40 families in the Centre d'Etude du Polymorphisme Humain (CEPH) reference panel. Probes that recognize 14 novel RFLPs at loci designated D1S9-D1S22 were isolated from a flow-sorted chromosome 1 library. A linkage map of chromosome 1p was constructed from the genotypic data at these 14 loci, RFLPs at eight cloned genes (PND, ALPL, FUCA1, SRC2, MYCL, GLUT, TSHB, and NGFB), two previously identified RFLPs (D1S2 and D1S57), two blood group antigens (RH and FY), and the isozyme PGM1. All 27 loci form a continuous linkage group, from FY to PND, of 102 cM in males and 230 cM in females. This map provides a basis for highly informative multipoint mapping studies for most of the short arm of chromosome 1.