GATA-1 Regulates Growth and Differentiation of Definitive Erythroid Lineage Cells During In Vitro ES Cell Differentiation

Gfi1b:green fluorescent protein knock-in mice reveal a dynamic expression pattern of Gfi1b during hematopoiesis that is largely complementary to Gfi1

Gfi1b and Gfi1 are 37- and 55-kDa transcriptional repressors that share common features such as a 20-amino acid (aa) N-terminal SNAG domain, a nonconserved intermediary domain, and 6 highly conserved C-terminal zinc fingers. Both gene loci are under autoregulatory and cross-regulatory feedback control. We have generated a reporter mouse strain by inserting the cDNA for green fluorescent protein (GFP) into the Gfi1b gene locus which allowed us to follow Gfi1b expression during hematopoiesis and lymphopoiesis by measuring green fluorescence. We found highly dynamic expression patterns of Gfi1b in erythroid cells, megakaryocytes, and their progenitor cells (MEPS) where Gfi1 is not detected. Vice versa, Gfi1b could not be found in granulocytes, activated macrophages, or their granulomonocytic precursors (GMPs) or in mature naive or activated lymphocytes where Gfi1 is expressed, suggesting a complementary regulation of both loci during hematopoiesis. However, Gfi1b was found to be up-regulated in early stages of B-cell and in a subset of early T-cell development, where Gfi1 is also present, suggesting that cross-regulation of both loci exists but is cell-type specific.

alpha4-Integrin(+) endothelium derived from primate embryonic stem cells generates primitive and definitive hematopoietic cells

The mechanism of commencement of hematopoiesis in blood islands of the yolk sac and the aorta-gonad-mesonephros (AGM) region during primate embryogenesis remains elusive. In this study, we demonstrated that VE-cadherin(+)CD45(-) endothelial cells derived from nonhuman primate embryonic stem cells are able to generate primitive and definitive hematopoietic cells sequentially, as revealed by immunostaining of floating erythrocytes and colony-forming assay in cultures. Single bipotential progenitors for hematopoietic and endothelial lineages are included in this endothelial cell population. Furthermore, hemogenic activity of these endothelial cells is observed exclusively in the alpha4-integrin(+) subpopulation; bipotential progenitors are 4-fold enriched in this subpopulation. The kinetics of this hemogenic subpopulation is similar to that of hemogenic endothelial cells previously reported in the yolk sac and the AGM region in vivo in that they emerge for only a limited time. We suggest that VE-cadherin(+)CD45(-)alpha4-integrin(+) endothelial cells are involved in primitive and definitive hematopoiesis during primate embryogenesis, though VE-cadherin(-)CD45(-)alpha4-integrin(+) cells are the primary sources for primitive hematopoiesis.

Genomic organization, promoter activity, and expression of the human choline transporter-like protein 1

Choline transporter-like (CTL) proteins of the CTL1 family are novel transmembrane proteins implicated in choline transport for phospholipid synthesis. In this study, we characterized the 5'-flanking region of the human (h)CTL1 gene and examined some of the possible mechanisms of its regulation, including promoter activity, splicing, and expression. The transcription start site of the hCTL1 gene was mapped by 5'-rapid amplification of cDNA ends (RACE), and the presence of two splice variants, hCTL1a and hCTL1b, was investigated using isoform-specific PCR and 3'-RACE. The hCTL1 promoter region of approximately 900 bp was isolated from MCF-7 human breast cancer cells. The promoter was TATA-less and driven by a long stretch of GC-rich sequence in accordance with widespread expression of hCTL1 at both mRNA and protein levels. Deletion analyses demonstrated that a very strong promoter is contained within 500 bp of the transcription start site, and more upstream regions did not increase its activity. The core promoter that conferred the minimal transcription is within the -188/+27-bp region, and its activity varied in human breast cancer and mouse skeletal muscle cells. Multiple motifs within the promoter regulatory region bound nuclear factors from both cultured cells and normal human skeletal muscle. The motifs within the three regions [S1 (-92/-61 bp), S2 (-174/-145 bp), and S3 (-289/-260 bp)] contained overlapping binding sites for hematopoietic transcription factors and ubiquitous transcription factors, in line with the expected gene function. Genomic analyses demonstrated a high conservation of hCTL1 and mouse CTL1 proximal promoters. Accordingly, mRNA profiles demonstrated that human splice variants were expressed ubiquitously, as demonstrated for the mouse transcripts; however, they differed from the profiles of rat CTL1 transcripts, which were more restricted to neurons and intestinal tissues. The shorter hCTL1b variant contained the cytosolic COOH-terminal motif L651KKR654 for endoplasmic reticulum retrieval/retention. This retention signal was conserved in hCTL1b and rat and mouse CTL1b and is typical for transmembrane proteins of type 1 topology.

In vitro differentiation of c-myb(-/-) ES cells reveals that the colony forming capacity of unilineage macrophage precursors and myeloid progenitor commitment are c-Myb independent

Mice homozygous for an inactivated c-myb allele exhibit embryonic (primitive) blood formation but die at about day 15 of gestation because of a failure to generate adult (definitive) haemopoiesis. Recently, it has been shown that commitment to definitive haemopoiesis does occur in vivo, but that some point in the subsequent development towards the differentiated lineages is compromised. Here we have asked whether it is possible to demonstrate this same distinction between the development of primitive and definitive haemopoiesis during the in vitro differentiation of c-myb null ES cells, and whether this can be used to define more precisely at which developmental stage the absence of c-Myb blocks the adult haemopoietic lineages. We investigated the kinetics of progenitor formation and commitment to differentiation using a combination of colony forming assays and analysis of RNA and surface antigen expression. Primitive unilineage macrophage and erythroid precursor commitment could develop in the absence of c-Myb. No precursors characteristic of definitive haemopoiesis were detected; nevertheless, we could show the expression of a programme of transcription and surface antigens which is consistent with the appearance of definitive progenitors blocked at an early multipotential stage.