DNA microarray analysis was combined with a modified single-cell PCR procedure to study gene expression profiles of single cells at different stages of pancreatic development. This method identifies distinct cell types at embryonic day 10.5, a stage when the pancreatic epithelium is morphologically uniform. Some cells express unexpected combinations of genes, and these expression patterns provide new insights into pancreas development. Following on these findings, we use PCR products from different cell types to identify novel pancreatic genes, some of which mark subtypes of developing pancreatic cells. By integrating these data with previous genetic and biochemical studies, we propose a pathway for pancreatic cell development. This form of single-cell transcriptional analysis can be applied to any developmental process or tissue to characterize distinct cell types.

Here we show that the Escherichia coli expressed monomers of placenta growth factor (PLGF) 129 and vascular endothelial growth factor (VEGF) 165 can be refolded in vitro to form PLGF/VEGF heterodimers. The purified recombinant PLGF/VEGF heterodimers and VEGF homodimers have potent mitogenic and chemotactic effects on endothelial cells. However, PLGF/VEGF heterodimers display 20 -50-fold less mitogenic activity than VEGF 165 homodimers. In contrast, PLGF 129 homodimers have little or no effect in these in vitro assays. We also demonstrate the presence of natural PLGF/ VEGF heterodimers in the conditioned media of various human tumor cell lines. While PLGF/VEGF heterodimers bind with high affinity to a soluble Flk-1/KDR receptor, PLGF 129 homodimers fail to bind to this receptor. Cross-linking of 125

BackgroundColibactin is a nonribosomal peptide-polyketide synthesized by multi-enzyme complexes encoded by the pks gene cluster. Colibactin-producing Escherichia coli have been demonstrated to induce host DNA damage and promote colorectal cancer (CRC) development. In Taiwan, the occurrence of pyogenic liver abscess (PLA) has been suggested to correlate with an increasing risk of CRC, and Klebsiella pneumoniae is the predominant PLA pathogen in TaiwanMethodology/Principal FindingsAt the asn tRNA loci of the newly sequenced K. pneumoniae 1084 genome, we identified a 208-kb genomic island, KPHPI208, of which a module identical to the E. coli pks colibactin gene cluster was recognized. KPHPI208 consists of eight modules, including the colibactin module and the modules predicted to be involved in integration, conjugation, yersiniabactin production, microcin production, and unknown functions. Transient infection of BALB/c normal liver cells with K. pneumoniae 1084 increased the phosphorylation of histone H2AX, indicating the induction of host DNA damage. Colibactin was required for the genotoxicity of K. pneumoniae 1084, as it was diminished by deletion of clbA gene and restored to the wild type level by trans-complementation with a clbA coding plasmid. Besides, BALB/c mice infected with K. pneumoniae 1084 exhibited enhanced DNA damage in the liver parenchymal cells when compared to the isogenic clbA deletion mutant. By PCR detection, the prevalence of pks-positive K. pneumoniae in Taiwan is 25.6%, which is higher than that reported in Europe (3.5%), and is significantly correlated with K1 type, which predominantly accounted for PLA in Taiwan.ConclusionsOur knowledge regarding how bacteria contribute to carcinogenesis has just begun. The identification of genotoxic K. pneumoniae and its genetic components will facilitate future studies to elucidate the molecular basis underlying the link between K. pneumoniae, PLA, and CRC.

The murine myeloproliferative leukemia virus has previously been shown to contain a fragment of the coding region of the c‐mpl gene, a member of the cytokine receptor superfamily. We have isolated cDNA and genomic clones encoding murine c‐mpl and localized the c‐mpl gene to mouse chromosome 4. Since some members of this superfamily function by transducing a proliferative signal and since the putative ligand of mpl is unknown, we have generated a chimeric receptor to test the functional potential of mpl. The chimera consists of the extracellular domain of the human interleukin‐4 receptor and the cytoplasmic domain of mpl. A mouse hematopoietic cell line transfected with this construct proliferates in response to human interleukin‐4, thereby demonstrating that the cytoplasmic domain of mpl contains all elements necessary to transmit a growth stimulatory signal. In addition, we show that 25–40% of mpl mRNA found in the spleen corresponds to a novel truncated and potentially soluble isoform of mpl and that both full‐length and truncated forms of mpl protein can be immunoprecipitated from lysates of transfected COS cells. Interestingly, however, although the truncated form of the receptor possesses a functional signal sequence and lacks a transmembrane domain, it is not detected in the culture media of transfected cells.