High-copy-number transposable elements comprise the majority of eukaryotic genomes where they are major contributors to gene and genome evolution. However, it remains unclear how a host genome can survive a rapid burst of hundreds or thousands of insertions because such bursts are exceedingly rare in nature and therefore difficult to observe in real time. In a previous study we reported that in a few rice strains the DNA transposon mPing was increasing its copy number by approximately 40 per plant per generation. Here we exploit the completely sequenced rice genome to determine 1,664 insertion sites using high-throughput sequencing of 24 individual rice plants and assess the impact of insertion on the expression of 710 genes by comparative microarray analysis. We find that the vast majority of transposable element insertions either upregulate or have no detectable effect on gene transcription. This modest impact reflects a surprising avoidance of exon insertions by mPing and a preference for insertion into 5' flanking sequences of genes. Furthermore, we document the generation of new regulatory networks by a subset of mPing insertions that render adjacent genes stress inducible. As such, this study provides evidence for models first proposed previously for the involvement of transposable elements and other repetitive sequences in genome restructuring and gene regulation.

Hepatoblasts are common progenitors for hepatocytes and biliary epithelial cells, although their nature remains largely unknown. In order to isolate and to characterize hepatoblasts, we searched for cell surface antigens expressed in mouse fetal hepatic cells by the signal sequence trap method and found that Dlk, also known as Pref-1, was strongly expressed in fetal liver. Immunohistochemical as well as northern analysis indicated that Dlk was highly expressed in the E10.5 liver bud. The strong expression continued until the E16.5 stage and was significantly downregulated thereafter. Using a monoclonal antibody against Dlk, we isolated Dlk+ cells either by a fluorescence-activated cell sorter or by an automatic magnetic cell sorter. Dlk+ cells isolated from fetal livers expressed albumin and formed colonies when cultured at low density with HGF and EGF for 5 days. Over 60% of colonies derived from E14.5 Dlk+ cells contained both albumin+ and cytokeratin 19+ cells, indicating that a majority of colony-forming Dlk+ cells are able to differentiate into both hepatocyte and biliary epithelial cell lineages. In addition,numerous microvilli were observed by electronmicroscopic analysis in most of those cultured cells, also indicating differentiation of Dlk+ cells under this condition. Furthermore, 7% of the colony-forming Dlk+cells were not only bipotential but also highly proliferative, forming a large colony containing more than 100 cells during 5 days of culture. By transplantation of Dlk+ cells into the spleen, donor-derived hepatocytes were found in the recipient liver, indicating that Dlk+cells differentiated into hepatocytes in vivo. These results indicate that Dlk+ cells are hepatoblasts and that Dlk is a useful marker to enrich highly proliferative hepatoblasts from fetal liver.

No abstract

Oncostatin M (OSM) is a member of the IL-6 family of cytokines. Mice deficient in the OSM receptor (OSMR -/-) showed impaired liver regeneration with persistent parenchymal necrosis after carbon tetrachloride (CCl 4 ) exposure. The recovery of liver mass from partial hepatectomy was also significantly delayed in OSMR -/-mice. In contrast to wildtype mice, CCl 4 administration only marginally induced expression of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 genes in OSMR -/-mice, correlating with the increased gelatinase activity of matrix metalloproteinase (MMP)-9 and matrix degradation in injured livers. The activation of STAT3 and expression of immediate early genes and cyclins were decreased in OSMR -/-liver, indicating that OSM signaling is required for hepatocyte proliferation and tissue remodeling during liver regeneration. We also found that CCl 4 administration in IL-6 -/-mice failed to induce OSM expression and that OSM administration in IL-6 -/-mice after CCl 4 injection induced the expression of cyclin D1 and proliferating cell nuclear antigen, suggesting that OSM is a key mediator of IL-6 in liver regeneration. Consistent with these results, administration of OSM ameliorated liver injury in wildtype mice by preventing hepatocyte apoptosis as well as tissue destruction. In conclusion, OSM and its signaling pathway may provide a useful therapeutic target for liver regeneration.

The crystallography, microstructure and mechanical property of as-quenched martensite of Fe-0.2C-Mn(-V) alloys of which the prior austenite grain sizes are 370-2 mm were studied. The prior austenite grain, whose size is larger than 28 mm, is divided by several packets. Those packets are subdivided by blocks containing sub-blocks, each of which corresponds to the Kurdjumov-Sachs variant. When the prior austenite grain size is about 2 mm, one packet tends to grow predominantly. Each packet is divided by blocks containing sub-blocks.