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Tetsuro Hirose

Publications and source records attributed to Tetsuro Hirose.

15 recordsLinked to original sources
PubMed2006

A spliceosomal intron binding protein, IBP160, links position-dependent assembly of intron-encoded box C/D snoRNP to pre-mRNA splicing.

Pre-mRNA splicing in vertebrates is molecularly linked to other processes. We previously reported that splicing is required for efficient assembly of intron-encoded box C/D small nucleolar ribonucleoprotein (snoRNP). In the spliceosomal C1 complex, snoRNP proteins efficiently assemble onto snoRNA sequences if they are located about 50 nt upstream of the intron branchpoint. Here, we identify the splicing factor responsible for coupling snoRNP assembly to intron excision. Intron binding protein (IBP) 160, a helicase-like protein previously detected in the spliceosomal C1 complex, binds the pre-mRNA in a sequence-independent manner, contacting nucleotides 33-40 upstream of the intron branch site, regardless of whether a snoRNA is present. Depletion of IBP160 abrogates snoRNP assembly in vitro. IBP160 binding directly to a snoRNA located too close to the intron branch site interferes with snoRNP assembly. Thus, IBP160 is the key factor linking snoRNP biogenesis and perhaps other postsplicing events to pre-mRNA splicing.

Animals↗
PubMed2004

Splicing of U12-type introns deposits an exon junction complex competent to induce nonsense-mediated mRNA decay.

Metazoan cells have two pathways for intron removal involving the U2- and U12-type spliceosomes, which contain mostly nonoverlapping sets of small nuclear ribonucleoproteins. We show that in vitro splicing of a U12-type intron assembles an exon junction complex (EJC) that is comparably positioned and contains many of the same components as that deposited by the U2-type spliceosome. The presence of a U12-type intron downstream of a premature termination codon within an open reading frame (ORF) induces nonsense-mediated decay of the mRNA in vivo. These findings suggest a common pathway for EJC assembly by the two spliceosomes and highlight the evolutionary age of the EJC and its downstream functions in gene expression.

Cell Line↗
PubMed2004

Multiple elements required for translation of plastid atpB mRNA lacking the Shine-Dalgarno sequence.

The mechanism of translational initiation differs between prokaryotes and eukaryotes. Prokaryotic mRNAs generally contain within their 5'-untranslated region (5'-UTR) a Shine-Dalgarno (SD) sequence that serves as a ribosome-binding site. Chloroplasts possess prokaryotic-like translation machinery, and many chloroplast mRNAs have an SD-like sequence, but its position is variable. Tobacco chloroplast atpB mRNAs contain no SD-like sequence and are U-rich in the 5'-UTR (-20 to -1 with respect to the start codon). In vitro translation assays with mutated mRNAs revealed that an unstructured sequence encompassing the start codon, the AUG codon and its context are required for translation. UV crosslinking experiments showed that a 50 kDa protein (p50) binds to the 5'-UTR. Insertion of an additional initiation region (SD-sequence and AUG) in the 5'-UTR, but not downstream, arrested translation from the authentic site; however, no inhibition was observed by inserting only an AUG triplet. We hypothesize for translational initiation of the atpB mRNA that the ribosome enters an upstream region, slides to the start codon and forms an initiation complex with p50 and other components.

5' Untranslated Regions↗
PubMed2004

Thy1-positive mesenchymal cells promote the maturation of CD49f-positive hepatic progenitor cells in the mouse fetal liver.

Previously, we reported a system to enrich mouse fetal hepatic progenitor cells (HPCs) by forming cell aggregates. In this study, we sorted two cell populations, CD49f(+)Thy1(-)CD45(-) cells (CD49f-positive cells) and CD49f(+/-)Thy1(+)CD45(-) cells (Thy1-positive cells), from the cell aggregates using a flow cytometer. CD49f-positive cells stained positive for endodermal specific markers such as alpha-fetoprotein (AFP), albumin (ALB), and cytokeratin 19 (CK19), and are thus thought to be HPCs. However, Thy1-positive cells were a morphologically heterogeneous population; reverse-transcription polymerase chain reaction (RT-PCR) and immunocytochemical analyses revealed the expression of mesenchymal cell markers such as alpha-smooth muscle actin, desmin, and vimentin, but not of AFP, ALB, or CK19. Therefore, Thy1-positive cells were thought to be of a mesenchymal lineage. When these two cell populations were co-cultured, the CD49f-positive colonies matured morphologically and stored a significant amount of glycogen. Furthermore, real-time RT-PCR demonstrated an increased expression of tyrosine amino transferase and tryptophan oxygenase mRNA, and transmission electron microscopy confirmed that co-cultured cells produced mature hepatocytes. However, when CD49f-positive cells were cultured alone or when the two populations were cultured separately, the CD49f-positive cells did not mature. These results indicate that CD49f-positive cells are primitive hepatic endodermal cells with the capacity to differentiate into hepatocytes, and that Thy1-positive cells promote the maturation of CD49f-positive cells by direct cell-to-cell contact. In conclusion, we were able to isolate CD49f-positive primitive hepatic endodermal cells and Thy1-positive mesenchymal cells and to demonstrate the requirement of cell-to-cell contact between these cell types for the maturation of the hepatic precursors.

Animals↗
PubMed2004

Commitment of bone marrow cells to hepatic stellate cells in mouse.

BACKGROUND/AIMS: Recently, several cells found within the liver have been reported to derive from bone marrow (BM). This study sought to examine the commitment of BM cells to hepatic stellate cell (HSC) lineage in mouse liver. METHODS: We transplanted BM cells from green fluorescent protein (GFP) transgenic mice into age-matched C57BL/J mice. Hepatic nonparenchymal cells were isolated from the livers of BM-transplanted mice using density gradient centrifugation with Nycodenz. The expression of lineage markers by the isolated cells was evaluated by RT-PCR and immunostaining. We then examined the histology of liver tissues obtained from BM-transplanted mice with and without carbon tetrachloride-induced injury. RESULTS: GFP-expressing cells with intracytoplasmic lipid droplets comprised 33.4 +/- 2.3% of the cells isolated by density gradient centrifugation. These cells expressed the HSC lineage markers, such as desmin and glial fibrillary acidic protein (GFAP), by both RT-PCR and immunostaining. During a 7-day culture, GFP-positive cells began to express alpha-smooth muscle actin, a marker of activated HSC. In the liver of BM-transplanted mice, GFP-positive nonparenchymal cells expressed GFAP and extended their process around hepatocytes. Upon liver injury, these cells also co-expressed desmin and alpha-smooth muscle actin. CONCLUSIONS: Nonparenchymal cells, derived from transplanted BM, acquired HSC characteristics in both quiescent and activated states.

Animals↗
PubMed2004

Functional Shine-Dalgarno-like sequences for translational initiation of chloroplast mRNAs.

Many of the chloroplast mRNAs possess Shine-Dalgarno (SD)-like sequences (typically GGAGG) in the 5'-untranslated regions, but the position is highly variable. Using a homologous in vitro translation system, we assessed the role for translation of SD-like sequences in four tobacco chloroplast mRNAs. The rbcL mRNA has a typical SD-like sequence at a position similar to the conserved position (-12 to -4 with respect to the start codon) observed in E. coli, and this sequence was found to be essential for translation. This was also the case for the atpE mRNA. However, SD-like sequences in the rps12 mRNA and in the petB mRNA is located far from (-44 to -42) and too close to (-5 to -2) the initiation codon, respectively, and these sequences were not essential for translation. These results indicate that functional SD-like sequences are located around 10 nucleotides upstream from the translational start codon. Competition assays confirmed that a functional SD-like sequence interacts with the 3' terminus of chloroplast 16S rRNA.

Base Sequence↗
PubMed2004

In vitro RNA editing systems from higher plant chloroplasts.

RNA editing in higher plant chloroplasts involves C-to-U conversion at ~30 specific sites. In vitro systems supporting accurate editing have been developed from tobacco and pea chloroplasts. mRNA substrates labeled with 32P at C residues to be edited provide sensitive detection of editing activity in vitro. The present systems allow the rapid identification of cis-elements using mutated mRNA substrates and trans-acting factors by ultraviolet crosslinking.

Base Sequence↗
PubMed2003

A trial on regeneration therapy of rat liver cirrhosis by controlled release of hepatocyte growth factor.

This paper is an investigation of therapeutic trial on the liver cirrhosis by the controlled release of hepatocyte growth factor (HGF). Biodegradable microspheres were prepared from gelatin for the controlled release of HGF. Rats with liver cirrhosis were prepared by the intraperitoneal injection of thioacetamide at a dose of 0.2 g/kg every other day for 10 weeks. The rats received single intraperitoneal injection of gelatin microspheres incorporating 2 or 0.4 mg of HGF, 2 or 0.4 mg of free HGF, and HGF-free, empty gelatin microspheres 3 weeks after the last thioacetamide injection. Histological observation of the rat liver revealed that injection of gelatin microspheres incorporating HGF effectively allowed to recovery from the liver fibrosis, inducing liver regeneration. When the histological score, the area of fibrous linkage, and the hydroxyproline content in the liver were evaluated, all values were significantly smaller than those of the free HGF and empty gelatin microspheres injection, irrespective of the HGF dose. It is concluded that the gelatin microspheres incorporating HGF are a promising therapeutic method of inducing successful liver regeneration by fibrosis digestion in rats with cirrhosis.

Animals↗
PubMed2003

Increased expression of collagenase in the liver induces hepatocyte proliferation with cytoplasmic accumulation of beta-catenin in the rat.

BACKGROUND/AIMS: Since the hepatic extracellular matrix is remodeled in liver regeneration, we investigated whether increased collagenase activity in the liver can induce hepatocyte proliferation in vivo. METHODS: To increase hepatic collagenase activity, human matrix metalloproteinase-1 was delivered to the rat liver by the recombinant adenoviral vector Ad5MMP-1. RESULTS: Hepatic delivery of Ad5MMP-1 increased the 5-bromo-2-deoxyuridine labeling index and mitotic index in hepatocytes, causing an increase in the dry liver weight; control adenovirus, Ad5LacZ, had minimal effect. Hepatocyte proliferation started approximately 48 h after infection with Ad5MMP-1 and ended after about 2 weeks. The increase in the dry liver weight also returned to baseline after 2 weeks. Transient liver injury by Ad5MMP-1, reflected by increased aspartate and alanine aminotransferase levels, peaked around 1 week, and was associated with hepatocyte apoptosis. Collagenase-induced hepatocyte proliferation was accompanied by cytoplasmic accumulation of beta-catenin and a transient decrease in E-cadherin expression. CONCLUSIONS: Modification of the hepatic extracellular matrix by collagenase induces transient hepatocyte proliferation in vivo, suggesting that the condition of the hepatic extracellular matrix per se plays a pivotal role in regulating hepatocyte proliferation.

Adenoviridae↗
PubMed2003

Purification of adult hepatic progenitor cells using green fluorescent protein (GFP)-transgenic mice and fluorescence-activated cell sorting.

BACKGROUND/AIMS: Recent advances in stem cell research have revealed that hepatic stem/progenitor cells may play an important role in liver development and regeneration. However, a lack of detectable definitive markers in viable cells has hindered their primary culture from adult livers. METHODS: Enzymatically dissociated liver cells from green fluorescent protein (GFP)-transgenic mice, which express GFP highly in liver endodermal cells, were sorted by GFP expression using a fluorescence-activated cell sorter. Sorted cells were characterized, and also low-density cultured for extended periods to determine their proliferation and clonal differentiation capacities. RESULTS: When CD45(-)TER119(-) side-scatter(low) GFP(high) cells were sorted, alpha-fetoprotein-positive immature endoderm-characterized cells, having high growth potential, were present in this population. Clonal analysis and electron microscopic evaluation revealed that each single cell of this population could differentiate not only into hepatocytes, but also into biliary epithelial cells, showing their bilineage differentiation activity. When surface markers were analyzed, they were positive for Integrin-alpha6 and -beta1, but negative for c-Kit and Thy1.1. CONCLUSIONS: Combination of GFP-transgenic mice and fluorescence-activated cell sorting enabled purification of hepatic progenitor cells from adult mouse liver. Further analysis of this population may lead to purification of their human correspondence that would be an ideal cell-source candidate for regenerative medicine.

Age Factors↗
PubMed2003

Splicing-dependent and -independent modes of assembly for intron-encoded box C/D snoRNPs in mammalian cells.

In mammalian cells, all small nucleolar RNAs (snoRNAs) that guide rRNA modification are encoded within the introns of host genes. An optimal position about 70 nts upstream of the 3' splice site of the host intron is critical for efficient expression of box C/D snoRNAs in vivo, suggesting synergy with splicing. Here, we have used a coupled in vitro splicing-snoRNA processing system to demonstrate that assembly of box C/D snoRNP proteins is the step affected by snoRNA location, and that active splicing is essential for snoRNP assembly. Splicing blockage experiments further reveal that snoRNP proteins bind specifically at the spliceosomal C1 complex stage. In contrast, splicing-independent snoRNP assembly can occur in vitro on snoRNAs that possess stable external stems. In vivo analyses confirm that a stable stem can compensate for the unusual position of those few box C/D snoRNAs located far from the 3' splice site of their host intron.

Animals↗
PubMed2003

Enrichment of hepatic progenitor cells from adult mouse liver.

Hepatic progenitor cells (HPCs) have been characterized in several drug-treated rodent models and in the fetal liver; however, their properties have not been fully clarified in the normal adult liver, presumably because of their relatively small population and the existence of mature hepatocytes. In an attempt to resolve this issue, we developed a new enrichment system for HPCs using their cell aggregate formation properties. Nonparenchymal cells (NPCs) derived from enzymatically digested liver cells in normal adult mouse liver were treated in a hypoxic 2-hour suspension culture under constant shaking. This procedure resulted in cell aggregate formation and almost complete elimination of mature hepatocytes. Cell aggregates were formed only in Ca(2+)-containing medium, suggesting cadherin-dependent cell-cell adhesion. In these cell aggregates, 95% consisted of vascular endothelial cells that expressed VE-cadherin. The remaining 5% consisted of rapidly proliferating, small epithelial cells that expressed alpha-fetoprotein (AFP), E-cadherin, and albumin but not cytokeratin 19 (CK19), alpha-smooth muscle actin, or VE-cadherin. These results are consistent with an immature hepatic cell phenotype. When these immature hepatic cells were cultured with 10(-7) mol/L dexamethasone and 1% dimethyl sulfoxide, the de novo expression of mature hepatocyte markers such as tryptophan-2,3-dioxygenase (TO) was induced concomitantly with the induction of morphologic characteristics such as mitochondria- and peroxisome-rich cytoplasm and bile canaliculi formation. In conclusion, our methodology allows the enrichment of immature hepatic cells from the normal adult mouse. These cells are capable of growth and maturation along the hepatocyte lineage, indicating that these cells are HPCs.

Animals↗
PubMed2002

Contribution of bone marrow cells to liver regeneration after partial hepatectomy in mice.

BACKGROUND/AIMS: We examined whether bone marrow (BM) cells can commit to liver-consisting cells during liver regeneration after partial hepatectomy, using mice transplanted with green fluorescent protein (GFP) positive BM from GFP transgenic mice. METHODS: Partial hepatectomy or sham operation was performed. Lineage marker analysis of GFP positive liver cells was by immunostaining and flow cytometry. DiI-labeled acetylated low-density lipoprotein uptake or microsphere phagocytosis was examined in vitro. Lineage marker expression in BM and peripheral blood (PB) cells, and the vascular endothelial growth factor (VEGF) concentration in the liver were also examined. RESULTS: In hepatectomized mice, significantly more GFP positive cells participated in liver sinusoid than in sham-operated mice, expressing CD31 but not albumin. The percentage of cells that incorporated acetylated low-density lipoprotein but not microspheres was 69.5+/-3.4%, while 28.3+/-2.6% incorporated both, revealing sinusoidal endothelial and Kupffer cells, respectively. Increased expression of the CD31 and CD16/CD32 on GFP positive liver cells was also detected. The elevation of the VEGF concentration during liver regeneration and the increase in the CD34 and Flk-1 expression in the liver, BM, and PB cells suggested endothelial progenitor cell mobilization. CONCLUSIONS: GFP cell-marking provided direct evidence of the BM cells participation in liver regeneration after hepatectomy, where the majority was committed to sinusoidal endothelial cells probably through endothelial progenitor cell mobilization.

Animals↗
PubMed2002

Establishment of a highly efficient gene transfer system for mouse fetal hepatic progenitor cells.

Because of a donor shortage problem in liver transplantation, cell transplantation has been anticipated as a useful bridge or substitute therapy, and has necessitated the development of cell sources other than donated organs. Therefore, the use of fetal hepatic progenitor cells (HPCs) is now being focused on. In this study, we intended to establish an efficient ex vivo nonviral gene-transfer system using a newly developed isolation and culture system for mouse fetal HPCs. Fetal HPCs, characterized using immunocytochemistry and reverse-transcription polymerase chain reaction (RT-PCR) for lineage markers, were collected from E13.5 Balb/c mice using change in size because of cell aggregation by their homophilic cell-to-cell binding occurring during suspension culture. Optimal conditions for culture and ex vivo gene transfection for fetal HPCs were determined by (3)H-thymidine incorporation and the expression efficacy of transfected red fluorescent protein (DsRed) gene in different culture media. The optimum timing for gene transfection was also evaluated. To evaluate the in vivo expression of the transferred gene, DsRed-transferred fetal HPCs were transplanted into 70% partially hepatectomized allogenic mice. The highest efficacy of DsRed gene transfection into fetal HPCs in vitro (45% +/- 12.3%) was achieved with culture media, which also enabled the highest (3)H-thymidine incorporation, containing the deleted form of hepatocyte growth factor (dHGF) and insulin, and when transfection was performed immediately after isolation. In vivo DsRed expression in fetal HPCs was maintained concomitantly with albumin expression even after HPC transplantation. In conclusion, we established a highly efficient in vitro gene transfer system for mouse fetal HPCs using a newly developed isolation and culture system.

Animals↗