Gene-trap mutagenesis using Mol/MSM-1 embryonic stem cells from MSM/Ms mice

4.5SH RNA counteracts deleterious exonization of SINE B1 in mice

4.5SH RNA is a highly abundant, small rodent-specific noncoding RNA that localizes to nuclear speckles enriched in pre-mRNA-splicing regulators. To investigate the physiological functions of 4.5SH RNA, we have created mutant mice that lack the expression of 4.5SH RNA. The mutant mice exhibited embryonic lethality, suggesting that 4.5SH RNA is an essential species-specific noncoding RNA in mice. RNA-sequencing analyses revealed that 4.5SH RNA protects the transcriptome from abnormal exonizations of the antisense insertions of the retrotransposon SINE B1 (asB1), which would otherwise introduce deleterious premature stop codons or frameshift mutations. Mechanistically, 4.5SH RNA base pairs with complementary asB1-containing exons via the target recognition region and recruits effector proteins including Hnrnpm via its 5' stem loop region. The modular organization of 4.5SH RNA allows us to engineer a programmable splicing regulator to induce the skipping of target exons of interest. Our results also suggest the general existence of splicing regulatory noncoding RNAs.

FOXO1 promotes endothelial cell elongation and angiogenesis by up-regulating the phosphorylation of myosin light chain 2

The forkhead box O1 (FOXO1) is an important transcription factor related to proliferation, metabolism, and homeostasis, while the major phenotype of FOXO1-null mice is abnormal vascular morphology, such as vessel enlargement and dilation. In in vitro mouse embryonic stem cell (ESC)-differentiation system, Foxo1-/- vascular endothelial cells (ECs) fail to elongate, and mimic the abnormalities of FOXO1-deficiency in vivo. Here, we identified the PPP1R14C gene as the FOXO1 target genes responsible for elongating using transcriptome analyses in ESC-derived ECs (ESC-ECs), and found that the FOXO1-PPP1R14C-myosin light chain 2 (MLC2) axis is required for EC elongation during angiogenesis. MLC2 is phosphorylated by MLC kinase (MLCK) and dephosphorylated by MLC phosphatase (MLCP). PPP1R14C is an inhibitor of PP1, the catalytic subunit of MLCP. The abnormal morphology of Foxo1-/- ESC-ECs was associated with low level of PPP1R14C and loss of MLC2 phosphorylation, which were reversed by PPP1R14C-introduction. Knockdown of either FOXO1 or PPP1R14C suppressed vascular cord formation and reduced MLC2 phosphorylation in human ECs (HUVECs). The mouse and human PPP1R14C locus possesses an enhancer element containing conserved FOXO1-binding motifs. In vivo chemical inhibition of MLC2 phosphorylation caused dilated vascular structures in mouse embryos. Furthermore, foxo1 or ppp1r14c-knockdown zebrafish exhibited vascular malformations, which were also restored by PPP1R14C-introduction. Mechanistically, FOXO1 suppressed MLCP activity by up-regulating PPP1R14C expression, thereby promoting MLC2 phosphorylation and EC elongation, which are necessary for vascular development. Given the importance of MLC2 phosphorylation in cell morphogenesis, this study may provide novel insights into the role of FOXO1 in control of angiogenesis.

Fibroblast growth factor 18 stimulates the proliferation of hepatic stellate cells, thereby inducing liver fibrosis

Liver fibrosis results from chronic liver injury triggered by factors such as viral infection, excess alcohol intake, and lipid accumulation. However, the mechanisms underlying liver fibrosis are not fully understood. Here, we demonstrate that the expression of fibroblast growth factor 18 (Fgf18) is elevated in mouse livers following the induction of chronic liver fibrosis models. Deletion of Fgf18 in hepatocytes attenuates liver fibrosis; conversely, overexpression of Fgf18 promotes liver fibrosis. Single-cell RNA sequencing reveals that overexpression of Fgf18 in hepatocytes results in an increase in the number of Lrat+ hepatic stellate cells (HSCs), thereby inducing fibrosis. Mechanistically, FGF18 stimulates the proliferation of HSCs by inducing the expression of Ccnd1. Moreover, the expression of FGF18 is correlated with the expression of profibrotic genes, such as COL1A1 and ACTA2, in human liver biopsy samples. Thus, FGF18 promotes liver fibrosis and could serve as a therapeutic target to treat liver fibrosis.

Topoisomerase IIIβ Deficiency Induces Neuro-Behavioral Changes and Brain Connectivity Alterations in Mice

Topoisomerase IIIβ (Top3β), the only dual-activity topoisomerase in mammals that can change topology of both DNA and RNA, is known to be associated with neurodevelopment and mental dysfunction in humans. However, there is no report showing clear associations of Top3β with neuropsychiatric phenotypes in mice. Here, we investigated the effect of Top3β on neuro-behavior using newly generated Top3β deficient (Top3β^-/-) mice. We found that Top3β^-/- mice showed decreased anxiety and depression-like behaviors. The lack of Top3β was also associated with changes in circadian rhythm. In addition, a clear expression of Top3β was demonstrated in the central nervous system of mice. Positron emission tomography/computed tomography (PET/CT) analysis revealed significantly altered connectivity between many brain regions in Top3β^-/- mice, including the connectivity between the olfactory bulb and the cerebellum, the connectivity between the amygdala and the olfactory bulb, and the connectivity between the globus pallidus and the optic nerve. These connectivity alterations in brain regions are known to be linked to neurodevelopmental as well as psychiatric and behavioral disorders in humans. Therefore, we conclude that Top3β is essential for normal brain function and behavior in mice and that Top3β could be an interesting target to study neuropsychiatric disorders in humans.

Bone morphogenetic protein 4 differently promotes distinct VE-cadherin+ precursor stages during the definitive hematopoietic development from embryonic stem cell-derived mesodermal cells

Definitive hematopoietic cells develop from fetal liver kinase 1 (Flk1)⁺ mesodermal cells during the in vitro differentiation of mouse embryonic stem cells (ESCs). VE-cadherin⁺CD41^-CD45^-(V⁺41^-45^-) hemogenic endothelial cells (HECs) and VE-cadherin⁺CD41⁺CD45^- (V⁺41⁺45^-) cells mediate the definitive hematopoietic development from Flk1⁺ cells. Bone morphogenetic protein 4 (BMP4) is known to be essential for the formation of mesoderm. However, the role of BMP4 in differentiation of the VE-cadherin⁺ definitive hematopoietic precursors from the mesoderm has been elusive. We addressed this issue using a co-aggregation culture of ESC-derived Flk1⁺ cells with OP9 stromal cells. This culture method induced V⁺41^-45^- cells, V⁺41⁺45^- cells, and CD45⁺ cells from Flk1⁺ cells. V⁺41⁺45^- cells possessed potential for erythromyeloid and T-lymphoid differentiation. When Flk1⁺ cells were cultured in the presence of a high concentration of BMP4, the generation of V⁺41^-45^- cells was enhanced. The increase in V⁺41^-45^- cells led to the subsequent increase in V⁺41⁺45^- and CD45⁺ cells. The addition of BMP4 also increased hematopoietic colony-forming cells of various lineages. Furthermore, BMP4 promoted the expansion of V⁺41⁺45^- cells independently of the preceding V⁺41^-45^- cell stage. These results suggest that BMP4 has promotive effects on the differentiation of V⁺41^-45^- HECs from Flk1⁺ mesodermal cells and the subsequent proliferation of V⁺41⁺45^- hematopoietic precursors. These findings may provide insights for establishing a culture system to induce definitive hematopoietic stem cells from ESCs.

Gene trapping reveals a new transcriptionally active genome element: The chromosome-specific clustered trap region

Nearly half of the human genome consists of repetitive sequences such as long interspersed nuclear elements. The relationship between these repeating sequences and diseases has remained unclear. Gene trapping is a useful technique for disrupting a gene and expressing a reporter gene by using the promoter activity of the gene. The analysis of trapped genes revealed a new genome element-the chromosome-specific clustered trap (CSCT) region. For any examined sequence within this region, an equivalent was found using the BLAT of the University of California, Santa Cruz (UCSC) Genome Browser. CSCT13 mapped to chromosome 13 and contained only three genes. To elucidate its in vivo function, the whole CSCT13 region (1.6 Mbp) was deleted using the CRISPR/Cas9 system in mouse embryonic stem cells, and subsequently, a CSCT13 knockout mouse line was established. The rate of homozygotes was significantly lower than expected according to Mendel's laws. In addition, the number of offspring obtained by mating homozygotes was significantly smaller than that obtained by crossing controls. Furthermore, CSCT13 might have an effect on meiotic homologous recombination. This study identifies a transcriptionally active CSCT with an important role in mouse development.

The canonical smooth muscle cell marker TAGLN is present in endothelial cells and is involved in angiogenesis

Elongation of vascular endothelial cells (ECs) is an important process in angiogenesis; however, the molecular mechanisms remain unknown. The actin-crosslinking protein TAGLN (transgelin, also known as SM22 or SM22α) is abundantly expressed in smooth muscle cells (SMCs) and is widely used as a canonical marker for this cell type. In the course of studies using mouse embryonic stem cells (ESCs) carrying an Tagln promoter-driven fluorescence marker, we noticed activation of the Tagln promoter during EC elongation. Tagln promoter activation co-occurred with EC elongation in response to vascular endothelial growth factor A (VEGF-A). Inhibition of phosphoinositide 3-kinase (PI3K)-Akt signaling and mTORC1 also induced EC elongation and Tagln promoter activation. Human umbilical vein endothelial cells (HUVECs) elongated, activated the TAGLN promoter and increased TAGLN transcripts in an angiogenesis model. Genetic disruption of TAGLN augmented angiogenic behaviors of HUVECs, as did the disruption of TAGLN2 and TAGLN3 genes. Tagln expression was found in ECs in mouse embryos. Our results identify TAGLN as a putative regulator of angiogenesis whose expression is activated in elongating ECs. This finding provides insight into the cytoskeletal regulation of EC elongation and an improved understanding of the molecular mechanisms underlying the regulation of angiogenesis.

A wild-derived inbred mouse strain, MSM/Ms, provides insights into novel skin tumor susceptibility genes

Cancer is one of the most catastrophic human genetic diseases. Experimental animal cancer models are essential for gaining insights into the complex interactions of different cells and genes in tumor initiation, promotion, and progression. Mouse models have been extensively used to analyze the genetic basis of cancer susceptibility. They have led to the identification of multiple loci that confer, either alone or in specific combinations, an increased susceptibility to cancer, some of which have direct translatability to human cancer. Additionally, wild-derived inbred mouse strains are an advantageous reservoir of novel genetic polymorphisms of cancer susceptibility genes, because of the evolutionary divergence between wild and classical inbred strains. Here, we review mapped Stmm (skintumor modifier of MSM) loci using a Japanese wild-derived inbred mouse strain, MSM/Ms, and describe recent advances in our knowledge of the genes responsible for Stmm loci in the 7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) two-stage skin carcinogenesis model.

Importin-11 is Essential for Normal Embryonic Development in Mice

Importin-11 (Ipo11) is a novel member of the human importin family of transport receptors (karyopherins), which are known to mediate the nucleocytoplasmic transport of protein and RNA cargos. Despite its role in the transport of protein, we found that knockout of Ipo11 nuclear import factor affects normal embryonic development and govern embryo-lethal phenotypes in mice. In this study, we for the first time produced a mouse line containing null mutation in Ipo11 gene utilized by gene trapping. The Ipo11^-/- embryos showed an embryonic lethal phenotype. The Ipo11^-/- embryos showed a reduced size at embryonic day 10.5 (E10.5) when compared with Ipo11^+/+ or Ipo11^+/- embryos and died by E11.5. Whereas Ipo11^+/- mice were healthy and fertile, and there was no detectable changes in embryonic lethality and phenotype when reviewed. In the X-gal staining with the Ipo11^-/- or Ipo11^+/- embryos, strong X-gal staining positivity was detected systematically in the whole mount embryos at E10.5, although almost no X-gal positivity was detected at E9.5, indicating that the embryos die soon after the process of Ipo11 expression started. These results indicate that Ipo11 is essential for the normal embryonic development in mice.

Fryl deficiency is associated with defective kidney development and function in mice

FRY like transcription coactivator ( Fryl) gene located on chromosome 5 is a paralog of FRY microtubule binding protein ( Fry) in vertebrates. It encodes a protein with unknown functions. Fryl gene is conserved in various species ranging from eukaryotes to human. Although there are several reports on functions of Fry gene, functions of Fryl gene remain unclear. A mouse line containing null mutation in Fryl gene by gene trapping was produced in this study for the first time. The survival and growth of Fryl^-/- mice were observed. Fryl gene expression levels in mouse tissues were determined and histopathologic analyses were conducted. Most Fryl^-/- mice died soon after birth. Rare Fryl^-/- survivors showed growth retardation with significantly lower body weight compared to their littermate controls. Although they could breed, more than half of Fryl^-/- survivors died of hydronephrosis before age 1. No abnormal histopathologic lesion was apparent in full-term embryo or adult tissues except the kidney. Abnormal lining cell layer detachments from walls of collecting and convoluted tubules in kidneys were apparent in Fryl^-/- neonates and full-term embryos. Fryl gene was expressed in renal tubular tissues including the glomeruli and convoluted and collecting tubules. This indicates that defects in tubular systems are associated with Fryl functions and death of Fryl^-/- neonates. Fryl protein is required for normal development and functional maintenance of kidney in mice. This is the first report of in vivo Fryl gene functions. Impact statement FRY like transcription coactivator ( Fryl) gene is conserved in various species ranging from eukaryotes to human. It expresses a protein with unknown function. We generated a Fryl gene mutant mouse line and found that most homozygous mice died soon after their birth. Rare Fryl^-/- survivors showed growth retardation with significantly lower body weight compared to their littermate controls. Although they could breed, more than half of Fryl^-/- survivors died of hydronephrosis before age 1. Full-term mutant embryos showed abnormal collecting and convoluted tubules in kidneys where Fryl gene was expressed. Collectively, these results indicate that Fryl protein is required for normal development and functional maintenance of kidney in mice. To the best of our knowledge, this is the first report on in vivo Fryl gene functions.

CXCR4 Signaling Negatively Modulates the Bipotential State of Hemogenic Endothelial Cells Derived from Embryonic Stem Cells by Attenuating the Endothelial Potential

Hemogenic endothelial cells (HECs) are considered to be the origin of hematopoietic stem cells (HSCs). HECs have been identified in differentiating mouse embryonic stem cells (ESCs) as VE-cadherin⁺ cells with both hematopoietic and endothelial potential in single cells. Although the bipotential state of HECs is a key to cell fate decision toward HSCs, the molecular basis of the regulation of the bipotential state has not been well understood. Here, we report that the CD41⁺ fraction of CD45^- CD31⁺ VE-cadherin⁺ endothelial cells (ECs) from mouse ESCs encompasses an enriched HEC population. The CD41⁺ ECs expressed Runx1, Tal1, Etv2, and Sox17, and contained progenitors for both ECs and hematopoietic cells (HCs) at a high frequency. Clonal analyses of cell differentiation confirmed that one out of five HC progenitors in the CD41⁺ ECs possessed the bipotential state that led also to EC colony formation. A phenotypically identical cell population was found in mouse embryos, although the potential was more biased to hematopoietic fate with rare bipotential progenitors. ESC-derived bipotential HECs were further enriched in the CD41⁺ CXCR4⁺ subpopulation. Stimulation with CXCL12 during the generation of VE-cadherin⁺ CXCR4⁺ cells attenuated the EC colony-forming ability, thereby resulted in a decrease of bipotential progenitors in the CD41⁺ CXCR4⁺ subpopulation. Our results suggest that CXCL12/CXCR4 signaling negatively modulates the bipotential state of HECs independently of the hematopoietic fate. Identification of signaling molecules controlling the bipotential state is crucial to modulate the HEC differentiation and to induce HSCs from ESCs. Stem Cells 2016;34:2814-2824.

Inhibition of the PI3K-Akt and mTORC1 signaling pathways promotes the elongation of vascular endothelial cells

Endothelial cell morphology needs to be properly regulated during angiogenesis. Vascular endothelial growth factor (VEGF) induces endothelial cell elongation, which promotes sprouting of pre-existing vessels. However, therapeutic angiogenesis using VEGF has been hampered by side effects such as elevated vascular permeability. Here, we attempted to induce endothelial cell elongation without an overdose of VEGF. By screening a library of chemical inhibitors, we identified phosphatidylinositol 3-kinase (PI3K)-Akt pathway inhibitors and mammalian target of rapamycin complex 1 (mTORC1) inhibitors as potent inducers of endothelial cell elongation. The elongation required VEGF at a low concentration, which was insufficient to elicit the same effect by itself. The elongation also depended on Foxo1, a transcription factor indispensable for angiogenesis. Interestingly, the Foxo1 dependency of the elongation was overridden by inhibition of mTORC1, but not by PI3K-Akt, under stimulation by a high concentration of VEGF. Dual inhibition of mTORC1 and mTORC2 failed to induce cell elongation, revealing mTORC2 as a positive regulator of elongation. Our findings suggest that the PI3K-Akt-Foxo1 and mTORC1-mTORC2 pathways differentially regulate endothelial cell elongation, depending on the microenvironmental levels of VEGF.

Generation and characterization of PDGFRα-GFPCreERT2 knock-In mouse line

Platelet-derived growth factor (PDGF) and its receptor play an important role in embryogenesis. PDGF receptor α (PDGFRα) is expressed specifically in the embryonic day 7.5 (E7.5) mesoderm and in the E9.5 neural crest among other tissues. PDGFRα-expressing cells and their descendants are involved in the formation of various tissues. To trace PDGFRα-expressing cells in vivo, we generated a knock-in mouse line that expressed a fusion protein of green fluorescent protein (GFP), Cre recombinase (Cre), and mutated estrogen receptor ligand-binding domain (ERT2) under the control of the PDGFRα promoter. In these mice, Cre activity in PDGFRα-expressing cells could be induced by tamoxifen treatment. Taken together, our results suggest that the knock-in mouse line generated here could be useful for studying PDGFRα-expressing cells and their descendants in vivo at various stages of development.

Database for exchangeable gene trap clones: pathway and gene ontology analysis of exchangeable gene trap clone mouse lines

Gene trapping in embryonic stem (ES) cells is a proven method for large-scale random insertional mutagenesis in the mouse genome. We have established an exchangeable gene trap system, in which a reporter gene can be exchanged for any other DNA of interest through Cre/mutant lox-mediated recombination. We isolated trap clones, analyzed trapped genes, and constructed the database for Exchangeable Gene Trap Clones (EGTC) [http://egtc.jp]. The number of registered ES cell lines was 1162 on 31 August 2013. We also established 454 mouse lines from trap ES clones and deposited them in the mouse embryo bank at the Center for Animal Resources and Development, Kumamoto University, Japan. The EGTC database is the most extensive academic resource for gene-trap mouse lines. Because we used a promoter-trap strategy, all trapped genes were expressed in ES cells. To understand the general characteristics of the trapped genes in the EGTC library, we used Kyoto Encyclopedia of Genes and Genomes (KEGG) for pathway analysis and found that the EGTC ES clones covered a broad range of pathways. We also used Gene Ontology (GO) classification data provided by Mouse Genome Informatics (MGI) to compare the functional distribution of genes in each GO term between trapped genes in the EGTC mouse lines and total genes annotated in MGI. We found the functional distributions for the trapped genes in the EGTC mouse lines and for the RefSeq genes for the whole mouse genome were similar, indicating that the EGTC mouse lines had trapped a wide range of mouse genes.