Polymorphisms in the coding and noncoding regions of murine Pgk-1 alleles

Clonal hematopoiesis in hematological disorders: Three different scenarios

Clonality studies can establish the single-cell origin of tumors and thus differentiate clonal malignant and premalignant processes from reactive polyclonal processes. Detection of clonal cells may be based on direct tracking of cell lineage-specific sequences or disease-specific somatic mutations identifying the clonal population. Historically, clonal hematopoiesis was defined using the principle of X-chromosome inactivation based on observation that in circulating clonal cells, only one of the active chromosomes was expressed. In myeloproliferative neoplasms (MPNs) virtually all circulating erythrocytes, platelets, and granulocytes are products of single mutated stem cells that preferentially differentiate into the myeloid rather than lymphoid lineage. Thus, clonal differentiated myeloid cells co-exist in circulation with polyclonal long-lived T lymphocytes that originated before the MPN-initiating somatic clonal event. Chronic lymphocytic leukemia (CLL) starts in a differentiating B cell, but other lymphoid lineages and myeloid cells remain polyclonal. Normal T and B cells co-exist with the CLL clone, but are diluted by the massively expanded CLL population, which outnumbers the residual normal cells. Clonal hematopoiesis of undetermined potential (CHIP) has been identified by whole-genome sequencing of healthy individuals. These clones contain a specific somatic mutation previously considered to be disease defining but are detected in only a small proportion of circulating leukocytes, and there is no obvious suppression of normal hematopoietic stem cells. However, more studies are needed to properly define these clones, their persistence or disappearance, and their relative propensity for transforming into leukemias, myeloproliferative neoplasms, or other clonal hematological malignancies.

Hematopoietic reconstitution of neonatal immunocompetent mice to study conditions with a perinatal window of susceptibility

Efficient hematopoietic reconstitution of wild type mice requires preconditioning. Established experimental protocols exist to transplant hematopoietic stem cells into lethally irradiated or chemically myeloablated adult mice or unirradiated immunodeficient mice. We sought to develop a protocol to reconstitute immuno-replete neonatal mice. We describe irradiation and injection procedures for two-day old mice that lead to efficient long-term reconstitution of primary and secondary lymphoid organs. We demonstrate that the frequencies of lymphoid and myeloid cells in primary and secondary lymphoid organs are indistinguishable from unirradiated uninjected sex- and age-matched control animals by 5 weeks post-reconstitution. Thus, this system will facilitate studies aimed at understanding the developmental and environmental mechanisms that contribute to conditions that have a window of susceptibility during the perinatal period.

Absence of BRINP1 in mice causes increase of hippocampal neurogenesis and behavioral alterations relevant to human psychiatric disorders

BACKGROUND

We have previously identified BRINP (BMP/RA-inducible neural-specific protein-1, 2, 3) family genes that possess the ability to suppress cell cycle progression in neural stem cells. Of the three family members, BRINP1 is the most highly expressed in various brain regions, including the hippocampus, in adult mice and its expression in dentate gyrus (DG) is markedly induced by neural activity. In the present study, we generated BRINP1-deficient (KO) mice to clarify the physiological functions of BRINP1 in the nervous system.

RESULTS

Neurogenesis in the subgranular zone of dentate gyrus was increased in BRINP1-KO mice creating a more immature neuronal population in granule cell layer. The number of parvalbumin expressing interneuron in hippocampal CA1 subregion was also increased in BRINP1-KO mice. Furthermore, BRINP1-KO mice showed abnormal behaviors with increase in locomotor activity, reduced anxiety-like behavior, poor social interaction, and slight impairment of working memory, all of which resemble symptoms of human psychiatric disorders such as schizophrenia and attention-deficit/hyperactivity disorder (ADHD).

CONCLUSIONS

Absence of BRINP1 causes deregulation of neurogenesis and impairments of neuronal differentiation in adult hippocampal circuitry. Abnormal behaviors comparable to those of human psychiatric disorders such as hyperactivity and poor social behavior were observed in BRINP1-KO mice. These abnormal behaviors could be caused by alteration of hippocampal circuitry as a consequence of the lack of BRINP1.

Determination of the optimal concentration of several selective drugs useful for generating multi-transgenic porcine embryonic fibroblasts

Porcine embryonic fibroblasts (PEFs) are widely used as donor cells for somatic cell nuclear transfer (SCNT) in pigs. Transfection of PEFs with exogenous DNA is essential for producing genetically modified (GM; transgenic or knockout) pigs via SCNT. In this case, selectable markers are strictly required selecting and enriching stably transfected cells. The most frequently used selective drug for this purpose is a neomycin analogue (G418/geneticin); neo has been widely used as a selectable marker gene in the genomic manipulation of pigs. However, little is known about optimal concentrations of other selection drugs. This often hampers functional analysis of the porcine genome and development of individual GM pigs. This study explores the optimal concentrations of selective drugs, other than neomycin, that can be used for the selection of transfected PEFs. Porcine embryonic fibroblasts were incubated in media containing different concentrations of drugs for up to 10 days, to determine the optimal drug concentrations fatal for PEFs. The following concentrations were found to be optimal selective concentrations for use with PEFs: G418/geneticin, 400 μg/ml; blasticidin S, 8 μg/ml; hygromycin B, 40 μg/ml; puromycin, 2 μg/ml; and zeocin, 800 μg/ml. Repeated transfections with plasmids carrying selectable markers resulted in the generation of multidrug-resistant swine transfectants. Furthermore, these markers were found to be independent. The present information will be useful for the production of SCNT-mediated GM piglets that express multiple transgenes.

A defucosylated anti-CD317 antibody exhibited enhanced antibody-dependent cellular cytotoxicity against primary myeloma cells in the presence of effectors from patients

The humanized monoclonal antibody (mAb) against CD317 antigen (anti-HM1.24 antibody; AHM), which is highly expressed on multiple myeloma (MM), induces antibody-dependent cellular cytotoxicity (ADCC). However, the antitumor activity of AHM in the clinical setting has not been clearly demonstrated. In this study, we produced defucosylated AHM and evaluated its potency for clinical application by performing autologous ADCC assays against primary MM cells from patients. Defucosylated AHM that was produced in rat myeloma YB2/0 cells expressing a low level of fucosyltransferase (FUT8) showed significant ADCC activity against three out of six primary MM cells in the presence of autologous PBMC, whereas conventional AHM did not. The results indicate that the potency of AHM to induce ADCC against primary MM cells was insufficient, but was significantly augmented by defucosylation. To generate more homogenous defucosylated monoclonal antibodies (mAb) for fermentation, we disrupted the GFT gene that encodes a GDP-fucose transporter in a CHO/DXB11 cell line by sequential homologous recombination. Analysis of the N-linked oligosaccharide in the defucosylated AHM produced by the established GFT(-/-)CHO cell line showed that a majority (93.4%) of the oligosaccharide was fucose free. The GFT(-/-) cells stably produced defucosylated mAb over passages. These results demonstrate that GTF(-/-)CHO-produced defucosylated AHM (GFTKO-AHM) will be a promising new therapeutic antibody against MM in the clinical setting.

X-inactivation analysis of embryonic lethality in Ocrl wt/-; Inpp5b-/- mice

Mutations in the human OCRL gene, which encodes a phosphatidylinositol(4,5)bisphosphate 5-phosphatase, result in the X-linked oculocerebrorenal syndrome of Lowe. Mice with a targeted disruption of Ocrl have no phenotypic abnormalities. Targeted disruption of its closest paralog, Inpp5b, causes male infertility in the 129S6 background. Mice with disruptions of both genes are lost in utero prior to 9.5-10.5 dpc, indicating that there is a functional overlap between the two paralogs early in development. We analyzed the pattern of X-inactivation in four tissues of distinct embryonic origin from Ocrl (wt/-);Inpp5b (-/-) females to explore the timing and tissue distribution of the functional overlap. X-inactivation was strongly skewed against the disrupted Ocrl (-) allele being on the active X chromosome in all four tissues tested, indicating that there is early selection against cell lineages lacking both Ocrl and Inpp5b. Extraembryonic tissue was also involved in the lethality because there were never any live-born Ocrl (wt/-);Inpp5b (-/-) females when the functional Ocrl (wt ) allele was on the paternal X chromosome, which is preferentially inactivated in trophoblast-derived extraembryonic tissues. Live-born Ocrl (wt/-);Inpp5b (-/-) females were found when the functional Ocrl (wt) allele was maternal, although in fewer numbers than expected. The importance of the extraembryonic tissues in the early embryonic lethality of embryos lacking both Ocrl and Inpp5b is reinforced by the successful isolation of a viable 40,XX Ocrl (-/-);Inpp5b (-/-) embryonic stem cell from the inner cell mass of a 3.5-dpc blastocyst prior to implantation. These results indicate a functional overlap of Ocrl and Inpp5b in most cell lineages, especially in extraembryonic tissues.

Knockout mice lacking cPGES/p23, a constitutively expressed PGE2 synthetic enzyme, are peri-natally lethal

Cytosolic prostaglandin (PG) E synthase (cPGES) is constitutively expressed in various cells and regulates cyclooxygenase (COX)-1-dependent immediate PGE(2) generation. Its primary structure is identical to co-chaperone p23, a heat shock protein 90 (Hsp90)-binding protein. We have revealed that Hsp90 regulated both cPGES/p23 and its client protein kinase CK2. In this study, in order to examine the role of cPGES/p23 in vivo, we generated mice deficient in cPGES/p23 by a targeted disruption of exons 2 and 3, containing Tyr9, which is essential for catalytic activity. Heterozygotes are viable, fertile, and appear normal, despite a decrease in cPGES/p23 protein level. A generation of offsprings derived from intercrosses of cPGES/p23 homozygous mice revealed that 109, 247, and 10 pups were wild type, heterozygous, and homozygous, respectively; however, all homozygotes died at birth. The absence of viable null mutants, with heterozygotes and wild-type offspring obtained at a ratio of approximately 2:1, indicated that homozygosity for the cPGES/p23 null mutant leads to peri-natal lethality. Embryos homozygous for cPGES/p23-null had lower body weights than wild-type embryos, and abnormal morphology of skin and lungs. Moreover, the PGE(2) content in the lungs of cPGES/p23-null embryos was lower than that of the wild type. These results indicate that cPGES-derived PGES is involved in the normal development of mouse embryonic lung.

Antigen-mediated growth control of hybridoma cells via a human artificial chromosome

Human artificial chromosome (HAC) vectors possess several characteristics sufficient for the requirements of gene therapy vectors, including stable episomal maintenance and mediation of long-term transgene expression. In this study, we adopted an antigen-mediated genetically modified cell amplification (AMEGA) system employing an antibody/cytokine receptor chimera that triggers a growth signal in response to a cognate non-toxic antigen, and applied it to growth control of HAC-transferred cells by adding an antigen that differed from cytokines that may manifest pleiotropic effects. We previously constructed a novel HAC vector, 21 Delta qHAC, derived from human chromosome 21, housed in CHO cells. Here, we constructed an HAC vector harboring an ScFv-gp130 chimera responsive to fluorescein-conjugated BSA (BSA-FL) as well as a model transgene, enhanced green fluorescent protein (EGFP), in CHO cells. The modified HAC was transferred into interleukin (IL)-6-dependent hybridoma 7TD1 cells by microcell-mediated chromosome transfer, and the cells were subsequently found to show BSA-FL-dependent cell growth and sustained expression of EGFP in the absence of IL-6. The AMEGA system in combination with HAC technology will be useful for increasing the efficacy of gene therapy by conferring a growth advantage on the genetically modified cells.

Ras/ERK1/2-mediated STAT3 Ser727 phosphorylation by familial medullary thyroid carcinoma-associated RET mutants induces full activation of STAT3 and is required for c-fos promoter activation, cell mitogenicity, and transformation

The precise role of STAT3 Ser(727) phosphorylation in RET-mediated cell transformation and oncogenesis is not well understood. In this study, we have shown that familial medullary thyroid carcinoma (FMTC) mutants RET(Y791F) and RET(S891A) induced, in addition to Tyr(705) phosphorylation, constitutive STAT3 Ser(727) phosphorylation. Using inhibitors and dominant negative constructs, we have demonstrated that RET(Y791F) and RET(S891A) induce STAT3 Ser(727) phosphorylation via a canonical Ras/ERK1/2 pathway and that integration of the Ras/ERK1/2/ELK-1 and STAT3 pathways was required for up-regulation of the c-fos promoter by FMTC-RET. Moreover, inhibition of ERK1/2 had a more severe effect on cell proliferation and cell phenotype in HEK293 cells expressing RET(S891A) compared with control and RET(WT)-transfected cells. The transforming activity of RET(Y791F) and RET(S891A) in NIH-3T3 cells was also inhibited by U0126, indicating a role of the ERK1/2 pathway in RET-mediated transformation. To investigate the biological significance of Ras/ERK1/2-induced STAT3 Ser(727) phosphorylation for cell proliferation and transformation, N-Ras-transformed NIH-3T3 cells were employed. These cells displayed elevated levels of activated ERK1/2 and Ser(727)-phosphorylated STAT3, which were inhibited by treatment with U0126. Importantly, overexpression of STAT3, in which the Ser(727) was mutated into Ala (STAT3(S727A)), rescued the transformed phenotype of N-Ras-transformed cells. Immunohistochemistry in tumor samples from FMTC patients showed strong nuclear staining of phosphorylated ERK1/2 and Ser(727) STAT3. These data show that FMTC-RET mutants activate a Ras/ERK1/2/STAT3 Ser(727) pathway, which plays an important role in cell mitogenicity and transformation.

NANOG maintains self-renewal of primate ES cells in the absence of a feeder layer

Nanog is a homeodomain transcription factor that is expressed specifically in undifferentiated embryonic stem (ES) cells and has been shown to be essential in the maintenance of pluripotency in mouse ES cells. To examine the function of NANOG in primate ES cells, we generated transgenic monkey ES cell lines expressing three- to seven-fold higher levels of NANOG protein compared to wild-type ES cells. These NANOG over-expressing cell lines retained their undifferentiated state in the absence of a feeder layer, as shown by expression of undifferentiated ES cell markers such as alkaline phosphatase (ALP) and OCT-4. We also demonstrated that in vitro differentiation of transgenic cell lines was mostly restricted to the ectodermal lineage, as examined by reverse transcriptase-polymerase chain reaction (RT-PCR). Knockdown experiments using NANOG small interfering (si) RNA resulted in induction of differentiation markers such as AFP, GATA4 and GATA6 for the endoderm and CDX2 for the trophectoderm. These results suggest that NANOG plays a crucial role in maintaining the pluripotent state of primate ES cells.

Inhibition of the transforming growth factor beta (TGFbeta) pathway by interleukin-1beta is mediated through TGFbeta-activated kinase 1 phosphorylation of SMAD3

Transforming growth factor beta is the prototype of a large family of secreted factors that regulate multiple biological processes. In the immune system, TGFbeta acts as an anti-inflammatory and immunosuppressive molecule, whereas the cytokine interleukin (IL)-1beta is a crucial mediator of inflammatory responses and induces proinflammatory genes and acute phase proteins. Here, we present evidence for the existence of a direct inhibitory interaction between the IL-1beta and TGFbeta signaling cascades that is not dependent on IL-1beta-induced SMAD7 expression. IL-1beta and its downstream mediator TAK1 inhibit SMAD3-mediated TGFbeta target gene activation, whereas SMAD3 nuclear translocation and DNA binding in response to TGFbeta are not affected. IL-1beta transiently induces association between TAK1 and the MAD homology 2 domain of SMAD3, resulting in SMAD3 phosphorylation. Furthermore, IL-1beta alleviates the inhibitory effect of TGFbeta on in vitro hematopoietic myeloid colony formation. In conclusion, our data provide evidence for the existence of a direct inhibitory effect of the IL-1beta-TAK1 pathway on SMAD3-mediated TGFbeta signaling, resulting in reduced TGFbeta target gene activation and restored proliferation of hematopoietic progenitors.

STAT3 is dispensable for maintenance of self-renewal in nonhuman primate embryonic stem cells

The leukemia inhibitory factor (LIF)/glycoprotein 130 (gp130)/signal transducer and activator of transcription 3 (STAT3) pathway plays an essential role in the maintenance of self-renewal and pluripotency in mouse embryonic stem (ES) cells. However, in primate ES cells, including those from humans and monkeys, LIF alone is not sufficient to maintain self-renewal. The precise role of the LIF/gp130/STAT3 pathway for self-renewal in primate ES cells is still unclear. In this study, we found that stimulation of cynomolgus monkey ES cells with LIF or interleukin (IL)-6/soluble IL-6 receptor leads to STAT3 phosphorylation, an effect seen previously in murine ES cells. Concomitant with this notion, nuclear translocalization and transcriptional activation of STAT3 were observed in a LIF-dependent manner. Moreover, the analysis of a dominant interfering mutant, STAT3F, showed that even though the phosphorylation, nuclear translocalization, and transcriptional activation of endogenous STAT3 after LIF stimulation were completely abrogated by over-expressing STAT3F in monkey ES cells, they continued to proliferate in an undifferentiated state, retaining their pluripotency. These results demonstrate that the LIF/gp130/STAT3 pathway functions in cynomolgus monkey ES cells but is not essential for the maintenance of self-renewal. They also suggest that cynomolgus monkey ES cells, unlike murine ES cells, are maintained in an undifferentiated state through LIF/gp130/STAT3-independent signaling.

Electroporation of cynomolgus monkey embryonic stem cells

Efficient genetic modification of primate embryonic stem (ES) cells is essential for the application for both basic and preclinical research. The transfection efficiency of primate ES cells is reportedly lower than that of mouse ES cells. Cynomolgus monkey ES cells provide a powerful model for understanding human development and disease. We evaluated electroporation as a method to introduce foreign genes into cynomolgus monkey ES cells. Our examination has allowed us to establish a protocol producing about 100 stably transfected clones from 10(7) cynomolgus monkey ES cells. Differences in efficiency, however, were observed for other ES cell lines. We compared the transcriptional activities of the PGK-1, CMV, and SV40 promoters in cynomolgus monkey ES cells generating efficient G418 selection. Although the PGK-1 and SV40 promoters efficiently drove neo gene expression, the CMV promoter was significantly less transcriptionally active in cynomolgus monkey ES cells. Using this electroporation method, we established fluorescent cynomolgus monkey ES cell lines. These cells may be useful tools for tracing grafted cells in transplantation studies using a variety of functional cells derived from cynomolgus monkey ES cells.

Production of functional platelets by differentiated embryonic stem (ES) cells in vitro

Megakaryocytes and functional platelets were generated in vitro from murine embryonic stem (ES) cells with the use of a coculture system with stromal cells. Two morphologically distinctive megakaryocytes were observed sequentially. Small megakaryocytes rapidly produced proplatelets on day 8 of the differentiation, and large hyperploid megakaryocytes developed after day 12, suggesting primitive and definitive megakaryopoiesis. Two waves of platelet production were consistently observed in the culture medium. A larger number of platelets was produced in the second wave; 104 ES cells produced up to 108 platelets. By transmission electron microscopy, platelets from the first wave were relatively rounder with a limited number of granules, but platelets from the second wave were discoid shaped with well-developed granules that were indistinguishable from peripheral blood platelets. ES-derived platelets were functional since they bound fibrinogen, formed aggregates, expressed P-selectin upon stimulation, and fully spread on immobilized fibrinogen. These results show the potential utility of ES-derived platelets for clinical applications. Furthermore, production of gene-transferred platelets was achieved by differentiating ES cells that were transfected with genes of interest. Overexpression of the cytoplasmic domain of integrin beta3 in the ES-derived platelets prevented the activation of alphaIIbbeta3, demonstrating that this system will facilitate functional platelet studies.

Pax6 autoregulation mediated by direct interaction of Pax6 protein with the head surface ectoderm-specific enhancer of the mouse Pax6 gene

The Pax6 gene plays crucial roles in eye development and encodes a transcription factor containing both a paired domain and a homeodomain. During embryogenesis, Pax6 is expressed in restricted tissues under the direction of distinct cis-regulatory regions. The head surface ectoderm-specific enhancer of mouse Pax6 directs reporter expression in the derivatives of the ectoderm in the eye, such as lens and cornea, but the molecular mechanism of its control remains largely unknown. We identified a Pax6 protein-responsive element termed LE9 (52 bp in length) within the head surface ectoderm-specific enhancer. LE9, a sequence well conserved across vertebrates, acted as a highly effective enhancer in reporter analyses. Pax6 protein formed in vitro a complex with the distal half of LE9 in a manner dependent on the paired domain. The proximal half of the LE9 sequence contains three plausible sites of HMG domain recognition, and HMG domain-containing transcription factors Sox2 and Sox3 activated LE9 synergistically with Pax6. A scanning mutagenesis experiment indicated that the central site is most important among the three presumptive HMG domain recognition sites. Furthermore, Pax6 and Sox2 proteins formed a complex when they were expressed together. Based on these findings, we propose a model in which Pax6 protein directly and positively regulates its own gene expression, and Sox2 and Sox3 proteins interact with Pax6 protein, resulting in modification of the transcriptional activation by Pax6 protein.

Erythropoietin-induced serine 727 phosphorylation of STAT3 in erythroid cells is mediated by a MEK-, ERK-, and MSK1-dependent pathway

OBJECTIVE

Erythropoietin (EPO) is a key regulator of erythropoiesis, playing a role in both the proliferation and differentiation of erythroid cells. One of the signal transduction molecules activated upon EPO stimulation is signal transducer and activator of transcription (STAT) 3. Besides tyrosine 705 phosphorylation of STAT3, serine 727 phosphorylation has been described upon EPO stimulation. In the present study, we investigated which molecular pathways mediate the STAT3 serine 727 phosphorylation and the functional implications of this phosphorylation.

METHODS

The EPO-dependent erythroid cell line ASE2 was used to investigate which signaling routes were involved in the STAT3 serine 727 phosphorylation. Western blotting using phosphospecific antibodies was used to assess the phosphorylation status of STAT3 molecules. Transfection analysis was performed to investigate the transactivational potential of STAT3, and quantitative RT-PCR was used to study the in vivo gene expression of STAT3-responsive genes.

RESULTS

Western blotting of extracts of cells exposed to various chemical inhibitors revealed that the MEK inhibitors PD98059 and U0126 abrogated the EPO-mediated STAT3 serine 727 phosphorylation without an effect on tyrosine phosphorylation. Further analysis showed that MSK1 is activated downstream of ERK, and retroviral transductions with kinase-inactive MSK1 revealed that MSK1 is necessary for STAT3 serine phosphorylation. Furthermore, the STAT3-mediated transactivation was reduced by blocking the STAT3 serine phosphorylation with the MEK inhibitor U0126 or by expression of kinase-inactive MSK1.

CONCLUSIONS

The EPO-induced STAT3 serine 727 phosphorylation is mediated by a pathway involving MEK, ERK, and MSK1. Furthermore, serine phosphorylation of STAT3 augments the transactivational potential of STAT3.

Plasminogen promotes sarcoma growth and suppresses the accumulation of tumor-infiltrating macrophages

The specific functions of plasminogen, stromal plasminogen activator, stromal plasminogen activator receptor, and stromal plasminogen activator inhibitor in the progression of the murine soft tissue sarcoma, T241 were investigated. Negation of plasminogen to the tumor blunted the orthotopic growth of the sarcoma in syngeneic mice. The reduced tumor growth was associated with a dramatic increase in tumor-infiltrating F4/80-positive macrophages and a diminution of vessel density, but not with obvious differences in fibrin and collagen deposition, or invasiveness of the tumor. Ablation of plasminogen activation by the tumor stroma only modestly impaired the prolonged growth of the sarcoma, suggesting that tumor cell-produced plasminogen activator is sufficient to mediate productive plasminogen activation. Plasminogen facilitated sarcoma progression, angiogenesis, and suppression of macrophage infiltration in the absence of either stromal urokinase plasminogen activator receptor or stromal plasminogen activator inhibitor. These data demonstrate that tumor cell-produced plasminogen activator and host plasminogen cooperate to facilitate soft tissue sarcoma growth and suppress the accumulation of tumor-infiltrating macrophages.

X chromosome effect on maternal recombination and meiotic drive in the mouse

We observed that maternal meiotic drive favoring the inheritance of DDK alleles at the Om locus on mouse chromosome 11 was correlated with the X chromosome inactivation phenotype of (C57BL/6-Pgk1(a) x DDK)F(1) mothers. The basis for this unexpected observation appears to lie in the well-documented effect of recombination on meiotic drive that results from nonrandom segregation of chromosomes. Our analysis of genome-wide levels of meiotic recombination in females that vary in their X-inactivation phenotype indicates that an allelic difference at an X-linked locus is responsible for modulating levels of recombination in oocytes.

Evidence for repeat-induced gene silencing in cultured Mammalian cells: inactivation of tandem repeats of transfected genes

Foreign DNA can be readily integrated into the genomes of mammalian embryonic cells by retroviral infection, DNA microinjection, and transfection protocols. However, the transgenic DNA is frequently not expressed or is expressed at levels far below expectation. In a number of organisms such as yeast, plants, Drosophila, and nematodes, silencing of transfected genes is triggered by the interaction between adjacent or dispersed copies of genes of identical sequence. We set out to determine whether a mechanism similar to repeat-induced gene silencing (RIGS) is responsible for the silencing of transgenes in murine embryonal carcinoma stem cells. We compared the expression of identical reporter gene constructs in cells carrying single or multiple copies and found that the level of expression per integrated copy was more than 10-fold higher in single-copy integrants. In cells carrying tandem copies of the transgene, many copies were methylated and clones frequently failed to express both copies of near-identical integrated alleles. Addition of extra copies of the reporter gene coding sequence reduced the level of expression from the same reporter driven by a eukaryotic promoter. We also found that inhibitors of histone deacetylase such as trichostatin A forestall the silencing of multicopy transgenes, suggesting that chromatin mediates the silencing of transfected genes. This evidence is consistent with the idea that RIGS does occur in mammalian embryonic stem cells although silencing of single-copy transgenes also occurs, suggesting that RIGS is only one of the mechanisms responsible for triggering transgene silencing.

A basolateral sorting motif in the MICA cytoplasmic tail

The MHC class I chain-related MICA molecule is a stress-induced, highly polymorphic, epithelia-specific, membrane-bound glycoprotein interacting with the activating NK cell receptor NKG2D and/or gut-enriched Vdelta1-bearing gammadelta T cells. We have previously reported the presence of a MICA transmembrane-encoded short-tandem repeat harboring a peculiar allele, A5.1, characterized by a frame shift mutation leading to a premature intradomain stop codon, thus denying the molecule of its 42-aa cytoplasmic tail. Given that this is the most common population-wide MICA allele found, we set out to analyze the functional consequences of cytoplasmic tail deletion. Here, we show native expression of MICA at the basolateral surface of human intestinal epithelium, the site of putative interaction with intraepithelial T and NK lymphocytes. We then demonstrate, in polarized epithelial cells, that although the full-length MICA protein is sorted to the basolateral membrane, the cytoplasmic tail-deleted construct as well as the naturally occurring A5.1 allele are aberrantly transported to the apical surface. Site-directed mutagenesis identified the cytoplasmic tail-encoded leucine-valine dihydrophobic tandem as the basolateral sorting signal. Hence, the physiological location of MICA within epithelial cells is governed by its cytoplasmic tail, implying impairment in A5.1 homozygous individuals, perhaps relevant to the immunological surveillance exerted by NK and T lymphocytes on epithelial malignancies.

Stathmin-deficient mice develop an age-dependent axonopathy of the central and peripheral nervous systems

Stathmin is a cytosolic protein that binds tubulin and destabilizes cellular microtubules, an activity regulated by phosphorylation. Despite its abundant expression in the developing mammalian nervous system and despite its high degree of evolutionary conservation, stathmin-deficient mice do not exhibit a developmental phenotype.(1) Here we report that aging stathmin(-/-) mice develop an axonopathy of the central and peripheral nervous systems. The pathological hallmark of the early axonal lesions was a highly irregular axoplasm predominantly affecting large, heavily myelinated axons in motor tracts. As the lesions progressed, degeneration of axons, dysmyelination, and an unusual glial reaction were observed. At the functional level, electrophysiology recordings demonstrated a significant reduction of motor nerve conduction velocity in stathmin(-/-) mice. At the molecular level, increased gene expression of SCG 10-like protein, a stathmin-related gene with microtubule destabilizing activity, was detected in the central nervous system of aging stathmin(-/-) mice. Together, these findings suggest that stathmin plays an essential role in the maintenance of axonal integrity.

TAK1 activation of the mouse JunB promoter is mediated through a CCAAT box and NF-Y

The JunB gene is activated by many stimuli including transforming growth factor beta (TGFbeta) family members and interleukin-6 (IL-6). Here the effect of TGFbeta activated kinase 1 (TAK1), a mitogen activated protein kinase kinase kinase (MAPKKK) implicated in TGFbeta, bone morphogenetic protein (BMP) and interleukin-1 (IL-1) signaling, on JunB promoter activity was investigated. Promoter analysis led to the identification of a CCAAT motif in the JunB gene, essential for activation by TAK1. Transfer of this CCAAT element to a heterologous minimal promoter conferred TAK1-responsiveness. The CCAAT-binding transcription factor, nuclear factor Y (NF-Y), activated the JunB promoter and a dominant negative NF-YA construct inhibited TAK1 activation of JunB. Our results demonstrate that JunB gene activation by TAK1 is mediated by the CCAAT-binding factor NF-Y.

The assembly of large BACs by in vivo recombination

We have developed a method for recombining bacterial artificial chromosomes (BACs) and P1 artificial chromosomes (PACs) containing large genomic DNA fragments into a single vector using the Cre-lox recombination system from bacteriophage P1 in vivo. This overcomes the limitations of in vitro methods for generating large constructs based on restriction digestion, ligation, and transformation of DNA into Escherichia coli cells. We used the method to construct a human artificial chromosome vector of 404 kb encompassing long tracts of alpha satellite DNA, telomeric sequences, and the human hypoxanthine phosphoribosyltransferase gene. The specificity of Cre recombinase for loxP sites minimizes the possibility of intramolecular rearrangements, unlike previous techniques using general homologous recombination in E. coli, and makes our method compatible with the presence of large arrays of repeated sequences in cloned DNA. This methodology may also be applied to retrofitting PACs or BACs with markers and functional sequences.

Stable integration of large (>100 kb) PAC constructs in HaCaT keratinocytes using an integrin-targeting peptide delivery system

Transfer of large DNA constructs in gene therapy studies is being recognised for its importance in maintaining the natural genomic environment of the gene of interest and providing tissue-specific regulation and control. However, methods used to deliver such constructs have been poorly studied. We used a receptor-mediated, integrin-targeting transfection system enhanced by liposomes, to deliver a 110 kb PAC (P1-based artificial chromosome) to HaCaT keratinocytes. The PAC contained the collagen VII locus, an EGFP (enhanced green fluorescent protein) reporter gene and the puromycin resistance gene (pac) to allow selection of stably transfected cells. Analysis of puromycin resistant and EGFP-expressing colonies by Western blot showed that collagen VII production increased dramatically after transfection, indicating successful transfer of a large fully functional genomic locus. Fluorescent in situ hybridisation (FISH) and Southern blot analysis revealed that the PAC had integrated as at least one copy per cell. EGFP expression has persisted for 35 weeks, suggesting stable transgene expression. We conclude that the integrin-targeting peptide method of gene delivery is an effective means of stably delivering large DNA constructs to human keratinocytes and could be of benefit for genomic gene therapy approaches.

Loss of connexin45 causes a cushion defect in early cardiogenesis

At around embryonic day 9, the primitive heart of a mouse embryo undergoes spectacular alterations within 24 hours. We created mice harboring an nls-lacZ gene in place of connexin45, which encodes the only known gap junction protein in the primitive heart before embryonic day 9, using the Cre-loxP system. Connexin45-deficient mice died of heart failure at around embryonic day 10. They initiated heart contractions, but conduction block appeared within 24 hours after the first contractions. Their cardiac walls displayed an endocardial cushion defect, while the cardiac jelly was present. These abnormalities were caused by impairment of the epithelial-mesenchymal transformation of the cardiac endothelium. Activation of the cardiac endothelium depended on the presence of the connexin45 gap junctions since signaling through Ca(2+)/calcineurin and NF-ATc1 (originally named NF-ATc) was disrupted in the mutant hearts. These results indicate a requirement for gap junction channels during early cardiogenesis and hence implicate connexin45 in congenital heart diseases. http://www.biologists.com/Development/movies/dev4369.html

Smad7 selectively interferes with different pathways of activin signaling and inhibits erythroid leukemia cell differentiation

Smad family proteins are essential for transforming growth factor β (TGF-β) signal mediation downstream of a heteromeric complex of the type I and type II receptor serine/threonine kinases. A distant family member, Smad7, is expressed in most mammalian tissues and cells and prevents TGF-β signaling. In this study, we examined the physiologic role of Smad7 in mediating the effects of activin, a member of the TGF-β superfamily of peptides that functions in a number of processes, including blood-cell development. We report here that Smad7 expression is specifically absent in particular hematopoietic cells that respond to activin by differentiating into the erythroid lineage and that ectopic production of Smad7 causes mouse erythroid leukemia (F5-5) cells to become resistant to activin induction of erythroid differentiation. When coexpressed with type I activin receptor ActR-I or ActR-IB in concert with type II receptor ActR-II, Smad7 efficiently reduced an early transcriptional response mediated by ActR-I but had only a minimal effect on the response mediated by ActR-IB. In the presence of Smad7, overexpression of an activated form of ActR-IB, but not of an activated form of ActR-I, induced F5-5 cells to differentiate. These results suggest that Smad7 selectively interferes with the ActR-I pathway in activin signal transduction. The findings also indicate the existence of a novel activity of Smad7 that inhibits erythroid differentiation by blocking intracellular signaling of activin.

Smad7 selectively interferes with different pathways of activin signaling and inhibits erythroid leukemia cell differentiation

Smad family proteins are essential for transforming growth factor β (TGF-β) signal mediation downstream of a heteromeric complex of the type I and type II receptor serine/threonine kinases. A distant family member, Smad7, is expressed in most mammalian tissues and cells and prevents TGF-β signaling. In this study, we examined the physiologic role of Smad7 in mediating the effects of activin, a member of the TGF-β superfamily of peptides that functions in a number of processes, including blood-cell development. We report here that Smad7 expression is specifically absent in particular hematopoietic cells that respond to activin by differentiating into the erythroid lineage and that ectopic production of Smad7 causes mouse erythroid leukemia (F5-5) cells to become resistant to activin induction of erythroid differentiation. When coexpressed with type I activin receptor ActR-I or ActR-IB in concert with type II receptor ActR-II, Smad7 efficiently reduced an early transcriptional response mediated by ActR-I but had only a minimal effect on the response mediated by ActR-IB. In the presence of Smad7, overexpression of an activated form of ActR-IB, but not of an activated form of ActR-I, induced F5-5 cells to differentiate. These results suggest that Smad7 selectively interferes with the ActR-I pathway in activin signal transduction. The findings also indicate the existence of a novel activity of Smad7 that inhibits erythroid differentiation by blocking intracellular signaling of activin.

New approach to cell lineage analysis in mammals using the Cre-loxP system

The Cre-loxP site-specific recombination system was used for cell lineage analysis in mammals. We constructed an expression plasmid, pCETZ-17, which consists of cytomegalovirus enhancer/chicken beta-actin promoter (CAG), a portion of the rabbit beta-globin gene, loxP-flanked DNA sequence (containing enhanced green fluorescent protein (EGFP) cDNA), and lacZ gene encoding E. coli beta-galactosidase (beta-gal). When circular pCETZ-17 plasmid DNA was microinjected into the pronuclei of fertilized eggs and these eggs were allowed to develop to two-cell stage, 62.8% (59/94) of the two-cell embryos exhibited distinct fluorescence in one or both blastomeres, but never expressed lacZ protein, as evaluated by histochemical staining with X-Gal, a substrate for beta-gal. When both circular plasmids, pCETZ-17 and pCAG/NCre (containing CAG and DNA sequences encoding nuclear location signal and Cre), were co-injected into fertilized eggs, almost all (87.0%, 47/54) embryos exhibited low or no fluorescence, but 51.9% (27/52) exhibited positive staining for beta-gal activity. This indicates that transient expression of the Cre recombinase gene removed the loxP-flanked DNA sequence in pCETZ-17 and then caused expression of the downstream lacZ sequence. We next microinjected pCETZ-17 into the pronuclei of fertilized eggs, cultured these injected eggs for 1 day, and collected only two-cell embryos expressing EGFP in both blastomeres. One blastomere of the EGFP-expressing two-cell embryos was microinjected with pCAG/NCre, and these treated embryos were cultured for 1 day up to four-cell stage. When the developing four-cell embryos were subjected to staining with X-Gal, cell lineage-related staining pattern for beta-gal activity was observed in most (77.8%, 7/9) embryos. These findings were further confirmed using two-cell embryos derived from a transgenic mouse line carrying CETZ-17 transgene. Thus, our system, which is based on transient expression of the Cre recombinase gene directly introduced into nuclei of embryonic cells by microinjection, is a powerful means for cell lineage analysis in mammals.

Structure of the mouse NDRF gene and its regulation during neuronal differentiation of P19 cells

We have isolated and characterized the mouse gene for NDRF (neuroD-related factor), a basic helix-loop-helix transcription factor implicated in neural development and function. The gene consists of two exons and the entire protein-coding sequence is encoded by a single downstream exon. RNA blot hybridization analysis revealed that NDRF mRNA was detectable at day 4 and increased to a maximal level at day 6 during neuronal differentiation of P19 cells. To elucidate the regulatory mechanisms of the NDRF gene expression during this process, a construct containing the genomic DNA fragment of about 3 kbp upstream of the NDRF coding region fused to a luciferase reporter gene was transfected into P19 cells, and stable transformants were pooled for assay of luciferase activities. When the stable transformants were treated with RA and aggregated to induce neuronal differentiation, the luciferase activities were induced in a temporal expression pattern similar to that of the endogenous NDRF mRNA. Further experiments using a series of deletion and mutation constructs indicated that the 376-bp sequence in the 5'-flanking region of the NDRF gene is important, and that one of the E boxes in the sequence plays a critical role in the regulated expression. Transient transfection experiments also showed that the same E box is required for the transactivation of the NDRF promoter activity by neurogenin 1. These results suggest that the NDRF gene expression is regulated by an E box-binding factor during neuronal differentiation of P19 cells.

The mouse homolog of Drosophila Vasa is required for the development of male germ cells

Restricted expression of a mouse Vasa homolog gene (Mvh) expression is first detected in primordial germ cells (PGCs) after colonization of the genital ridges. Subsequently,Mvh is maintained until postmeiotic germ cells are formed. Here, we demonstrate that male mice homozygous for a targeted mutation of Mvh exhibit a reproductive deficiency. Male homozygotes produce no sperm in the testes, where premeiotic germ cells cease differentiation by the zygotene stage and undergo apoptotic death. In addition, the proliferation of PGCs that colonize homozygous male gonads is significantly hampered, and OCT-3/4 expression appears to be reduced. These results indicate that the loss ofMvh function causes a deficiency in the proliferation and differentiation of mouse male germ cells.

Mouse Pitx2 deficiency leads to anomalies of the ventral body wall, heart, extra- and periocular mesoderm and right pulmonary isomerism

Pitx2, a bicoid-related homeobox gene, is involved in Rieger's syndrome and the left-right (L-R) asymmetrical pattern formation in body plan. In order to define the genomic structure and roles of Pitx2, we analyzed the genomic structure and generated Pitx2-deficient mice with the lacZ gene in the homeobox-containing exon of Pitx2. We were able to show that among three isoforms of Pitx2, Pitx2c shows asymmetrical expression whereas Pitx2a, Pitx2b and Pitx2c show symmetrical expression. In Pitx2(-)(/)(-) embryos there was an increase in mesodermal cells in the distal end of the left lateral body wall and an amnion continuous with the lateral body wall thickened in its mesodermal layer. These changes resulted in a failure of ventral body wall closure. In lung and heart in which Pitx2 is expressed asymmetrically, right pulmonary isomerism, atrioventricular canals with prominent swelling, and juxtaposition of the atrium were detected. The hearts failed to develop tricuspid and mitral valves and a common atrioventricular valve forms. Further, dysgenesis of the Pitx2(-)(/)(-) extraocular muscle and thickening of the mesothelial layer of cornea were observed in the ocular system where Pitx2 is expressed symmetrically, and these resulted in enophthalmos. The present study shows that Pitx2 expressed in various sites participates in morphogenesis through three types of actions: the involvement of asymmetric Pitx2 expression in the entire morphogenetic process of L-R asymmetric organs; the involvement of asymmetric Pitx2 expression in the regional morphogenesis of asymmetric organs; and finally the involvement of symmetric Pitx2 expression in the regional morphogenesis of symmetric organs.

Cell-cell interaction modulates myoD-induced skeletal myogenesis of pluripotent P19 cells in vitro

P19 embryonal carcinoma cells can be induced to differentiate in culture to develop into a wide variety of cell types that include skeletal muscle. Skeletal myogenesis is controlled by transcription factors of the bHLH class, such as myoD. Expression of myoD from transfected genes did not induce significant amounts of myogenesis in P19 cells and it was possible to establish lines of undifferentiated P19[myoD] cells that express high levels of myoD mRNA. These P19[myoD] cells remained undifferentiated when cultured on solid surfaces but when allowed to aggregate, P19[myoD] cells differentiated efficiently into skeletal muscle. Aggregation did not increase the amount of myoD mRNA or the amount of myoD protein in P19[myoD] cells. The myoD protein was present in the nucleus in cells grown as attached or aggregated cultures and, in both culture conditions, the myoD protein was associated with transcription factors of the E2A family and was able to bind DNA at E-box sequences. Thus, the aggregation-induced myogenesis of P19[myoD] cells occurs in the absence of change in the myoD protein, suggesting that the cell-cell contact achieved in aggregates may result in the induction of an activity that increases accessibility of the myoD transcription factor to muscle-specific genes in chromatin.

Factors affecting de novo methylation of foreign DNA in mouse embryonic stem cells

Integration of foreign DNA into an established host genome can lead to changes in methylation in both the inserted DNA and in host sequences and potentially alters transgene and cellular transcription patterns. This work addresses the questions of what factors influence de novo methylation, and whether the integration site or inserted DNA can affect de novo methylation. Homologous recombination was used to integrate foreign DNA into a specific gene, B lymphocyte kinase (BLK), in mouse embryonic stem (ES) cells. Two plasmids were chosen for integration; one contained the adenovirus type 2 E2AL promoter upstream of the luciferase reporter gene, and the second carried the early SV40 promoter. The methylation patterns were analyzed using HpaII and MspI restriction endonucleases for both homologously recombined and randomly integrated foreign DNA in the ES cell clones. Upon homologous reinsertion of the BLK gene into the genome of mouse ES cells, methylation patterns in this gene were reestablished. In DNA segments adjoined to the BLK gene, the de novo patterns of DNA methylation depended on the viral sequences in these clones and on the locations of the inserts, i.e. on whether the insertions resulted from homologously recombined or randomly integrated foreign DNA. In homologously recombined DNA, sequences carrying the adenovirus type 2 promoter were heavily methylated, and those with an SV40 promoter and an SV40 enhancer element remained unmethylated or hypomethylated. Upon removal of the enhancer element, these inserted constructs also became heavily methylated. In addition, all randomly integrated constructs were heavily methylated independently of the promoter and enhancer element present in the construct. These results indicate that modes and sites of integration as well as the inserted nucleotide sequence, possibly promoter strength, are factors affecting de novo methylation.

Ablation of a specific cell population by the replacement of a uniquely expressed gene with a toxin gene

The transgenic expression of a toxin gene or a thymidine kinase gene under the control of cell type-specific promoter/enhancer has been shown to be useful for removing a specific cell population in mice. However, this approach requires extensive analysis of the control elements for gene expression in the preparation of the transgenic constructs, and furthermore, the toxin gene might be expressed ectopically because of random integration, resulting in aberrant depletion of unrelated cells. To avoid such difficulties with the transgenic approach, we established a method for the specific depletion of a cell population by replacing a uniquely expressed gene in the population with the diphtheria toxin gene by using homologous recombination. The NKR-P1 gene, a specific cell surface marker of natural killer (NK) cells, was selected as the target gene for depleting NK cells. In chimeric mice reconstituted with embryonic stem cells in which the NKR-P1 gene was replaced by the toxin gene, NKR-P1(+) cells were almost completely depleted, and NK cell function was abrogated in the embryonic stem cell-derived lymphoid cells. Other cell lineages developed normally. These results show that all NK cells express NKR-P1, that NKR-P1(+) cells do not influence the development of T and B cells, and further, that this technology of cell targeting is a fast and powerful method of generating mice lacking any chosen cell population.

Functional equivalency between Otx2 and Otx1 in development of the rostral head

Mice have two Otx genes, Otx1 and Otx2. Prior to gastrulation, Otx2 is expressed in the epiblast and visceral endoderm. As the primitive streak forms, Otx2 expression is restricted to the anterior parts of all three germ layers. Otx1 expression begins at the 1 to 3 somite stage in the anterior neuroectoderm. Otx2 is also expressed in cephalic mesenchyme. Otx2 homozygous mutants fail to develop structures anterior to rhombomere 3 (r3), and Otx2 heterozygotes exhibit craniofacial defects. Otx1 homozygous mutants do not show apparent defects in early brain development. In Otx1 and Otx2 double heterozygotes, rostral neuroectoderm is induced normally, but development of the mes/diencephalic domain is impaired starting at around the 3 to 6 somite stage, suggesting cooperative interactions between the two genes in brain regionalization. To determine whether Otx1 and Otx2 genes are functionally equivalent, we generated knock-in mice in which Otx2 was replaced by Otx1. In homozygous mutants, gastrulation occurred normally, and rostral neuroectoderm was induced at 7.5 days postcoitus (7.5 dpc), but the rostral brain failed to develop. Anterior structures such as eyes and the anterior neural ridge were lost by 8.5 dpc, but the isthmus and r1 and r2 were formed. In regionalization of the rostral neuroectoderm, the cooperative interaction of Otx2 with Otx1 revealed by the phenotype of Otx2 and Otx1 double heterozygotes was substitutable by Otx1. The otocephalic phenotype indicative of Otx2 haploinsufficiency was also largely restored by knocked-in Otx1. Thus most Otx2 functions were replaceable by Otx1, but the requirement for Otx2 in the anterior neuroectoderm prior to onset of Otx1 expression was not. These data indicate that Otx2 may have evolved new functions required for establishment of anterior neuroectoderm that Otx1 cannot perform.

CD38 disruption impairs glucose-induced increases in cyclic ADP-ribose, [Ca2+]i, and insulin secretion

Increases in [Ca2+]i in pancreatic beta cells, resulting from Ca2+ mobilization from intracellular stores as well as Ca2+ influx from extracellular sources, are important in insulin secretion by glucose. Cyclic ADP-ribose (cADPR), accumulated in beta cells by glucose stimulation, has been postulated to serve as a second messenger for intracellular Ca2+ mobilization for insulin secretion, and CD38 is thought to be involved in the cADPR accumulation (Takasawa, S., Tohgo, A., Noguchi, N., Koguma, T., Nata, K., Sugimoto, T., Yonekura, H., and Okamoto, H. (1993) J. Biol. Chem. 268, 26052-26054). Here we created "knockout" (CD38(-/-)) mice by homologous recombination. CD38(-/-) mice developed normally but showed no increase in their glucose-induced production of cADPR in pancreatic islets. The glucose-induced [Ca2+]i rise and insulin secretion were both severely impaired in CD38(-/-) islets, whereas CD38(-/-) islets responded normally to the extracellular Ca2+ influx stimulants tolbutamide and KCl. CD38(-/-) mice showed impaired glucose tolerance, and the serum insulin level was lower than control, and these impaired phenotypes were rescued by beta cell-specific expression of CD38 cDNA. These results indicate that CD38 plays an essential role in intracellular Ca2+ mobilization by cADPR for insulin secretion.

Identification and functional characterization of a Smad binding element (SBE) in the JunB promoter that acts as a transforming growth factor-beta, activin, and bone morphogenetic protein-inducible enhancer

Smad proteins have been identified as mediators of intracellular signal transduction by members of the transforming growth factor-beta (TGF-beta) superfamily, which affect cell proliferation, differentiation, as well as pattern formation during early vertebrate development. Following receptor activation, Smads are assembled into heteromeric complexes consisting of a pathway-restricted Smad and the common Smad4 that are subsequently translocated into the nucleus where they are thought to play an important role in gene transcription. Here we report the identification of Smad Binding Elements (SBEs) composed of the sequence CAGACA in the promoter of the JunB gene, an immediate early gene that is potently induced by TGF-beta, activin, and bone morphogenetic protein (BMP) 2. Two JunB SBEs are arranged as an inverted repeat that is transactivated in response to Smad3 and Smad4 co-overexpression and shows inducible binding of a Smad3- and Smad4-containing complex in nuclear extracts from TGF-beta-treated cells. Bacterial-expressed Smad proteins bind directly to the SBE. Multimerization of the SBE creates a powerful TGF-beta-inducible enhancer that is also responsive to activin and BMPs. The identification of the sequence CAGACA as a direct binding site for Smad proteins will facilitate the identification of regulatory elements in genes that are activated by members of the TGF-beta superfamily.

Male-to-female sex reversal in M33 mutant mice

Polycomb genes in Drosophila maintain the repressed state of homeotic and other developmentally regulated genes by mediating changes in higher-order chromatin structure. M33, a mouse homologue of Polycomb, was isolated by means of the structural similarity of its chromodomain. The fifth exon of M33 contains a region of homology shared by Drosophila and Xenopus. In Drosophila, its deletion results in the loss of Polycomb function. Here we have disrupted M33 in mice by inserting a poly(A) capture-type neo(r) targeting vector into its fifth exon. More than half of the resultant M33cterm/M33cterm mutant mice died before weaning, and survivors showed male-to-female sex reversal. Formation of genital ridges was retarded in both XX and XY M33cterm/M33cterm embryos. Gonadal growth defects appeared near the time of expression of the Y-chromosome-specific Sry gene, suggesting that M33 deficiency may cause sex reversal by interfering with steps upstream of Sry. M33cterm/M33cterm mice may be a valuable model in which to test opposing views regarding sex determination.

Differential replication timing of X-linked genes measured by a novel method using single-nucleotide primer extension

The ratio of two differentially replicating alleles is not constant during S phase. Using this fact, we have developed a method for determining allele-specific replication timing for alleles differing by at least a single base pair. Unsynchronized cells in tissue culture are first sorted into fractions based on DNA content as a measure of position in S phase. DNA is purified from each fraction and used for PCR with primers that bracket the allelic difference, amplifying both alleles. The ratio of alleles in the amplified product is then determined by a single nucleotide primer extension (SNuPE) assay, modified as described [Singer-Sam,J. and Riggs,A.D. (1993) Methods Enzymol., 225, 344-351]. We report here use of this SNuPE-based method to analyze replication timing of two X-linked genes, Pgk-1 and Xist, as well as the autosomal gene Gabra-6. We have found that the two alleles of the Gabra-6 gene replicate synchronously, as expected; similarly, the active allele of the Pgk-1 gene on the active X chromosome (Xa) replicates early relative to the silent allele on the inactive X chromosome (Xi). In contrast, the expressed allele of the Xist gene, which is on the Xi, replicates late relative to the silent allele on the Xa.

Mice lacking bombesin receptor subtype-3 develop metabolic defects and obesity

Mammalian bombesin-like peptides are widely distributed in the central nervous system as well as in the gastrointestinal tract, where they modulate smooth-muscle contraction, exocrine and endocrine processes, metabolism and behaviour. They bind to G-protein-coupled receptors on the cell surface to elicit their effects. Bombesin-like peptide receptors cloned so far include, gastrin-releasing peptide receptor (GRP-R), neuromedin B receptor (NMB-R), and bombesin receptor subtype-3 (BRS-3). However, despite the molecular characterization of BRS-3, determination of its function has been difficult as a result of its low affinity for bombesin and its lack of an identified natural ligand. We have generated BRS-3-deficient mice in an attempt to determine the in vivo function of the receptor. Mice lacking functional BRS-3 developed a mild obesity, associated with hypertension and impairment of glucose metabolism. They also exhibited reduced metabolic rate, increased feeding efficiency and subsequent hyperphagia. Our data suggest that BRS-3 is required for the regulation of endocrine processes and metabolism responsible for energy balance and adiposity. BRS-3-deficient mice provide a useful new model for the investigation of human obesity and associated diseases.

Tertiary hypothyroidism and hyperglycemia in mice with targeted disruption of the thyrotropin-releasing hormone gene

Thyrotropin-releasing hormone (TRH) is a brain hypothalamic hormone that regulates thyrotropin (TSH) secretion from the anterior pituitary and is ubiquitously distributed throughout the brain and other tissues including pancreas. To facilitate studies into the role of endogenous TRH, we have used homologous recombination to generate mice that lack TRH. These TRH-/- mice are viable, fertile, and exhibit normal development. However, they showed obvious hypothyroidism with characteristic elevation of serum TSH level and diminished TSH biological activity. Their anterior pituitaries exhibited an apparent decrease in TSH immunopositive cells that was not due to hypothyroidism. Furthermore, this decrease could be reversed by TRH, but not thyroid hormone replacement, suggesting a direct involvement of TRH in the regulation of thyrotrophs. The TRH-/- mice also exhibited hyperglycemia, which was accompanied by impaired insulin secretion in response to glucose. These findings indicate that TRH-/- mice provide a model of exploiting tertiary hypothyroidism, and that TRH gene abnormalities cause disturbance of insulin secretion resulting in marked hyperglycemia.

Expression of the protein tyrosine phosphatase beta2 gene in mouse erythroleukemia cells induces terminal erythroid differentiation

We have cloned cDNA for protein tyrosine phosphatase beta2, which had been implicated in erythroid differentiation of mouse erythroleukemia cells. Expression of cDNA constructs, in which beta2 cDNA is placed under the control of mouse metallothionein-I promoter, by ZnCl2 converted a significant portion (20 to 38%) of the cells to erythroid-like cells, which is 25-50% of the erythroid differentiation efficiency observed by conventional erythroid-inducing agents. Furthermore, introduction and expression of altered protein tyrosine phosphatase beta2 cDNA constructs designed to produce the enzyme lacking the phosphatase activity inhibited erythroid differentiation by 100-20%, depending upon the concentration of erythroid-inducing agents employed. These results strongly suggest that protein tyrosine phosphatase beta2 is involved in triggering erythroid differentiation in mouse erythroleukemia cells.

Genes transfected into embryonal carcinoma stem cells are both lost and inactivated at high frequency

Embryonal carcinoma (EC) cells can be efficiently transfected with cloned DNAs but there is a strong tendency for expression from transfected genes to be lost from stably transformed cells. To investigate the mechanism responsible for this loss of expression, we transfected P19 EC cells with a gene encoding the E. coli beta-galactosidase and examined expression of this gene in clonal populations of cells. Cells that carry and express the beta-galactosidase gene give rise to cells that do not express at a rate of about 0.02 events per cell per cell division. These non-expressing cells were of two types, some had lost the transfected genes while others had inactivated them. In those cells that retained but inactivated the transfected genes, the inactive state was stable and suppression was at the level of transcription initiation but not associated with increased DNA methylation. Because transfected DNAs integrate into the genome as tandem arrays, the gene loss and inactivation seen in EC cells may be analogous to the repeat-induced gene inactivation seen in lower eukaryotes.

Negative interaction between the RelA(p65) subunit of NF-kappaB and the progesterone receptor

Interactions between transcription factors are an important means of regulating gene transcription. The present study describes the mutual repression of two transcription factors, the RelA(p65) subunit of NF-kappaB and the progesterone receptor (PR). This trans-repression is shown to occur independent of PR isoform, reporter construct, or cell type used. Together with the demonstration of an interaction between PR and RelA in vitro, these findings suggest that the mutual repression is due to a direct interaction between these proteins. Furthermore, activation of NF-kappaB by tumor necrosis factor-alpha also results in repression of PR, while PR is able to repress tumor necrosis factor-alpha-induced NF-kappaB activity. Since NF-KB-regulating cytokine receptors are expressed in progesterone target tissues, like breast and endometrium, the mutual repression of PR and RelA could play an important role in a wide variety of physiological processes in these tissues, including maintenance of pregnancy, immunosuppression, and tumorigenesis.

A novel Tth111I restriction fragment length polymorphism (RFLP) allows tracing of X-chromosome inactivation in the (Xid) heterozygote

The X-linked immunodeficiency (Xid) in CBA/N mice serves as a model for the X-linked agammaglobulinemia (XLA) syndrome in man. X-chromosome inactivation in F1 heterozygotes derived from CBA/N (Xxid/Xxid) and B6.Pgk-1a (X+/Y) was investigated by monitoring the methylation status of the individual Pgk-1 alleles, Pgk-1b and Pgk-1a, respectively, using a novel Tth111I RFLP. Results indicate that in circulating B lymphocytes of female heterozygotes, only the X chromosomes carrying the normal alleles (X+) are active (nonrandom inactivation of the X chromosome), whereas in non-B cells both the X chromosomes (X+ and Xxid) are active (random inactivation of the X chromosome). These results were further confirmed by direct evaluation of transcription of the Btk gene, the gene mutated both in Xid and in XLA.

Mouse Otx2 functions in the formation and patterning of rostral head

The anterior part of the vertebrate head expresses a group of homeo box genes in segmentally restricted patterns during embryogenesis. Among these, Otx2 expression covers the entire fore- and midbrains and takes place earliest. To examine its role in development of the rostral head, a mutation was introduced into this locus. The homozygous mutants did not develop structures anterior to rhombomere 3, indicating an essential role of Otx2 in the formation of the rostral head. In contrast, heterozygous mutants displayed craniofacial malformations designated as otocephaly; affected structures appeared to correspond to the most posterior and most anterior domains of Otx expression where Otx1 is not expressed. The homo- and heterozygous mutant phenotypes suggest Otx2 functions as a gap-like gene in the rostral head where Hox code is not present. The evolutionary significance of Otx2 mutant phenotypes was discussed for the innovation of the neurocranium and the jaw.

DNA ligase I mediates essential functions in mammalian cells

DNA replication, repair, and recombination are essential processes in mammalian cells. Hence, the application of gene targeting to the study of these DNA metabolic pathways requires the creation of nonnull mutations. We have developed a method for introducing partially defective mutants in murine embryonic stem cells that circumvents the problem of cellular lethality of targeted mutations at essential loci. Using this approach, we have determined that mammalian DNA ligase I is essential for cell viability. Thus, DNA ligases II and III are not redundant with DNA ligase I for the function(s) associated with cell proliferation. Partial complementation of the lethal DNA ligase I null mutation allowed the creation of deficient embryonic stem cell lines. We found that a wild-type DNA ligase I cDNA, as well as a variant DNA ligase I cDNA, was able to rescue the lethality of the homozygous null mutation, whereas an N-terminal deletion mutant consisting of the minimal DNA ligase I catalytic domain was not. This observation demonstrates that sequences outside the DNA ligase I catalytic domain are essential for DNA ligase I function in vivo.

A new strategy of gene trapping in ES cells using 3'RACE

"Gene trapping" in embryonic stem (ES) cells is a novel approach to identify a series of genes in mammals concomitant with the production of the corresponding mutant mice. However, this approach is currently unable to identify genes that are not expressed in ES cells. Here we describe a strategy to identify gene trapping clones which is not based on expression of a reporter gene. It uses the neor gene which lacks a polyadenylation signal and has a splice donor signal. Expression of the neor gene as fusion transcripts with the 3' end containing the polyadenylation signal of tagged genes allows the identification of these clones by 3' rapid amplification of the cDNA end in undifferentiated ES cells, even if the genes are not expressed in ES cells. Amplification was observed in about 25% of G418-resistant clones. Sequence analyses suggested the amplifications represent gene trapping events. The feasibility of this approach was further assessed by analysing one clone, PAT-12, in detail.