SAG/RBX/ROC protein is an essential RING component of SCF E3 ubiquitin ligase. The role of SAG during embryogenesis remains unknown. We report here a critical role for SAG in controlling vascular and neural development by modulating RAS activity via promoting degradation of neurofibromatosis type 1 (NF1). Mice mutant for Sag died at embryonic day 11.5-12.5 with severe abnormalities in vascular and nervous system. Sag inactivation caused Nf1 accumulation and Ras inhibition, which blocks embryonic stem (ES) cells from undergoing endothelial differentiation and inhibits angiogenesis and proliferation in teratomas. Simultaneous Nf1 deletion fully rescues the differentiation defects in Sag−/− ES cells, and partially rescues vascular and neural defects in Sag−/− embryos, suggesting that the effects of Sag deletion may not be solely explained by Nf1 misregulation. Collectively, our study identifies NF1 as a physiological substrate of SAG-CUL1-FBXW7 E3 ligase and establishes a ubiquitin-dependent regulatory mechanism for the NF1-RAS pathway during embryogenesis.
Apoptosis; Endothelial differentiation; mouse knockout; NF1-RAS; SAG-CUL1-FBXW7 E3 ubiquitin ligase; vascular and neural development
Transgenic mice are widely used in biomedical research to study gene expression, developmental biology, and gene therapy models. Bacterial artificial chromosome (BAC) transgenes direct gene expression at physiological levels with the same developmental timing and expression patterns as endogenous genes in transgenic animal models. We generated 707 transgenic founders from 86 BAC transgenes purified by three different methods. Transgenesis efficiency was the same for all BAC DNA purification methods. Polyamine microinjection buffer was essential for successful integration of intact BAC transgenes. There was no correlation between BAC size and transgenic rate, birth rate, or transgenic efficiency. A narrow DNA concentration range generated the best transgenic efficiency. High DNA concentrations reduced birth rates while very low concentrations resulted in higher birth rates and lower transgenic efficiency. Founders with complete BAC integrations were observed in all 47 BACs for which multiple markers were tested. Additional founders with BAC fragment integrations were observed for 65% of these BACs. Expression data was available for 79 BAC transgenes and expression was observed in transgenic founders from 63 BACs (80%). Consistent and reproducible success in BAC transgenesis required the combination of careful DNA purification, the use of polyamine buffer, and sensitive genotyping assays.
Mice; Transgenic; Gene Transfer Techniques; Chromosomes; Artificial; Bacterial; BAC; Electrophoresis; Gel; Pulsed-Field; DNA; Gene Expression
Mouse early transposon insertions are responsible for ∼10% of spontaneous mutant phenotypes. We previously reported the phenotypes and genetic mapping of Polypodia, (Ppd), a spontaneous, X-linked dominant mutation with profound effects on body plan morphogenesis. Our new data shows that mutant mice are not born in expected Mendelian ratios secondary to loss after E9.5. In addition, we refined the Ppd genetic interval and discovered a novel ETnII-β early transposon insertion between the genes for Dusp9 and Pnck. The ETn inserted 1.6 kb downstream and antisense to Dusp9 and does not disrupt polyadenylation or splicing of either gene. Knock-in mice engineered to carry the ETn display Ppd characteristic ectopic caudal limb phenotypes, showing that the ETn insertion is the Ppd molecular lesion. Early transposons are actively expressed in the early blastocyst. To explore the consequences of the ETn on the genomic landscape at an early stage of development, we compared interval gene expression between wild-type and mutant ES cells. Mutant ES cell expression analysis revealed marked upregulation of Dusp9 mRNA and protein expression. Evaluation of the 5′ LTR CpG methylation state in adult mice revealed no correlation with the occurrence or severity of Ppd phenotypes at birth. Thus, the broad range of phenotypes observed in this mutant is secondary to a novel intergenic ETn insertion whose effects include dysregulation of nearby interval gene expression at early stages of development.
Mobile genetic elements, particularly early transposons (ETn), cause malformations by inserting within genes leading to disruption of exons, splicing or polyadenylation. Few mutagenic early transposon insertions have been found outside genes and the effects of such insertions on surrounding gene regulation is poorly understood. We discovered a novel intergenic ETnII-β insertion in the mouse mutant Polypodia (Ppd). We reproduced the mutant phenotype after engineering the mutation in wild-type cells with homologous recombination, proving that this early transposon insertion is Ppd. Mutant mice are not born in expected Mendelian ratios secondary to loss after E9.5. Embryonic stem cells from mutant mice show upregulated transcription of an adjacent gene, Dusp9. Thus, at an early and critical stage of development, dysregulated gene transcription is one consequence of the insertion mutation. DNA methylation of the ETn 5′ LTR is not correlated with phenotypic outcome in mutant mice. Polypodia is an example of an intergenic mobile element insertion in mice causing dramatic morphogenetic defects and fetal death.
Multiple cell types have been proposed to create niches for haematopoietic stem cells (HSCs). However, the expression patterns of HSC maintenance factors have not been systematically studied and no such factor has been conditionally deleted from any candidate niche cell. Thus, the cellular sources of these factors are undetermined. Stem Cell Factor (SCF) is a key niche component that maintains HSCs. Using Scfgfp knock-in mice we found Scf was primarily expressed by perivascular cells throughout bone marrow. HSC frequency and function were not affected when Scf was conditionally deleted from haematopoietic cells, osteoblasts, Nestin-Cre, or Nestin-CreER-expressing cells. However, HSCs were depleted from bone marrow when Scf was deleted from endothelial cells or Leptin receptor (Lepr)-expressing perivascular stromal cells. Most HSCs were lost when Scf was deleted from both endothelial and Lepr-expressing perivascular cells. HSCs reside in a perivascular niche in which multiple cell types express factors that promote HSC maintenance.
A recent study revealed that ES (embryonic stem) cell lines derived from the 129 murine strain carry an inactivating mutation within the caspase 11 gene (Casp4) locus [Kayagaki, Warming, Lamkanfi, Vande Walle, Louie, Dong, Newton, Qu, Liu, Heldens, Zhang, Lee, Roose-Girma and Dixit (2011) Nature 479, 117–121]. Thus, if 129 ES cells are used to target genes closely linked to caspase 11, the resulting mice might also carry the caspase 11 deficiency as a passenger mutation. In the present study, we examined the genetic loci of mice targeted for the closely linked c-IAP (cellular inhibitor of apoptosis) genes, which were generated in 129 ES cells, and found that, despite extensive backcrossing into a C57BL/6 background, c-IAP1−/− animals are also deficient in caspase 11. Consequently, data obtained from these mice should be re-evaluated in this new context.
129 mouse strain; caspase 1; caspase 11; inhibitor of apoptosis protein (IAP); lipopolysaccharide (LPS); sepsis; c-IAP, cellular inhibitor of apoptosis; ES, embryonic stem; IAP, inhibitor of apoptosis; LPS, lipopolysaccharide; MEF, mouse embryonic fibroblast; RT, reverse transcription; TBS-T, Tris-buffered saline with 0.1% Tween 20; XIAP, X-linked inhibitor of apoptosis
Mutations in human SLC26A4 are a common cause of hearing loss associated with enlarged vestibular aqueducts (EVA). SLC26A4 encodes pendrin, an anion-base exchanger expressed in inner ear epithelial cells that secretes HCO3– into endolymph. Studies of Slc26a4-null mice indicate that pendrin is essential for inner ear development, but have not revealed whether pendrin is specifically necessary for homeostasis. Slc26a4-null mice are profoundly deaf, with severe inner ear malformations and degenerative changes that do not model the less severe human phenotype. Here, we describe studies in which we generated a binary transgenic mouse line in which Slc26a4 expression could be induced with doxycycline. The transgenes were crossed onto the Slc26a4-null background so that all functional pendrin was derived from the transgenes. Varying the temporal expression of Slc26a4 revealed that E16.5 to P2 was the critical interval in which pendrin was required for acquisition of normal hearing. Lack of pendrin during this period led to endolymphatic acidification, loss of the endocochlear potential, and failure to acquire normal hearing. Doxycycline initiation at E18.5 or discontinuation at E17.5 resulted in partial hearing loss approximating the human EVA auditory phenotype. These data collectively provide mechanistic insight into hearing loss caused by SLC26A4 mutations and establish a model for further studies of EVA-associated hearing loss.
Little is known about metabolic regulation in stem cells and how this modulates tissue regeneration or tumour suppression. We studied the Lkb1 tumour suppressor, and its substrate AMPK, kinases that coordinate metabolism with cell growth. Lkb1 deletion caused increased haematopoietic stem cell (HSC) division, rapid HSC depletion, and pancytopenia. HSCs depended more acutely on Lkb1 for cell cycle regulation and survival than many other haematopoietic cells. HSC depletion did not depend on mTOR activation or oxidative stress. Lkb1-deficient HSCs, but not myeloid progenitors, had reduced mitochondrial membrane potential and ATP. AMPK-deficient HSCs showed similar changes in mitochondrial function but remained able to reconstitute irradiated mice. Lkb1-deficient HSCs, but not AMPK-deficient HSCs, exhibited defects in centrosomes and mitotic spindles in culture, and became aneuploid. Lkb1 is therefore required for HSC maintenance through AMPK-dependent and AMPK-independent mechanisms, revealing differences in metabolic and cell cycle regulation between HSCs and some other haematopoietic progenitors.
The mechanisms that regulate peripheral nervous system (PNS) gliogenesis are incompletely understood. For example, gut neural crest stem cells (NCSCs) do not respond to known gliogenic factors, suggesting that yet unidentified factors regulate gut gliogenesis. To identify new mechanisms, we performed gene expression profiling to identify factors secreted by gut neural crest stem cells (NCSCs) during the gliogenic phase of development. These cells highly expressed Leucine-rich glioma inactivated 4 (Lgi4) despite the fact that Lgi4 has never been implicated in stem cell function or enteric nervous system development. Lgi4 is known to regulate peripheral nerve myelination (having been identified as the mutated gene in spontaneously arising claw paw mutant mice) but Lgi4 is not known to play any role in PNS development outside of peripheral nerves. To systematically analyze Lgi4 function we generated gene-targeted mice. Lgi4 deficient mice exhibited a more severe phenotype than claw paw mice and had gliogenic defects in sensory, sympathetic and enteric ganglia. We found that Lgi4 is required for the proliferation and differentiation of glial restricted progenitors throughout the PNS. Analysis of compound mutant mice revealed that the mechanism by which Lgi4 promotes enteric gliogenesis involves binding the ADAM22 receptor. Our results identify a new mechanism regulating enteric gliogenesis as well as novel functions for Lgi4 regulating the proliferation and maturation of glial lineage cells throughout the PNS.
Lgi4; peripheral nervous system; gliogenesis; neural crest; stem cell
During spermatogenesis, global nucleosome removal occurs where histones are initially replaced by transition proteins and subsequently by protamines. This chromatin reorganization is thought to facilitate the compaction of the paternal genome into the sperm head and to protect the DNA from damaging agents. Histone ubiquitination has been suggested to be important for sex chromosome inactivation during meiotic prophase and nucleosome removal at post-meiotic stages. However, the mechanisms regulating these ubiquitin-mediated processes are unknown. In this study, we investigate the role of the ubiquitin ligase RNF8 during spermatogenesis and find that RNF8-deficient mice are proficient in meiotic sex chromosome inactivation (MSCI), but deficient in global nucleosome removal. Moreover, we show that RNF8-dependent histone ubiquitination induces H4K16 acetylation, which may be an initial step in nucleosome removal. Thus, our results show that RNF8 plays an important role during spermatogenesis through histone ubiquitination, resulting in trans-histone acetylation and global nucleosome removal.
RNA interference (RNAi) is a powerful strategy for studying the phenotypic consequences of reduced gene expression levels in model systems. To develop a method for the rapid characterization of the developmental consequences of gene dysregulation, we tested the use of RNAi for “transient transgenic” knockdown of mRNA in mouse embryos. These methods included lentiviral infection as well as transposition using the Sleeping Beauty (SB) and PiggyBac (PB) transposable element systems. This approach can be useful for phenotypic validation of putative mutant loci, as we demonstrate by confirming that knockdown of Prdm16 phenocopies the ENU-induced cleft palate (CP) mutant, csp1. This strategy is attractive as an alternative to gene targeting in embryonic stem cells, as it is simple and yields phenotypic information in a matter of weeks. Of the three methodologies tested, the PB transposon system produced high numbers of transgenic embryos with the expected phenotype, demonstrating its utility as a screening method.
Epithelial–mesenchymal transition (EMT) is required for mesodermal differentiation during development. The zinc-finger transcription factor, Snail1, can trigger EMT and is sufficient to transcriptionally reprogram epithelial cells toward a mesenchymal phenotype during neoplasia and fibrosis. Whether Snail1 also regulates the behavior of terminally differentiated mesenchymal cells remains unexplored. Using a Snai1 conditional knockout model, we now identify Snail1 as a regulator of normal mesenchymal cell function. Snail1 expression in normal fibroblasts can be induced by agonists known to promote proliferation and invasion in vivo. When challenged within a tissue-like, three-dimensional extracellular matrix, Snail1-deficient fibroblasts exhibit global alterations in gene expression, which include defects in membrane type-1 matrix metalloproteinase (MT1-MMP)-dependent invasive activity. Snail1-deficient fibroblasts explanted atop the live chick chorioallantoic membrane lack tissue-invasive potential and fail to induce angiogenesis. These findings establish key functions for the EMT regulator Snail1 after terminal differentiation of mesenchymal cells.
T cell-specific adapter protein (TSAd) and adapter protein in lymphocytes of unknown function (ALX) are two related src-homology-2 (SH2) domain-containing signaling adapter molecules that have both been shown to regulate TCR signal transduction in T cells. TSAd is required for normal TCR-induced synthesis of IL-2 and other cytokines in T cells and acts at least in part by promoting activation of the LCK protein tyrosine kinase at the outset of the TCR signaling cascade. By contrast, ALX functions as a negative-regulator of TCR-induced IL-2 synthesis through as yet undetermined mechanisms. Herein, we report a novel T cell-expressed adapter protein named SH2D4A that contains an SH2 domain that is highly homologous to the TSAd and ALX SH2 domains and which shares other structural features with these adapters. To examine the function of SH2D4A in T cells we produced SH2D4A-deficient mice by homologous recombination in embryonic stem cells. T cell development, homeostasis, proliferation and function were all found to be normal in these mice. Furthermore, knockdown of SH2D4A expression in human T cells did not impact upon their function. We conclude that in contrast to TSAd and ALX, SH2D4A is dispensable for TCR signal transduction in T cells.
T cell; signal transduction; transgenic/knockout mice
Polo-like kinases (Plks) are serine/threonine kinases that are highly conserved in organisms from yeasts to humans. Previous reports have shown that Plk1 is critical for all stages of mitosis and may play a role in DNA replication during S phase. While much work has focused on Plk1, little is known about the physiological function of Plk1 in vivo. To address this question, we generated Plk1 knockout mice. Plk1 homozygous null mice were embryonic lethal, and early Plk1−/− embryos failed to survive after the eight-cell stage. Immunocytochemistry studies revealed that Plk1-null embryos were arrested outside the mitotic phase, suggesting that Plk1 is important for proper cell cycle progression. It has been postulated that Plk1 is a potential oncogene, due to its overexpression in a variety of tumors and tumor cell lines. While the Plk1 heterozygotes were healthy at birth, the incidence of tumors in these animals was threefold greater than that in their wild-type counterparts, demonstrating that the loss of one Plk1 allele accelerates tumor formation. Collectively, our data support that Plk1 is important for early embryonic development and may function as a haploinsufficient tumor suppressor.
Fetal stem cells differ phenotypically and functionally from adult stem cells in diverse tissues. However, little is known about how these differences are regulated. To address this we compared the gene expression profiles of fetal versus adult hematopoietic stem cells (HSCs) and discovered that the Sox17 transcriptional regulator is specifically expressed in fetal and neonatal but not adult HSCs. Germline deletion of Sox17 led to severe fetal hematopoietic defects, including a lack of detectable definitive HSCs. Conditional deletion of Sox17 from hematopoietic cells led to the loss of fetal and neonatal but not adult HSCs. HSCs stopped expressing Sox17 approximately 4 weeks after birth. During this transition, loss of Sox17 expression correlated with slower proliferation and the acquisition of an adult phenotype by individual HSCs. Sox17 is thus required for the maintenance of fetal and neonatal HSCs and distinguishes their transcriptional regulation from adult HSCs.
Ribosomal protein mutations, termed Minutes, have been instrumental in studying the coordination of cell and tissue growth in Drosophila. Although abundant in flies, equivalent defects in mammals are relatively unknown. Belly spot and tail (Bst) is a semidominant mouse mutation that disrupts pigmentation, somitogenesis and retinal cell fate determination. Here, we identify Bst as a deletion within the Rpl24 riboprotein gene. Bst significantly impairs Rpl24 splicing and ribosome biogenesis. Bst/+ cells have decreased rates of protein synthesis and proliferation, and are outcompeted by wild-type cells in C57BLKS↔ROSA26 chimeras. Bacterial artificial chromosome (BAC) and cDNA transgenes correct the mutant phenotypes. Our findings establish Bst as a mouse Minute and provide the first detailed characterization of a mammalian ribosomal protein mutation.
Mouse; Genetics; Minute; Ribosome; Cell cycle; Retina; Bst
Signal transduction via guanine nucleotide binding proteins (G proteins) is involved in cardiovascular, neural, endocrine, and immune cell function. Regulators of G protein signaling (RGS proteins) speed the turn-off of G protein signals and inhibit signal transduction, but the in vivo roles of RGS proteins remain poorly defined. To overcome the redundancy of RGS functions and reveal the total contribution of RGS regulation at the Gαi2 subunit, we prepared a genomic knock-in of the RGS-insensitive G184S Gnai2 allele. The Gαi2G184S knock-in mice show a dramatic and complex phenotype affecting multiple organ systems (heart, myeloid, skeletal, and central nervous system). Both homozygotes and heterozygotes demonstrate reduced viability and decreased body weight. Other phenotypes include shortened long bones, a markedly enlarged spleen, elevated neutrophil counts, an enlarged heart, and behavioral hyperactivity. Heterozygous Gαi2+/G184S mice show some but not all of these abnormalities. Thus, loss of RGS actions at Gαi2 produces a dramatic and pleiotropic phenotype which is more evident than the phenotype seen for individual RGS protein knockouts.
Meprins are multidomain zinc metalloproteases that are highly expressed in mammalian kidney and intestinal brush border membranes and in leukocytes and certain cancer cells. Mature meprins are oligomers of evolutionarily related, separately encoded α and/or β subunits. Homooligomers of meprin α are secreted; oligomers containing meprin β are plasma membrane associated. Meprin substrates include bioactive peptides and extracellular matrix proteins. Meprins have been implicated in cancer and intestinal inflammation. Additionally, meprin β is a candidate gene for diabetic nephropathy. To elucidate in vivo functions of these metalloproteases, meprin β null mice were generated by targeted disruption of the meprin β gene on mouse chromosome 18q12. Analyses of meprin β knockout mice indicated that (i) 50% fewer null mice are born than the Mendelian distribution predicts, (ii) null mice that survive develop normally and are viable and fertile, (iii) meprin β knockout mice lack membrane-associated meprin α in kidney and intestine, and (iv) null mice have changes in renal gene expression profiles compared to wild-type mice as assessed by microarray analyses. Thus, disruption of the meprin β allele in mice affects embryonic viability, birth weight, renal gene expression profiles, and the distribution of meprin α in kidney and intestine.
The fucose α(1→2) galactose β structure is expressed by uterine epithelial cells in the mouse and has been implicated in blastocyst adhesion events thought to be required for murine implantation. Fucα(1→2)Galβ moieties and cognate fucosyltransferases are also expressed by epithelial cells of the male reproductive tract and have been implicated in sperm maturation events that may contribute to fertilization. To determine directly if Fucα(1→2)Galβ moieties are required for fertility, we have generated strains of mice that are deficient in genes encoding FUT1 and FUT2, a pair of GDP-l-fucose:β(1→4)-d-galactosyl-R 2-α-l-fucosyltransferase enzymes (EC 184.108.40.206) responsible for Fucα(1→2)Galβ synthesis and expression. FUT1 null mice and FUT2 null mice develop normally and exhibit no gross phenotypic abnormalities. The Fucα(1→2)Galβ epitope is absent from the uterine epithelia of FUT2 null mice and from the epithelia of the epididymis of FUT1 null mice. Fully normal fertility is observed in FUT1 null intercrosses and in FUT2 null intercrosses. These observations indicate that Fucα(1→2)Galβ moieties are not essential to blastocyst-uterine epithelial cell interactions required for implantation and are not required for sperm maturation events that permit fertilization and that neither the FUT loci nor their cognate fucosylated glycans are essential to normal development.
Glomerular epithelial protein 1 (GLEPP1) is a receptor tyrosine phosphatase present on the apical cell surface of the glomerular podocyte. The GLEPP1 gene (Ptpro) was disrupted at an exon coding for the NH2-terminal region by gene targeting in embryonic stem cells. Heterozygote mating produced the expected genotypic ratio of 1:2:1, indicating that the Ptpro–/– genotype does not lead to embryonic or neonatal lethality. Kidney and glomerular structure was normal at the gross and light microscopic levels. Scanning and transmission electron microscopy showed that Ptpro–/– mice had an amoeboid rather than the typical octopoid structure seen in the wild-type mouse podocyte and that there were blunting and widening of the minor (foot) processes in association with altered distribution of the podocyte intermediate cytoskeletal protein vimentin. Reduced filtration surface area in association with these structural changes was confirmed by finding reduced glomerular nephrin content and reduced glomerular filtration rate in Ptpro–/– mice. There was no detectable increase in the urine albumin excretion of Ptpro–/– mice. After removal of one or more kidneys, Ptpro–/– mice had higher blood pressure than did their wild-type littermates. These data support the conclusion that the GLEPP1 (Ptpro) receptor plays a role in regulating the glomerular pressure/filtration rate relationship through an effect on podocyte structure and function.