The Transcriptional Modulator Interferon-Related Developmental Regulator 1 in Osteoblasts Suppresses Bone Formation and Promotes Bone Resorption

Bone homeostasis is maintained by the synergistic actions of bone-resorbing osteoclasts and bone-forming osteoblasts. Although interferon-related developmental regulator 1 (Ifrd1) has been identified as a transcriptional coactivator/repressor in various cells, little attention has been paid to its role in osteoblastogenesis and bone homeostasis thus far. Here, we show that Ifrd1 is a critical mediator of both the cell-autonomous regulation of osteoblastogenesis and osteoblast-dependent regulation of osteoclastogenesis. Osteoblast-specific deletion of murine Ifrd1 increased bone formation and decreased bone resorption, causing high bone mass. Ifrd1 deficiency enhanced osteoblast differentiation and maturation along with increased expression of Runx2 and osterix (Osx). Mechanistically, Ifrd1 deficiency increased the acetylation status of p65, a component of NF-κB, at residues K122 and K123 via the attenuation of the interaction between p65 and histone deacetylase (HDAC). This led to the nuclear export of p65 and a decrease in NF-κB-dependent Smad7 expression and the subsequent enhancement of Smad1/Smad5/Smad8-dependent transcription. Moreover, a high bone mass phenotype in the osteoblast-specific deletion of Ifrd1 was markedly rescued by the introduction of one Osx-floxed allele but not of Runx2-floxed allele. Coculture experiments revealed that Ifrd1-deficient osteoblasts have a higher osteoprotegerin (OPG) expression and a lower ability to support osteoclastogenesis. Ifrd1 deficiency attenuated the interaction between β-catenin and HDAC, subsequently increasing the acetylation of β-catenin at K49, leading to its nuclear accumulation and the activation of the β-catenin-dependent transcription of OPG. Collectively, the expression of Ifrd1 in osteoblasts repressed osteoblastogenesis and activated osteoclastogenesis through modulating the NF-κB/Smad/Osx and β-catenin/OPG pathways, respectively. These findings suggest that Ifrd1 has a pivotal role in bone homeostasis through its expression in osteoblasts in vivo and represents a therapeutic target for bone diseases.

PKN3 is the major regulator of angiogenesis and tumor metastasis in mice

PKN, a conserved family member related to PKC, was the first protein kinase identified as a target of the small GTPase Rho. PKN is involved in various functions including cytoskeletal arrangement and cell adhesion. Furthermore, the enrichment of PKN3 mRNA in some cancer cell lines as well as its requirement in malignant prostate cell growth suggested its involvement in oncogenesis. Despite intensive research efforts, physiological as well as pathological roles of PKN3 in vivo remain elusive. Here, we generated mice with a targeted deletion of PKN3. The PKN3 knockout (KO) mice are viable and develop normally. However, the absence of PKN3 had an impact on angiogenesis as evidenced by marked suppressions of micro-vessel sprouting in ex vivo aortic ring assay and in vivo corneal pocket assay. Furthermore, the PKN3 KO mice exhibited an impaired lung metastasis of melanoma cells when administered from the tail vein. Importantly, PKN3 knock-down by small interfering RNA (siRNA) induced a glycosylation defect of cell-surface glycoproteins, including ICAM-1, integrin β1 and integrin α5 in HUVECs. Our data provide the first in vivo genetic demonstration that PKN3 plays critical roles in angiogenesis and tumor metastasis, and that defective maturation of cell surface glycoproteins might underlie these phenotypes.

Calcilytic Ameliorates Abnormalities of Mutant Calcium-Sensing Receptor (CaSR) Knock-In Mice Mimicking Autosomal Dominant Hypocalcemia (ADH)

Activating mutations of calcium-sensing receptor (CaSR) cause autosomal dominant hypocalcemia (ADH). ADH patients develop hypocalcemia, hyperphosphatemia, and hypercalciuria, similar to the clinical features of hypoparathyroidism. The current treatment of ADH is similar to the other forms of hypoparathyroidism, using active vitamin D3 or parathyroid hormone (PTH). However, these treatments aggravate hypercalciuria and renal calcification. Thus, new therapeutic strategies for ADH are needed. Calcilytics are allosteric antagonists of CaSR, and may be effective for the treatment of ADH caused by activating mutations of CaSR. In order to examine the effect of calcilytic JTT-305/MK-5442 on CaSR harboring activating mutations in the extracellular and transmembrane domains in vitro, we first transfected a mutated CaSR gene into HEK cells. JTT-305/MK-5442 suppressed the hypersensitivity to extracellular Ca(2+) of HEK cells transfected with the CaSR gene with activating mutations in the extracellular and transmembrane domains. We then selected two activating mutations locating in the extracellular (C129S) and transmembrane (A843E) domains, and generated two strains of CaSR knock-in mice to build an ADH mouse model. Both mutant mice mimicked almost all the clinical features of human ADH. JTT-305/MK-5442 treatment in vivo increased urinary cAMP excretion, improved serum and urinary calcium and phosphate levels by stimulating endogenous PTH secretion, and prevented renal calcification. In contrast, PTH(1-34) treatment normalized serum calcium and phosphate but could not reduce hypercalciuria or renal calcification. CaSR knock-in mice exhibited low bone turnover due to the deficiency of PTH, and JTT-305/MK-5442 as well as PTH(1-34) increased bone turnover and bone mineral density (BMD) in these mice. These results demonstrate that calcilytics can reverse almost all the phenotypes of ADH including hypercalciuria and renal calcification, and suggest that calcilytics can become a novel therapeutic agent for ADH.

Intestinal deletion of Claudin-7 enhances paracellular organic solute flux and initiates colonic inflammation in mice

OBJECTIVE

To design novel anti-inflammation treatments, it is important to recognise two distinct steps of inflammation: initiation and acceleration. In IBDs, intestinal inflammation is reported to be accelerated by dysfunction in the epithelial paracellular barrier formed by tight junctions (TJs). However, it is unclear whether changes in paracellular barrier function initiate inflammation. Some of the intestinal claudin-family proteins, which form the paracellular barrier, show aberrant expression levels and localisations in IBDs. We aimed to elucidate the role of paracellular-barrier change in initiating colonic inflammation.

DESIGN

We generated intestine-specific conditional knockout mice of claudin-7 (Cldn7), one of the predominant intestinal claudins.

RESULTS

The intestine-specific Cldn7 deficiency caused colonic inflammation, even though TJ structures were still present due to other claudins. The paracellular flux (pFlux), determined by measuring the paracellular permeability across the colon epithelium, was enhanced by the Cldn7 deficiency for the small organic solute Lucifer Yellow (457 Da), but not for the larger organic solute FITC-Dextran (4400 Da). Consistent with these results, the intestine-specific claudin-7 deficiency enhanced the pFlux for N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) (438 Da), a major bacterial product, to initiate colonic inflammation.

CONCLUSIONS

These findings suggest that specific enhancement of the pFlux for small organic solutes across the claudin-based TJs initiates colonic inflammation.

The Parkinson's Disease-Associated Protein Kinase LRRK2 Modulates Notch Signaling through the Endosomal Pathway

Leucine-rich repeat kinase 2 (LRRK2) is a key molecule in the pathogenesis of familial and idiopathic Parkinson’s disease (PD). We have identified two novel LRRK2-associated proteins, a HECT-type ubiquitin ligase, HERC2, and an adaptor-like protein with six repeated Neuralized domains, NEURL4. LRRK2 binds to NEURL4 and HERC2 via the LRRK2 Ras of complex proteins (ROC) domain and NEURL4, respectively. HERC2 and NEURL4 link LRRK2 to the cellular vesicle transport pathway and Notch signaling, through which the LRRK2 complex promotes the recycling of the Notch ligand Delta-like 1 (Dll1)/Delta (Dl) through the modulation of endosomal trafficking. This process negatively regulates Notch signaling through cis-inhibition by stabilizing Dll1/Dl, which accelerates neural stem cell differentiation and modulates the function and survival of differentiated dopaminergic neurons. These effects are strengthened by the R1441G ROC domain-mutant of LRRK2. These findings suggest that the alteration of Notch signaling in mature neurons is a component of PD etiology linked to LRRK2.

LRRK2 is linked to autosomal dominant late-onset Parkinson’s disease, suggesting that LRRK2 gain-of-function mutations lead to age-dependent degeneration of the midbrain dopaminergic neurons. In this study, we describe two novel LRRK2-associated proteins HERC2 and NEURL4, which are a ubiquitin ligase and an adaptor-like protein, respectively. HERC2 and NEURL4 direct LRRK2 to Notch signaling pathway, in which the LRRK2-NEURL4-HERC2 complex promotes the recycling of the Notch ligand Delta-like 1 (Dll1)/Delta (Dl) through the modulation of endosomal trafficking. As a result, the amounts of Dll1/D1 on the plasma membrane are increased, which affects negatively Notch signaling through cis-inhibition. The effect is enhanced by a Parkinson’s-disease associated mutation of LRRK2. Inhibition of Notch signaling in adult dopaminergic neurons impairs its functions and survival. These findings indicate a possible link between Notch pathway and Parkinson’s disease.

AVE protein expression and visceral endoderm cell behavior during anterior-posterior axis formation in mouse embryos: Asymmetry in OTX2 and DKK1 expression

The initial landmark of anterior-posterior (A-P) axis formation in mouse embryos is the distal visceral endoderm, DVE, which expresses a series of anterior genes at embryonic day 5.5 (E5.5). Subsequently, DVE cells move to the future anterior region, generating anterior visceral endoderm (AVE). Questions remain regarding how the DVE is formed and how the direction of the movement is determined. This study compares the detailed expression patterns of OTX2, HHEX, CER1, LEFTY1 and DKK1 by immunohistology and live imaging at E4.5-E6.5. At E6.5, the AVE is subdivided into four domains: most anterior (OTX2, HHEX, CER1-low/DKK1-high), anterior (OTX2, HHEX, CER1-high/DKK1-low), main (OTX2, HHEX, CER1, LEFTY1-high) and antero-lateral and posterior (OTX2, HHEX-low). The study demonstrates how this pattern is established. AVE protein expression in the DVE occurs de novo at E5.25-E5.5. Neither HHEX, LEFTY1 nor CER1 expression is asymmetric. In contrast, OTX2 expression is tilted on the future posterior side with the DKK1 expression at its proximal domain; the DVE cells move in the opposite direction of the tilt.

Angiopoietin-1 guides directional angiogenesis through integrin αvβ5 signaling for recovery of ischemic retinopathy

Retinopathy of prematurity (ROP) and proliferative diabetic retinopathy (PDR) are ischemic retinal diseases caused by insufficient vascular network formation and vascular regression in addition to aberrant angiogenesis. We examined the role of angiopoietin-1 (Ang1) in retinal vascular network formation during postnatal development using Ang1 gain- and loss-of-function mouse models, and tested the effects of intraocular administration of Ang1 in an oxygen-induced retinopathy (OIR) mouse model that mimics cardinal features of ROP and PDR. We observed that Ang1 plays a substantial role in the formation of the retinal vascular network during postnatal development and that Ang1 supplementation can rescue vascular retinopathies by simultaneously promoting healthy vascular network formation and inhibiting subsequent abnormal angiogenesis, vascular leakage, and neuronal dysfunction in the retinas of the OIR model. We attribute these Ang1-induced effects to a dual signaling pathway-Tie2 signaling in the vascular region and integrin αvβ5 signaling in the astrocytes. The activation of integrin αvβ5 signaling promoted fibronectin accumulation and radial distribution along the sprouting endothelial cells, which consequently stimulated guided angiogenesis in the retina. These findings shed light on the role of Ang1 in the recovery of ischemic retinopathies such as ROP, PDR, and retinal vascular occlusive disease.

Meiosis-specific cohesin mediates homolog recognition in mouse spermatocytes

During meiosis, homologous chromosome (homolog) pairing is promoted by several layers of regulation that include dynamic chromosome movement and meiotic recombination. However, the way in which homologs recognize each other remains a fundamental issue in chromosome biology. Here, we show that homolog recognition or association initiates upon entry into meiotic prophase before axis assembly and double-strand break (DSB) formation. This homolog association develops into tight pairing only during or after axis formation. Intriguingly, the ability to recognize homologs is retained in Sun1 knockout spermatocytes, in which telomere-directed chromosome movement is abolished, and this is the case even in Spo11 knockout spermatocytes, in which DSB-dependent DNA homology search is absent. Disruption of meiosis-specific cohesin RAD21L precludes the initial association of homologs as well as the subsequent pairing in spermatocytes. These findings suggest the intriguing possibility that homolog recognition is achieved primarily by searching for homology in the chromosome architecture as defined by meiosis-specific cohesin rather than in the DNA sequence itself.

The gut microbiota suppresses insulin-mediated fat accumulation via the short-chain fatty acid receptor GPR43

The gut microbiota affects nutrient acquisition and energy regulation of the host, and can influence the development of obesity, insulin resistance, and diabetes. During feeding, gut microbes produce short-chain fatty acids, which are important energy sources for the host. Here we show that the short-chain fatty acid receptor GPR43 links the metabolic activity of the gut microbiota with host body energy homoeostasis. We demonstrate that GPR43-deficient mice are obese on a normal diet, whereas mice overexpressing GPR43 specifically in adipose tissue remain lean even when fed a high-fat diet. Raised under germ-free conditions or after treatment with antibiotics, both types of mice have a normal phenotype. We further show that short-chain fatty acid-mediated activation of GPR43 suppresses insulin signalling in adipocytes, which inhibits fat accumulation in adipose tissue and promotes the metabolism of unincorporated lipids and glucose in other tissues. These findings establish GPR43 as a sensor for excessive dietary energy, thereby controlling body energy utilization while maintaining metabolic homoeostasis.

The gut microbiota produces metabolites such as short-chain fatty acids (SCFAs), which can influence the development of obesity. Here Kimura et al. show that SCFAs act via the receptor GPR43, which acts as a sensor for excessive dietary energy and controls body energy utilization as well as metabolic homoeostasis.

In vivo analysis of Aicda gene regulation: a critical balance between upstream enhancers and intronic silencers governs appropriate expression

The Aicda gene encodes activation-induced cytidine deaminase (AID). Aicda is strongly transcribed in activated B cells to diversify immunoglobulin genes, but expressed at low levels in various other cells in response to physiological or pathological stimuli. AID’s mutagenic nature has been shown to be involved in tumor development. Here, we used a transgenic strategy with bacterial artificial chromosomes (BACs) to examine the in vivo functions of Aicda regulatory elements, which cluster in two regions: in the first intron (region 2), and approximately 8-kb upstream of the transcription start site (region 4). Deleting either of these regions completely abolished the expression of Aicda-BAC reporters, demonstrating these elements’ critical roles. Furthermore, we found that selectively deleting two C/EBP-binding sites in region 4 inactivated the enhancer activity of the region despite the presence of intact NF-κB-, STAT6- and Smad-binding sites. On the other hand, selectively deleting E2F- and c-Myb-binding sites in region 2 increased the frequency of germinal-center B cells in which the Aicda promoter was active, indicating that E2F and c-Myb act as silencers in vivo. Interestingly, the silencer deletion did not cause ectopic activation of the Aicda promoter, indicating that Aicda activation requires enhancer-specific stimulation. In summary, precise regulation of the Aicda promoter appears to depend on a coordinated balance of activities between enhancer and silencer elements.

Visualization of cell cycle in mouse embryos with Fucci2 reporter directed by Rosa26 promoter

Fucci technology makes possible the distinction between live cells in the G(1) and S/G(2)/M phases by dual-color imaging. This technology relies upon ubiquitylation-mediated proteolysis, and transgenic mice expressing Fucci provide a powerful model system with which to study the coordination of the cell cycle and development. The mice were initially generated using the CAG promoter; lines expressing the G(1) and S/G(2)/M phase probes that emitted orange (mKO2) and green (mAG) fluorescence, respectively, were separately constructed. Owing to cell type-biased strength of the CAG promoter as well as the positional effects of random transgenesis, however, we noticed some variability in Fucci expression levels. To control more reliably the expression of cell cycle probes, we used different genetic approaches to create two types of reporter mouse lines with Fucci2 and Rosa26 transcriptional machinery. Fucci2 is a recently developed Fucci derivative, which emits red (mCherry) and green (mVenus) fluorescence and provides better color contrast than Fucci. A new transgenic line, R26p-Fucci2, utilizes the Rosa26 promoter and harbors the G(1) and S/G(2)/M phase probes in a single transgene to preserve their co-inheritance. In the other R26R-Fucci2 approach, the two probes are incorporated into Rosa26 locus conditionally. The Cre-mediated loxP recombination technique thus allows researchers to design cell-type-specific Fucci2 expression. By performing time-lapse imaging experiments using R26p-Fucci2 and R26-Fucci2 in which R26R-Fucci2 had undergone germline loxP recombination, we demonstrated the great promise of these mouse reporters for studying cell cycle behavior in vivo.

Osterix regulates calcification and degradation of chondrogenic matrices through matrix metalloproteinase 13 (MMP13) expression in association with transcription factor Runx2 during endochondral ossification

Endochondral ossification is temporally and spatially regulated by several critical transcription factors, including Sox9, Runx2, and Runx3. Although the molecular mechanisms that control the late stages of endochondral ossification (e.g. calcification) are physiologically and pathologically important, these precise regulatory mechanisms remain unclear. Here, we demonstrate that Osterix is an essential transcription factor for endochondral ossification that functions downstream of Runx2. The global and conditional Osterix-deficient mice studied here exhibited a defect of cartilage-matrix ossification and matrix vesicle formation. Importantly, Osterix deficiencies caused the arrest of endochondral ossification at the hypertrophic stage. Microarray analysis revealed that matrix metallopeptidase 13 (MMP13) is an important target of Osterix. We also showed that there exists a physical interaction between Osterix and Runx2 and that these proteins function cooperatively to induce MMP13 during chondrocyte differentiation. Most interestingly, the introduction of MMP13 stimulated the calcification of matrices in Osterix-deficient mouse limb bud cells. Our results demonstrated that Osterix was essential to endochondral ossification and revealed that the physical and functional interaction between Osterix and Runx2 were necessary for the induction of MMP13 during endochondral ossification.

Malat1 is not an essential component of nuclear speckles in mice

Malat1 is an abundant long, noncoding RNA that localizes to nuclear bodies known as nuclear speckles, which contain a distinct set of pre-mRNA processing factors. Previous studies in cell culture have demonstrated that Malat1 interacts with pre-mRNA splicing factors, including the serine- and arginine-rich (SR) family of proteins, and regulates a variety of biological processes, including cancer cell migration, synapse formation, cell cycle progression, and responses to serum stimulation. To address the physiological function of Malat1 in a living organism, we generated Malat1-knockout (KO) mice using homologous recombination. Unexpectedly, the Malat1-KO mice were viable and fertile, showing no apparent phenotypes. Nuclear speckle markers were also correctly localized in cells that lacked Malat1. However, the cellular levels of another long, noncoding RNA--Neat1--which is an architectural component of nuclear bodies known as paraspeckles, were down-regulated in a particular set of tissues and cells lacking Malat1. We propose that Malat1 is not essential in living mice maintained under normal laboratory conditions and that its function becomes apparent only in specific cell types and under particular conditions.

Epidermal phospholipase Cδ1 regulates granulocyte counts and systemic interleukin-17 levels in mice

Phospholipase C is a key enzyme in phosphoinositide turnover. Although its functions have been extensively studied at the cellular level, many questions remain concerning its functions at the organ and individual animal levels. Here we demonstrate that mice lacking phospholipase Cδ1 develop granulocytosis associated with elevated serum levels of the granulopoietic cytokine interleukin-17. Re-introduction of phospholipase Cδ1 into keratinocytes of phospholipase Cδ1-deficient mice reverses this phenotype, whereas conditional ablation of phospholipase Cδ1 in keratinocytes recreates it. Interleukin-17 and its key upstream regulator interleukin-23 are also upregulated in epidermis. Loss of phospholipase Cδ1 from keratinocytes causes features of interleukin-17-associated inflammatory skin diseases. Phospholipase Cδ1 protein is downregulated in the epidermis of human psoriatic skin and in a mouse model of psoriasis. These results demonstrate that phosphoinositide turnover in keratinocytes regulates not only local inflammatory responses but also serum cytokine levels and systemic leukocyte counts, and affects distant haematopoietic organs.

Neural tube defects by NUAK1 and NUAK2 double mutation

BACKGROUND

NUAK1 and NUAK2, members of the AMP-activated protein kinase family of serine/threonine kinases, are prominently expressed in neuroectoderm, but their functions in neurulation have not been elucidated.

RESULTS

NUAK1 and NUAK2 double mutants exhibited exencephaly, facial clefting, and spina bifida. Median hinge point was formed, but dorsolateral hinge point formation was not apparent in cranial neural plate; neither apical constriction nor apico-basal elongation took place efficiently in the double mutants during the 5-10-somite stages. Concomitantly, the apical concentration of phosphorylated myosin light chain 2, F-actin, and cortactin was insignificant, and development of acetylated α-tubulin-positive microtubules was poor. However, the distribution of F-actin, cortactin, Shroom3, Rho, myosin heavy chain IIB, phosphorylated myosin light chain 2, α-tubulin, γ-tubulin, or acetylated α-tubulin was apparently normal in the double mutant neuroepithelia at the 5-somite stage.

CONCLUSIONS

NUAK1 and NUAK2 complementarily function in the apical constriction and apico-basal elongation that associate with the dorsolateral hinge point formation in cephalic neural plate during the 5- to 10-somite stages. In the double mutant neural plate, phosphorylated myosin light chain 2, F-actin, and cortactin did not concentrate efficiently in apical surfaces, and acetylated α-tubulin-positive microtubules did not develop significantly.

Regulation of Six1 expression by evolutionarily conserved enhancers in tetrapods

The Six1 homeobox gene plays critical roles in vertebrate organogenesis. Mice deficient for Six1 show severe defects in organs such as skeletal muscle, kidney, thymus, sensory organs and ganglia derived from cranial placodes, and mutations in human SIX1 cause branchio-oto-renal syndrome, an autosomal dominant developmental disorder characterized by hearing loss and branchial defects. The present study was designed to identify enhancers responsible for the dynamic expression pattern of Six1 during mouse embryogenesis. The results showed distinct enhancer activities of seven conserved non-coding sequences (CNSs) retained in tetrapod Six1 loci. The activities were detected in all cranial placodes (excluding the lens placode), dorsal root ganglia, somites, nephrogenic cord, notochord and cranial mesoderm. The major Six1-expression domains during development were covered by the sum of activities of these enhancers, together with the previously identified enhancer for the pre-placodal region and foregut endoderm. Thus, the eight CNSs identified in a series of our study represent major evolutionarily conserved enhancers responsible for the expression of Six1 in tetrapods. The results also confirmed that chick electroporation is a robust means to decipher regulatory information stored in vertebrate genomes. Mutational analysis of the most conserved placode-specific enhancer, Six1-21, indicated that the enhancer integrates a variety of inputs from Sox, Pax, Fox, Six, Wnt/Lef1 and basic helix-loop-helix proteins. Positive autoregulation of Six1 is achieved through the regulation of Six protein-binding sites. The identified Six1 enhancers provide valuable tools to understand the mechanism of Six1 regulation and to manipulate gene expression in the developing embryo, particularly in the sensory organs.

Muscle-specific knock-out of NUAK family SNF1-like kinase 1 (NUAK1) prevents high fat diet-induced glucose intolerance

NUAK1 is a member of the AMP-activated protein kinase-related kinase family. Recent studies have shown that NUAK1 is involved in cellular senescence and motility in epithelial cells and fibroblasts. However, the physiological roles of NUAK1 are poorly understood because of embryonic lethality in NUAK1 null mice. The purpose of this study was to elucidate the roles of NUAK1 in adult tissues. We determined the tissue distribution of NUAK1 and generated muscle-specific NUAK1 knock-out (MNUAK1KO) mice. For phenotypic analysis, whole body glucose homeostasis and muscle glucose metabolism were examined. Quantitative phosphoproteome analysis of soleus muscle was performed to understand the molecular mechanisms underlying the knock-out phenotype. Nuak1 mRNA was preferentially expressed in highly oxidative tissues such as brain, heart, and soleus muscle. On a high fat diet, MNUAK1KO mice had a lower fasting blood glucose level, greater glucose tolerance, higher insulin sensitivity, and higher concentration of muscle glycogen than control mice. Phosphoproteome analysis revealed that phosphorylation of IRS1 Ser-1097 was markedly decreased in NUAK1-deficient muscle. Consistent with this, insulin signaling was enhanced in the soleus muscle of MNUAK1KO mice, as evidenced by increased phosphorylation of IRS1 Tyr-608, AKT Thr-308, and TBC1D4 Thr-649. These observations suggest that a physiological role of NUAK1 is to suppress glucose uptake through negative regulation of insulin signaling in oxidative muscle.

Deletion of the Mint3/Apba3 gene in mice abrogates macrophage functions and increases resistance to lipopolysaccharide-induced septic shock

Two major metabolic systems are usually used to generate ATP: oxidative phosphorylation (OXPHOS) in the mitochondria and glycolysis. Most types of cells employ OXPHOS for ATP production during normoxia but then shift energy production from OXPHOS to glycolysis when exposed to hypoxia. Hypoxia-inducible factor-1 (HIF-1) is the master transcription factor regulating this metabolic shift. On the other hand, macrophages are unique in making use of glycolysis for ATP generation constitutively even during normoxia. We recently proposed that in macrophages, Mint3/APBA3 inhibits factor inhibiting HIF-1 (FIH-1) during normoxia, which in turn releases the suppression of HIF-1 activity by FIH-1. To demonstrate the physiological function of APBA3 in macrophages, we established Apba3(-/-) mice. The mutant mice presented no apparent gross phenotype but exhibited significant resistance against LPS-induced septic shock. The level of ATP in macrophages obtained from the mutant mice was reduced to 60% of the level observed in wild type cells, which in turn led to reduced ATP-dependent activities such as glycolysis, cytokine production, and motility. We also generated mutant mice with the Apba3 gene deleted specifically from cells of the myeloid lineage and confirmed that LPS-induced septic shock is mitigated significantly. Thus, we show cell type-specific regulation of energy production by APBA3 in macrophages using genetically manipulated mice. The specific function of APBA3 in macrophages might allow us to develop therapeutics to regulate aberrant macrophage function during infection and diseases.

A mouse reporter line to conditionally mark nuclei and cell membranes for in vivo live-imaging

Live-imaging is an essential tool to visualize live cells and monitor their behaviors during development. This technology demands a variety of mouse reporter lines, each uniquely expressing a fluorescent protein. Here, we developed an R26R-RG reporter mouse line that conditionally and simultaneously expresses mCherry and EGFP in nuclei and plasma membranes, respectively, from the Rosa26 locus. The intensity and resolution of mCherry nuclear localization and EGFP membrane localization were demonstrated to be sufficient for live-imaging with embryos that express RG (mCherry and EGFP) ubiquitously and specifically in fetal Sertoli cells. The conditional R26R-RG reporter mouse line should be a useful tool for labeling nuclei and membranes simultaneously in distinct cell populations.

Paraspeckles are subpopulation-specific nuclear bodies that are not essential in mice

Nuclei of higher organisms are well structured and have multiple, distinct nuclear compartments or nuclear bodies. Paraspeckles are recently identified mammal-specific nuclear bodies ubiquitously found in most cells cultured in vitro. To investigate the physiological role of paraspeckles, we examined the in vivo expression patterns of two long noncoding RNAs, NEAT1_1 and NEAT1_2, which are essential for the architectural integrity of nuclear bodies. Unexpectedly, these genes were only strongly expressed in a particular subpopulation of cells in adult mouse tissues, and prominent paraspeckle formation was observed only in the cells highly expressing NEAT1_2. To further investigate the cellular functions of paraspeckles, we created an animal model lacking NEAT1 by gene targeting. These knockout mice were viable and fertile under laboratory growth conditions, showing no apparent phenotypes except for the disappearance of paraspeckles. We propose that paraspeckles are nonessential, subpopulation-specific nuclear bodies formed secondary to particular environmental triggers.

Conserved expression of mouse Six1 in the pre-placodal region (PPR) and identification of an enhancer for the rostral PPR

All cranial sensory organs and sensory neurons of vertebrates develop from cranial placodes. In chick, amphibians and zebrafish, all placodes originate from a common precursor domain, the pre-placodal region (PPR), marked by the expression of Six1/4 and Eya1/2. However, the PPR has never been described in mammals and the mechanism involved in the formation of PPR is poorly defined. Here, we report the expression of Six1 in the horseshoe-shaped mouse ectoderm surrounding the anterior neural plate in a pattern broadly similar to that of non-mammalian vertebrates. To elucidate the identity of Six1-positive mouse ectoderm, we searched for enhancers responsible for Six1 expression by in vivo enhancer assays. One conserved non-coding sequence, Six1-14, showed specific enhancer activity in the rostral PPR of chick and Xenopus and in the mouse ectoderm. These results strongly suggest the presence of PPR in mouse and that it is conserved in vertebrates. Moreover, we show the importance of the homeodomain protein-binding sites of Six1-14, the Six1 rostral PPR enhancer, for enhancer activity, and that Dlx5, Msx1 and Pax7 are candidate binding factors that regulate the level and area of Six1 expression, and thereby the location of the PPR. Our findings provide critical information and tools to elucidate the molecular mechanism of early sensory development and have implications for the development of sensory precursor/stem cells.

Structural basis for self-renewal of neural progenitors in cortical neurogenesis

In mammalian brain development, neuroepithelial cells act as progenitors that produce self-renewing and differentiating cells. Recent technical advances in live imaging and gene manipulation now enable us to investigate how neural progenitors generate the 2 different types of cells with unprecedented accuracy and resolution, shedding new light on the roles of epithelial structure in cell fate decisions and also on the plasticity of neurogenesis.

Neuroepithelial progenitors undergo LGN-dependent planar divisions to maintain self-renewability during mammalian neurogenesis

During mammalian development, neuroepithelial cells function as mitotic progenitors, which self-renew and generate neurons. Although spindle orientation is important for such polarized cells to undergo symmetric or asymmetric divisions, its role in mammalian neurogenesis remains unclear. Here we show that control of spindle orientation is essential in maintaining the population of neuroepithelial cells, but dispensable for the decision to either proliferate or differentiate. Knocking out LGN, (the G protein regulator), randomized the orientation of normally planar neuroepithelial divisions. The resultant loss of the apical membrane from daughter cells frequently converted them into abnormally localized progenitors without affecting neuronal production rate. Furthermore, overexpression of Inscuteable to induce vertical neuroepithelial divisions shifted the fate of daughter cells. Our results suggest that planar mitosis ensures the self-renewal of neuroepithelial progenitors by one daughter inheriting both apical and basal compartments during neurogenesis.