Pedro Muniesa

Targeted gene disruption reveals a leptin-independent role for the mouse beta3-adrenoceptor in the regulation of body composition.

Targeted disruption of mouse beta3-adrenoceptor was generated by homologous recombination, and validated by an acute in vivo study showing a complete lack of effect of the beta3-adrenoceptor agonist CL 316,243 on the metabolic rate of homozygous null (-/-) mice. In brown adipose tissue, beta3-adrenoceptor disruption induced a 66% decrease (P < 0.005) in beta1-adrenoceptor mRNA level, whereas leptin mRNA remained unchanged. Chronic energy balance studies in chow-fed mice showed that in -/- mice, body fat accumulation was favored (+41%, P < 0.01), with a slight increase in food intake (+6%, NS). These effects were accentuated by high fat feeding: -/- mice showed increased total body fat (+56%, P < 0.025) and food intake (+12%, P < 0.01), and a decrease in the fat-free dry mass (-10%, P < 0.05), which reflects a reduction in body protein content. Circulating leptin levels were not different in -/- and control mice regardless of diet. The significant shift to the right in the positive correlation between circulating leptin and percentage of body fat in high fat-fed -/- mice suggests that the threshold of body fat content inducing leptin secretion is higher in -/- than in control mice. Taken together, these studies demonstrate that beta3-adrenoceptor disruption creates conditions which predispose to the development of obesity.

Microarray analysis of hepatic gene expression identifies new genes involved in steatotic liver

Trans-10, cis-12-conjugated linoleic acid (CLA)-enriched diets promote fatty liver in mice, while cis-9, trans-11-CLA ameliorates this effect, suggesting regulation of multiple genes. To test this hypothesis, apoE-deficient mice were fed a Western-type diet enriched with linoleic acid isomers, and their hepatic gene expression was analyzed with DNA microarrays. To provide an initial screening of candidate genes, only 12 with remarkably modified expression between both CLA isomers were considered and confirmed by quantitative RT-PCR. Additionally mRNA expression of 15 genes involved in lipid metabolism was also studied. Ten genes (Fsp27, Aqp4, Cd36, Ly6d, Scd1, Hsd3b5, Syt1, Cyp7b1, and Tff3) showed significant associations among their expressions and the degree of hepatic steatosis. Their involvement was also analyzed in other models of steatosis. In hyperhomocysteinemic mice lacking Cbs gene, only Fsp27, Cd36, Scd1, Syt1, and Hsd3b5 hepatic expressions were associated with steatosis. In apoE-deficient mice consuming olive-enriched diet displaying reduction of the fatty liver, only Fsp27 and Syt1 expressions were found associated. Using this strategy, we have shown that expression of these genes is highly associated with hepatic steatosis in a genetic disease such as Cbs deficiency and in two common situations such as Western diets containing CLA isomers or a Mediterranean-type diet. Conclusion: The results highlight new processes involved in lipid handling in liver and will help to understand the complex human pathology providing new proteins and new strategies to cope with hepatic steatosis.

Over-expression of Neuron-derived Orphan Receptor-1 (NOR-1) exacerbates neointimal hyperplasia after vascular injury

We have previously shown that NOR-1 (NR4A3) modulates the proliferation and survival of vascular cells in culture. However, in genetically modified animal models, somewhat conflicting results have been reported concerning the involvement of NOR-1 in neointimal formation after vascular injury. The aim of this study was to generate a transgenic mouse model over-expressing NOR-1 in smooth muscle cells (SMCs) and assess the consequence of a gain of function of this receptor on intimal hyperplasia after vascular injury. The transgene construct (SM22-NOR1) was prepared by ligating the full-length human NOR-1 cDNA (hNOR-1) and a mouse SM22α minimal promoter able to drive NOR-1 expression to SMC. Two founders were generated and two stable transgenic mouse lines (TgNOR-1) were established by backcrossing the transgene-carrying founders with C57BL/6J mice. Real-time PCR and immunohistochemistry confirmed that hNOR-1 was mainly targeted to vascular beds such as aorta and carotid arteries, and was similar in both transgenic lines. Vascular SMC from transgenic animals exhibit increased NOR-1 transcriptional activity (assessed by electrophoretic mobility shift assay and luciferase assays), increased mitogenic activity (determined by [(3)H]-thymidine incorporation; 1.58-fold induction, P < 0.001) and increased expression of embryonic smooth muscle myosin heavy chain (SMemb) than wild-type cells from control littermates. Using the carotid artery ligation model, we show that neointima formation was increased in transgenic versus wild-type mice (2.36-fold induction, P < 0.01). Our in vivo data support a role for NOR-1 in VSMC proliferation and vascular remodelling. This NOR-1 transgenic mouse could be a useful model to study fibroproliferative vascular diseases.

Expression of endogenous retroviruses is negatively regulated by the pluripotency marker Rex1/Zfp42

Rex1/Zfp42 is a Yy1-related zinc-finger protein whose expression is frequently used to identify pluripotent stem cells. We show that depletion of Rex1 levels notably affected self-renewal of mouse embryonic stem (ES) cells in clonal assays, in the absence of evident differences in expression of marker genes for pluripotency or differentiation. By contrast, marked differences in expression of several endogenous retroviral elements (ERVs) were evident upon Rex1 depletion. We demonstrate association of REX1 to specific elements in chromatin-immunoprecipitation assays, most strongly to muERV-L and to a lower extent to IAP and musD elements. Rex1 regulates muERV-L expression in vivo, as we show altered levels upon transient gain-and-loss of Rex1 function in pre-implantation embryos. We also find REX1 can associate with the lysine-demethylase LSD1/KDM1A, suggesting they act in concert. Similar to REX1 binding to retrotransposable elements (REs) in ES cells, we also detected binding of the REX1 related proteins YY1 and YY2 to REs, although the binding preferences of the two proteins were slightly different. Altogether, we show that Rex1 regulates ERV expression in mouse ES cells and during pre-implantation development and suggest that Rex1 and its relatives have evolved as regulators of endogenous retroviral transcription.

Differential expression of α-CGRP and β-CGRP genes within hypoglossal motoneurons in response to axotomy

In this study we have analysed, by in situ hybridization, the expression of the genes for both α-CGRP and β-CGRP in hypoglossal motor nuclei following transection of the left hypoglossal nerve. Our results show that the gene for α-CGRP displays a peculiar sequence of regulation (a successive up-down-up-recovery sequence) within ipsilateral hypoglossal motoneurons in response to axotomy. It is initially up-regulated, then down-regulated (displaying mRNA levels below basal), and later again up-regulated before recovery. By contrast, the gene for β-CGRP displays a successive and distinct up-down-recovery sequence of regulation (it does not display a second increase in mRNA production). The first up-regulation of the α-CGRP gene occurs just during the early period of perineuronal glial reaction and the second up-regulation just during the period of delayed astrocyte reaction and muscle reinnervation. Because α-CGRP is a neuron-derived factor for many types of cells, including astrocytes and skeletal myocytes, our results suggest that the pleiotropic α-CGRP may be a motoneuron-derived trophic signal for both glial and skeletal muscle cells in order to maintain the motoneuron itself and, in consequence, might be of therapeutic interest in treating degenerative diseases of motoneurons. β-CGRP might be redundant within the hypoglossal motoneurons.

Expression of the genes for α-type and β-type calcitonin gene-related peptide during postnatal rat brain development

Abstract In this study we have analysed the expression of the genes for both α -type and β -type calcitonin gene-related peptide (CGRP) during postnatal development of the rat brain and compared it with the expression of CGRP-like immunoreactivity. At birth both α -type and β -type CGRP messenger RNA were present in the parabrachial nucleus, inferior olive and motor nuclei (except for abducens nucleus), and only α -type CGRP messenger RNA in some posterior thalamic nuclei. As development advanced, new nuclei started to express either only α -CGRP gene (superior olive, parabigeminal, sagulum, and some hypothalamic and cranial thalamic nuclei) or both genes (abducens nucleus). In the inferior olive both genes were transiently expressed. β -CGRP messenger RNA disappeared by postnatal day 10 and α -CGRP messenger RNA by postnatal day 20. During the whole postnatal development β -CGRP gene expression predominated over that of α -CGRP in the trigeminal and eye motor nuclei, while in the remainder nuclei α -CGRP messenger RNA was either the predominant isoform or the sole one. CGRP-like immunoreactivity, which does not distinguish between α -type and β -type CGRP, was detected in those nuclei containing either α -CGRP messenger RNA or β -CGRP messenger RNA. However, no CGRP messenger RNA was detected in areas such as superior colliculus, lateral pontine nucleus, pars reticulata of the substantia nigra, perifornical area, or zona incerta in which CGRP-like immunoreactivity was prominent. CGRP-like immunoreactivity, but not CGRP messenger RNA, was also transiently detected by postnatal day 5 in some cells of the globus pallidus. In the adult brain, the levels of α - and β -CGRP messenger RNA as well as those of CGRP-like immunoreactivity were considerably reduced. This fact, similar to that of other growth- and development-associated factors, suggests a role for CGRP as a neuron-derived neurotrophic factor. The transient expression in neurons of the inferior olive, matching the period when climbing fibres and cerebellar cortex are developing, seems to support such an idea. The results of this study show that those nuclei expressing β -CGRP gene also express α -CGRP gene. However, there are a number of nuclei that only express α -CGRP gene. On the other hand, CGRP-like immunoreactivity is detected in some nuclei which express no CGRP messenger RNA. It suggests that such nuclei express any CGRP-related protein (identified by the antibodies against CGRP) or, if they really contain CGRP protein, this is produced from undetectable amounts (using our in situ hybridization histochemistry procedure) of CGRP messenger RNA or it comes from other nuclei that connect with them in which CGRP protein is synthesized and then transferred.

Regulation of mouse retroelement MuERV-L/MERVL expression by REX1 and epigenetic control of stem cell potency

About half of the mammalian genome is occupied by DNA sequences that originate from transposable elements. Retrotransposons can modulate gene expression in different ways and, particularly retrotransposon-derived long terminal repeats, profoundly shape expression of both surrounding and distant genomic loci. This is especially important in pre-implantation development, during which extensive reprograming of the genome takes place and cells pass through totipotent and pluripotent states. At this stage, the main mechanism responsible for retrotransposon silencing, i.e., DNA methylation, is inoperative. A particular retrotransposon called muERV-L/MERVL is expressed during pre-implantation stages and contributes to the plasticity of mouse embryonic stem cells. This review will focus on the role of MERVL-derived sequences as controlling elements of gene expression specific for pre-implantation development, two-cell stage-specific gene expression, and stem cell pluripotency, the epigenetic mechanisms that control their expression, and the contributions of the pluripotency marker REX1 and the related Yin Yang 1 family of transcription factors to this regulation process.

A morphological study of primordial germ cells at pregastrular stages in the chick embryo.

The spatial distribution, germ layer location, number and appearance of primordial germ cells (PGCs) are studied. Blastoderms from stage X (Eyal-Giladi and Kochav, 1976) to stage 2 (Hamburger and Hamilton, 1951) were serially sectioned and distribution patterns of PGCs were reconstructed. The presence of PGCs in clusters was noted at all stages examined. PGCs were found in relation to the epiblast, the primary hypoblast and in the blastocoel, during the whole period under examination. These observations show that PGCs can be directly studied at blastula stages. The results are consistent with observations on an early segregation of chick germ line that begins as early as stage X.

Association of Rex-1 to target genes supports its interaction with Polycomb function

Rex-1/Zfp42 displays a remarkably restricted pattern of expression in preimplantation embryos, primary spermatocytes, and undifferentiated mouse embryonic stem (ES) cells and is frequently used as a marker gene for pluripotent stem cells. To understand the role of Rex-1 in selfrenewal and pluripotency, we used Rex-1 association as a measure to identify potential target genes, and carried out chromatin-immunoprecipitation assays in combination with gene specific primers to identify genomic targets Rex-1 associates with. We find association of Rex-1 to several genes described previously as bivalently marked regulators of differentiation and development, whose repression in mouse embryonic stem (ES) cells is Polycomb Group-mediated, and controlled directly by Ring1A/B. To substantiate the hypothesis that Rex-1 contributes to gene regulation by PcG, we demonstrate interactions of Rex-1 and YY2 (a close relative of YY1) with Ring1 proteins and the PcG-associated proteins RYBP and YAF2, in line with interactions reported previously for YY1. We also demonstrate the presence of Rex-1 protein in both trophectoderm and Inner Cell Mass of the mouse blastocyst and in both ES and in trophectoderm stem (TS) cells. In TS cells, we were unable to demonstrate association of Rex-1 to the genes it associates with in ES cells, suggesting that association may be cell-type specific. Rex-1 might fine-tune pluripotency in ES cells by modulating Polycomb-mediated gene regulation.

Apolipoprotein E determines the hepatic transcriptional profile of dietary maslinic acid in mice.

The hypothesis that the maslinic acid (MA) of olive oil (OO) dramatically influences hepatic gene expression was tested in mice. Two OOs only differing in the presence of MA were prepared. Using DNA microarrays, we analyzed hepatic gene expression in apolipoprotein E (apoE)-deficient mice with a C57BL/6J genetic background that were fed with isocaloric, isonitrogenous diets containing either 10% (w/w) OO or 10% MA-enriched OO. As an initial screening of potential candidate genes involved in a differential response, this study further considered only genes with remarkably modified expression (signal log(2) ratio higher than1.5 or lower than -1.5). The nine genes fulfilling these prerequisites were confirmed by quantitative reverse transcriptase polymerase chain reaction and analyzed in C57BL/6J wild-type mice. Only Cyp2b9, Cyp2b13 and Dbp expressions appeared significantly increased, and Marco was significantly decreased in apoE-deficient mice receiving the MA-enriched diet. Dbp was up-regulated to an extent depending on the genetic background of the mice and negatively associated with the expression of Marco, a gene strongly up-regulated by the absence of apoE. These expression changes could be used as markers of the intake of the MA-enriched OO and are influenced by genetic background generated by the absence or the presence of apoE. Overall, these results (a) indicate that MA in virgin OO is highly active in controlling hepatic gene expression and (b) highlight the important interaction between the response to MA and the presence of apoE. They also confirm that virgin OO cannot be simplistically classified as monounsaturated fatty-enriched oil without paying attention to its active minor components.