Biomedical subjects

P Brûlet

Publications and source records attributed to P Brûlet.

At least 19 recordsLinked to original sources

PubMed2003

Study of Fgf15 gene expression in developing mouse brain.

Fibroblast growth factor 15 (Fgf15) is a gene regulated by the expression of Otx2 in developing mouse brain (Proc Natl Acad Sci USA 97 (2000) 14388). Otx2 gene codes for a transcription factor and is fundamental for the regionalisation and development of the anterior neural plate and cephalic region of the vertebrate embryo (Development 124 (1997) 3639). In addition, the thalamic expression of Fgf15 has been recently reported under the control of Shh signalling gene, expressed in the diencephalic basal plate (Development 129 (2002) 4807). In the present work, we have analysed Fgf15 expression pattern during mouse neural development. Fgf15 appeared early in the developing neural epithelium, in domains where Fgf8 gene is also expressed and, at later stages, in specific groups of neural cells. Fgf8 is an important signalling protein with demonstrated morphogenetic activity in several embryonic regions. Fgf15 expression is localized, like Fgf8, in secondary neural tube organizers: the isthmic organizer (IsO) and the anterior neural ridge (ANR).

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PubMed2001

Axial skeletal patterning in mice lacking all paralogous group 8 Hox genes.

We present a detailed study of the genetic basis of mesodermal axial patterning by paralogous group 8 Hox genes in the mouse. The phenotype of Hoxd8 loss-of-function mutants is presented, and compared with that of Hoxb8- and Hoxc8-null mice. Our analysis of single mutants reveals common features for the Hoxc8 and Hoxd8 genes in patterning lower thoracic and lumbar vertebrae. In the Hoxb8 mutant, more anterior axial regions are affected. The three paralogous Hox genes are expressed up to similar rostral boundaries in the mesoderm, but at levels that strongly vary with the axial position. We find that the axial region affected in each of the single mutants mostly corresponds to the area with the highest level of gene expression. However, analysis of double and triple mutants reveals that lower expression of the other two paralogous genes also plays a patterning role when the mainly expressed gene is defective. We therefore conclude that paralogous group 8 Hox genes are involved in patterning quite an extensive anteroposterior (AP) axial region. Phenotypes of double and triple mutants reveal that Hoxb8, Hoxc8 and Hoxd8 have redundant functions at upper thoracic and sacral levels, including positioning of the hindlimbs. Interestingly, loss of functional Hoxb8 alleles partially rescues the phenotype of Hoxc8- and Hoxc8/Hoxd8-null mutants at lower thoracic and lumbar levels. This suggests that Hoxb8 affects patterning at these axial positions differently from the other paralogous gene products. We conclude that paralogous Hox genes can have a unique role in patterning specific axial regions in addition to their redundant function at other AP levels.

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PubMed2001

Otx2 is required for visceral endoderm movement and for the restriction of posterior signals in the epiblast of the mouse embryo.

Genetic and embryological experiments have demonstrated an essential role for the visceral endoderm in the formation of the forebrain; however, the precise molecular and cellular mechanisms of this requirement are poorly understood. We have performed lineage tracing in combination with molecular marker studies to follow morphogenetic movements and cell fates before and during gastrulation in embryos mutant for the homeobox gene Otx2. Our results show, first, that Otx2 is not required for proliferation of the visceral endoderm, but is essential for anteriorly directed morphogenetic movement. Second, molecules that are normally expressed in the anterior visceral endoderm, such as Lefty1 and Mdkk1, are not expressed in Otx2 mutants. These secreted proteins have been reported to antagonise, respectively, the activities of Nodal and Wnt signals, which have a role in regulating primitive streak formation. The visceral endoderm defects of the Otx2 mutants are associated with abnormal expression of primitive streak markers in the epiblast, suggesting that anterior epiblast cells acquire primitive streak characteristics. Taken together, our data support a model whereby Otx2 functions in the anterior visceral endoderm to influence the ability of the adjacent epiblast cells to differentiate into anterior neurectoderm, indirectly, by preventing them from coming under the influence of posterior signals that regulate primitive streak formation.

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PubMed1999

Cortical neurons require Otx1 for the refinement of exuberant axonal projections to subcortical targets.

Information processing in the nervous system depends on the creation of specific synaptic connections between neurons and targets during development. The homeodomain transcription factor Otx1 is expressed in early-generated neurons of the developing cerebral cortex. Within layer 5, Otx1 is expressed by neurons with subcortical axonal projections to the midbrain and spinal cord. Otx1 is also expressed in the precursors of these neurons, but is localized to the cytoplasm. Nuclear translocation of Otx1 occurs when layer 5 neurons enter a period of axonal refinement and eliminate a subset of their long-distance projections. Otx1 mutant mice are defective in the refinement of these exuberant projections, suggesting that Otx1 is required for the development of normal axonal connectivity and the generation of coordinated motor behavior.

Animals↗

PubMed1998

Structure and expression of Wnt13, a novel mouse Wnt2 related gene.

We have identified a novel mouse member of the Wnt family, Wnt13. Among mouse Wnt genes, Wnt13 is most closely related to Wnt2. Sequence comparisons and chromosomal localization strongly suggest that Wnt13, rather than Wnt2, is the mouse orthologue of both the human WNT13 and Xenopus XWnt2 genes. Wnt13 is expressed in the embryonic mesoderm during gastrulation. At later stages, transcripts are detected in the dorsal midline of the diencephalon and mesencephalon, the heart primordia, the periphery of the lung bud and the otic and optic vesicles. These data suggest that Wnt13 function might partially overlap with those of other Wnt genes in the cell signaling mechanisms controlling mesoderm specification during gastrulation and some aspects of brain, heart and lung formation.

Amino Acid Sequence↗

PubMed1998

Increased apoptosis of motoneurons and altered somatotopic maps in the brachial spinal cord of Hoxc-8-deficient mice.

Mice deficient for the homeotic gene Hoxc-8 suffer from a congenital prehension deficiency of the forepaw. During embryogenesis, Hoxc-8 is highly expressed in motoneurons within spinal cord segments C7 to T1. These motoneurons innervate forelimb distal muscles that move the forepaw. In Hoxc-8 mutant embryos, formation of these muscles is normal, but their innervation is perturbed. From E13.5 onwards, distal muscles normally supplied by C(7-8) MNs also receive ectopic projections from C(5-6) and T1 motoneurons. Coordinates of motor pools are altered along the rostrocaudal and also the mediolateral axes. Following this aberrant connectivity pattern and during the time of naturally occurring cell death, apoptosis is specifically enhanced in C7-T1 motoneurons. Loss of Hox-encoded regional specifications subsequently leads to a numerical deficit of motoneurons and an irreversible disorganization of motor pools. In Hoxc-8 null mutants, C(7-8) motoneurons lose their selective advantage in growth cone pathfinding behavior and/or target recognition, two essential steps in the establishment and maintenance of a functional nervous system.

Animals↗

PubMed1998

Transient dwarfism and hypogonadism in mice lacking Otx1 reveal prepubescent stage-specific control of pituitary levels of GH, FSH and LH.

Genetic and molecular approaches have enabled the identification of regulatory genes critically involved in determining cell types in the pituitary gland and/or in the hypothalamus. Here we report that Otx1, a homeobox-containing gene of the Otx gene family, is postnatally transcribed and translated in the pituitary gland. Cell culture experiments indicate that Otx1 may activate transcription of the growth hormone (GH), follicle-stimulating hormone (betaFSH), luteinizing hormone (betaLH) and alpha-glycoprotein subunit (alphaGSU) genes. Analysis of Otx1 null mice indicates that, at the prepubescent stage, they exhibit transient dwarfism and hypogonadism due to low levels of pituitary GH, FSH and LH hormones which, in turn, dramatically affect downstream molecular and organ targets. Nevertheless, Otx1-/- mice gradually recover from most of these abnormalities, showing normal levels of pituitary hormones with restored growth and gonadal function at 4 months of age. Expression patterns of related hypothalamic and pituitary cell type restricted genes, growth hormone releasing hormone (GRH), gonadotropin releasing hormone (GnRH) and their pituitary receptors (GRHR and GnRHR) suggest that, in Otx1-/- mice, hypothalamic and pituitary cells of the somatotropic and gonadotropic lineages appear unaltered and that the ability to synthesize GH, FSH and LH, rather than the number of cells producing these hormones, is affected. Our data indicate that Otx1 is a new pituitary transcription factor involved at the prepubescent stage in the control of GH, FSH and LH hormone levels and suggest that a complex regulatory mechanism might exist to control the physiological need for pituitary hormones at specific postnatal stages.

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PubMed1997

Construction of hybrid proteins that migrate retrogradely and transynaptically into the central nervous system.

The nontoxic proteolytic C fragment of tetanus toxin (TTC peptide) has the same ability to bind nerve cells and be retrogradely transported through a synapse as the native toxin. We have investigated its potential use as an in vivo neurotropic carrier. In this work we show that a hybrid protein encoded by the lacZ-TTC gene fusion retains the biological functions of both proteins in vivo-i.e. , retrograde transynaptic transport of the TTC fragment and beta-galactosidase enzymatic activity. After intramuscular injection, enzymatic activity could be detected in motoneurons and connected neurons of the brainstem areas. This strategy could be used to deliver a biological activity to neurons from the periphery to the central nervous system. Such a hybrid protein could also be used to map synaptic connections between neural cells.

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PubMed1996

Epilepsy and brain abnormalities in mice lacking the Otx1 gene.

The morphogenesis of the brain and the differentiation of the neural structures are highly complex processes. A series of temporally and spatially regulated morphogenetic events gives rise to smaller areas that are phylogenetically, functionally and often morphogenetically different. Candidate genes for positional information and differentiation during morphogenesis have been isolated. Both in vivo inactivation in mice and impairment in human diseases revealed, that they are required in regional specification and/or correct cell-type induction. We have previously cloned and characterized the murine Otx1 gene, which is related to orthodenticle (otd), a homeobox-containing gene required for Drosophila head development. Expression data during murine embryogenesis and postnatal brain development support the idea that Otx1 could be required for correct brain and sense organs development. To decipher its role in vivo we produced null mice by replacing Otx1 with the lacZ gene. Otx1-/- mice showed spontaneous epileptic behaviour and multiple abnormalities affecting mainly the telencephalic temporal and perirhinal areas, the hippocampus, the mesencephalon and the cerebellum, as well as the acoustic and visual sense organs. Our findings indicate that the Otx1 gene product is required for proper brain functions.

Animals↗

PubMed1996

Role of leukemia inhibitory factor during mammalian development.

Leukemia inhibitory factor (LIF) is a cytokine that exhibits proliferative, survival and differentiation activities on a wide range of cell types. A role for LIF in embryonic development is suggested by: i) its ability to stimulate the proliferation of embryonic stem (ES) cells in vitro, while maintaining their totipotency and ii) by both its maternal and embryonic expression at the time of blastocyst implantation. Functional studies of LIF and its receptor during mouse embryogenesis have been performed using the techniques of targeted gene replacement and transgene expression in ES cells to produce transgenic mice bearing either loss- or gain-of-function mutations for LIF activity. Whereas, the phenotype observed in the LIF gain-of-function mutant mice supports a role for LIF in early embryogenesis, the loss-of-function phenotypes point to more specialized functions for LIF in development and further reveal the redundant feature of the LIF cytokine/receptor family.

Animals↗

PubMed1995

Abnormal avoidance learning in mice lacking functional high-affinity nicotine receptor in the brain.

Nicotine affects many aspects of behaviour including learning and memory through its interaction with neuronal nicotinic acetylcholine receptors (nAChR). Functional nAChRs are pentameric proteins containing at least one type of alpha-subunit and one type of beta-subunit. The involvement of a particular neuronal nicotinic subunit in pharmacology and behaviour was examined using gene targeting to mutate beta 2, the most widely expressed nAChR subunit in the central nervous system. We report here that high-affinity binding sites for nicotine are absent from the brains of mice homozygous for the beta 2-subunit mutation. Further, electrophysiological recording from brain slices reveals that thalamic neurons from these mice do not respond to nicotine application. Finally, behavioural tests demonstrate that nicotine no longer augments the performance of beta 2-1- mice on passive avoidance, a test of associative memory. Paradoxically, mutant mice are able to perform better than their non-mutant siblings on this task.

Animals↗

PubMed1995

Forebrain and midbrain regions are deleted in Otx2-/- mutants due to a defective anterior neuroectoderm specification during gastrulation.

We have replaced part of the mouse homeogene Otx2 coding region with the E. coli lacZ coding sequence, thus creating a null allele of Otx2. By 9.5 dpc, homozygous mutant embryos are characterized by the absence of forebrain and midbrain regions. From the early to midstreak stages, endomesodermal cells expressing lacZ fail to be properly localized anteriorly. In the ectodermal layer, lacZ transcription is progressively extinguished, being barely detectable by the late streak stage. These data suggest that Otx2 expression in endomesoderm and ectoderm is required for anterior neuroectoderm specification. In gastrulating heterozygous embryos, a post-transcriptional repression acts on lacZ transcripts in the ectoderm, but not in the external layer, suggesting that different post-transcriptional mechanisms control Otx2 expression in both layers.

Animals↗

PubMed1993

Leukaemia inhibitory factor is necessary for maintenance of haematopoietic stem cells and thymocyte stimulation.

Leukaemia inhibitory factor (LIF) has a variety of effects on different cell types in vitro, inhibiting the differentiation of embryonic stem cells and promoting the survival and/or proliferation of primitive haematopoietic precursors and primordial germ cells. Here we show that LIF-deficient mice derived by gene targeting techniques have dramatically decreased numbers of stem cells in spleen and bone marrow. Injection of spleen and marrow cells from these mice promotes long-term survival of lethally irradiated wild-type animals, however, showing that the LIF- stem cells remain pluripotent. The numbers of committed progenitors are also reduced in the spleen but not the bone marrow, suggesting that stem cells interact differently with the splenic and medullary microenvironment. Heterozygous animals are intermediate in phenotype, implying that LIF has a dosage effect, and defects in stem cell number can be compensated by exogenous LIF. LIF thus appears to be required for the survival of the normal pool of stem cells, but not their terminal differentiation.

Animals↗

PubMed1993

Altering the spatial determinations in the mouse embryos by manipulating the Hox genes.

Developmental genetics in Drosophila led to the isolation of the homeotic genes which are involved in the cellular positional information. In vertebrates, homologous genes have been characterized and play similar roles in the spatial determination. However, the subtle mechanisms by which positional identity is specified by the Hox genes co-expression are little known. The Hoxc-8 null mutation can induce homeosis at the anterior margin of Hoxc-8 expression, where the mosaicism observed suggests that, at least in the segmented paraxial mesoderm, the number of cells expressing a Hox gene is a determinant parameter. A combinatorial model is also suggested by several genetic experiments where the level of Hox genes expression is modified. Expression of some related Hox genes in Hoxc-8 homozygous mutants is not altered, suggesting the absence of genetic interregulations between these genes.

Animals↗

PubMed1992

Inhibited gastrulation in mouse embryos overexpressing the leukemia inhibitory factor.

Leukemia inhibitory factor (LIF) is a cytokine active in vitro on different target cells. It is detected in vivo during mouse gestation in both extraembryonic membranes and maternal tissues. Two isoforms have been described maintaining embryonic stem cells in culture in a pluripotent state. However, overexpression of their cDNAs in chimeric mouse embryos observed between 6.5 and 9.5 days postcoitus gave strikingly different phenotypes. Embryos overexpressing the diffusible form of LIF cDNA looked essentially normal. Chimerae expressing LIF associated with the extracellular matrix cDNA showed an abnormal proliferation of tissues and the absence of differentiated mesoderm. They have not undertaken the normal pathway of gastrulation.

Animals↗

PubMed1992

Homeosis in the mouse induced by a null mutation in the Hox-3.1 gene.

We have replaced the Hox-3.1 coding sequence with the E. coli lacZ gene by means of homologous recombination in embryonic stem cells and thus produced null mutant mice. Homozygous mice were born alive, but most of them died within a few days. In the trunk region of homozygotes, several skeletal segments were transformed into the likeness of more anterior ones, as observed in Drosophila with loss-of-function homeotic mutations. The most obvious transformations were the attachment of the 8th pair of ribs to the sternum and the appearance of a 14th pair of ribs on the 1st lumbar vertebra. The pattern of beta-galactosidase activity was identical in heterozygotes and homozygotes and reflected faithfully the Hox-3.1 expression pattern. Thus, the mutation modified the identity, rather than the position, of embryonic cells that would normally express Hox-3.1.

Animals↗

PubMed1990

Targeted replacement of the homeobox gene Hox-3.1 by the Escherichia coli lacZ in mouse chimeric embryos.

Through gene targeting based upon homologous recombination in embryonic stem cells, a chosen gene can be inactivated and eventually a strain of mutant mice created. We have devised a procedure to specifically replace a targeted gene by another gene. A murine homeobox gene was disrupted at high frequency in embryonic stem cells by its replacement with Escherichia coli lacZ. Injection of such stem cells into blastocysts yielded chimeric embryos in which beta-galactosidase activity was driven by the Hox-3.1 promoter. This technique will allow the visual assessment at the cellular level of gene inactivation effects in transgenic mice.

Animals↗

PubMed1990

Developmental expression of myeloid leukemia inhibitory factor gene in preimplantation blastocysts and in extraembryonic tissue of mouse embryos.

Murine leukemia inhibitory factor (LIF) protein is a growth factor which has the ability to maintain the developmental potential of pluripotent embryonic stem cells through a specific receptor. We have examined the expression pattern of the LIF gene from the preimplantation stage (3.5 days post coitum) to the midgestation stage (12.5 days post coitum) of the mouse embryo. LIF transcripts were detected at the preimplantation blastocyst stage, whereas no transcripts were detectable in embryonic stem cells. LIF gene transcription continued in the extraembryonic tissue of the 7.5-day and in the placenta of 9.5-, 10.5-, and 12.5-day post coitum embryos. No transcripts were detected in the embryo proper of the corresponding stages. Our results suggest that this growth factor is synthesized in the extraembryonic part of the embryo and acts on the embryonic tissues during early mouse development.

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