Molecular dissection of Krox20 gene regulation in bone: NFAT and/or Srf dependence?

International audienc

Analysis of Krox20 gene regulation reveals Srf function in bone and cooperation with NFAT1

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NFAT and Srf transcription factors cooperate to regulate Krox20 gene expression in bone

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[Hormonal control of the expression of alpha fetoprotein in newborn rats. Evidence for a selective action of glucocorticoids on gene transcription].

International audienceAdministration of glucocorticoid hormones to the newborn rat results in a rapid decrease in the synthesis of alpha-fetoprotein (AFP) by the liver. The molecular basis of this hormonal action was investigated by examining the steady-state levels of AFP mRNA and albumin mRNA sequences in polysomal and total RNA preparations isolated from dexamethasone-treated and control animals. Following dexamethasone treatment the number of polysomal and total mRNA sequences hybridizable to specific (32P) cDNA probes was drastically decreased for AFP while it was unchanged for albumin. These data indicate that glucocorticoids exert a selective action on AFP mRNA levels and suggest that dexamethasone operate at the transcriptional level

Alpha-fetoprotein gene expression in human lymphoblastoid cells and in PHA-stimulated normal T-lymphocytes

International audienceAlpha-fetoprotein (AFP) is mainly synthesized by the fetal liver, the yolk sac and, to a much lower extent, by a few non-hepatic fetal tissues (i.e. kidney, pancreas, lung). This property is considered to be lost in mature quiescent cells of the adult. In the present we have studied the expression of AFP mRNA sequences in phytohemagglutinin (PHA)-stimulated normal human T-lymphocytes and in several human lymphoma cell lines. The amount of mRNA transcripts detected in quiescent T-lymphocytes by dot and Northern blot analysis was very low. It increased rapidly after PHA-activation, reached a maximum at 72 hours (six fold the level observed for quiescent T-lymphocytes) and decreased thereafter. The lymphoma cell lines Daudi, Raji, Rh6 et CEM, all expressed elevated levels of AFP mRNA. The transcripts had the size expected for human AFP, suggesting that they were functional and probably translated into protein. The possible role of AFP synthesis in lymphocyte blastogenesis and in lymphoma growth is discussed in relation with the strong binding affinity of this protein for polyunsaturated fatty acids

Krox20 hindbrain cis-regulatory landscape: interplay between multiple long-range initiation and autoregulatory elements

International audienceThe vertebrate hindbrain is subject to a transient segmentation process leading to the formation of seven or eight metameric territories termed rhombomeres (r). This segmentation provides the basis for the subsequent establishment of hindbrain neuronal organization and participates in the patterning of the neural crest involved in craniofacial development. The zinc-finger gene Krox20 is expressed in r3 and r5, and encodes a transcription factor that plays a key role in hindbrain segmentation, coordinating segment formation, specification of odd- and even-numbered rhombomeres, and cell segregation between adjacent segments, through the regulation of numerous downstream genes. In order to further elucidate the genetic network underlying hindbrain segmentation, we have undertaken the analysis of the cis-regulatory sequences governing Krox20 expression. We have found that the control of Krox20 transcription relies on three very long-range (200 kb) enhancer elements (A, B and C) that are conserved between chick, mouse and human genomes. Elements B and C are activated at the earliest stage of Krox20 expression in r5 and r3-r5, respectively, and do not require the Krox20 protein. These elements are likely to function as initiators of Krox20 expression. Element B contains a binding site for the transcription factor vHNF1, the mutation of which abolishes its activity, suggesting that vHNF1 is a direct initiator of Krox20 expression in r5. Element A contains Krox20-binding sites, which are required, together with the Krox20 protein, for its activity. This element therefore allows the establishment of a direct positive autoregulatory loop, which takes the relay of the initiator elements and maintains Krox20 expression. Together, our studies provide a basis for a model of the molecular mechanisms controlling Krox20 expression in the developing hindbrain and neural crest

Molecular plasticity of adult Bergmann fibers is associated with radial migration of grafted Purkinje cells.

International audienceEmbryonic Purkinje cells (PCs) from cerebellar primordia grafted in adult pcd mutant cerebellum replace missing PCs of the host, and become synaptically integrated into the defective cerebellar circuit. This process of neuronal replacement starts with the invasion of grafted PCs into the host cerebellum, and their radial migration through its molecular layer. The present study is aimed at determining whether the glial axes for this migration are embryonic radial glial cells that comigrate with the grafted PCs, or adult Bergmann fibers of the host, transiently reexpressing the molecular cues needed for their guidance of the migration. Transplants from a transgenic mouse line (Krox-20/lacZ14) in which Bergmann fibers could be identified by lacZ expression reveal that, despite the presence of X-gal-stained Bergmann fibers in the graft remnants and of grafted PCs in the host molecular layer, all Bergmann fibers in the host cerebellum lack of beta-galactosidase activity. Thus, these migratory axes belong to the host, not to the donor. Transplants from normal isogenic mouse embryos show that during the radial migration of grafted PCs (7 d after grafting) the involved host Bergmann fibers reexpress nestin (identified with monoclonal antibody Rat-401 immunostaining), normally expressed only by immature Bergmann fibers. Five days later, when grafted PCs have arrested their migration, host Bergmann fibers again become Rat-401 negative. These results indicate that embryonic PCs can trigger in adult cerebellum the molecular changes necessary for their own migration and ultimate synaptic integration in the host cortical circuitry

Molecular plasticity of adult Bergmann fibers is associated with radial migration of grafted Purkinje cells.

International audienceEmbryonic Purkinje cells (PCs) from cerebellar primordia grafted in adult pcd mutant cerebellum replace missing PCs of the host, and become synaptically integrated into the defective cerebellar circuit. This process of neuronal replacement starts with the invasion of grafted PCs into the host cerebellum, and their radial migration through its molecular layer. The present study is aimed at determining whether the glial axes for this migration are embryonic radial glial cells that comigrate with the grafted PCs, or adult Bergmann fibers of the host, transiently reexpressing the molecular cues needed for their guidance of the migration. Transplants from a transgenic mouse line (Krox-20/lacZ14) in which Bergmann fibers could be identified by lacZ expression reveal that, despite the presence of X-gal-stained Bergmann fibers in the graft remnants and of grafted PCs in the host molecular layer, all Bergmann fibers in the host cerebellum lack of beta-galactosidase activity. Thus, these migratory axes belong to the host, not to the donor. Transplants from normal isogenic mouse embryos show that during the radial migration of grafted PCs (7 d after grafting) the involved host Bergmann fibers reexpress nestin (identified with monoclonal antibody Rat-401 immunostaining), normally expressed only by immature Bergmann fibers. Five days later, when grafted PCs have arrested their migration, host Bergmann fibers again become Rat-401 negative. These results indicate that embryonic PCs can trigger in adult cerebellum the molecular changes necessary for their own migration and ultimate synaptic integration in the host cortical circuitry

Permanent N-cadherin overexpression in pre-osteoblasts decreases osteoblast differentiation in vitro and bone mass in vivo by antagonizing Wnt signaling.

International audienc

No evidence for post-transcriptional control of albumin and α-fetoprotein gene expression in developing rat liver and neoplasis

International audienceRot analysis of hybridization data using highly labeled alpha-fetoprotein (AFP) and albumin (32P)cDNA probes has been used to quantitate AFP and albumin mRNA sequences in RNA preparations from different subcellular fractions of developing rat liver and Morris hepatoma 7777. In addition, size analysis of these mRNA sequences has been carried out by electrophoretic fractionation on agarose gels containing methylmercury hydroxyde and hybridization to radioactive cloned albumin and AFP cDNA probes. In all the tissues examined (fetal, newborn and adult rat liver, and hepatoma 7777) most of the albumin and AFP mRNA sequences were found associated with the polysomes as mature mRNA molecules; less than 2% of these sequences were present in the nuclear or the non polysomal cytoplasmic compartments. The number of AFP mRNA molecules was found to decrease in parallel in all the cellular compartments during rat liver development. In Morris hepatoma 7777 the content of albumin mRNA was considerably decreased in all the cellular fractions as compared to normal liver. These results demonstrate that post-transcriptional control mechanisms leading to an accumulation of non-functional mRNA molecules are not implicated in the changes of expression of albumin and AFP genes during rat liver development and neoplasia