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PDF Version      Mouse Molecular Genetics - URA CNRS 1947

  Director : Philip AVNER (pavner@pasteur.fr)



Research in the Unit is centred around three projects :

1) Inactivation of the mouse X chromosome

2) Genetic analysis of type 1 diabetes in the mouse as a model for traits under multifactorial and polygenic control

3) The role of the X-linked gene Nap1l2 in the control of neuronal cell division and neuronal stem cell proliferation



One of the major research interests of the Mouse Molecular Genetics Unit is X chromosome inactivation.This is a complex biological process which depends on the presence of two copies of the X-inactivation centre (Xic) and which results in the inactivation of one of the two X chromosomes present in the female cell. The process involves both the sensing and counting of the number of X chromosomes in the cell in relation to the autosomal complement. The X chromosome chosen to remain active is thought to be protected by an as yet hypothetical blocking factor. Several genetic elements including the genetically identified locus Xce (X-controlling element) seem to be able to affect the choice of which X chromosome will be chosen to be inactivated. Xce is distinct from Xist (X-inactive specific transcript) which codes for a large non-coding RNA which plays a major role in the initiation of the inactivation process.

The candidate region for the Xce locus was recently refined to a region of less than 50kb and targeted deletion approaches to the candidate region initiated. The in vitro and in vivo studies of the effect of the mutation which have been initiated are providing important insights into the functions of this part of the Xic region and should lead to the molecular characterisation of the Xce locus first identified some forty years ago.

Other experiments undertaken in the laboratory are aimed at the functional identification and analysis of the various components of the Xic by a double approach involving on the one hand the creation of novel mutations by targeted mutagenesis using the cre-lox system, on the other the complementation of pre-existing engineered deletions. Such deletions have allowed us to define a region lying 3' to Xist which both controls Xist expression and the counting process, possibly functioning as a binding site for the hypothesised 'blocking' factor. Use of a complementation or so-called add-back strategy has allowed at least two subregions to be defined one of which is implicated in the counting process. The other which controls both the expression of Xist and Tsix antisense appears to influence, amongst other things the retention of Xist RNA at its chromosomal site of transcription.

A better understanding of some of the processes involved in the initiation of X-inactivation is likely to come from combining such genetic and cell biology approaches with an analysis of chromatin structure. Several different approaches to such an analysis including ChIP (Chromatin Immunoprecipitation) have been established in the laboratory. ChIP studies have recently proved of great importance in characterising the role played by histone H3 methylation in the earliest stages of X-inactivation. A region 5' to Xist was defined which may act as a nucleation centre allowing the inactivation to spread from the Xic over the whole X chromosome. Detailed analysis of histone modifications occurring in this region have been undertaken and a correlative analysis of such epigenetic changes with the underlying genomic sequence initiated.

Genetics factors involved in the X-inactivation process lying outside of the Xic and in all probability elsewhere than on the X chromosome, are being looked for by a complementary approach based on a comparative transcriptome analysis of 6.5 dpc female and male embryos using SAGE (Serial Analysis of Gene Expression) analysis. Currently 50000 transcript tags from each are being exploited. Tags showing differential expression have been subject to serial screens aimed at confirming their status potential prior to extended functional analysis. The latter is based on inhibition of gene function in vitro by RNAi and observation of the resulting status of the inactivation process and the inactive X chromosome.

Genome Research and Mouse Disease Models

Another of the Unit's interest concerns the study of mouse phenotypes under multifactorial and polygenic control. We have taken as our prototype type 1 diabetes or insulin- dependent diabetes for which the NOD mouse represents an interesting model. Our studies are aimed at defining the genetic factors (Idd) implicated in this pathology which is known to depend on a complex interaction between environmental and genetic factors. Our studies are concentrated on the characterisation of Idd loci controlling diabetes susceptibility/resistance locating to the distal part of mouse chromosome 6. The past year has seen major advances in the definition and localisation of three loci Idd6, Idd19 and Idd20 lying in the distal part of mouse chromosome 6.

The continued refining of the candidate regions for these loci by establishment of congenic mouse strains has allowed candidate gene approaches to be undertaken to defining and characterising the genes responsible for these traits and in particular for Idd6. The immunological characterisation of these congenic strains has allowed definition of the probable site of action/tissue involved in resistance to diabetes onset conferred by the Idd6 locus. Varied approaches including transcriptional profiling and mutational analysis have allowed candidate genes for the Idd6 locus to be restrained to less than half a dozen.

A second disease subject to both environmental and complex genetic control is spina bifida. In the mouse spina bifida can be induced by mutation in the X-linked, Nap1l2 gene. Mutations in this gene are associated with embryonic lethality, spina bifida and exencephaly linked to a massive overproliferation of neuronal cells. We have initiated experiments which are aimed at understanding the role and mechanism of action of this gene in tissue specific cell cycle regulation, characterise by conditional mutagenesis its role in the adult and to better define the population of neuronal cells, including neuronal stem cells which are the site of its action.

Keywords: X-inactivation, Type 1 diabetes, Mouse, Genetics, QTL, Multigenic inheritance, Genomics


puce Publications of the unit on Pasteur's references database


  Office staff Researchers Scientific trainees Other personnel
  DEMOND Anne, ademond@pasteur.fr orlabavner@pasteur.fr AVNER Philip Unit Head - INSTITUT PASTEUR, pavner@pasteur.fr



Senior Staff Scientist and Laboratory

Head at the Institut Pasteur , pclerc@pasteur.fr

ROGNER Ute CNRS - Senior Staff Scientist , urogner@pasteur.fr

ROUGEULLE Claire CNRS - Senior Staff Scientist , rougeull@pasteur.fr

BOURDET Agnès PhD student agnesb@pasteur.fr

CIAUDO Constance PhD student ciaudo@pasteur.fr

GRIMM Christina Postdoctoral fellow , cgrimm@pasteur.fr

HUNG Ming-Shiu Postdoctoral fellow , mhung@pasteur.fr

MISE Natan Postdoctoral fellow, nmise@pasteur.fr

NAVARRO Pablo PhD student , pnavarro@pasteur.fr

MOREY Céline PhD student , cmorey@pasteur.fr

ARNAUD Danielle CNRS – Engineer , darnaud@pasteur.fr

BOUCONTET Michelle IP - Research support staff

CHUREAU Corinne IP - Technician , cchureau@pasteur.fr

DEMOND Anne IP - The Unit’s Secretary , ademond@pasteur.fr

VERON Corinne IP - Research support staff

Activity Reports 2002 - Institut Pasteur

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