The gene coding for the α1 subunit of the skeletal dihydropyridine receptor (Cchl1a3=mdg) maps to mouse Chromosome 1 and human 1q32

Using both chromosomal in situ hybridization and molecular techniques, we report the genetic localization of the gene coding for the alpha 1 subunit of the skeletal slow Ca²⁺ current channel/DHP receptor gene (Cchl1a3) on human Chromosome (Chr) 1 (1q31–1q32 region) and on mouse Chr 1 region (F-G). On the basis of single-strand conformation polymorphism (SSCP-PCR) analysis in an interspecific backcross, we have determined that the Cchl1a3=mdg (muscular dysgenesis) locus is very closely linked to the myogenin (Myog) locus.     

Fine genetic mapping of the proximal part of mouse Chromosome 2 excludes Pax-8 as a candidate gene for Danforth's short tail (Sd)

Danforth's short tail (Sd) is a semidominant mutation of the mouse with effects on the skeleton and the urogenital system. In view of its phenotype and its position in the proximal part of Chromosome (Chr) 2, three genes qualified as possible candidates: Pax-8, a paired box-containing gene; Midkine (Mdk), a retinoic acid-responsive gene; and a new locus (Etl-4) identified by enhancer trapping with a lacZ reporter gene which showed expression in the notochord, the mesonephric mesenchyme, and the apical ectodermal ridge. Three different backcrosses involving all three genes in different combinations were set up and analyzed. From our results we conclude that Sd, Etl-4, Pax-8, and Mdk are independent loci, with Etl-4 being the closest genetic marker (1.1±1.4 cM) to the Danforth's short tail (Sd) gene.     

Mouse chromosome 19

Chair of Committee for Mouse Chromosome 19     

Further progress towards a catalogue of all Arabidopsis genes: analysis of a set of 5000 non-redundant ESTs

Nearly 7000 Arabidopsis thaliana -expressed sequence tags (ESTs) from 10 cDNA libraries have been sequenced, of which almost 5000 non-redundant tags have been submitted to the EMBL data bank. The quality of the cDNA libraries used is analysed. Similarity searches in international protein data banks have allowed the detection of significant similarities to a wide range of proteins from many organisms. Alignment with ESTs from the rice systematic sequencing project has allowed the detection of amino acid motifs which are conserved between the two organisms, thus identifying tags to genes encoding highly conserved proteins. These genes are candidates for a common framework in genome mapping projects in different plants.     

Modelling of fluid-phase endocytosis kinetics in the amoebae of the cellular slime mouldDictyostelium discoideum. A multicompartmental approach

Fluid-phase endocytosis (pinocytosis) kinetics were studied inDictyostelium discoideum amoebae from the axenic strain Ax-2 that exhibits high rates of fluid-phase endocytosis when cultured in liquid nutrient media. Fluorescein-labelled dextran (FITC-dextran) was used as a marker in continuous uptake- and in pulse-chase exocytosis experiments. In the latter case, efflux of the marker was monitored on cells loaded for short periods of time and resuspended in marker-free medium. A multicompartmental model was developed which describes satisfactorily fluid-phase endocytosis kinetics. In particular, it accounts correctly for the extended latency period before exocytosis in pulse-chase experiments and it suggests the existence of some sorts of maturation stages in the pathway.     

Ataxia with Vitamin E Deficiency: Refinement of Genetic Localization and Analysis of Linkage Disequilibrium by Using New Markers in 14 Families

Ataxia with vitamin E deficiency (AVED) is an autosomal recessive disease characterized clinically by neurological symptoms with often striking resemblance to those of Friedreich ataxia. This disorder has been reported previously as familial isolated vitamin E deficiency. We have mapped recently the AVED locus to a 5-cM confidence interval on chromosome 8q by homozygosity mapping in six Mediterranean families. We have now analyzed six new and two previously described families and demonstrate genetic homogeneity despite important clinical variability and wide geographic origins. Analysis of nine new tightly linked microsatellite markers, including four characterized in this study, revealed a predominant but not unique mutation in northern African populations, where this condition is more frequent. Haplotype analysis but also classical recombinations allowed us to refine the AVED position to a 1-cM interval. A YAC contig over this interval was constructed from marker STSs and YAC fingerprint data, in order to facilitate the search of the AVED gene.     

Sexual tetramorphism in Thymelaea hirsuta (Thymelaeaceae): morph ratios in open-pollinated progeny

Natural populations of Thymelaea hirsuta have previously been shown to comprise four distinct sexual morphs: males, females, protogynous individuals, i.e., first female then male, and protandrous individuals, i.e., first male then female. The objective of the present study has been to confirm the genetic basis of this sexual tetramorphism by quantifying morph ratios in the open-pollinated progeny of the four sexual phenotypes growing in a natural population. All four phenotypes were recovered in the progeny of each morph. All observed plants displayed a single sexual phenotype, thus confirming the genetic basis of the tetramorphism. The progeny sex ratios indicate that the genetic determination of sex in this species may be influenced by cytoplasmic factors, while the observed levels of functional female fertility suggest a near-dioecious system. The evolutionary significance of this tetramorphism as a transitional stage in the evolution of dioecy is discussed.     

Abnormality of 2-deoxyglucose uptake kinetics in fibroblasts at low concentrations

2-deoxyglucose uptake rates at low sugar concentrations (less than 500 μM) appeared to be lower than those predicted by the Michaelis-Menten model which correctly described higher concentrations. This phenomenon which we will call concentration-dependent transport lag, was also observed for L-glucose uptake which suggest that this phenomenon is carrier-independent. A model involving the perimembrane space is developed which, for L-glucose, gives k₁ = 0.931 ± 0.072 × 10^?6 l. mg protein^?1. minute^?1, k₂ = 2.97 ± 0.19 × 10^?7 l. mg protein^?1. minute^?1 and So = 88,8 ± 4,3 μM; where k₁ is the diffusion constant in the cell membrane, k₂ is the diffusion constant in the perimembrane space and S_o the sugar concentration required in the external medium in order to provide an équivalent sugar concentration in the transport carrier area.