Differential basal synthesis of Hsp70/Hsc70 contributes to interindividual variation in Hsp70/Hsc70 inducibility

The source of intraspecies variation in the expression of heat shock proteins (HSPs) remains unresolved but could shed light on differential stress tolerance and disease susceptibility. This study investigated the influence of variable basal HSP synthesis on differential inducibility of HSP synthesis. Basal and heat-induced synthesis of the major HSP families in peripheral blood monocytes from healthy donors (n=42) were analysed using biometabolic labelling and densitometry. Basal Hsp70/Hsc70 synthesis and percentage induction of Hsp70/Hsc70 synthesis were significantly correlated (r=−0.57, p<0.0001), and described most accurately by an exponential decay equation (R=0.68, R²=0.46). This regression equation suggests that increasing levels of basal Hsp70/Hsc70 synthesis are accompanied byan exponential decrease in the percentage induction of Hsp70/Hsc70 synthesis. The model fits data from European and non-European population groups independently, although both coefficients in the regression equation were larger for non-Europeans. This implies population group as an additional factor influencing differential HSP expression. The differential inducibility of Hsp70/Hsc70 due to variable basal synthesis of Hsp70/Hsc70 and based upon population group may contribute to differential stress tolerance or disease susceptibility. Received 27 March 2000; received after revision 19 June 2000; accepted 20 June 2000     

Estimate of human gene number provided by genome-wide analysis using Tetraodon nigroviridis DNA sequence

The number of genes in the human genome is unknown, with estimates ranging from 50,000 to 90,000 (refs 1, 2), and to more than 140,000 according to unpublished sources. We have developed 'Exofish', a procedure based on homology searches, to identify human genes quickly and reliably. This method relies on the sequence of another vertebrate, the pufferfish Tetraodon nigroviridis, to detect conserved sequences with a very low background. Similar to Fugu rubripes, a marine pufferfish proposed by Brenner et al. as a model for genomic studies, T. nigroviridis is a more practical alternative with a genome also eight times more compact than that of human. Many comparisons have been made between F. rubripes and human DNA that demonstrate the potential of comparative genomics using the pufferfish genome. Application of Exofish to the December version of the working draft sequence of the human genome and to Unigene showed that the human genome contains 28,000-34,000 genes, and that Unigene contains less than 40% of the protein-coding fraction of the human genome.     

Insertion of Inhbb into the Inhba locus rescues the Inhba-null phenotype and reveals new activin functions

The activins (dimers of betaA or betaB subunits, encoded by the genes Inhba and Inhbb, respectively) are TGF-beta superfamily members that have roles in reproduction and development. Whereas mice homozygous for the Inhba-null allele demonstrate disruption of whisker, palate and tooth development, leading to neonatal lethality, homozygous Inhbb-null mice are viable, fertile and have eye defects. To determine if these phenotypes were due to spatiotemporal expression differences of the ligands or disruption of specific ligand-receptor interactions, we replaced the region of Inhba encoding the mature protein with Inhbb, creating the allele Inhbatm2Zuk (hereafter designated InhbaBK). Although the craniofacial phenotypes of the Inhba-null mutation were rescued by the InhbaBK allele, somatic, testicular, genital and hair growth were grossly affected and influenced by the dosage and bioactivity of the allele. Thus, functional compensation within the TGF-beta superfamily can occur if the replacement gene is expressed appropriately. The novel phenotypes in these mice further illustrate the usefulness of insertion strategies for defining protein function.     

Juxtaposed regions of extensive and minimal linkage disequilibrium in human Xq25 and Xq28

Linkage disequilibrium (LD), or the non-random association of alleles, is poorly understood in the human genome. Population genetic theory suggests that LD is determined by the age of the markers, population history, recombination rate, selection and genetic drift. Despite the uncertainties in determining the relative contributions of these factors, some groups have argued that LD is a simple function of distance between markers. Disease-gene mapping studies and a simulation study gave differing predictions on the degree of LD in isolated and general populations. In view of the discrepancies between theory and experimental observations, we constructed a high-density SNP map of the Xq25-Xq28 region and analysed the male genotypes and haplotypes across this region for LD in three populations. The populations included an outbred European sample (CEPH males) and isolated population samples from Finland and Sardinia. We found two extended regions of strong LD bracketed by regions with no evidence for LD in all three samples. Haplotype analysis showed a paucity of haplotypes in regions of strong LD. Our results suggest that, in this region of the X chromosome, LD is not a monotonic function of the distance between markers, but is more a property of the particular location in the human genome.