No apparent reduction of gene flow in a hybrid zone between the West and North European karyotypic groups of the common shrew, Sorex araneus.

The common shrew, Sorex araneus, exhibits an unusually high level of karyotypic variation. Populations with identical or similar karyotypes are defined as chromosome races, which are, in turn, grouped into larger evolutionary units, karyotypic groups. Using six microsatellite markers, we investigated the genetic structure of a hybrid zone between the Sidensjö and Abisko chromosome races, representatives of two distinct karyotypic groups believed to have been separated during the last glacial maximum, the West European karyotypic group (western group) and the North European karyotypic group (northern group), respectively. Significant FST values among populations suggest some weak genetic structure. All hierarchical levels show similar levels of genetic differentiation, equivalent to levels of genetic structure in several intraracial studies of common shrew populations from central Europe. Notably, genetic differentiation was of the same order of magnitude between and within karyotypic groups. Although the genetic differentiation was weak, the correlation between genetic and geographical distance was positive and significant, suggesting that the genetic variation observed between populations is a function of geographical distance rather than racial origin. Hence, considerable chromosomal differences do not seem to prevent extensive gene flow.

The ACE gene and Alzheimer's disease susceptibility.

A recent study suggested that the insertion (I) allele in intron 16 of the angiotensin converting enzyme gene (ACE) is associated with Alzheimer's disease (AD) risk. In our series of 239 necropsy confirmed late onset AD cases and 342 elderly non-demented controls aged >73 years, we found significantly different ACE genotype distributions in the case and control groups (p=0.007). Homozygotes for both the I and D alleles were associated with a higher risk compared to DI heterozygotes. While the APOE epsilon4 allele was strongly associated with AD risk in our series, we found no evidence for an interaction between the APOE and ACE loci. In addition, no interactions were observed between ACE and gender or age at death of the AD cases. A meta-analysis of all published reports (12 case-control series in total) suggested that both the II and ID ACE genotypes are associated with increased AD risk (odds ratio (OR) for II v DD 1.36, 95% confidence interval (CI)=1.13-1.63, OR for DI v DD 1.33, 95% CI=1.14-1.53, p=0.0002).

Alpha-synuclein overexpression promotes aggregation of mutant huntingtin.

Protein aggregates are a neuropathological feature of Huntington's disease and Parkinson's disease. Mutant huntingtin exon 1 with 72 CAG repeats fused to enhanced green fluorescent protein (EGFP) forms hyperfluorescent inclusions in PC12 cells. Inclusion formation is enhanced in cells co-transfected with EGFP-huntingtin-(CAG)(72) and alpha-synuclein, a major component of Parkinson's disease aggregates. However, alpha-synuclein does not form aggregates by itself, nor does it appear in huntingtin inclusions in vitro.

Effects of heat shock, heat shock protein 40 (HDJ-2), and proteasome inhibition on protein aggregation in cellular models of Huntington's disease.

Huntington's disease (HD), spinocerebellar ataxias types 1 and 3 (SCA1, SCA3), and spinobulbar muscular atrophy (SBMA) are caused by CAG/polyglutamine expansion mutations. A feature of these diseases is ubiquitinated intraneuronal inclusions derived from the mutant proteins, which colocalize with heat shock proteins (HSPs) in SCA1 and SBMA and proteasomal components in SCA1, SCA3, and SBMA. Previous studies suggested that HSPs might protect against inclusion formation, because overexpression of HDJ-2/HSDJ (a human HSP40 homologue) reduced ataxin-1 (SCA1) and androgen receptor (SBMA) aggregate formation in HeLa cells. We investigated these phenomena by transiently transfecting part of huntingtin exon 1 in COS-7, PC12, and SH-SY5Y cells. Inclusion formation was not seen with constructs expressing 23 glutamines but was repeat length and time dependent for mutant constructs with 43-74 repeats. HSP70, HSP40, the 20S proteasome and ubiquitin colocalized with inclusions. Treatment with heat shock and lactacystin, a proteasome inhibitor, increased the proportion of mutant huntingtin exon 1-expressing cells with inclusions. Thus, inclusion formation may be enhanced in polyglutamine diseases, if the pathological process results in proteasome inhibition or a heat-shock response. Overexpression of HDJ-2/HSDJ did not modify inclusion formation in PC12 and SH-SY5Y cells but increased inclusion formation in COS-7 cells. To our knowledge, this is the first report of an HSP increasing aggregation of an abnormally folded protein in mammalian cells and expands the current understanding of the roles of HDJ-2/HSDJ in protein folding.

A molecular investigation of true dominance in Huntington's disease.

Huntington's disease (HD) is thought to show true dominance, since subjects with two mutant alleles have been reported to have similar ages at onset of disease compared to heterozygous sibs. We have investigated this phenomenon using a cell culture model. Protein aggregate formation was used as an indicator for pathology, as intraneuronal huntingtin inclusions are associated with pathology in vitro and in vivo. We showed that cytoplasmic and nuclear aggregates are formed by constructs comprising part of exon 1 of huntingtin with 41, 51, 66, or 72 CAG repeats, in a rate that correlates with repeat number. No inclusions were seen with 21 CAG repeat constructs. Mutant and wild type huntingtin fragments can be sequestered into inclusions seeded by a mutant huntingtin. Wild type huntingtin did not enhance or interfere with protein aggregation. The rate of protein aggregation was dose dependent for all mutant constructs tested. These experiments suggested a model for the dominance observed in HD; the decrease in the age at onset of a mutant homozygote may be small compared to the variance in the age at onset for that specific repeat number in heterozygotes. Our experiments also provide a model, which may explain the different repeat size ranges seen in patients and healthy controls for the different polyglutamine diseases.

Spermatogenesis in common shrews, Sorex araneus, from a hybrid zone with extensive Robertsonian polymorphism.

The analysis of the fertility of hybrid and nonhybrid individuals from a chromosomal contact zone gives us the possibility of studying the role of chromosomes in speciation processes. In this study, homozygous, "simple" and "complex" Robertsonian heterozygous male common shrews (Sorex araneus) from the Abisko-Sidensjö chromosomal hybrid zone in Sweden were analysed. The degree of germ cell death was estimated, sperm counts were performed and the testis and seminal vesicles weighed in each individual. Chromosome interactions and synapsis at pachytene were examined under the EM. The weight of the testis was significantly different in the three karyotypic groups and "complex" heterozygotes suffered higher germ cell death than homozygotes and "simple" heterozygotes. Interactions between chromosomes at pachytene were rare. Nonhomologous pairing in the centromeric regions of autosomal trivalents (side arms) was common while asynapsed segments were seldom found. Thus, the difference in the reproductive characteristics of the common shrew might be due to genetic factors rather than Robertsonian translocations.

Meiosis and fertility in common shrews, Sorex araneus, from a chromosomal hybrid zone in central Sweden.

Adult male common shrews from the Uppsala and Hällefors Robertsonian chromosomal races and hybrids were collected from the area of Surahammar in Sweden. Meiosis and fertility of hybrid (complex heterozygotes) and nonhybrid (homozygotes) individuals were compared based on an analysis of chromosomal interactions and synapsis at pachytene, chiasma characteristics at diakinesis, and germ-cell death. No individuals suffered severe germ-cell loss, and the differences found among the Uppsala and Hällefors homozygotes and the hybrids were not significant. In complex heterozygotes, ring configurations of four elements were observed at meiosis I, with one chiasma per chromosome arm. Abnormal rings were frequent at pachytene, but interactions between the ring and other chromosomes were seldom found. There is no indication from this study of a differential fertility between homozygotes and ring IV-forming complex heterozygotes in males.