Genetic variation in a human odorant receptor alters odour perception

Human olfactory perception differs enormously between individuals, with large reported perceptual variations in the intensity and pleasantness of a given odour. For instance, androstenone (5alpha-androst-16-en-3-one), an odorous steroid derived from testosterone, is variously perceived by different individuals as offensive ("sweaty, urinous"), pleasant ("sweet, floral") or odourless. Similar variation in odour perception has been observed for several other odours. The mechanistic basis of variation in odour perception between individuals is unknown. We investigated whether genetic variation in human odorant receptor genes accounts in part for variation in odour perception between individuals. Here we show that a human odorant receptor, OR7D4, is selectively activated in vitro by androstenone and the related odorous steroid androstadienone (androsta-4,16-dien-3-one) and does not respond to a panel of 64 other odours and two solvents. A common variant of this receptor (OR7D4 WM) contains two non-synonymous single nucleotide polymorphisms (SNPs), resulting in two amino acid substitutions (R88W, T133M; hence 'RT') that severely impair function in vitro. Human subjects with RT/WM or WM/WM genotypes as a group were less sensitive to androstenone and androstadienone and found both odours less unpleasant than the RT/RT group. Genotypic variation in OR7D4 accounts for a significant proportion of the valence (pleasantness or unpleasantness) and intensity variance in perception of these steroidal odours. Our results demonstrate the first link between the function of a human odorant receptor in vitro and odour perception.     

Phosphatidylinositol-3,5-bisphosphate lipid-binding-induced activation of the human two-pore channel 2

Mammalian two-pore channels (TPCs) are activated by the low-abundance membrane lipid phosphatidyl-(3,5)-bisphosphate (PI(3,5)P₂) present in the endo-lysosomal system. Malfunction of human TPC1 or TPC2 (hTPC) results in severe organellar storage diseases and membrane trafficking defects. Here, we compared the lipid-binding characteristics of hTPC2 and of the PI(3,5)P₂-insensitive TPC1 from the model plant Arabidopsis thaliana. Combination of simulations with functional analysis of channel mutants revealed the presence of an hTPC2-specific lipid-binding pocket mutually formed by two channel regions exposed to the cytosolic side of the membrane. We showed that PI(3,5)P₂ is simultaneously stabilized by positively charged amino acids (K203, K204, and K207) in the linker between transmembrane helices S4 and S5 and by S322 in the cytosolic extension of S6. We suggest that PI(3,5)P₂ cross links two parts of the channel, enabling their coordinated movement during channel gating.     

High levels of mitochondrial DNA deletions in substantia nigra neurons in aging and Parkinson disease

Here we show that in substantia nigra neurons from both aged controls and individuals with Parkinson disease, there is a high level of deleted mitochondrial DNA (mtDNA) (controls, 43.3% +/- 9.3%; individuals with Parkinson disease, 52.3% +/- 9.3%). These mtDNA mutations are somatic, with different clonally expanded deletions in individual cells, and high levels of these mutations are associated with respiratory chain deficiency. Our studies suggest that somatic mtDNA deletions are important in the selective neuronal loss observed in brain aging and in Parkinson disease.     

CCN1: a novel inflammation-regulated biphasic immune cell migration modulator

In this study, we performed a comprehensive analysis of the effect of CCN1 on the migration of human immune cells. The molecule CCN1, produced by fibroblasts and endothelial cells, is considered as an important matrix protein promoting tissue repair and immune cell adhesion by binding various integrins. We recently reported that CCN1 therapy is able to suppress acute inflammation in vivo. Here, we show that CCN1 binds to various immune cells including T cells, B cells, NK cells, and monocytes. The addition of CCN1 in vitro enhances both actin polymerization and transwell migration. Prolonged incubation with CCN1, however, results in the inhibition of migration of immune cells by a mechanism that involves downregulation of PI3Kγ, p38, and Akt activation. Furthermore, we observed that immune cells themselves produce constitutively CCN1 and secretion is induced by pro-inflammatory stimuli. In line with this finding, patients suffering from acute inflammation had enhanced serum levels of CCN1. These findings extend the classical concept of CCN1 as a locally produced cell matrix adhesion molecule and suggest that CCN1 plays an important role in regulating immune cell trafficking by attracting and locally immobilizing immune cells.     

Evolution and biology of supernumerary B chromosomes

B chromosomes (Bs) are dispensable components of the genome exhibiting non-Mendelian inheritance and have been widely reported on over several thousand eukaryotes, but still remain an evolutionary mystery ever since their first discovery over a century ago [1]. Recent advances in genome analysis have significantly improved our knowledge on the origin and composition of Bs in the last few years. In contrast to the prevalent view that Bs do not harbor genes, recent analysis revealed that Bs of sequenced species are rich in gene-derived sequences. We summarize the latest findings on supernumerary chromosomes with a special focus on the origin, DNA composition, and the non-Mendelian accumulation mechanism of Bs.     

MYO5B mutations cause microvillus inclusion disease and disrupt epithelial cell polarity

Following homozygosity mapping in a single kindred, we identified nonsense and missense mutations in MYO5B, encoding type Vb myosin motor protein, in individuals with microvillus inclusion disease (MVID). MVID is characterized by lack of microvilli on the surface of enterocytes and occurrence of intracellular vacuolar structures containing microvilli. In addition, mislocalization of transferrin receptor in MVID enterocytes suggests that MYO5B deficiency causes defective trafficking of apical and basolateral proteins in MVID.