Systematic documentation and analysis of human genetic variation in hemoglobinopathies using the microattribution approach

We developed a series of interrelated locus-specific databases to store all published and unpublished genetic variation related to hemoglobinopathies and thalassemia and implemented microattribution to encourage submission of unpublished observations of genetic variation to these public repositories. A total of 1,941 unique genetic variants in 37 genes, encoding globins and other erythroid proteins, are currently documented in these databases, with reciprocal attribution of microcitations to data contributors. Our project provides the first example of implementing microattribution to incentivise submission of all known genetic variation in a defined system. It has demonstrably increased the reporting of human variants, leading to a comprehensive online resource for systematically describing human genetic variation in the globin genes and other genes contributing to hemoglobinopathies and thalassemias. The principles established here will serve as a model for other systems and for the analysis of other common and/or complex human genetic diseases.     

Mutations in the gene encoding pejvakin, a newly identified protein of the afferent auditory pathway, cause DFNB59 auditory neuropathy

Auditory neuropathy is a particular type of hearing impairment in which neural transmission of the auditory signal is impaired, while cochlear outer hair cells remain functional. Here we report on DFNB59, a newly identified gene on chromosome 2q31.1-q31.3 mutated in four families segregating autosomal recessive auditory neuropathy. DFNB59 encodes pejvakin, a 352-residue protein. Pejvakin is a paralog of DFNA5, a protein of unknown function also involved in deafness. By immunohistofluorescence, pejvakin is detected in the cell bodies of neurons of the afferent auditory pathway. Furthermore, Dfnb59 knock-in mice, homozygous for the R183W variant identified in one DFNB59 family, show abnormal auditory brainstem responses indicative of neuronal dysfunction along the auditory pathway. Unlike previously described sensorineural deafness genes, all of which underlie cochlear cell pathologies, DFNB59 is the first human gene implicated in nonsyndromic deafness due to a neuronal defect.     

Conjugated action of two species-specific invasion proteins for fetoplacental listeriosis

The ability to cross host barriers is an essential virulence determinant of invasive microbial pathogens. Listeria monocytogenes is a model microorganism that crosses human intestinal and placental barriers, and causes severe maternofetal infections by an unknown mechanism. Several studies have helped to characterize the bacterial invasion proteins InlA and InlB. However, their respective species specificity has complicated investigations on their in vivo role. Here we describe two novel and complementary animal models for human listeriosis: the gerbil, a natural host for L. monocytogenes, and a knock-in mouse line ubiquitously expressing humanized E-cadherin. Using these two models, we uncover the essential and interdependent roles of InlA and InlB in fetoplacental listeriosis, and thereby decipher the molecular mechanism underlying the ability of a microbe to target and cross the placental barrier.     

TRPM6 kinase activity regulates TRPM7 trafficking and inhibits cellular growth under hypomagnesic conditions

The channel kinases TRPM6 and TRPM7 are both members of the melastatin-related transient receptor potential (TRPM) subfamily of ion channels and the only known fusions of an ion channel pore with a kinase domain. TRPM6 and TRPM7 form functional, tetrameric channel complexes at the plasma membrane by heteromerization. TRPM6 was previously shown to cross-phosphorylate TRPM7 on threonine residues, but not vice versa. Genetic studies demonstrated that TRPM6 and TRPM7 fulfill non-redundant functions and that each channel contributes uniquely to the regulation of Mg²⁺ homeostasis. Although there are indications that TRPM6 and TRPM7 can influence each other’s cellular distribution and activity, little is known about the functional relationship between these two channel-kinases. In the present study, we examined how TRPM6 kinase activity influences TRPM7 serine phosphorylation, intracellular trafficking, and cell surface expression of TRPM7, as well as Mg²⁺-dependent cellular growth. We found TRPM7 serine phosphorylation via the TRPM6 kinase, but no TRPM6 serine phosphorylation via the TRPM7 kinase. Intracellular trafficking of TRPM7 was altered in HEK-293 epithelial kidney cells and DT40 B cells in the presence of TRPM6 with intact kinase activity, independently of the availability of extracellular Mg²⁺, but TRPM6/7 surface labeling experiments indicate comparable levels of the TRPM6/7 channels at the plasma membrane. Furthermore, using a complementation approach in TRPM7-deficient DT40 B-cells, we demonstrated that wild-type TRPM6 inhibited cell growth under hypomagnesic cell culture conditions in cells co-expressing TRPM6 and TRPM7; however, co-expression of a TRPM6 kinase dead mutant had no effect—a similar phenotype was also observed in TRPM6/7 co-expressing HEK-293 cells. Our results provide first clues about how heteromer formation between TRPM6 and TRPM7 influences the biological activity of these ion channels. We show that TRPM6 regulates TRPM7 intracellular trafficking and TRPM7-dependent cell growth. All these effects are dependent upon the presence of an active TRPM6 kinase domain. Dysregulated Mg²⁺-homeostasis causes or exacerbates many pathologies. As TRPM6 and TRPM7 are expressed simultaneously in numerous cell types, understanding how their relationship impacts regulation of Mg²⁺-uptake is thus important knowledge.