ABSTRACT
Consanguineous Pakistani pedigrees segregating deafness have contributed decisively to the discovery of 31 of the 68 genes associated with nonsyndromic autosomal recessive hearing loss (HL) worldwide. In this study, we utilized genome-wide genotyping, Sanger and exome sequencing to identify 163 DNA variants in 41 previously reported HL genes segregating in 321 Pakistani families. Of these, 70 (42.9%) variants identified in 29 genes are novel. As expected from genetic studies of disorders segregating in consanguineous families, the majority of affected individuals (94.4%) are homozygous for HL-associated variants, with the other variants being compound heterozygotes. The five most common HL genes in the Pakistani population are SLC26A4, MYO7A, GJB2, CIB2 and HGF, respectively. Our study provides a profile of the genetic etiology of HL in Pakistani families, which will allow for the development of more efficient genetic diagnostic tools, aid in accurate genetic counseling, and guide application of future gene-based therapies. These findings are also valuable in interpreting pathogenicity of variants that are potentially associated with HL in individuals of all ancestries. The Pakistani population, and its infrastructure for studying human genetics, will continue to be valuable to gene discovery for HL and other inherited disorders.
Subject(s)
Chromosome Segregation/genetics , Consanguinity , Hearing Loss/genetics , Family , Female , Genes, Recessive , Genetic Predisposition to Disease , Humans , Male , Mutation/genetics , Pakistan , PedigreeABSTRACT
The transcription factor Pax6 is an important regulator of development and cell differentiation in various organs. Thus, Pax6 was shown to promote neural development in the cerebral cortex and spinal cord, and to control pancreatic endocrine cell genesis. However, the role of Pax6 in distinct endocrine cells of the adult pancreas has not been addressed. We report the conditional inactivation of Pax6 in insulin and glucagon producing cells of the adult mouse pancreas. In the absence of Pax6, beta- and alpha-cells lose their molecular maturation characteristics. Our findings provide strong evidence that Pax6 is responsible for the maturation of beta-, and alpha-cells, but not of delta-, and PP-cells. Moreover, lineage-tracing experiments demonstrate that Pax6-deficient beta- and alpha-cells are shunted towards ghrelin marked cells, sustaining the idea that ghrelin may represent a marker for endocrine cell maturation.
Subject(s)
Eye Proteins/genetics , Ghrelin/genetics , Glucagon-Secreting Cells/metabolism , Homeodomain Proteins/genetics , Insulin-Secreting Cells/metabolism , Paired Box Transcription Factors/genetics , Pancreatic Polypeptide-Secreting Cells/metabolism , Repressor Proteins/genetics , Somatostatin-Secreting Cells/metabolism , Animals , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Cell Differentiation , Cell Lineage/drug effects , Cell Lineage/genetics , Crosses, Genetic , Eye Proteins/metabolism , Female , Gene Expression Regulation, Developmental , Genes, Reporter , Ghrelin/metabolism , Glucagon-Secreting Cells/cytology , Glucagon-Secreting Cells/drug effects , Homeodomain Proteins/metabolism , Insulin/genetics , Insulin/metabolism , Insulin-Secreting Cells/cytology , Insulin-Secreting Cells/drug effects , Integrases/genetics , Integrases/metabolism , Luminescent Proteins/genetics , Luminescent Proteins/metabolism , Male , Mice , Mice, Knockout , PAX6 Transcription Factor , Paired Box Transcription Factors/metabolism , Pancreatic Polypeptide-Secreting Cells/cytology , Pancreatic Polypeptide-Secreting Cells/drug effects , Repressor Proteins/metabolism , Signal Transduction , Somatostatin-Secreting Cells/cytology , Somatostatin-Secreting Cells/drug effects , Tamoxifen/pharmacologyABSTRACT
The two compositionally distinct extracellular cochlear fluids, endolymph and perilymph, are separated by tight junctions that outline the scala media and reticular lamina. Mutations in TRIC (also known as MARVELD2), which encodes a tricellular tight junction protein known as tricellulin, lead to nonsyndromic hearing loss (DFNB49). We generated a knockin mouse that carries a mutation orthologous to the TRIC coding mutation linked to DFNB49 hearing loss in humans. Tricellulin was absent from the tricellular junctions in the inner ear epithelia of the mutant animals, which developed rapidly progressing hearing loss accompanied by loss of mechanosensory cochlear hair cells, while the endocochlear potential and paracellular permeability of a biotin-based tracer in the stria vascularis were unaltered. Freeze-fracture electron microscopy revealed disruption of the strands of intramembrane particles connecting bicellular and tricellular junctions in the inner ear epithelia of tricellulin-deficient mice. These ultrastructural changes may selectively affect the paracellular permeability of ions or small molecules, resulting in a toxic microenvironment for cochlear hair cells. Consistent with this hypothesis, hair cell loss was rescued in tricellulin-deficient mice when generation of normal endolymph was inhibited by a concomitant deletion of the transcription factor, Pou3f4. Finally, comprehensive phenotypic screening showed a broader pathological phenotype in the mutant mice, which highlights the non-redundant roles played by tricellulin.
