Physical and genetic maps of the deafwaddler region on distal mouse Chr 6

Human NB-2 of the contactin subgroup molecules: chromosomal localization of the gene (CNTN5) and distinct expression pattern from other subgroup members

NB-2 is one of the neural recognition molecules in the contactin subgroup, which belongs to the immunoglobulin superfamily. In rat, the six molecules in this subgroup that have been reported to date are contactin, TAG-1, BIG-1, BIG-2, NB-2, and NB-3. We have isolated cDNAs encoding the two splicing isoforms of human NB-2. The long isoform of human NB-2 consists of 1100 amino acids residues that are 91% homologous to rat NB-2 at the amino acid sequence level. The short isoform lacks 74 amino acid residues between residues 19 and 93 of the long isoform. Among various regions of the adult human brain, high-level expression of NB-2 was detected in the amygdala and occipital lobe, whereas expression was low in the corpus callosum, caudate nucleus, and spinal cord. Although there were some differences, the expression pattern of NB-2 was the most similar to that of BIG-1 in the brain. Likewise, contactin and BIG-2 exhibited similar expression patterns. The expression of TAG-1 showed the least regional differences. The human NB-2 gene (CNTN5) was mapped to chromosome 11q21-q22.2 by fluorescence in situ hybridization. Our results suggest that the NB-2 gene may contribute to human neurological disorders.

Mutations in a plasma membrane Ca2+-ATPase gene cause deafness in deafwaddler mice

Hearing loss is the most common sensory deficit in humans. Because the auditory systems of mice and humans are conserved, studies on mouse models have predicted several human deafness genes and identified new genes involved in hearing. The deafwaddler (dfw) mouse mutant is deaf and displays vestibular/motor imbalance. Here we report that the gene encoding a plasma membrane Ca2+-ATPase type 2 pump (Atp2b2, also known as Pmca2) is mutated in dfw. An A-->G nucleotide transition in dfw DNA causes a glycine-to-serine substitution at a highly conserved amino-acid position, whereas in a second allele, dfw2J, a 2-base-pair deletion causes a frameshift that predicts a truncated protein. In the cochlea, the protein Atp2b2 is localized to stereocilia and the basolateral wall of hair cells in wild-type mice, but is not detected in dfw2J mice. This indicates that mutation of Atp2b2 may cause deafness and imbalance by affecting sensory transduction in stereocilia as well as neurotransmitter release from the basolateral membrane. These mutations affecting Atp2b2 in dfw and dfw2J are the first to be found in a mammalian plasma membrane calcium pump and define a new class of deafness genes that directly affect hair-cell physiology.