Atp2b2, encoding plasma membrane Ca2+-ATPase type 2, (PMCA2) exhibits tissue-specific first exon usage in hair cells, neurons, and mammary glands of mice

Atp2b2 encodes the plasma membrane Ca2+-ATPase type 2 (PMCA2) expressed in various tissues, including stereocilia of cochlear and vestibular hair cells, cerebellar Purkinje cells, and lactating mammary epithelia. Mutations of the gene lead to deafness, ataxia, and reduced Ca2+ levels in milk. Heterozygous mutants also have abnormal hearing, suggesting that precise regulation of Atp2b2 is required for normal function. In this study, we describe Atp2b2 5′-untranslated region genomic structure and transcript usage in mice. Using 5′-rapid amplification of cDNA ends, we observed four transcripts: types α, β, μ and δ, each splicing into a common ATG-containing exon. Types α and β correspond to previously published mammalian cDNA sequences. Types μ and δ constitute novel 5′-untranslated region sequences, and were observed at high levels only in lactating mammary gland. Using real-time reverse transcriptase polymerase chain reaction, we quantified relative transcript usage across several tissues. We show that α and β are abundant throughout the CNS, as well as the cochlea. When we microdissected the cochlea into hair cell and spiral ganglion containing fractions, we found that cochlear hair cell expression is mediated through the type α transcript. In situ hybridization studies in cerebellum using exon-specific probes revealed that α dominates in Purkinje neurons, while β is enriched in cerebellar granule neurons. We compared 5′-untranslated region sequence across multiple species, and found high conservation around the first exons for α and β in mammals, but not other species. The regions around the μ and δ first exons are highly conserved between rat and mouse, but less so with other species. Our results show that expression of Atp2b2 is highly regulated, using four different transcriptional start regions, two of which are differentially expressed in neuronal tissue. This suggests that unique regulatory mechanisms are used to control Atp2b2 expression in different types of cells.