Cloning and expression of Shaker alpha- and beta-subunits during inner ear development

Sensory cells of the chicken cochlea exhibit different ion channels relative to their position along the epithelium. One of these channels conducts an A-type potassium current which is found primarily in 'short' hair cells. Here, we report the first full length cloning and developmental expression of Shaker genes from this endorgan. Clones were obtained by screening a chicken (Gallus gallus) cochlea cDNA library, using probes made from RHK1 (i.e., Kvalpha1.4) cDNA, a Shaker homologue isolated from rat heart, and hKvbeta1.2 cDNA, a beta homologue isolated from human heart. Sequence analysis revealed a chick homologue of Kvalpha1.4, with a deduced amino acid similarity of 76-79% to mammalian Kvalpha1.4, and a chick homologue of Kvbeta1.1, with a similarity of 95% to mammalian Kvbeta1.1. In addition, we isolated a variant of cKvalpha1. 4 (cKvalpha1.4(m)) that differs in its untranslated regions and shows complete similarity in its coding region, except for the deletion of a single nucleotide. During development of the inner ear, reverse transcription-polymerase chain reaction (RT-PCR) studies show that the beta-subunit is expressed as early as embryonic day 3, whereas alpha- and beta-subunits are coexpressed on embryonic days 7 to 10, 14, and in adult.