Mouse brain potassium channel beta1 subunit mRNA: cloning and distribution during development

The pore-forming alpha subunits of voltage-gated potassium channels in neurons and other excitable cells are expressed in association with accessory beta subunits. These subunits both promote insertion of channel complexes into surface membranes and influence their electrophysiological properties. As part of an effort to understand the regulation of voltage-gated potassium channels during development, we cloned the mouse homolog of the rat Kvbeta1 potassium channel subunit. Kvbeta1 subunits are known to associate preferentially with Shaker (Kv1)-related alpha subunits. We then used a digoxigenin-tagged cRNA probe and in situ hybridization techniques to visualize the appearance of Kvbeta1 mRNA transcripts during late embryonic and early neonatal development of the mouse brain. We detected Kvbeta1-specific labeling of cells in hippocampus, cerebral cortex, caudate putamen, colliculus, and cerebellum. In hippocampus, we observed Kvbeta1 mRNA in CA3 pyramidal neurons at the earliest time examined, embryonic day 16 (E16). Between E16 and postnatal day 7 (P7), cell labeling increased uniformly across the pyramidal neurons of Ammon's horn (CA1, CA2, and CA3). Subsequently, between P7 and P22, regional differences characteristic of mature hippocampus appeared-intense labeling of neurons in CA3 and CA1, and less in CA2. In cortex, labeling of cells in the subplate and cortical plate layers was observed at E16. During development, the intensity of this labeling increased, and labeled cells persisted into the adult stage in the deep cortical layer (VIb) formed from subplate neurons. Additional labeling of scattered solitary cells in cortical layers II-VIa emerged between P3 and P7 and was prominent in mature cortex. In caudate putamen, Kvbeta1-labeled cells were observed at P1 and were restricted to the lateral and rostral half of the caudate. During development, labeling expanded caudally and medially and eventually filled the mature caudate putamen. In colliculus, a small population of inferior colliculus cells showed labeling at P7, and additional labeling of scattered cells appeared during development. In superior colliculus, labeling was observed only in the adult deep gray layer. In cerebellum, intense labeling was observed in Purkinje cells at all stages between P1 and adult. Labeling was also seen in granule neurons in the external granule layer at early postnatal stages and in the inner granule layer beginning at P7.