Abstract
Developmentally regulated action potentials are a hallmark of Rohon-Beard cells, a class of sensory neurons. In these neurons as well as other primary spinal neurons of Xenopus laevis, the functional differentiation of delayed-rectifier potassium current regulates the waveform of the action potential during the initial day of its appearance. Later, the acquisition of another voltage-dependent potassium current--the A current--plays a major role in regulating excitability. In order to understand the molecular basis of this functional differentiation, genes encoding voltage-dependent potassium currents expressed in the embryonic amphibian nervous system are being cloned. Here, we report the functional properties and developmental localization of a second Xenopus Shaker-like gene (Xenopus Kv 1.1; XSha1; GenBank accession number M94258) encoding a potassium current. Homology screening with the mouse gene MBK1 led to its isolation. Functional expression in oocytes identifies it as a delayed-rectifier current when assembled as a homooligomeric structure. Specific transcripts corresponding to XSha1 and to the previously cloned gene XSha2 are both detectable by RNase protection in RNA isolated from the embryonic nervous system. However, whole-mount in situ hybridization reveals the temporal pattern and cellular localization of XSha1 but not XSha2 mRNA, suggesting that the concentration of XSha2 transcripts in individual cells is lower than the threshold for detection by this method. Of particular interest, Rohon-Beard cells express XSha1 mRNA. In addition, XSha1 mRNA is detected in several structures containing neural crest derivatives including spinal ganglia, the trigeminal ganglion, and branchial arches; its presence in motor nerves and lateral spinal tracts suggests that both CNS and PNS glia express the mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)