title: Primary structure, functional characterization and developmental expression of the ascidian Kv4-class potassium channel.
abstract: Ascidians belong to the primitive chordates and their larvae show symmetrical beating of the tail, which is reminiscent of the swimming pattern in primitive vertebrates. Since ascidian larva contains only a small number of neurons in their entire larval nervous system, they will potentially provide a simple model for the study of animal locomotion. In a step towards the goal of establishing the molecular basis underlying ascidian larval neurophysiology, we describe here a Kv4 class of voltage-gated potassium channel, TuKv4, from Halocynthia roretzi. Whole mount in situ hybridization indicates that TuKv4 is expressed in most of larval neurons including motor neurons. TuKv4-currents reconstituted in Xenopus oocytes show currents with similar properties to the lower-threshold A-type currents from cleavage-arrested ascidian blastomeres of neural lineage. However, the voltage-dependency of the steady-state inactivation and activation was shifted leftward by 20 mV, as compared with native A-type currents, suggesting that other components may be required to restore full function of the Kv4 channel. Unexpectedly, another isoform lacking C-terminal cytoplasmic region was also isolated. This truncated isoform did not lead to a functional current in Xenopus oocytes. RT-PCR analysis showed that the truncated form is transiently expressed during larval development, suggesting some developmental role for potassium channel expression.
authors.affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Nakajo
authors.forename: You
authors.initials: Y
authors.lastname: Katsuyama
authors.forename: Fumihito
authors.initials: F
authors.lastname: Ono
authors.forename: Yukio
authors.initials: Y
authors.lastname: Ohtsuka
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Okamura
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001757:Blastomeres / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000502:physiology; D047108:Embryonic Development; D018507:Gene Expression Regulation, Developmental; D017403:In Situ Hybridization; D007814:Larva / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology*; D008969:Molecular Sequence Data; D009046:Motor Neurons / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010957:Plasmids; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000096:biosynthesis* / Q000235:genetics; D024642:Potassium Channels, Voltage-Gated; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051672:Shal Potassium Channels; D014561:Urochordata / Q000033:anatomy & histology / Q000378:metabolism*; D014981:Xenopus
chemical_list: D018076:DNA, Complementary; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051672:Shal Potassium Channels; D011188:Potassium