title: Visualization in zebrafish larvae of Na(+) uptake in mitochondria-rich cells whose differentiation is dependent on foxi3a.
abstract: Uptake of Na(+) from the environment is an indispensable strategy for the survival of freshwater fish, as they easily lose Na(+) from the plasma to a diluted environment. Nevertheless, the location of and molecules involved in Na(+) uptake remain poorly understood. In this study, we utilized Sodium Green, a Na(+)-dependent fluorescent reagent, to provide direct evidence that Na(+) absorption takes place in a subset of the mitochondria-rich (MR) cells on the yolk sac surface of zebrafish larvae. Combined with immunohistochemistry, we revealed that the Na(+)-absorbing MR cells were exceptionally rich in vacuolar-type H(+)-ATPase (H(+)-ATPase) but moderately rich in Na(+)-K(+)-ATPase. We also addressed the function of foxi3a, a transcription factor that is specifically expressed in the H(+)-ATPase-rich MR cells. When foxi3a was depleted from zebrafish embryos by antisense morpholino oligonucleotide injection, differentiation of the MR cells was completely blocked and Na(+) influx was severely reduced, indicating that MR cells are the primary sites for Na(+) absorption. Additionally, foxi3a expression is initiated at the gastrula stage in the presumptive ectoderm; thus, we propose that foxi3a is a key gene in the control of MR cell differentiation. We also utilized a set of ion transport inhibitors to assess the molecules involved in the process and discuss the observations.
authors.affiliation: Department of Biological Sciences, Tokyo Institute of Technology, 4259-B-19 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Esaki
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Hoshijima
authors.forename: Sayako
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Fukuda
authors.forename: Koichi
authors.initials: K
authors.lastname: Kawakami
authors.forename: Shigehisa
authors.initials: S
authors.lastname: Hirose
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors; D002454:Cell Differentiation / Q000187:drug effects; D051543:Hepatocyte Nuclear Factor 3-gamma / Q000235:genetics*; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007814:Larva / Q000502:physiology*; D008928:Mitochondria / Q000378:metabolism*; D009025:Morpholines / Q000494:pharmacology; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D009930:Organic Chemicals; D006180:Proton-Translocating ATPases / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D012979:Sodium Radioisotopes; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D015017:Yolk Sac / Q000166:cytology / Q000378:metabolism; D015027:Zebrafish / Q000502:physiology*
chemical_list: D027682:Cation Transport Proteins; D009025:Morpholines; D016376:Oligonucleotides, Antisense; D009930:Organic Chemicals; D012979:Sodium Radioisotopes; D017923:Sodium-Hydrogen Exchangers; C098118:sodium green; D051543:Hepatocyte Nuclear Factor 3-gamma; D012964:Sodium; D006180:Proton-Translocating ATPases; D002118:Calcium