Specific expression and regulation of glucose transporters in zebrafish ionocytes.
Glucose, a carbohydrate metabolite, plays a major role in the energy supply for fish iono- and osmoregulation, and the way that glucose is transported in ionocytes is a critical process related to the functional operations of ionocytes. Eighteen members of glucose transporters (GLUTs, SLC2A) were cloned and identified from zebrafish. Previously, Na(+),K(+)-ATPase-rich (NaR), Na(+)-Cl(-) cotransporter-expressing (NCC), H(+)-ATPase-rich (HR), and glycogen-rich (GR) cells have been identified to be responsible for Ca(2+) uptake, Cl(-) uptake, Na(+) uptake, and the energy deposition, respectively, in zebrafish skin/gills. The purpose of the present study was to test the hypothesis of whether GLUT isoforms are specifically expressed and function in ionocytes to supply energy for ion regulatory mechanisms. On the basis of translational knockdown of foxi3a/3b (2 transcriptional factors related to the ionocytes' differentiation) and triple in situ hybridization/immunocytochemistry, 3 GLUT isoforms, zglut1a, -6, and -13.1, were specifically localized in NaR/NCC cells, GR cells, and HR cells, respectively. mRNA expression of zglut1a in embryos and adult gills were stimulated by the low Ca(2+) or low Cl(-) freshwater, which has been previously reported to upregulate the functions (monitored by epithelial Ca(2+) channel, NCC mRNA) of NaR/NCC cells, respectively while that of zglut13.1 was stimulated only by low Na(+), a situation to upregulate the function (monitored by carbonic anhydrase 15a mRNA) of HR cells. On the other hand, ambient ion compositions did not affect the zglut6 mRNA expression. Taken together, zGLUT1a, -6, and 13.1, the specific transporters in NaR/NCC cells, GR cells, and HR cells, may absorb glucose into the respective cells to fulfill different physiological demands.
Tseng
Yung-Che
YC
Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei, Taiwan 11529, ROC.
Chen
Ruo-Dong
RD
Lee
Jay-Ron
JR
Liu
Sian-Tai
ST
Lee
Shyh-Jye
SJ
Hwang
Pung-Pung
PP
D000064:Acclimatization / Q000235:genetics; D000595:Amino Acid Sequence; D000825:Animal Structures / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004847:Epithelial Cells / Q000378:metabolism*; D051858:Forkhead Transcription Factors / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects / Q000235:genetics; D005786:Gene Expression Regulation; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D023061:Gene Order / Q000235:genetics; D005880:Gills / Q000166:cytology* / Q000378:metabolism; D051246:Glucose Transport Proteins, Facilitative / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007814:Larva / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry; D008969:Molecular Sequence Data; D016376:Oligonucleotides, Antisense / Q000235:genetics; D010802:Phylogeny; D020033:Protein Isoforms / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012867:Skin / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology; D015027:Zebrafish / Q000235:genetics / Q000378:metabolism*; D029961:Zebrafish Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D002712:Chlorides; D018076:DNA, Complementary; D051858:Forkhead Transcription Factors; D051246:Glucose Transport Proteins, Facilitative; D008565:Membrane Proteins; D016376:Oligonucleotides, Antisense; D020033:Protein Isoforms; D029961:Zebrafish Proteins; D012964:Sodium; D002118:Calcium