Hall Jennifer R, Short Connie E, Driedzic William R
Ocean Sciences Centre, Memorial University of Newfoundland, St John's, Newfoundland, A1C 5S7, Canada.
J Exp Biol. 2006 Nov;209(Pt 22):4490-502. doi: 10.1242/jeb.02532.
cDNAs of putative glucose transporters, GLUT4 and GLUT2, were cloned from Atlantic cod (Gadus morhua). The GLUT4 cDNA encodes a 503 amino acid and the GLUT2 cDNA a 506 amino acid protein. Phylogenetic analysis, amino acid sequence alignment, and tissue distribution support categorizing them as homologues of mammalian GLUT4 and 2. GLUT4 clusters with GLUT4s from fish and other vertebrates. It shows 84% amino acid identity to GLUT4 from coho salmon and brown trout and 65% identity with other vertebrates. It is most highly expressed in heart, strongly expressed in red and white skeletal muscle and present at lower levels in gill, gonad, intestine, and kidney. GLUT2 clusters with GLUT2 from rainbow trout and other vertebrates. It shows 75% amino acid identity with rainbow trout and 62% identity with chicken GLUT2. In Atlantic cod, GLUT2 is most highly expressed in liver with lower levels noted in intestine and kidney. Food deprivation for 2 months was used as a vehicle to monitor GLUT expression at different blood glucose levels. Starvation resulted in a decrease in blood glucose and liver glycogen that recovered following 20 days of re-feeding. GLUT4 expression in heart was decreased with starvation and increased with re-feeding. GLUT4 mRNA level in heart correlated with blood glucose. It is suggested that this relationship is related to insulin responsiveness. GLUT4 expression in white muscle increased with starvation and decreased with re-feeding. It is proposed that this is due to the necessity to maintain high levels of the glucose transporter protein in the face of starvation-associated proteolysis. GLUT2 expression in liver correlated with blood glucose, consistent with higher rates of glucose transport from liver to blood in the fed state than in the food-deprived state. Glycerol-3-phosphate dehydrogenase (GPDH) cDNA was also cloned. It encodes a 351 amino acid protein, which is 73-90% identical to GPDH from numerous other fish species. GPDH is ubiquitously expressed. Expression in heart decreased with starvation and increased with refeeding, whereas expression in liver did not change with starvation. In other studies, gene expression was monitored at nine time points from fertilization of eggs to larval development. GLUT4 is detectable in fertilized eggs and is fully expressed by the halfway to hatching point. GLUT2 is not evident at fertilization, is detectable at halfway to hatching, and fully expressed at hatching. GPDH expression was evident from fertilization.
从大西洋鳕鱼（Gadus morhua）中克隆了假定的葡萄糖转运蛋白GLUT4和GLUT2的cDNA。GLUT4 cDNA编码一个含503个氨基酸的蛋白质，GLUT2 cDNA编码一个含506个氨基酸的蛋白质。系统发育分析、氨基酸序列比对和组织分布支持将它们归类为哺乳动物GLUT4和GLUT2的同源物。GLUT4与来自鱼类和其他脊椎动物的GLUT4聚类在一起。它与银大麻哈鱼和褐鳟的GLUT4有84%的氨基酸同一性，与其他脊椎动物有65%的同一性。它在心脏中表达最高，在红肌和白肌中强烈表达，在鳃、性腺、肠道和肾脏中表达水平较低。GLUT2与虹鳟和其他脊椎动物的GLUT2聚类在一起。它与虹鳟的GLUT2有75%的氨基酸同一性，与鸡的GLUT2有62%的同一性。在大西洋鳕鱼中，GLUT2在肝脏中表达最高，在肠道和肾脏中表达水平较低。禁食2个月被用作监测不同血糖水平下GLUT表达的手段。饥饿导致血糖和肝糖原下降，再喂食20天后恢复。心脏中GLUT4的表达随饥饿而降低，随再喂食而增加。心脏中GLUT4 mRNA水平与血糖相关。提示这种关系与胰岛素反应性有关。白肌中GLUT4的表达随饥饿而增加，随再喂食而降低。推测这是由于在饥饿相关的蛋白水解情况下需要维持高水平的葡萄糖转运蛋白。肝脏中GLUT2的表达与血糖相关，这与进食状态下肝脏向血液中葡萄糖转运速率高于禁食状态一致。还克隆了甘油-3-磷酸脱氢酶（GPDH）的cDNA。它编码一个含351个氨基酸的蛋白质，与许多其他鱼类物种的GPDH有73 - 90%的同一性。GPDH在各处都有表达。心脏中的表达随饥饿而降低，随再喂食而增加，而肝脏中的表达不随饥饿而变化。在其他研究中，从卵子受精到幼体发育的九个时间点监测基因表达。GLUT4在受精卵中可检测到，到孵化中期时完全表达。GLUT2在受精时不明显，在孵化中期可检测到，在孵化时完全表达。GPDH的表达从受精时就很明显。
