Molecular identification of glucose transporter 4: The responsiveness to starvation, glucose, insulin and glucagon on glucose transporter 4 in common carp (Cyprinus carpio L.)

Differential modulation of digestive enzymes and energy reserves at different times after feeding in juveniles of the marine estuarine-dependent flatfish Paralichthys orbignyanus (Valenciennes, 1839)

Integrative studies are lacking on the responses of digestive enzymes and energy reserves in conjunction with morphological traits at distinct postprandial times in marine estuarine-dependent flatfishes of ecological and economic importance, such as Paralichthys orbignyanus. We determined total weight (TW), hepato-somatic index (IH), activities of digestive enzymes in the intestine, and the concentration of energy reserves in the liver and the muscle at 0, 24, 72, and 360 h after feeding in juveniles of P. orbignyanus. Amylase activity decreased at 72 h (about 30%). Maltase, sucrose, and lipase activities reached peak at 24 h (67%, 600%, and 35%, respectively). Trypsin and aminopeptidase-N activities at 24 and 72 h, respectively, were lower than those at t = 0 (53% and 30%). A peak increase in the concentration of glycogen and triglycerides in the liver (24 h) (86% and 89%, respectively) occurred. In muscle, glycogen and triglyceride concentrations were unchanged at 24 h and higher at 72 and 360 h (100% and 60%). No changes were found in TW, IH, free glucose in the liver and muscle, and protein in the liver. The protein concentration in the muscle sharply increased at 24 and 360 h after feeding (60%). The results indicate a distinct and specific response of central components of carbohydrate, lipid, and protein metabolism that could be adjustments at the biochemical level upon periods of irregular feeding and even of long-term food deprivation inside coastal lagoons or estuaries. The distinct responses of digestive enzymes in the intestine and energy reserves in the liver and muscle suggest the differential modulation of tissue-specific anabolic and catabolic pathways that would allow the maintenance of physical conditions.

Chicken GLUT4 undergoes complex alternative splicing events and its expression in striated muscle changes dramatically during development

Glucose transporter protein 4 (GLUT4) plays an important role in regulating insulin-mediated glucose homeostasis in mammals. Until now, studies on GLUT4 have focused on mammals mostly, while chicken GLUT4 has been rarely investigated. In this study, chicken GLUT4 mRNA sequences were obtained by combining conventional amplification, 5'- and 3'- rapid amplification of cDNA ends technique (RACE), then bioinformatics analysis on its genomic structure, splicing pattern, subcellular localization prediction and homologous comparisons were carried out. In addition, the distribution of GLUT4 was detected by RT-qPCR in bird's liver and striated muscles (cardiac muscle, pectoralis and leg muscle) at different ages, including embryonic day 14 (E14), E19, 7-day-old (D7), D21 and D49 (n = 3-4). Results showed that chicken GLUT4 gene produced at least 14 transcripts (GenBank accession No: OP491293-OP491306) through alternative splicing and polyadenylation, which predicted encoding 12 types of amino acid (AA) sequences (with length ranged from 65 AA to 519 AA). These proteins contain typical major facilitator superfamily domain of glucose transporters with length variations, sharing a common sequence of 59 AA, and were predicted to have distinct subcellular localization. The dominant transcript (named as T1) consists of 11 exons with an open reading frame being predicted encoding 519 AA. In addition, analyzing on the spatio-temporal expression of chicken GLUT4 showed it dominantly expressed in pectoralis, leg muscles and cardiac muscle, and the mRNA level of chicken GLUT4 dramatically fluctuated with birds' development in cardiac muscle, pectoralis and leg muscles, with the level at D21 significantly higher than that at E14, E19, and D49 (P < 0.05). These data indicated that chicken GLUT4 undergoes complex alternative splicing events, and GLUT4 expression level in striated muscle was subjected to dynamic regulation with birds' development. Results indicate these isoforms may play overlapping and distinct roles in chicken.