RESUMO
The body temperatures of teleost species fluctuate following changes in the aquatic environment. As such, decreased water temperature lowers the rates of biochemical reactions and affects many physiological processes, including active transport-dependent ion absorption. Previous studies have focused on the impacts of low temperature on the plasma ion concentrations or membrane transporters in fishes. However, very few in vivo or organism-level studies have been performed to more thoroughly elucidate the process of acclimation to low temperatures. In the present study, we compared the strategies for cold acclimation between stenothermic tilapia and eurythermic goldfish. Whole-body calcium content was more prominently diminished in tilapia than in goldfish after long-term cold exposure. This difference can be attributed to alterations in the transportation parameters for Ca2+ influx, i.e., maximum velocity (Vmax ) and binding affinity (1/Km ). There was also a significant difference in the regulation of Ca2+ efflux between the two fishes. Transcript levels for Ca2+ related transporters, including the Na+/Ca2+ exchanger and epithelial Ca2+ channel, were similarly regulated in both fishes. However, upregulation of plasma membrane Ca2+ATPase expression was more pronounced in goldfish than in tilapia. In addition, enhanced Na+/K+-ATPase abundance, which provides the major driving force for ion absorption, was only detected in tilapia, while upregulated Na+/K+-ATPase activity was only detected in goldfish. Based on the results of the present study, we have found that goldfish and tilapia differentially regulate gill epithelial plasma membrane Ca2+-ATPase (PMCA) expression and Na+/K+-ATPase activity in response to cold environments. These regulatory differences are potentially linked to more effective regulation of Ca2+ influx kinetics and better maintenance of whole body calcium content in goldfish than in tilapia.
RESUMO
p150(glued) is the largest subunit of dynactin protein complex, through which cargo vesicles link to the microtubule minus-end directed motor protein dynein. In addition, p150(glued) also locates in the mother centriole where it organizes the subdistal appendage. The components of appendage are dynamically regulated throughout the cell cycle stages, but it is still unclear whether the centrosomal residency of p150(glued) correlated with cell cycle progression. Here we found that p150(glued) was located in the mother centriole during G1/S stage and its centrosomal residency was independent of microtubule transportation. However, the centrosomal p150(glued) became blurred at G2/M phase and this event was not regulated by its phosphorylation. Entering into mitosis, p150(glued) was robustly enriched in the mitotic spindle nearby the spindle poles but not in the centrosome. During serum starvation (G0 stage), p150(glued) appeared at the base of primary cilium and its depletion attenuated starvation-induced primary cilium formation. We also checked its role in the maintenance of centrosome homeostasis and configuration, and found depletion of p150(glued) did not induce centrosome amplification or splitting but inhibited U2OS cell growth. G1 arrest and reduced EdU incorporation were observed in p150(glued) deficient U2OS cells. In addition, cyclin E was downregulated following p150(glued) depletion. The p53/p21 signaling was activated indicating that CDKs were inactivated. The reduced cell growth was ameliorated in the p150(glued) depleted cells when treated with p53 inhibitor. Thus, we have identified the centrosomal targeting of p150(glued) in distinct cell cycle stage and uncovered its role in controlling G1/S transition.
