Can we project changes in fish abundance and distribution in response to climate?

Large-scale and long-term changes in fish abundance and distribution in response to climate change have been simulated using both statistical and process-based models. However, national and regional fisheries management requires also shorter term projections on smaller spatial scales, and these need to be validated against fisheries data. A 26-year time series of fish surveys with high spatial resolution in the North-East Atlantic provides a unique opportunity to assess the ability of models to correctly simulate the changes in fish distribution and abundance that occurred in response to climate variability and change. We use a dynamic bioclimate envelope model forced by physical-biogeochemical output from eight ocean models to simulate changes in fish abundance and distribution at scales down to a spatial resolution of 0.5°. When comparing with these simulations with annual fish survey data, we found the largest differences at the 0.5° scale. Differences between fishery model runs driven by different biogeochemical models decrease dramatically when results are aggregated to larger scales (e.g. the whole North Sea), to total catches rather than individual species or when the ensemble mean instead of individual simulations are used. Recent improvements in the fidelity of biogeochemical models translate into lower error rates in the fisheries simulations. However, predictions based on different biogeochemical models are often more similar to each other than they are to the survey data, except for some pelagic species. We conclude that model results can be used to guide fisheries management at larger spatial scales, but more caution is needed at smaller scales.

Both conditional ablation and overexpression of E2 SUMO-conjugating enzyme (UBC9) in mouse pancreatic beta cells result in impaired beta cell function

AIMS/HYPOTHESIS

Post-translational attachment of a small ubiquitin-like modifier (SUMO) to the lysine (K) residue(s) of target proteins (SUMOylation) is an evolutionary conserved regulatory mechanism. This modification has previously been demonstrated to be implicated in the control of a remarkably versatile regulatory mechanism of cellular processes. However, the exact regulatory role and biological actions of the E2 SUMO-conjugating enzyme (UBC9)-mediated SUMOylation function in pancreatic beta cells has remained elusive.

METHODS

Inducible beta cell-specific Ubc9 (also known as Ube2i) knockout (KO; Ubc9^Δbeta) and transgenic (Ubc9^Tg) mice were employed to address the impact of SUMOylation on beta cell viability and functionality. Ubc9 deficiency or overexpression was induced at 8 weeks of age using tamoxifen. To study the mechanism involved, we closely examined the regulation of the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) through SUMOylation in beta cells.

RESULTS

Upon induction of Ubc9 deficiency, Ubc9^Δbeta islets exhibited a 3.5-fold higher accumulation of reactive oxygen species (ROS) than Ubc9^f/f control islets. Islets from Ubc9^Δbeta mice also had decreased insulin content and loss of beta cell mass after tamoxifen treatment. Specifically, at day 45 after Ubc9 deletion only 40% of beta cell mass remained in Ubc9^Δbeta mice, while 90% of beta cell mass was lost by day 75. Diabetes onset was noted in some Ubc9^Δbeta mice 8 weeks after induction of Ubc9 deficiency and all mice developed diabetes by 10 weeks following tamoxifen treatment. In contrast, Ubc9^Tg beta cells displayed an increased antioxidant ability but impaired insulin secretion. Unlike Ubc9^Δbeta mice, which spontaneously developed diabetes, Ubc9^Tg mice preserved normal non-fasting blood glucose levels without developing diabetes. It was noted that SUMOylation of NRF2 promoted its nuclear expression along with enhanced transcriptional activity, thereby preventing ROS accumulation in beta cells.

CONCLUSIONS/INTERPRETATION

SUMOylation function is required to protect against oxidative stress in beta cells; this mechanism is, at least in part, carried out by the regulation of NRF2 activity to enhance ROS detoxification. Homeostatic SUMOylation is also likely to be essential for maintaining beta cell functionality.