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Figure 1. CUL4B deficiency in pancreatic δ cells impairs glucose metabolism. (A and B)Western blots and quantitative data for CUL4A and CUL4B protein levels in islets from 12-week-old diabetic db/db mice and their heterozygous littermates (db/+). n = 6 mice per group. Representative Western blots from at least 3 independent experiments are shown. (C) Immunostaining for CUL4B (green) and somatostatin (SST, red) in pancreatic sections from db/db and db/+ mice. Scale bar: 100 μm. n = 6 mice per group; 4-7 random areas were selected from each islet section, and 10 sections were randomly selected from each mouse. Insulininduced decreases in blood glucose levels were significantly lower in Sst-Cre +/-Cul4b fl/Y mice than in their WT littermates, and they did not return to baseline levels at the 2-hour time point, whereas the levels of their WT littermates did (n = 9-11). *P < 0.05; **P < 0.01; ***P < 0.001. db/db mice were compared with their db/+ littermates, and Sst-Cre +/-Cul4b fl/Y mice were compared with their WT littermates. Error bars in F represent mean ± SD; other bars represent mean ± SEM. All data were analyzed using 1-way ANOVA. The Journal of Clinical Investigation R E S E A R C H A R T I C L E2 6 3 3 jci.orgVolume 127 Number 7 July 2017mental Figure 1E). Immunofluorescence also showed no significant differences in islet or β or δ cell numbers between +/-mice, the knockout mice exhibited increased glucose levels after 2 hours of feeding following a 16-hour fast ( Figure 1G). Accordingly, during a glucose tolerance test, the blood glucose levels of Sst-Cre +/-Cul4b fl/Y mice were 33% and 30% higher at 30 minutes and 120 minutes, respectively, than those of the control group consisting of both Sst-Cre +/-and Cul4b fl/Y mice ( Figure 1H). In addition, during the insulin tolerance test, the blood glucose levels of Sst-Cre +/-Cul4b fl/Y mice unexpectedly decreased more dramatically and rapidly than those of the Sst-Cre +/-control mice in response to insulin stimulation ( Figure 1I). Insulin and somatostatin content as well as kidney, brain, heart, liver, and stomach weights were not found to be significantly different between the mice was 140% and 40% higher than that of Sst-Cre +/-mice at 5 minutes and 60 minutes, respectively ( Figure 2H). In contrast to the results found for the Sst-Cre +/-Cul4b fl/Y mice, CUL4B defistrated that CRL4 ubiquitinates WD repeat-containing protein 5 (WDR5), a core subunit of H3K4 methyltransferase complexes, for degradation in the nucleus, thereby promoting increased H3K4 methylation levels (30). However, whether CUL4B or its E3 ligase complex CRL4B-PRC2 participates in the functioning or development of Langerhans islets has not been studied. In this study, we found that CUL4B expression levels are decreased in db/db mice. Therefore, we crossed mice expressing Cre under the insulin II promotor (Ins2-Cre) and mice expressing Cre under the somatostatin promoter (Sst-Cre) with Cul4b fl/fl mice to characterize CUL4B functions in specific cell types of the islet circuit. Although In...

Abstract. In this paper, we propose the use of machine learning techniques operating on sets of student solutions in order to automatically infer structure on these spaces. Feedback opportunities can then be derived from the clustered data. A validation of the approach based on data from a programming course confirmed the feasibility of the approach.

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