Sei1 in Cancer and Diabetes Figure 7. Glucose homeostasis in Sei1-null mice. (A) Blood glucose levels were measured in groups of at least 4 male mice with the indicated genotypes maintained under ad libitum feeding. (B) Glucose tolerance test (GTT) on male mice (n = 8 per genotype), of 8 weeks of age. The area under the curve (AUC) for each genotype is represented to the right. (C) Insulin release test (IR) and its AUC performed in the same mice as in B (one week after the GTT). Values correspond to the average and s.d. Statistical differences were determined by the Student’s t-test; *p,0.05; **p,0.01; and ***p,0.001. doi:10.1371/journal.pone.0008744.g007 mice showed a significant reduction in the number of pancreatic islets (Fig. 8B), as well as, a decrease of approximately 50% in b- cell area (Fig. 8C). The reduction in b-cell surface observed in Sei1-null mice was of intermediate magnitude when compared with the severe defect characteristic of Cdk4-null mice (Fig. 8C). Sei1-null islets presented a normal architecture, with a-cells predominantly located at the periphery of the islet and b-cells in the core (see below Fig. 8F). In an effort to understand the mechanisms that lead to decreased b-cell surface in the absence of Sei1, we measured apoptosis and proliferation by TUNEL and Ki67 immunohistochemistry, respectively, however the number of positive islet cells for both markers was very low (,1%) and quantifications could not detect significant differences between wt and Sei1-null islets (data not shown). In an alternative approach, immunohistochemical detection of the cell cycle inhibitors p21Cip1 and p27Kip1 revealed higher levels of positive nuclei in Sei1-null pancreatic islets compared to wt islets (Fig. 8D–F). Interestingly, the mRNA levels of p21Cip1 and p27Kip1 were similar in the islets, as were the protein levels of p53 and p27Kip1 (Supp. Fig. S5). These observations suggest that the increase in nuclei positive for p21Cip1 and p27Kip1 is due to an altered balance in the subcellular localization of these proteins. From these data, we conclude that Sei1 plays a relevant role in the maintenance and function of pancreatic b-cells. Absence of Sei1 results in higher levels of the cell cycle inhibitors p21Cip1 and p27Kip1, reduced b-cell area, decreased insulin secretion and, consequently, glucose intolerance. PLoS ONE | www.plosone.org 7 January 2010 | Volume 5 | Issue 1 | e8744