Sei1 in Cancer and Diabetes Figure 6. Cancer susceptibility in Sei1-null mice. (A) Spontaneous cancer incidence and spectrum in old moribund mice (n = 15 for wt mice, and n = 26 for Sei1-null mice). Presence and type of cancer was determined upon detailed histopathological analyses by one of the authors (J.M.F.). Fisher’s exact test was used to determine statistical differences in total cancer incidence. (B) Latency of fibrosarcoma development after intramuscular injection with 3MC represented by Kaplan-Meier curves (n = 16 for wt mice, and n = 13 for Sei1-null mice). Statistical analysis was performed using the Logrank test. (C) Papilloma latency, incidence and size after DMBA/TPA tumorigenesis in mice of the indicated genotypes (n = 14 per genotype). Bars correspond to the s.d. of the average number of total papillomas per mouse. Student’s t-test was used to compare the two genotypes but no significant differences were found. doi:10.1371/journal.pone.0008744.g006 performed a classical skin carcinogenesis protocol based on initiation by DMBA and promotion by TPA. Again, Sei1-null mice developed papillomas with similar kinetics and incidence as wt mice (Fig. 6C). No significant differences could be observed between the number of papillomas or their size; also no conversion to carcinoma was observed in any genotype during the 34 weeks of observation. In summary, Sei1-ablation does not seem to have a major effect on the development of spontaneous or chemically- induced tumors in mice. Defective Pancreatic b-Cell Function in Sei1-Deficient Mice Genetic ablation of Cdk4 activity, cyclin D2, or combined E2f1 and E2f2, results in defective maintenance of adult pancreatic b- cells, eventually resulting in severe diabetes [5–7]. Considering the implication of Sei1 in the positive regulation of the above- mentioned set of proteins (see Introduction), we wondered whether Sei1-null mice could have mild, but detectable, defects in pancreatic islets. For this, we first measured blood glucose levels of wt, Sei1-het and Sei1-null mice during the first months of life, but no significant differences were observed in basal glycemia under conditions of ad libitum feeding (Fig. 7A). Interestingly, when subjected to the glucose tolerance test, Sei1-deficient mice showed a poorer clearance of glucose from blood compared to wt mice, both under standard diet (Fig. 7B) or under high fat diet (Supp. Fig. S4A). When insulin release was measured after injection of glucose, Sei1-null mice showed a dramatically impaired secretion of insulin to the bloodstream (Fig. 7C). Finally, sensitivity to insulin was not altered in the absence of Sei1 (Supp. Fig. S4B). Together, the above data point towards a specific defect in pancreatic b-cell function in Sei1-null mice. To further reinforce a role of Sei1 in b-cells, we evaluated the expression of Sei1, Sertad2 and Sertad3 in isolated pancreatic islets (being Sertad2 the closest paralog of Sei1). Interestingly, the mRNA levels of Sei1, Sertad2 and Sertad3 were similar in wt islets, and no compensatory changes in Sertad2 or Sertad3 were observed in Sei1-null islets (Fig. 8A). As a control for the isolation of islets, we detected the transcript for Kir6.2 (also known as Kcnj11), which is expressed in the islets but not in the exocrine pancreas [24] and no changes were observed associated to the status of Sei1 (Fig. 8A). Of note, compared with a large set of tissues (a total of 17 tissues), islets presented the highest levels of Sei1 expression (Suppl. Fig. S1). Moreover, the ratio between the levels of Sei1 and Sertad2 mRNAs was also maximal in the islets (Suppl. Fig. S1). Therefore, it can be concluded that the levels of Sei1 in islets are uniquely high. In recent years, it has been established that Cdk4/cyclinD2 plays an important role in the maintenance of b-cells noticeable after 3 months of age [5–7]. We wondered whether Sei1-null mice could have a similar defect. We measured the size of the pancreatic islets in 4- to 6-months old mice of wt, Sei1-null and Cdk4-null genotypes. Interestingly, pancreatic islets of Sei1-null PLoS ONE | www.plosone.org 6 January 2010 | Volume 5 | Issue 1 | e8744