Survivin Regulation of Beta-Cell Mass Expansion Figure 2. Beta cell-specific deletion of survivin. (a) Immunohistochemistry showing survivin deletion in pancreatic beta cells at P1 from RIPcre+survivinfl/fl mice (original magnification, 6400). (b) Western blots (left panel) and quantification (right panel) showing decreased expression of survivin in isolated islets from RIPcre+survivinfl/fl mice in both sexes (n = 5 per genotype). Mutant mice, white bars; controls, black bars. (c) PCR analysis of Cre-mediated recombination of the survivin locus (Dflox) in islet and mouse tail DNA. (d) Expression of survivin in the liver and kidney is unchanged. +/+, RIPcre+survivin+/+ mice; 2/2, RIPcre+survivinfl/fl mice; wt, wildtype. The data represent as means 6 SE. **, p,0.01vs control. doi:10.1371/journal.pone.0041976.g002 only about 42% beta-cell mass of that in controls and displayed glucose intolerance during IPGTTs (Fig. 3a,b). However, the female mutant mice still remained glucose tolerant despite an approximate 39% decrease in beta-cell mass (Fig. 3a,b). In both male and female mutant mice, the beta cell size and nucleus size were increased, likely as a compensatory measure (P,0.05, Fig. 3c,e,f).The total islet number was markedly decreased, mainly due to the decrease in the number of larger islets, while small islet number remained similar (P,0.05, Fig. 3d). Absence of Survivin in Beta Cells Leads to Glucose Intolerance after PDL To determine whether survivin is necessary for beta-cell expansion following PDL, we subjected female RIPcre+survivinfl/ fl and control littermates to PDL or sham operation at 2-month of age. IPGTTs were performed at day 7 after PDL or sham operation. Female mice were chosen to eliminate any confounding effects of pre-existing glucose intolerance on beta-cell expansion. The mutant mice exhibited markedly higher glucose excursion compared to controls (Fig. 4a). To further understand this process, we assessed for beta-cell function by GSIS. Insulin secretion in response to an i.p. glucose challenge was markedly compromised in the mutant mice (Fig. 4b), suggesting that glucose intolerance is due to the inadequate supply of insulin from insufficient beta-cell mass. Expansion of Beta-cell Mass is Impaired in RIPCre+Survivinfl/fl Mice after PDL To further explore the effects of survivin on beta-cell mass expansion, we examined pancreatic islet morphology after PDL. In wild-type control mice, compared to the sham operation group, beta-cell mass significantly increased by 2.3-fold in the ligated tail of pancreas at day 7 post PDL (P,0.05, Fig. 5a). The individual beta cell size and nucleus size remained similar while a 2-fold PLoS ONE | www.plosone.org 4 August 2012 | Volume 7 | Issue 8 | e41976