Total RNA was extracted from mouse liver using the RNeasy kit (Qiagen). Results are expressed as the means ± standard deviation (SD) or ± standard error of the mean (SEM). Student’s t test was used for comparison between groups. P values <0.05 were considered statistically significant. Upon initial examination after hepatectomy, no gross morphologic differences were noted between wildtype and β2SP+/− mouse livers at any X-396 timepoint (Fig. 1A). At baseline, liver mass in β2SP+/− mice is greater; however, the liver mass to body weight

ratio is almost the same in β2SP+/− mice in comparison to wildtype mice (4%) (Fig. 1B). However, this ratio in β2SP+/− mice was significantly lower in comparison to wildtype mice at 48 hours post-PHx, (P < 0.05). Although β2SP+/− mice had yet to return to pre-PHx levels (Fig. 1B), the ratio was nearly identical between wildtype and β2SP+/− mice by 72 hours and at 168 hours. The continued presence of mitotic figures only in mutant mouse livers at 168 hours post-PHx suggests that there is a potential defect in termination LY2157299 of liver regeneration in β2SP+/− mice compared with wildtype mice (Fig. 1C). Immunohistochemical and protein expression analysis of pRb (Ser249/Thr252) demonstrated positive labeling

beginning at 24 hours in wildtype and mutant mice, with persistently intense labeling in mutant mice through 72 hours post-PHx. Peak labeling in wildtype mice, however, was at 48 hours (Fig. 2A,B). The reduction in the level of pRb (Ser249/Thr252) in β2SP+/− mouse at 48 hours after PHx in comparison to wildtype mice supports the alteration of G1/S checkpoint regulation.

There was no significant difference in pRb (Ser249/Thr252), proliferative cell nuclear antigen (PCNA), and pH3 (Ser10) staining between the untreated wildtype mice and β2SP+/− mice (Supporting Fig. 3). Further analysis of cyclin D1 expression found significantly elevated levels in β2SP+/− mouse livers at baseline and 24, 72, and 168 selleck screening library hours posthepatectomy and the absence of a 48-hour peak as seen in wildtype mice (Fig. 2B). These results do suggest that while quiescent hepatocytes in mutant mice respond to the mitogenic stimulus of hepatectomy, exit G0, and proceed through G1 to S phase of the cell cycle, this transition is not synchronized, as it is in wildtype mice. We demonstrated significant impairment in the expression of PCNA, cyclin A and cyclin E in β2SP+/− mouse livers in comparison to wildtype at different timepoints (Fig. 2B, Supporting Table 2). These results suggest β2SP+/− mice seemed to demonstrate accelerated DNA synthesis beginning at 24 hours, with dysregulated levels of pRb (Ser249/Thr252), cyclin D1, and cyclin A post-PHx. Wildtype mice, on the other hand, underwent synchronized G1/S-phase transition and DNA synthesis at about 48 hours.