Fto and Postnatal Growth Fto+/+, Fto+/D and FtoD/D mice. For each genotype (Fto+/+/Fto+/D/FtoD/D), n = 12/16/17 (4-week-old male), and 11/13/15 (4-week-old female); n = 14/13/ 13 (16-week-old male), and 17/25/32 (16-week-old female). (F) Bone mineral density of 16-week-old Fto+/+, Fto+/D and FtoD/D mice. The femur bone mineral densities were measured by DEXA (dual energy X-ray absorptiometry). For each genotype (Fto+/+/Fto+/D/FtoD/D), n = 14/13/13 (male); n = 17/ 25/32 (female). (G) Relative serum IGF-1 levels of 4-week-old mice. The serum IGF-1 levels were measured with ELISA. For each genotype (Fto+/+/FtoD/D), n = 7/8 (male), n = 5/6 (female). P,0.0001 (male), P = 0.0356 (female). Statistical analyses were performed by one-way ANOVA, except that unpaired t-test was used in (G). *P,0.05, **P,0.01. All values are mean 6 s.e.m. doi:10.1371/journal.pone.0014005.g003 accumulation. The FtoND mice had similar fat mass as to the controls, with a trend of slightly less fat mass in males, and more in females (Figure 8A). Here the difference in the fat mass in females was not statistically significant as in the complete knockout (possibly due to the incomplete depletion of Fto, the genetic background introduced by the Nestin-Cre transgene, or a sampling issue of individual variance). The deficit in lean mass of FtoND mice remained the same as the complete knockout (Figure 8B). Taken together, the FtoND mice had less total tissue mass than the controls (Figure 8C). When normalized to the total tissue mass, FtoND mice had relatively higher fat content (fat mass/total tissue mass %) (Figure 8D), which was more obvious in the case of females, similar to the complete knockout mice (Figure 4D). Thus, the general trend of body composition (increasing fat content) in neural-specific Fto knockout is similar to that in the complete knockout. The metabolic parameters of neural-specific Fto knockout mice are increased similarly as in the complete knockout mice The metabolic rates and food intake were also measured in 16,17-week-old male FtoN+ and FtoND mice. Similarly, when the raw VO2 and VCO2 values were compared, FtoND mice showed relatively lower O2 consumption and CO2 production rate than the control mice (Figure 9A, C), during both light and dark periods. Again, when normalized to lean mass by the simple division, the FtoND mice seemed to have relatively higher metabolic rates (Figure 9B, D). As the set of data of neural-specific knockout mice did not show a significant linear relationship to lean mass within groups (Figure S3E, F), ANCOVA analyses could not be applied here. FtoND mice also had similar food consumption as of FtoN+ mice during a period of 72 hours (Figure 9E), and appeared to have consumed more food when normalized to the lean mass (Figure 9F). Discussion We report here the analysis of two mouse models of Fto deficiencies. The whole body deletion of Fto resulted in postnatal growth retardation manifested as reduced body weight and length, lower bone mineral density and lower serum IGF-1 levels, but did not affect fat accumulation when fed on either normal or high fat diet. Interestingly, the deletion of Fto in the nervous system resulted in the similar growth retardation phenotypes as the whole Figure 4. Fto knockout mice do not display a lean phenotype. (A, B, C) Lean mass (A), fat mass (B) and total tissue mass (C) of 16-week-old mice of each genotype. (D) Body composition (fat mass/total tissue mass %) of 16-week-old mice of each genotype. P = 0.35(male), and P,0.0001(female). In (A)–(D), all mice were fed on normal chow after weaning at 3-week-old and were 16-week-old at the time of DEXA (dual energy X-ray absorptiometry) measurement. For each genotype (Fto+/+/Fto+/D/FtoD/D), n = 14/13/13 (male), 17/25/32 (female). Statistical analyses were performed by one-way ANOVA. **P,0.01. All values are mean 6 s.e.m. doi:10.1371/journal.pone.0014005.g004 PLoS ONE | www.plosone.org 6 November 2010 | Volume 5 | Issue 11 | e14005