Quantitative trait locus for body weight identified on rat chromosome 4 in inbred alcohol-preferring and -nonpreferring rats: potential implications for neuropeptide Y and corticotrophin releasing hormone 2

Abstract

The alcohol-preferring (P) and -nonpreferring (NP) rat lines were developed using bidirectional selective breeding for alcohol consumption (g/kg/day) and alcohol preference (water:ethanol ratio). During a preliminary study, we detected a difference in body weight between inbred P (iP) and inbred NP (iNP) rats that appeared to be associated with the transfer of the Chromosome 4 quantitative trait locus (QTL) seen in the P.NP and NP.P congenic strains. After the initial confirmation that iP rats displayed lower body weight when compared to iNP rats (data not shown), body weight and growth rates of each chromosome 4 reciprocal congenic rat strain (P.NP and NP.P) were measured, and their body weight was consistent with their respective donor strain phenotype, confirming that a quantitative trait locus for body weight mapped to the chromosome 4 interval. Utilizing the newly developed interval-specific congenic strains (ISCS-A and ISCS-B), the QTL interval was further narrowed identifying the following candidate genes of interest: neuropeptide Y (Npy), juxtaposed with another zinc finger gene 1 (Jazf1), corticotrophin releasing factor receptor 2 (Crfr2) and LanC lantibiotic synthetase component C-like 2 (Lancl2). These findings indicate that a biologically active variant(s) regulates body weight on rat chromosome 4 in iP and iNP rats. This QTL for body weight was successfully captured in the P.NP and NP.P congenic strains, and interval-specific congenic strains (ISCSs) were subsequently employed to fine-map the QTL interval identifying the following candidate genes of interest: Npy, Jazf1, Crfr2 and Lancl2. Both Npy and Crfr2 have been previously identified as candidate genes of interest underlying the chromosome 4 QTL for alcohol consumption in iP and iNP rats.

Figure 1

Male and female body weight at 10 weeks age in iP, iNP, P.NP, and NP.P congenic strains. The effect of the Chr 4 QTL for body weight was detected in both (A) male and (B) female rats. The transfer of the Chr 4 QTL into P.NP rats is associated with increased body weight compared to the iP line, while the transfer of the Chr 4 QTL into NP.P rats leads to decreased body weight compared to the iNP line. Significant body weight differences were also observed between P.NP and NP.P in both male and female rats. * indicates p<0.05 and bars show ± SEM.

Figure 2

The growth curves of male and female inbred and congenic rats. The growth rates were determined in both male (A) and female (B) congenic rats. These findings indicate that the growth rate of the congenics P.NP and NP.P is consistent with that of the donor strain iNP and iP, respectively. Further statistical analysis indicated that the body weight changes in the congenic rats are more significant in the male than the female rats.

Figure 3

ISCS-A and ISCS-B strains show differences in body weight compared to their respective iP background. ISCS-A and ISCS-B were generated by back crossing P. NP with iP rats. The transferred Chr 4 genomic region was confirmed by marker-assisted genotyping. Similar to the P.NP strain, the replacement of iP genomic regions with iNP genomic regions in ISCS-A rats significantly increased body weight in both female (P<0.002) and male (P<0.008) when compared to iP rats. No difference in body weight was detected in the ISCS-B rats compared to their background. The overlapping genomic region (dashed line) contains potential candidate genes. P: alcohol-preferring rat, N: alcohol-nonpreferring rat. P.NP: congenic rat in which the iNP Chr 4 QTL interval was transferred to the iP rat.