A functional variant in the 5′-flanking region of the chicken serotonin transporter gene is associated with increased body weight and locomotor activity

In this study, we identified a polymorphism in the 5′-flanking region of the chicken serotonin transporter (5-HTT) gene. Sequencing analysis revealed that in comparison with the wild type variant (W), a deleted variant (D) is generated by deletion of four nucleotides (5′-AATT-3′) and a single nucleotide change (A[RIGHTWARDS ARROW]T). Using a polyacrylamide gel electrophoresis system, we found that the 360-bp DNA fragment containing the W variant with the wild type sequence 5′-AATTAATT-3′ shows intrinsic DNA curvature while the 356-bp fragment containing the D variant lacking the four base pairs AATT is not curved. Quantitative real-time RT-PCR and ELISA demonstrated that the expression of 5-HTT in D/D chickens was higher than that in W/W and W/D chickens. In addition, transient transfection experiments with CAT reporter gene constructs revealed increased 5-HTT promoter activity mediated by the D variant and a silencer activity of the W variant. Interestingly, females and males with D/D genotype showed significant greater increase in body weight from 6 weeks and 16 weeks of age, respectively, and higher body mass index (BMI). Moreover, we found that D/D chickens of both genders were physically more active than W/W and W/D chickens.