PTPN1 and obesity due to melanocortin 4 receptor deficiency: We next studied whether the photoperiod and/or fruit consumption directly modulated hypothalamic leptin signaling in obesity by determining the gene expression of Obrb, Socs3 and Ptp1b. Among them, only Socs3 mRNA levels were sensitive to the photoperiod, increasing its values in the SD photoperiod (Fig. 5C,D).