LEP and obesity due to melanocortin 4 receptor deficiency: In contrast, mice with overexpression of the protein X-box binding protein 1, which is a transcription factor for de novo uridine synthesis, exhibited high levels of circulating and adipose tissue uridine, higher energy expenditure, lower body weight, lower temperature, and protection against obesity even when on a high-fat diet or in a model of decreased leptin expression (ob gene knockout) [99].