SP1 and obesity due to melanocortin 4 receptor deficiency: In humans, it has been shown that Sp3 (encoded by an mammalian orthologue of sp3a) and Sp1 can have synergistic or opposite regulatory effects on transcription, while binding to the same regulatory element upstream of genes playing a role in lipid metabolism and the pathogenesis of obesity in adipose tissues (Barth et al. 2003; Hoffmann et al. 2013).