DLK1 and obesity due to melanocortin 4 receptor deficiency: RA can activate the cellular retinoic acid binding protein 2 (CRABP-II)/RARγ pathway by upregulating the expression of the adipogenesis inhibitors preadipocyte factor 1 (Pref-1), SRY (sex determining region Y)-box 9 (Sox9), and Kruppel like factor 2 (KLF2) to block adipogenesis and suppress diet-induced obesity [11].