MUC21 and obesity due to melanocortin 4 receptor deficiency: The expression levels of immune-related genes (interleukin 8, il-8, also referred to as cxcl8a), microbial defense-related genes (lysozyme, lyz, interleukin 10, and il-10), and obesity-related genes (aquaporin 8a, aqp8, mucin 2.1, muc2.1, fibroblast growth factor 2, fgf2, and proopiomelanocortin a, pomca) were significantly up-regulated in zebrafish, except the down-regulated expressions of toll-like receptor-5 (tlr-5) and interleukin 1β (il-1β) in the females and pomca in the males, respectively.