FGF19 is a fibroblast growth factor protein and hormone with mitogenic and cell survival activity. It is involved in embryonic development, cell growth, morphogenesis, bile acid synthesis, glucose and lipid metabolism, tissue repair, tumor growth and invasion. It is thought to be required for the initiation of inner ear development. FGF19 is of interest in diabetes, as administrations of systemic FGF19 in mice have shown a resulting improvement in insulin-independent glucose disposal and glucose tolerance in the brain. In immunohistochemistry, FGF19 has cytoplasmic positivity (and also stains extracellular deposits) in all tissues. References: J Clin Invest. 2013 Nov 1; 123(11): 4799–4808, PMID: 24084738; Cytokine. 11 (10): 729–35, PMID: 10525310.