Meeting Abstract
S5.5 Monday, Jan. 5 Brown adipocyte differentiation pathway in birds: an evolutionary road not taken MEZENTSEVA, Nadejda/V*; KUMARTILAKE, Jaliya; NEWMAN, Stuart; New York Medical College, Valhalla; The university of Adelaide, Adelaide, Australia; New York Medical College, Valhalla mesen2000@gmail.com
The adipose organ of mammals consists of white (WAT) and brown (BAT) adipose tissue. The main function of WAT is to store energy; in contrast, BAT dissipates energy for heat production. BAT thermogenic function is possible due to uncoupling protein 1 (UCP1). Thermogenic BAT has been considered to be an evolutionary novelty in mammals. In contrast to BAT, UCP1 is not a new gene because it is present in fish and amphibians. In both: mammals and fish, UCP1 expression is under the control of temperature. In mammalian BAT, temperature control is achieved via activation of the beta-adrenergic receptors (beta-ARs). We have demonstrated that avian brown adipocyte-like cells (ABALC) can be induced from embryonic limb bud mesenchymal cells under in vitro conditions. We have also shown that avian and lizard species lack the gene for UCP1 and, therefore, ABALC are not functional brown adipocytes. Nevertheless ABALC are generated by a developmental pathway virtually identical to brown fat differentiation in mammals. Furthermore, ABALC induction resulted in strong transcription from a transfected mouse UCP1 promoter. Treatment with beta-AR agonists activated lipolysis in ABALC. Activation of the exogenous UCP1 promoter in these cells is also under control of beta-ARs, as is the endogenous one in mammals. These findings strongly suggest that the brown fat differentiation and thermoregulation pathways evolved in a common ancestor of birds and mammals, and that its thermogenicity was lost in the avian lineage, with the degradation of UCP1, after it separated from the mammalian lineage. Since this event occurred no later than the saurian ancestor of birds and lizards, an implication of this work is that dinosaurs had neither UCP1 nor canonically thermogenic brown fat.
