Teleostean leptin was
first cloned in 2005, more than a decade after the discovery of mammalian leptin.
The reason for this delay lies in the very poor primary sequence conservation (13–25%) between
mammalian and
fish leptins. These low sequence conservations indicate a high degree of molecular
evolvability and warrant a search for different and original functions of leptin in teleosts. Indeed, new and
original insights are obtained because of the unique phylogenetic position of teleostean
fish as the
earliest vertebrates and because of their ectothermy, which means that teleosts are more
flexible in
changing their metabolism than mammals and leptin could play a role in this
flexibility. Research during
the last decade reveals that leptin is a truly pleiotropic hormone in
fish and mammals alike, with
functions among others in the regulation of food intake and body weight, development, but also in the
regulation of the stress axis and acclimation processes to for instance low oxygen levels in the water. In
this review, we provide an overview of the teleostean leptin work done in the last ten years, and
demonstrate that the power of a comparative approach leads to new insights on the origins of leptin