BSX

Energy expenditure of an organism is the result of 3 components:

• the basal metabolic rate that accounts for about 60% and is mainly determined by the weight of our muscles

• thermogenesis (10%), which is required for food digestion

• and overall physical activity (30%).

From these three parameters physical activity is obviously the most variable one. However, it is unclear which genetic and molecular factors determine our physical activity.

It was generally believed that increased body weight always goes hand in hand with reduced physical activity. In other words, reducing body weight leads to increased physical activity. However, we could show that despite reducing body weight of the ob/ob mouse by deleting BSX, locomotor activity levels were not restored (Sakkou et al, Cell Metabolism, 2007). Thus, our findings demonstrated for the first time that physical activity is at least in part genetically determined; hence, BSX was called by others the “fidgeting gene” (see Nature Highlights).

In the future, we will employ state-of-the-art techniques such as CLARITY to uncover the BSX neuronal network in the hypothalamus.