Direct observation of the crystallization of fat in a Drosophila fly body by small- and wide-angle X-ray scattering

Many overwintering livings accumulate fat (triacylglycerol) before winter and use it for basal metabolism. However, triacylglycerol in solid state is not digested by lipase. Therefore, it is expected that livings using fat during overwintering have some special strategies to avoid crystallization of fat at low temperatures. In order to clarify the strategies, Ohtsu et al. have studied the phase behavior of fat extracted from the cold-adapted Drosophila flies [Ohtsu, T., Katagiri, C., Kimura, M. T. & Hori, S. H. (1993). J. Biol. Chem. 268, 1830-1834]. It is, however, uncertain that the results obtained from the extracted fat can reflect the in vivo phenomena. In the present study, we investigated the crystallization of fat in a fly body with small- and wide-angle X-ray scattering, and detected the Bragg diffraction peaks that can be assigned to those originated from the solid triacylglycerol crystallized in the fly body below 253 K (- 20 ^oC).