Isolation of a fat body factor which stimulates evagination ofGalleria mellonella wing disksin vitro.

In previous papers we have reported that wing disks ofGalleria mellonella complete tracheole migration and evagination when they are cultured in a chemically defined medium containing alpha-ecdysone. The presence of larval fat body in the culture medium greatly improved the response of the disks. We have isolated this fat body factor from culture medium. It is dialyzable, heat stable (100° C, 5 min), and insensitive to pronase digestion. The fat body factor, recovered from thin layer plates, stimulated evagination in the absence of alpha-ecdysone. Furthermore, radiochromatography studies with tritiated alpha-ecdysone and spectral analysis of the factor indicated that it was neither a metabolite of alpha-ecdysone nor an ecdysone-like molecule.