GC/MS-based metabolomics analysis reveals active fatty acids biosynthesis in the Filippi's gland of the silkworm, Bombyx mori, during silk spinning.

The Filippi's gland, also called the Lyonet's gland, is in truth a pair of tiny glands that are unique to lepidopteran insects. Although the ultrastructure of the Filippi's gland has been well-understood, the specific biological function of this gland in silk spinning is still unclear. Previous studies proposed a hypothesis that this gland might synthesize and secrete some substances into the anterior silk gland (ASG) to help silk spinning. In order to identify these metabolites, a GC/MS-based metabolomics technique was introduced. A total of 59 metabolites, including fatty acids, amino acids, and sugars, were identified in glands from silkworm larvae in the feeding and silk spinning stages. Abundance and pathway analyses revealed that these metabolites had different abundances during gland development and silk spinning, which may facilitate the transport of small molecules and ions. The most interesting result is that the Filippi's gland has a very active fatty acid biosynthesis process during spinning, suggesting that it may synthesize lipids or waxes and secrete them into the ASG to promote silk spinning. This data provides instructive insight into the biological functions of Filippi's gland from both silkworms and other lepidoptera.