A novel arrangement of midgut epithelium and hepatic cells implies a novel regulation of the insulin signaling pathway in long-lived millipedes

• Millipede midgut epithelial cells and hepatic cells interdigitate and exchange.
• Exosomes are observed at the midgut epithelium-hepatic cell interface.
• Nutrients from the midgut cells are stored as glycogen in hepatic cells.
• This novel arrangement of cell layers is hypothesized to represent reduced insulin signaling.
• Reduced insulin signaling extends lifespan; millipedes have long lives for arthropods.

Nutrients absorbed by the epithelial cells of the millipede midgut are channeled to a contiguous population of hepatic cells where sugars are stored as glycogen. In insects and other arthropods, however, nutrients absorbed by midgut epithelia are first passed across the epithelial basal surface to the hemolymph before storage in fat body. The inter-digitation of cellular processes at the interface of hepatic and midgut epithelial cells offers a vast surface area for exchange of nutrients. At this interface, numerous small vesicles with the dimensions of exosomes (∼30 nm) may represent the mediators of nutrient exchange. Longevity and the developmental arrest of diapause are associated with reduced insulin signaling. The long lifespans for which millipedes are known may be attributable to a novel pathway with reduced insulin signaling represented by the novel arrangement of hepatic storage cells and midgut epithelial absorbing cells.

Figure optionsDownload as PowerPoint slide