Chemical Treatments for Insect Cell Differentiation: The Effects of 20-Hydroxyecdysone and Veratridine on Cultured Spodoptera frugiperda ( Sf 21) Insect Cell Ultrastructure.

Previous studies have shown that insect cell cultures stop dividing, form clumps, and can be induced to grow processes reminiscent of axons, when the culture medium is supplemented with 20-hydroxyecdysone, insulin, or an agent that mimics their action, such as the ecdysone agonist, methoxyfenozide. Those cell growing processes resemble nerve cells, and the present study evaluates the ultrastructure of these cultures by transmission electron microscopy. Sf 21 cells treated with 20-hydroxyecdysone (with or without veratridine amendment) and subjected to ultrastructural analysis had a similar somatic appearance to control cells, with slight changes in organelles and organization, such as a greater number of cytoplasmic vacuoles and mitochondrial granules. Finger-like projections were observed between control and treated cells. However, no structural markers of synaptic contacts (e.g., vesicles or synaptic thickenings) were observed in controls, 20-hydroxyecdysone, or 20-hydroxyecdysone + veratridine treated cells. It is concluded that additional agents would be required to induce functional synaptogenesis in Sf 21 cells.