Abstract
Simple SummaryCultured insect Sf21 cells treated with the hormone 20-hydroxyecdysone grow long processes and resemble neurons. They also make physical contact with one another and appear to have the potential to form synapses, areas in which nerve cells are in close contact and communicate with one another electrically or by the release of chemical transmitters. This study uses electron microscopy to look for structural evidence of synapses in 20-hydroxyexdysone treated Sf21 cell cultures. Unfortunately, no evidence of synaptic structures were observed, suggesting that other factors are required for the formation of functional synapses in these cultures.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. Sf21 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 Sf21 cells.
Highlights
The active metabolite of ecdysone is 20-hydroxyecdysone (20-HE), and many insect species use it as a regulator of molting and other processes, including the control of neuronal ion channel expression during development [1]
Similar effects on cell growth were observed in Sf 9 (Spodoptera frugiperda) cells treated with the insecticide methoxyfenozide, which mimics the actions of 20-HE and blocked cell proliferation and initiated cell arrest [8]
Ultrastructural analysis was performed on closely apposed cells, in order to document any membrane structures reminiscent of chemical synapses
Summary
The active metabolite of ecdysone is 20-hydroxyecdysone (20-HE), and many insect species use it as a regulator of molting and other processes, including the control of neuronal ion channel expression during development [1]. Similar effects were documented in subsequent studies with lepidopteran cell lines [3,4,5,6,7]. Subsequent studies demonstrated the expression of neuron-like pharmacological properties in 20-HE treated insect cell lines. Baculovirus expression studies, as well as virus identification and replication, have been widely documented in insect cell lines using transmission electron microscopy [15,16]. No ultrastructural information is available following 20-HE application to insect cell lines, including those documenting the stimulation of cell process growth mentioned above. We are interested in whether 20-HE treatment can induce the presence of ultrastructural markers of synaptogenesis in Sf 21 cells, the results of which are presented here
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