The effects of 20-hydroxyecdysone on the differentiationin vitro of cells from the eye imaginal disc fromDrosophila melanogaster |
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Authors: | Chinglu Li Dr I A Meinertzhagen |
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Institution: | (1) Neuroscience Institute, Dalhousie University, B3H 4J1 Halifax, Nova Scotia, Canada;(2) Present address: Faculty of Medicine, Dalhousie University, Sir Charles Tupper Medical Building, Box 141, Halifax, Nova Scotia, Canada B3H 4H7 |
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Abstract: | We have examined the effects of the insect ecdysteroid, 20-hydroxyecdysone, on the differentiation of neuronal and non-neuronal
elements in the developing adult visual system, usingin vitro methods inDrosophila. We examined the differentiation of early neuronal markers in the presence and absence of 1 μg/ml 20-hydroxyecdysone. Immunoreactivity
to 22C10, a marker of an early neuronal antigen, as well as to the photoreceptor-specific antibody 24B10, suggests that differentiation
of neuronal and photoreceptor antigens does not require 20-hydroxyecdysone. In eye-discs cultured from animals 5 hours after
the white prepupa (P+5), ommochrome pigmentation first appeared after 2 days in 1 μg/ml 20-hydroxyecdysone, but cultures lacked
pigmentation without 20-hydroxyecdysone. Our culture conditions failed to support the formation of the second screening pigment,
drosopterins, even with 20-hydroxyecdysone. Eye discs from P+5 also formed lenses and interommatidial bristles in culture
when 20-hydroxyecdysone was added but not in cultures devoid of the hormone. The differentiation of synaptotagmin and the
elongation of extending photoreceptor neurites from eye disc fragments both occur in the absence of 20-hydroxyecdysone in
cultures, but adding the hormone increased average neurite length. The threshold for enhanced neurite length was less than
125 ng/ml 20-hydroxyecdysone. Eye-disc cultures also developed immunoreactivity to histamine, the photoreceptor transmitter,
from synthesis not re-uptake, in both the presence and in the absence of 20-hydroxyecdysone. These findings suggest that photoreceptor
axons may be able to release transmitterin vivo both when they grow into the optic lobe and during the subsequent events in synapse formation. |
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Keywords: | photoreceptor histamine synaptotagmin neurite compound eye |
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