Study on the neural mechanisms fix insect photoperiodism: from the photoreceptor to the effecter

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The present study aims to clarify the photoreceptor, photoperiodic clock and effecter system for photoperiodism in the bean bug Riptortus pedestris and the blow fly Protophormia terraenovae.In R. pedestris, we examined the projection from the ommatidia in the central part of the compound eye, which had been shown to be important in photoperiodic photoreception, to the brain, and then identified two kinds of neurons terminating in the retrocerebral complex including corpus allatum, the endocrine effecter of the photoperiodism. Selective ablation of these neurons showed that neurons in the pars lateralis are important in the photoperiodism. Moreover, both of the two groups of neurons in the pars lateralis are involved in the photoperiodism. In P. terraenovae, we described the morphology of circadian clock neurons in the brain, and found synaptic connection between circadian clock neurons and the pars lateralis neurons; the latter have been shown to be important in photoperiodism of this … More species also. From the results of ablation experiments, we suggest the involvement of the circadian clock neurons in photoperiodism. This is the first finding in the neuron level that shows the involvement of the circadian clock neurons in photoperiodism.In R. pedestris, we identified four circadian clock genes, period, cycle, vrille and cryptochrome2. However, there were no distinctive daily fluctuations in the expression of these genes, and no difference between the photoperiodic conditions. In P. terraenovae, two .circadian clock genes, period and timeless showed similar daily fluctuation in the expression, but no photoperiodic difference between the photoperiodic conditions. It has been proposed based on the experimental result obtained in other insect species that the expression pattern of circadian clock genes plays an important role in photoperiodism. However, this is not plausible in these two species, and we have to examine other mechanisms for molecular mechanisms in photoperiodism. Less