Abstract
Photoperiodic system consists of several functional units: (I) photoreceptor, (II) circadian/photoperiodic clock, (III) photoperiodic counter and (IV) endocrine switch. To tweeze out these subunits in Antheraea pernyi, we used the probes for the following targets: (1) neurotransmitters, (2) neurotransmitter receptors, (3) neurotransmitter enzymes and (4) circadian clock gene products. We also followed dynamics of these transmitters, the receptor transcripts, clock gene products, cyclic nucleotides, ecdysteroid titer and neurotransmitter enzyme activities.
The results showed; (1) PER- and DBT-expressing cells were identical. These seem to be the circadian clock cells in Antheraea. (2) These cells express melatonin synthesizing penultimate enzyme, arylalkylamine N-acetyltransferase (NAT). (3) These cells also express ultimate melatonin synthesizing enzyme, hydroxyindol O-methytransferase (HIOMP) and melatonin itself. (4) Melatonin content and NAT activity in the brain fluctuated in a circadian manner. These data suggest that melatonin is the output signal mediator of the photoperiodic/circadian clock in Antheraea. (5) Dynamics of neurotransmitter monoamines showed parallel change to the fate of development. Catecolamines decreased, while 5HT increased as diapause was being terminated either by chilling or long days. NAT activity increased when the brain was activated both by long days and low temperature. This means that regulation of NAT activity could function as the photoperiodic counter. (6) PER-expressing cells and PTTH-producing cells juxtapose to each other and the cell expressing 5HT receptor (5HTR)-like IHC reactivity also is located in this vicinity and IHC reactivity against human melatonin receptor, MT2 is also shown in the PTTH cells, which suggests that melatonin could function as a neuroendocrine switch mechanism, binding to this 5HT receptor. Thus NAT-indolamine pathway constitutes the core mechanism for photoperiodism in Antheraea pupae. A tentative synthesis for current knowledge was proposed.
