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Distribution of Circadian Clock-Related Proteins in the Cephalic Nervous System of the Silkworm, Bombyx Mori

Division of Molecular Science, Graduate School of Science and Technology, Kobe University, Japan; Institute of Entomology, Czech Academy of Sciences, eské Budjovice, Czech Republic

Elitza P. Markova

Division of Molecular Science, Graduate School of Science and Technology, Kobe University, Japan

Frantisek Sehnal

Institute of Entomology, Czech Academy of Sciences, eské Budjovice, Czech Republic

Makio Takeda

Division of Molecular Science, Graduate School of Science and Technology, 1-1 Rokkodai, Nada, Kobe 657-8501, Japanmtakeda{at}kobe-u.ac.jp

In the circadian timing systems, input pathways transmit information on the diurnal environmental changes to a core oscillator that generates signals relayed to the body periphery by output pathways. Cryptochrome (CRY) protein participates in the light perception; period (PER), Cycle (CYC), and Doubletime (DBT) proteins drive the core oscillator; and arylalkylamines are crucial for the clock output in vertebrates. Using antibodies to CRY, PER, CYC, DBT, and arylalkylamine N-acetyltransferase (aaNAT), the authors examined neuronal architecture of the circadian system in the cephalic ganglia of adult silkworms. The antibodies reacted in the cytoplasm, never in the nuclei, of specific neurons. Acluster of 4 large Ia₁ neurons in each dorsolateral protocerebrum, a pair of cells in the frontal ganglion, and nerve fibers in the corpora cardiaca and corpora allata were stained with all antibodies. The intensity of PER staining in the Ia₁ cells and in 2 to 4 adjacent small cells oscillated, being maximal late in subjective day and minimal in early night. No other oscillations were detected in any cell and with any antibody. Six small cells in close vicinity to the Ia₁ neurons coexpressed CYC-like and DBT-like, and 4 to 5 of them also coexpressed aaNATlike immunoreactivity; the PER- and CRY-like antigens were each present in separate groups of 4 cells. The CYC- and aaNAT-like antigens were further colocalized in small groups of neurons in the pars intercerebralis, at the venter of the optic tract, and in the subesophageal ganglion. Remaining antibodies reacted with similarly positioned cells in the pars intercerebralis, and the DBT antibody also reacted with the cells in the subesophageal ganglion, but antigen colocalizations were not proven. The results imply that key components of the silkworm circadian system reside in the Ia₁ neurons and that additional, hierarchically arranged oscillators contribute to overt pacemaking. The retrocerebral neurohemal organs seem to serve as outlets transmitting central neural oscillations to the hemolymph. The frontal ganglion may play an autonomous function in circadian regulations. The colocalization of aaNAT- and CYC-like antigens suggests that the enzyme is functionally linked to CYC as in vertebrates and that arylalkylamines are involved in the insect output pathway.

Key Words: circadian rhythm • PER • CYC • DBT • NAT • CRY • photoreceptor

Journal of Biological Rhythms, Vol. 19, No. 6, 466-482 (2004)
DOI: 10.1177/0748730404269153


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