Daily Expression Patterns ofCycleandClockGenes in the Head of the Silkworm,Bombyx Mori

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

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.

Molecular structure, expression patterns, and localization of the circadian transcription modulator CYCLE in the cricket, Dianemobius nigrofasciatus

CYCLE (CYC), also known as BMAL1 in vertebrate nomenclature, is a transcription modulator of the circadian genes period and timeless of Drosophila melanogaster. We cloned a cDNA encoding a CYC homologue from the head of the ground cricket, Dianemobius nigrofasciatus (Dncyc), the first CYC from Hemimetabola. The deduced sequence corresponded to a 601 amino-acid polypeptide, with well-defined bHLH, PAS-A, PAS-B, PAC, and BTCR domains. The amino-acid sequence showed 70.7% identity with the CYC protein of Athalia rosae, 63.8% with D. melanogaster, and 52% identity with the human homologue. A cyc transcript of around 3.6kb occurs in the brain, midgut, testis, fatbody, and muscle. An additional band of around 1.1kb gave a hybridization signal in the head. No temporal oscillation in cyc mRNA abundance was observed in the head of the adult cricket when investigated by Northern blot analysis. CYC-like immunohistochemical reactivity (ir) and its dimerization partner CLOCK (CLK)-ir appeared in the pars intercerebralis (PI), tritocerebrum, dorsolateral protocerebrum, and subesophageal ganglion (SOG), but no CYC-ir was observed in the optic lobe (OL) that showed CLK-ir. The deutocerebrum showed a unique CLK-ir but no CYC-ir pattern. Double-labelling experiments showed that both antigens were co-localized in the mandibular and maxillary neuromeres of the SOG. CYC-ir showed no daily oscillation in intensity and the staining pattern was always cytoplasmic. CLK-ir occurred in the nucleus at ZT 16, but was cytoplasmic at other ZT times. A neuronal network equivalent to adult system occurred in the second nymphal stadium.