Photoperiodic Induction of Diapause Requires Regulated Transcription of timeless in the Larval Brain of Chymomyza costata

• Published in: Journal of biological rhythms 2008-04, Vol.23 (2), p.129-139
• Main Authors: Stehlík, J, Závodská, R, Shimada, K, Šauman, I, Koštál, V
• Format: Article
• Language: English
• Subjects: Abundance; Analysis; Animals; Biological Clocks - physiology; Brain; Chymomyza; Circadian rhythm; Circadian Rhythm - physiology; Circadian rhythms; Clock systems; Complications and side effects; Diapause; Diptera; Drosophilidae - physiology; Gene deletion; Gene mutations; Genetic aspects; Immunohistochemistry; Insect Proteins - genetics; Insect Proteins - metabolism; Instars; Larva - cytology; Larva - metabolism; Larvae; Life Cycle Stages; Mutants; Mutation; Neurons; Oscillations; Photoperiod; Polymerase chain reaction; RNA, Messenger - metabolism; Timeless protein; Transcription; Transcription, Genetic
• ISSN: 0748-7304; 1552-4531
• DOI: 10.1177/0748730407313364

Photoperiodic signal stimulates induction of larval diapause in Chymomyza costata. Larvae of NPD strain (npd-mutants) do not respond to photoperiod. Our previous results indicated that the locus npd could code for the timeless gene and its product might represent a molecular link between circadian and photoperiodic clock systems. Here we present results of tim mRNA (real time-PCR) and TIM protein (immunohistochemistry) analyses in the larval brain. TIM protein was localized in 2 neurons of each brain hemisphere of the 4-d-old 3rd instar wild-type larvae. In a marked contrast, no TIM neurons were detected in the brain of 4-day-old 3rd instar npd -mutant larvae and the level of tim transcripts was approximately 10-fold lower in the NPD than in the wild-type strain. Daily changes in tim expression and TIM presence appeared to be under photoperiodic control in the wild-type larvae. Clear daily oscillations of tim transcription were observed during the development of 3rd instars under the short-day conditions. Daily oscillations were less apparent under the long-day conditions, where a gradual increase of tim transcript abundance appeared as a prevailing trend. Analysis of the genomic structure of tim gene revealed that npd-mutants carry a 1855 bp-long deletion in the 5'-UTR region. This deletion removed the start of transcription and promoter regulatory motifs E-box and TER-box. The authors hypothesize that this mutation was responsible for dramatic reduction of tim transcription rates, disruption of circadian clock function, and disruption of photoperiodic calendar function in npd-mutant larvae of C. costata.