Year: 2011
Type: dissertation
Abstract: Circadian and photoperiodic phenomena serve to organize the temporal\npattern of various biological processes. While the former generates endogenous daily\nrhythms, the latter is related to seasonality. In Drosophila melanogaster, the gene\ntimeless (tim) encodes a cardinal component of the circadian clock and also\ncontributes to photoperiodism, which is observed as an adult reproductive diapause.\nIn this work, natural tim variants were examined for diapause across different\ntemperatures and photoperiods. The newly derived allele, ls-tim, exhibited\nconsistently higher diapause levels than the ancestral one, s-tim, implicating a putative\nadaptive advantage in the seasonal European environment and providing a perfect\nsubstrate for the recently proposed scenario of directional selection.\nTo investigate further genetic links between circadian and photoperiodic\nmechanisms, classical clock mutations and transgenes were placed on a natural\ncongenic background and assayed for locomotor activity behaviour and diapause\nresponse. Surprisingly, the results not only highlighted the importance of tim, and its\nnatural alleles, but also revealed the participation of other clock components in\ndiapause, suggesting that both daily and seasonal timers might have molecularly coevolved.\nThe phenotypic effects promoted by ls-tim arise from the protein isoform LTIM,\nwhich expresses an additional N-terminal fragment. To study the adaptive\nsignificance of the N-terminal residues, including putative phosphorylation sites, a\nnumber of mutagenized TIM constructs were generated and functionally analysed. At\nthe molecular level, it was demonstrated that both the N-terminus length and the order\nof its residues are important variables modulating the interaction dynamics between\nTIM and CRYPTOCHROME (CRY). At the behaviour level, the overall amino acid\ncomposition, rather than a particular order, appeared to be more critical for the phaseshift\nresponses. Interestingly, despite the functional importance of the N-terminus, a\ndeletion mapping analysis revealed that CRY directly binds to a protein sequence\nlocated at TIM C-terminus.
Source: Figshare
Author: João Silveira Moledo Gesto
Language: English
Subfield: Endocrine and Autonomic Systems
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W812425074