Evantal, N. | bioRxiv Science

bioRxiv2018

Thermosensitive alternative splicing senses and mediates temperature adaptation in Drosophila

Circadian rhythms are generated by the cyclic transcription, translation and degradation of clock genes, including timeless (tim). Currently, little is known about the mechanisms by which the circadian clock senses and adapts to temperature changes. Here we show that temperature dramatically changes the splicing pattern of tim. We found that at 18{degrees}C TIM protein levels are diminished due to the induction of two cold-specific splicing isoforms (tim-cold and tim-short&cold). At 29{degrees}C, another isoform, tim-Medium is strongly upregulated. We found that this isoform switching mechanism allows flies to regulate the levels and activity of TIM by setting miRNA-dependent thresholds for expression as well as by expressing isoforms with specific functions. Flies in which the production of tim-short&cold is abrogated display altered patterns of locomotor activity and altered tim expression. Interestingly, the introns of tim carry the information for the temperature sensitivity, suggesting that tim splicing per se is the temperature sensor.

neuroscience↗

bioRxiv2018

PSI controls tim splicing and circadian period in Drosophila

The Drosophila circadian pacemaker consists of transcriptional feedback loops subjected to both post-transcriptional and post-translational regulation. While post-translational regulatory mechanisms have been studied in detail, much less is known about circadian post-transcriptional control. To have a better understanding of the role and mechanisms of circadian post-transcriptional regulation, we targeted 364 RNA binding and RNA associated proteins with RNA interference. Among the 43 genes we identified was the alternative splicing regulator P-element somatic inhibitor (PSI). PSI downregulation shortens the period of circadian rhythms both in the brain and in peripheral tissues. Interestingly, we found that PSI regulates the thermosensitive alternative splicing of timeless (tim), promoting splicing events favored at warm temperature over those increased at cold temperature. Moreover, the period of circadian behavior was insensitive to PSI downregulation when flies could produce functional TIM proteins only from a transgene that cannot form the thermosensitive splicing isoforms. Therefore, we conclude that PSI regulates the period of Drosophila circadian rhythms through its modulation of the tim splicing pattern.

neuroscience↗