Period and timeless mRNA Splicing Profiles under Natural Conditions in Drosophila melanogaster

Previous analysis of Drosophila circadian behavior under natural conditions
has revealed a number of novel and unexpected features. Here we focus
on the oscillations of per and tim mRNAs and their posttranscriptional regulation
and observe significant differences in molecular cycling under laboratory
and natural conditions. In particular, robust per mRNA cycling from fly heads
is limited to the summers, whereas tim RNA cycling is observed throughout the
year. When both transcripts do cycle, their phases are similar, except for the
very warmest summer months. We also study the natural splicing profiles of
per and tim transcripts and observe a clear relationship between temperature
and splicing. In natural conditions, we confirm the relationship between accumulation
of the perspliced variant, low temperature, and the onset of the evening
component of locomotor activity, first described in laboratory conditions.
Intriguingly, in the case of tim splicing, we detect the opposite relationship,
with timspliced expression increasing at higher temperatures. A first characterization
of the 4 different TIM protein isoforms (resulting from the combination of
the natural N-terminus length polymorphism and the C-terminus alternative
splicing) using the 2-hybrid assay showed that the TIMunspliced isoforms have a
stronger affinity for CRY, but not for PER, suggesting that the tim 3′ splicing
could have physiological significance, possibly in temperature entrainment
and/or adaptation to seasonal environments