Inter and intraspecific clock gene variations in Drosophila
thesisposted on 02.09.2013, 08:42 by Shumaila Noreen
Circadian clock genes have undergone many structural and functional modifications during their evolution. Even in closely related evolutionary lineages, the circadian molecules can be variable and perform the same or different tasks. I studied three important clock genes Cryptochrome (cry), period (per) and timeless (tim) in D. melanogaster. The study of the cry L232H polymorphism revealed no difference in the distribution of the two alleles across Europe. Population cages with different initial cry allelic frequencies, nevertheless converged to a ~1:1 ratio after 16 generation, mimicking natural population frequencies. The analysis of locomotor activity in the laboratory showed a temporal difference in the phase of activity for the males and females, with female cry[superscript HH] and male cry[superscript LL] active significantly earlier than other genotypes. If this increases the probability of disassortative mating, intermediate frequencies of the two alleles might be generated. I also studied the intermolecular co-evolution between the two interacting circadian proteins TIM and PER. The individual per and tim transgenes from D. pseudoobscura in D. melanogaster mutant hosts showed more than 50% rhythmicity but very long (29h) period for per and very short period (21h) for tim. By combining them in the D. melanogaster double mutant background, the hemizygous flies showed no improvement in rhythmicity but an excellent rescue of periodicity of ~24h. This suggest that TIM and PER may form a heterospecific coevolved module that interacts more robustly with the other host clock proteins. Finally, using my transgenes and null mutants I showed that Par Domain Protein 1ε (Pdp1ε) participates in the expression of residual rhythmicity of mutants for the negative limb of the circadian clock.