An Evolutionary Angle: “Jumping Genes” Generate Interest in Hsp Genes
Translation of heat shock proteins (Hsp) is enhanced under heat stress due to factors like decondensed chromatin and nucleosomes found in the promoter. This exposure of the promoter in turn gives easy access to P elements. P elements are a specific class of TEs that are highly clustered in the promoters and can have either forward or reverse orientation.
There could an evolutionary link between Hsp being specifically targeted by the P elements and Hsp having evolved distinctively from the genome which makes them efficient at dealing with heat stress. Hsp help fold up proteins correctly and degrade denatured proteins but mutations get exposed under stress leading to selection. TEs are powerful mutagens that alter the genome enabling selection to act. Even though mutations are mostly deleterious, P element insertion can be advantageous for Drosophila. P element insertions in Hsp have mostly resulted in decreased gene expression. This helps prevent Hsp accumulation, which can be harmful when not under heat stress, leading to positive selection for P element insertions.
Only in the last century have P elements been found in the Drosophila genome. This could be attributed to the mutation studies being done which have caused such rapid evolution. Since the generation time is very short for Drosophila, evolution can be accelerated and future generations can be tested and compared with the present.
Primary reference:
Walser, J., Chen, B., Feder, M.E., 2006, “Heat-Shock Promoters: Targets for Evolution by P Transposable Elements in Drosophila” PLoS Genetics, Vol.2, No. 10, pp. 1541-1554 Web Address: http://genetics.plosjournals.org/perlserv?request=get-document&doi=10.1371/journal.pgen.0020165
Written by: Vinisha Kapadia (41061554)
