Microsatellite variation associated with prolactin expression and growth of salt-challenged tilapia.

Biologists have long argued that runs of alternating purines and pyrimidines could form alternative DNA structures, which might regulate transcription. Here, we report that simple sequence repeat polymorphisms in the tilapia prolactin 1 (prl 1) promoter are associated with differences in prl 1 gene expression and the growth response of salt-challenged fishes. Individuals homozygous for long microsatellite alleles express less prl 1 in fresh water but more prl 1 in half-seawater than fishes with other genotypes. Our work provides the first in vivo evidence that differences in microsatellite length among individuals may indeed affect gene expression and that variance in expression has concomitant physiological consequences. These results suggest that dinucleotide microsatellites represent an under-appreciated source of genetic variation for regulatory evolution.