Big dogs, little dogs...

Dogs, interestingly enough, show greater size variation than any other terrestrial mammal. Last week in Science, Sutter et al. reported finding the locus controlling size variation among dogs. A single allele (with a single nucleotide difference from large dogs) at the IGF1 locus is found in all small dogs (but probably not Sarah, at right). IGF1 produces an insulin-like growth factor and is linked to size mice and humans. Presumably, if you knock out IGF1 function, you will get a dog no bigger than a large rodent. Although Sutter et al. didn't speculate as such, I will boldly predict that this locus is pleiotropic (i.e. one gene, many functions). My guess is that IGF1 also functions as a Yap repressor. In the absence of IGF1, the Yap pathway is active and much yapping ensues. For want of a Yap repressor, those very small friends of ours have an unfortunate tendency to yap incessantly.