The Genetics Behind Miniature Fish: A New understanding of Body Size Control
Scientists are increasingly focused on understanding the mechanisms that control animal body size, as size profoundly impacts an organism’s lifestyle, habitat, diet, and reproduction. Recent research,led by Troyer and Arcila at the University of Michigan and Scripps Institution of Oceanography respectively,has begun too unravel the genetic basis for extreme miniaturization in gobies - small fish often found in coral reefs.
The study focused on gobies because of their remarkable size variation; some species are small enough to live their entire lives within a single head of coral, occupying a range of just two square meters. While the why of small size – the ecological advantages of fitting into tiny niches – is somewhat understood, the underlying genetics remained largely a mystery.
To investigate, researchers constructed a phylogenetic tree encompassing 162 goby species, concentrating on three groups exhibiting repeated instances of both miniaturization and larger body sizes. They employed comparative transcriptomic techniques, analyzing the RNA molecules produced from genes to determine which genes were actively “turned on” in different goby sizes. This allowed them to pinpoint genes associated with growth through differential gene expression analysis.
The research revealed that two genes, CDKN1B and ING2, were significantly upregulated – meaning their activity was increased – in miniature goby species. These genes are known to regulate and limit cell growth. Conversely,genes promoting cell multiplication and proliferation were more active in larger goby species.
CDKN1B proved especially noteworthy. This gene functions as a growth inhibitor by blocking cell division, thereby limiting overall cell proliferation. Remarkably, CDKN1B has also been shown to control body size in mammals; mice with a deleted CDKN1B gene grow to twice their normal size due to increased cell numbers.
This discovery highlights a surprising parallel between model organisms like mice and non-model species like gobies. As troyer notes, understanding these processes in “random gobies” is crucial, given the limited knowledge currently available about non-model organisms.
The findings suggest that the genetic mechanisms governing body size are deeply conserved across vertebrates, spanning millions of years of evolution. This research provides valuable insight into the basic rules of growth and size regulation in the animal kingdom.
