August 9, 2011
Guest post by Viviane Callier, Duke biology
Sea urchin embryos have a lot more variation in the genes that regulate their early development than scientists thought, a new study shows.
Because getting early development “right” is fundamental, researchers believed that organisms that deviate from the typical pattern could not survive into adulthood. They also thought there was a strong constraint on the amount of genetic variation that could exist in the genes that regulate early development.
But David Garfield, a recent graduate from biologist Greg Wray’s lab, has shown that sea urchin embryos show variable patterns of gene expression even in the earliest stages of life. Given that this early genetic variation should be harmful to a developing sea urchin, it was a mystery why the variation was not eliminated by natural selection.
The answer, Garfield says, may lie in the nature of interactions between early developmental genes. These genes do not act in isolation. They interact, forming a network of genes that regulate each other.
Garfield’s study is the first to link a gene’s place in a developmental gene network to the consequences of variation in that gene.
To study the networks, Garfield examined the correlations between the expression of genes and that of their downstream targets. He also studied how genetic variation was related to variation in the shapes of larval sea urchin skeletons.
He found that in early sea urchin development, gene interactions are typically switch-like. Genes are either turned on or off. This switch-like behavior might prevent a lot of the variation from being expressed, unless it crossed a very specific on/off genomic threshold.
These interactions, however, are in direct contrast to the interactions of genes in the mid- to late-developmental stages. In these later stages, genes respond linearly to the amount of variation, so the differences will appear in the sea urchins’ skeletons, and affect their ability to survive in the wild.
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