“Ultimately this work shows the power of studying diverse systems,” Koenig said. The lab plans to keep studying these genes and compare their function in lens development to their function in the development of other morphological features. This is what led the scientists to believe that differences in how WNT signaling acts on these genes may be important for how the squid controls gene expression in the limb versus the lens. They ran the experiment on squid embryos and found that over-activating this pathway resulted in loss of the eye lens. The researchers wondered how a group of genes important for leg development made the eye lens and what the WNT signaling pathway was doing in lens development. In fruit flies, it is the pathway known for igniting the genes that lead to limb development. Researchers got a better idea of the role these genes play in squid eye development by manipulating a cellular path called the WNT signaling pathway. McCulloch, a postdoctoral fellow in the Koenig lab and lead author on the study. “Our finding breaks down the idea that the network evolved solely for ‘limb outgrowth’ function, but rather serves a broader function for any sort of patterning requiring this concentric-circle-like motif, including limbs, lens, tooth growth, and potentially others we have yet to identify,” said Kyle J. Limbs and eye lenses, for instance, start out as a flat sheet of cells that becomes patterned into concentric circles, a bullseye-like design, and develops from there to their final forms. These other developmental functions could include precise gene expression that places the right types, numbers, and shapes of cells in the right place at the right time. The scientists from the Koenig lab theorize that the network of genes they discovered in squid may not be important for creating specific organs, but they may be doing something more generic that is useful for certain developmental functions, including both limb and lens development. What this work implies is that you have to take the tools that you have and use them for new purposes.” They had to make a lens from scratch to be able to see really well. The squid lens is a novelty to their lineage. “One of the big questions in biology is how do you make novel. “This was pretty shocking because very few people think that an eye lens is very much like a leg,” said Kristen Koenig, a John Harvard Distinguished Science Fellow and senior author of the study. They also provide an innovative example of how different animal lineages can skillfully hijack the genetic tools in their arsenal and adapt them to accomplish surprising evolutionary feats. The results could help researchers understand how these genes and the cellular pathways they are known to work on truly function in both cephalopods and vertebrates. The scientists say these genes have been repurposed in squid to make camera-lens-type eyes. The researchers from the FAS Center for Systems Biology discovered a network of genes important in squid eye development that are known to also play a crucial role in limb development across animals, including vertebrates and insects. In research published this week in BMC Biology, a Harvard lab moves closer to unraveling the mystery. The similarity has had scientists wondering for decades how squid and their cousins get their eyes. Even so, the two lineages independently evolved camera-lens-style eyes with very similar features: a single lens in the front and a cup-shaped, image-sensing retina in the back. In fact, a squid is more closely related to a clam than it is a to a person. The last common ancestor of cephalopods and vertebrates existed more than 500 million years ago.
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