The genes for developing cephalopod eyes are the same as those forming our legs

The squid totam, the species involved in the study. | Laptew Productions

Scientists presented the results of evolutionary analysis of genes responsible for eye formation in cephalopods. They have shown that they are present in humans, but with a totally different role.

Cephalopods are a class of molluscs that includes marine animals with tentacles such as octopus, squid or cuttlefish. Compared to vertebrates, they have evolved closely. Some of their organs such as the brain or the eyes have developed with such complexity that many scientists are still trying to understand the mechanisms behind this unique evolutionary mystery in these invertebrates.

A team of biologists presented at a meeting, the results of their study on the eyes of cephalopods, which also have a lens whose role is to do the tuning (accommodation), as in humans. This allows them to benefit from excellent vision.

The researchers worked on totam ( Doryteuthis pealeii ) squid embryos and examined which genes are responsible for the first stages of eye formation, and when and under what circumstances they activate or deactivate. After comparing with vertebrate genes, biologists have found that the genes involved in the early stages of lower limb formation are the same as those related to cephalopod eye development.

And yet the formation of these two parts of the body is not identical, and these genes play no role for the eyes of vertebrates, whose development takes place differently.

During lens formation in cephalopods, long membranes emerge to allow overlapping of eye cells and form the typical sphere of the lens, while in vertebrates, degraded cells are kept compacted by a specific protein.

The astonishment of the researchers was considerable during this discovery. To confirm this, they administered small squids of WNT, a well-known protein in developmental biology. The latter naturally stops certain processes of organ formation, including those involved in the formation of the lower limbs, by inhibiting the expression of these genes. They then found that the lens was no longer formed, proving that the genes involved in its formation are the same as those involved in the development of lower limbs in humans.

The group is continuing its research to discover other possible similarities between cephalopods and vertebrates. The next step is to understand the role of each of these genes in the formation of cephalopod eyes.


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