The overwhelming majority of snails live in shells that coil to the right. But occasionally some are born with shells that turn the other way. And then there was Jeremy, the garden snail with a left-coiled shell. His struggle to find a left-coiled mate made him famous. Just before dying in 2017, he was finally paired up, leaving behind a litter that was born all right.
How Jeremy and other chiral or mirror-image snails — including a few species that are all-left — turn out like this has long baffled scientists. Studying these snails offers clues to the evolution of body plans in many animals. It also could be important for understanding why approximately 1in 10,000 people are born with a condition where their internal organs are flipped like a lefty snail’s shell.
Now scientists are turning to Crispr — the powerful
gene editing tool — to figure out why some snails turn out this way. A team in
Japan led by
Reiko Kuroda, a chemist and biologist, has successfully used the technique to manipulate a single gene responsible for shell direction in a species of great pond snail. A few years ago, Kuroda and Davison’s groups independently stumbled upon Lsdia1, a gene that might explain shell direction. But lefties had one less copy of the gene than righties, and compensated with a nearly identical gene, Lsdia2. Which one caused the handedness?
In the current study, Kuroda and Masanori Abe used Crispr to edit out the Lsdia1 gene, and then raised the resulting mutant snails. Confirming previous work, they showed that even in the first embryonic cell, genetic information started picking sides. And by the third cleavage, wh-en four cells become eight, the mutant cells were rotating in the opposite direction of what is expected. These snails grew into lefties, and so did their offspring. Without two working copies of Lsdia1, snails can survive with Lsdia2 — but their shells won’t coil to the right. As for Jeremy, Davison will be studying the lefty garden snail’s great-grand-snails for clues to what made their progenitor’s unusual coil. “We’ve got a lab full of snails, but we’re still working to understand what it was that made Jeremy a lefty,” he said. “Unfortunately, snail research doesn’t move quickly.”