Light-sensing proteins help marine animals figure out the right phase of the moon to synchronise their reproduction


09 September – Many marine animals time their reproduction precisely with the phases of the moon. However, scientists did not know how they kept track of the lunar cycle. Now, researchers at the Institute of Molecular Biology (IMB)/Johannes Gutenberg University Mainz, Germany, and the Max Perutz Labs, Vienna, Austria/Alfred Wegener Institute and University of Oldenburg, Germany, have uncovered a major piece of this mystery by studying the marine bristle worm (Platynereis dumerilii). The key lies in a light-sensing protein called L-cryptochrome (L-Cry), which helps it to distinguish between different phases of the moon, as well as moonlight from other types of light.

Once a month, approximately five days after the night of the full moon, millions of marine bristle worms swim to the surface of the Mediterranean Sea. They come out en masse for an enormous spawning event. Everything depends on the worms spawning together at the same time, as this maximises their chances of fertilisation.

Like the bristle worm, many other marine animals such as corals, starfish, worms, turtles and fish also rely on the phases of the moon to synchronise their reproduction precisely. In the case of the bristle worm, the light of the full moon is responsible for synchronising the worms’ inner monthly clock (also known as a circalunar oscillator). But how do these animals distinguish the light of the full moon from other types of light, such as sunlight?

To answer this question, the lab of Prof. Eva Wolf (Institute of Molecular Biology [IMB] and Johannes Gutenberg University Mainz, Germany) teamed up with the lab of Prof. Kristin Tessmar-Raible (Max Perutz Labs, Vienna, Austria, and Alfred Wegener Institute and University of Oldenburg, Germany). They discovered that bristle worms synchronise their monthly clocks with the help of a light-sensing protein called L-cryptochrome (L-Cry), which is able to distinguish between different types of light, such as sunlight and moonlight.

L-Cry contains a molecule called FAD (or flavin adenine dinucleotide), which undergoes a biochemical change when exposed to light. This allows L-Cry to shift between a ‘dark state’ and a ‘light state’. Importantly, L-Cry proteins come in pairs. The researchers found that under light with same intensity and spectrum as the light of the full moon, it took about 6 hours for only one of the two L-Cry molecules to change to the light state. In contrast, under (much brighter) sunlight, both L-Cry molecules converted to the light state within minutes. This suggests that one of the two L-Cry molecules acts as a ‘low light sensor’ for moonlight, while the other acts as a ‘high light sensor’ that only responds to sunlight.  In other words, L-Cry can actually adopt three distinct molecular states: a ‘dark state’, a ‘moonlight state’ and a ‘sunlight state’.

Prof. Wolf says, “Based on these molecular properties, we see that L-Cry can act as a light interpreter that not only discriminates between darkness, sunlight and moonlight, but also between different moon phases.”  The researchers propose that during a full moon, when the moon shines for at least 6 hours, moonlight can activate the ‘low light’ L-Cry sensor, which enables the worms to adjust their monthly timing system to the correct moon phase.

These findings could have many implications beyond the reproduction of bristle worms. Prof. Tessmar-Raible says, “We think that similar mechanisms could also be used by many other organisms to discriminate between naturally-occurring light sources, which is of key importance for any organism that depends on light to adjust its physiology and behaviour. Moonlight is not just a dim version of sunlight; nocturnal versus diurnal light has very different meanings for organisms.” Moreover, the proliferation of human cities means that many animals (and humans) are now constantly exposed to artificial lights, which could disrupt natural ecosystems and pose serious threats to human health. By understanding how organisms sense and react to different types of light, the researchers hope to better understand and find ways to prevent the negative effects of artificial lights on human health and the environment.

The findings were published this week in the journal Nature Communications.

Further details

Cheryl Li is a Science Writer at the Institute of Molecular Biology.

Further information can be found at www.nature.com/articles/s41467-022-32562-z

Eva Wolf is an Adjunct Director at IMB and a Professor of Biology at Johannes Gutenberg University Mainz. Further information about research in Wolf lab can be found at www.imb.de/wolf

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