//
you're reading...

Biology

Candidate compass genes in fish

Fitak, R.R., B.R. Wheeler, D.A Ernst, K.J. Lohmann, and S. Johnsen. 2017. Candidate genes mediating magnetoreception in rainbow trout (Oncorhynchus mykiss). Biology Letters. 13: 20170142. http://dx.doi.org/10.1098/rsbl.2017.0142

Many migrating animals are able to sense the Earth’s magnetic field.

Many animals, like homing pigeons and bats, have internal compasses that detect the Earth’s magnetic field. This six sense of magnetoreception is important in orientation and navigation, and provides information about an animal’s altitude, direction, and/or location. Experiments have shown that this sense is particularly on cloudy days and nights, when animals can’t use the Sun or stars to navigate.

But while we’ve known about magnetoreception for a long time, the molecular and cellular mechanisms responsible for sensing magnetism remain mysterious. How does a biological system detect a magnetic field? Researchers from Duke University and the University of North Carolina Chapel Hill used a shotgun approach (RNA-seq) to identify genes potentially involved in magnetoreception in rainbow trout (Oncorhynchus mykiss), a migratory salmonid known to sense magnetic stimuli.

Animal magnetism

The aurora is caused by the Earth’s magnetic field interacting with solar wind from the Sun [Flickr].

The single biggest issue in the study of magnetoreception is that a sensory receptor has yet to be conclusively identified. We know that exposing some animals to strong magnetic field disrupts their ability to navigate. But what proteins or cellular structures react to magnetism, and what part of the brain is responsible for processing that information?

Most studies have focused on two potential mechanisms: chemical magnetoreception, where the magnetic field affects the biochemistry of the cryptochrome protein, and magnetite-based receptors, which contain metals that interact with the Earth’s magnetic field directly, and then convey that information to the nervous system (similar to how vibrations in the air are transduced by hair cells to provide information that the auditory system interprets as sound).

One of the difficulties in investigating the validity of these proposed mechanisms is that the magnetoreception system probably requires only very small amounts of magnetic material. Locating this tiny amount of magnetism is like finding a needle in a haystack.

Spying on intracellular messages

The central dogma of molecular biology: DNA is transcribed into RNA, which is used to create proteins [Flickr]

How do you find a needle in a haystack when you’re not entirely sure what that needle looks like? Fitak et al. took a shotgun approach: they exposed rainbow trout to a strong magnetic field, and then compared any and all changes in RNA between these pulsed fish and unexposed fish.

RNAs are key molecules for communication within a cell. Messenger RNA is formed when small sections of DNA are transcribed. Unlike DNA, this RNA is able to leave the protective shell of nucleus, and give the rest of the cell instructions for synthesizing proteins. Proteins are the workhorses of a cell, and are involved in everything a cell does, including metabolism, immunity, growth, and reproduction. There are many other kinds of RNA in the cell, and pinning down each of their functions is an area of active research.

By categorizing which RNAs are present in a cell, researchers can intercept the orders sent by the nucleus and make inferences about which genes were activated (or inactivated) by a magnetic stimulus. Categorizing these RNAs allows researchers to guess which metabolic pathways and proteins are important in sensing and responding to magnetic fields.

Genes that respond to a magnetic pulse

Broad view of the Earth’s magnetic field [Wikimedia].

A total of 181 genes significantly increased or decreased in expression when fish when exposed to a magnetic pulse compared to unexposed fish. These genes included clusters of genes thought to be involved in iron regulation and magnetoreception as well as genes associated with photosensitive structures like the retina in the eye.

The researchers noted the eighteen of the nineteen (95%) of ferritin-coding genes increased in expression with exposure to a magnetic pulse. Ferritin is a protein that isolates excess iron in cells and stores it to prevent oxidative damage. The team reasoned that perhaps the magnetic pulse allowed the stored iron to break free from the ferritin, causing the cells to respond by increasing ferritin levels to soak up the excess iron. Along the same lines, the expression of genes involved in protecting cells from oxidative damage caused by free iron also increased with a magnetic pulse. The strong activation of these systems suggests ferritin might be involved in the maintenance of iron-based magnetoreceptors after a strong magnetic pulse.

Two magnets repelling each other, with their magnetic fields visible [Wikimedia].

Several genes associated with light-sensing structures and pathways were also differentially expressed between pulsed and unpulsed fish. Interestingly, there were no differences in the expression of cryptochromes, the proteins hypothesized to be involved in chemical magnetoreception. Why a magnetic pulse affected these light-sensitive genes is unclear, but perhaps the magnetoreception and visual systems are closely associated, either in physical space or by using some of the same cellular machinery.

Sensing magnetic fields

Rainbow trout migrate between freshwater streams and the ocean during their life cycle [Flickr].

This study was the first to use a broad-based approach (testing the expression of all genes, instead of picking a few likely to show changes) to ask questions about magnetoreception in animals. By looking at the whole-cell response to a magnetic pulse, the researchers identified candidate genes, such as those controlling the ferritin protein and some aspects of the visual system, as potentially important in helping trout sense magnetic fields. Further studies can use these candidate genes as a starting point to figure out exactly how some animals are able to sense magnetic fields.

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 5 days ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 2 weeks ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 3 weeks ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 1 month ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 3 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 3 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 4 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 4 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 5 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 5 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 6 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 6 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
  • by oceanbites 7 months ago
    Feeling a bit flattened by the week? So are these summer flounder larvae. Fun fact: flounder larvae start out with their eyes set like normal fish, but as they grow one of their eyes migrates to meet the other and
  • by oceanbites 7 months ago
    Have you seen a remote working setup like this? This is a photo from one of our Oceanbites team members Anne Hartwell. “A view from inside the control can of an underwater robot we used to explore the deep parts
  • by oceanbites 8 months ago
    Today is the day of  #shutdownacademia  and  #shutdownstem  and many of us at the Oceanbites team are taking the day to plan solid actions for how we can make our organization and the institutions we work at a better place
  • by oceanbites 8 months ago
    Black lives matter. The recent murders of Ahmaud Arbery, Breonna Taylor, and George Floyd have once again brought to light the racism in our country. All of us at Oceanbites stand with our Black colleagues, friends, readers, and family. The
WP2Social Auto Publish Powered By : XYZScripts.com