Illuminating research sheds new light on the evolution of light-response systems

Date:
February 11, 2022
Source:
University of Tsukuba
Summary:
Researchers found that sea urchin larvae exhibited ciliary responses
to strong photoirradiation by swimming backward. As ciliary
responses are difficult to detect in deuterostomes because they
may be masked by more obvious muscular activities, identifying
cilia-based responses to light in sea urchins provides key
information on the evolution and diversification of light-response
systems in macroscopic animals.



FULL STORY ========================================================================== Light is essential for most life on Earth, and single-celled or small multicellular organisms were most likely first to develop the ability
to respond to light. But now, researchers from Japan have identified interesting behavior in sea urchin larvae that may provide insights
into the evolution of light-responsive tissues/organelles in macroscopic animals.


==========================================================================
In a study published this month in PLOS Genetics, researchers from
the University of Tsukuba have revealed that sea urchin larvae reverse
their swimming direction when exposed to strong photoirradiation (light) because of the impact of light on the neuron pathways that typically
make them swim forward.

Light-response systems usually involve a combination of photoreceptors
(cells in the retina that respond to light), nervous system components,
and organs that respond to nerve impulses. These organs tend to be
muscles in most macroscopic animals, and cilia (hair-like structures)
play a role in microscopic aquatic organisms. The cilia-based response
probably developed first, before being replaced by muscle-based responses during the evolution of deuterostomes, or more complex animals. However, ciliary responses are so subtle that they are difficult to identify.

"Cilia-based responses to light are poorly understood in deuterostomes, possibly because muscle activities are more obvious than ciliary
activity," explains lead author of the study, Professor Shunsuke
Yaguchi. "Sea urchins have free-living planktonic larvae that mainly
move using cilia rather than muscles, so they offer a rare opportunity
to investigate the presence and mechanisms of cilia-based responses in deuterostomes." To do this, the researchers used a strong light source
to irradiate larvae from different species of sea urchins in dishes of
seawater and observed their behavior using a microscope. Before exposure
to the light, the larvae had stayed mainly at the surface of the water.

"The results were intriguing," says Professor Yaguchi. "The larvae dropped
from the surface immediately, and some of them swam backward. We observed similar behavior in several species, suggesting that the response is
common among sea urchin groups." To visualize and quantify the behavior,
the researchers added diatoms, or single-celled algae, to the dishes. The movements of these diatoms reflect the water current changes caused by
ciliary beating from the larvae, indicating that ciliary responses are
present and functional in sea urchins.

Given that cilia are present on tissue cells and facilitate key functions
in most organisms, including humans, the identification of this ciliary response in sea urchins may be key in understanding the mechanisms
of human behavior or feelings in response to light. Revealing these
signaling pathways in sea urchins thus sheds new light on the evolution
and diversification of light- response systems.

The article, "Planktonic sea urchin larvae change their swimming direction
in response to strong photoirradiation," was published in PLOS Genetics.

This work is supported, in part, by JST PRESTO Grant number JPMJPR194C,
the Toray Science Foundation and Takeda Science Foundation to S.Y., and
JSPS KAKENHI Grant number JP19K16199 to J.Y. H.S. was a JSPS Research
Fellow with research grant (DC1: 19J20629).

========================================================================== Story Source: Materials provided by University_of_Tsukuba. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Shunsuke Yaguchi, Yuri Taniguchi, Haruka Suzuki, Mai Kamata, Junko
Yaguchi. Planktonic sea urchin larvae change their swimming
direction in response to strong photoirradiation. PLOS Genetics,
2022; 18 (2): e1010033 DOI: 10.1371/journal.pgen.1010033 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220210154152.htm

--- up 9 weeks, 6 days, 7 hours, 13 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)