summary: Researchers are turning to jellyfish and fruit flies to explore motivation for feeding and to shed new light on the mechanisms underlying feeding regulation.
source: Tohoku University
Decades of research has shown that the drive to feed, namely hunger and the feeling of fullness, is controlled by hormones and small proteins called neuropeptides. They are found in a wide variety of organisms such as humans, mice, and fruit flies.
Such a widespread occurrence suggests a common evolutionary origin. To explore this phenomenon, a research group turned to jellyfish and fruit flies, and discovered some surprising results.
Although jellyfish shared a common ancestor with mammals at least 600 million years ago, their bodies are simpler. They have diffuse nervous systems called neural networks, unlike mammals which have more concrete structures like the brain or ganglia. However, jellyfish possess a rich repertoire of behaviors, including elaborate foraging strategies, mating rituals, sleeping, and even learning.
Despite their important position on the tree of life, these remarkable creatures remain unstudied, and almost nothing is known about how they control their food intake.
The group, led by Hiromu Tanimoto and Vladimiros Toma of Tohoku University’s Graduate School of Life Sciences, focused on cladonema, a small jellyfish with forked tentacles that can be cultured in the lab. Jellyfish regulate how much they eat based on how hungry they are.
“First, to understand the mechanisms underlying feeding regulation, we compared gene expression profiles in starved and fed jellyfish,” said Tanimoto.
Feeding status altered the expression levels of several genes, including some that encode neuropeptides. By synthesizing and testing these neuropeptides, we found five that reduced feeding in hungry jellyfish.”
The researchers then refined how a neuropeptide, GLWamide, controls feeding. A detailed behavioral analysis revealed that GLWamide inhibits tentacle shortening, a critical step for moving captured prey to the mouth. When the researchers named it GLWamide, they found that it is present in motor neurons located at the bases of tentacles, fueling increased GLWamide levels.
This led to the conclusion that GLWamide, in Cladonema, acts as a satiety signal – a signal sent to the nervous system indicating that the body has enough to eat.
However, the researchers’ quest to explore the evolutionary significance of this finding did not stop there. Instead, they looked to other species. Drosophila feeding patterns are regulated by a neuromuscular peptide (MIP).
Fruit flies lacking MIP eat more food, and eventually become obese. Interestingly, MIP and GLWamide share similarities in their structure, indicating that they are related through evolution.
“Since the functions of GLWamide and MIP have been conserved despite 600 million years of divergence, this prompted us to consider whether the two might be interchangeable,” said Toma. “And we did just that, first by administering MIP to the jellyfish and then expressing GLWamide in flies without MIP.”
Amazingly, MIP reduced Cladonema feeding, just as GLWamide did. Moreover, GLWamide in flies averted abnormal overeating, indicating functional conservation of the GLWamide/MIP system in jellyfish and insects.
Tanimoto notes that their research highlights the deep evolutionary origins of this conserved satiety signal and the importance of harnessing a comparative approach. “We hope that our comparative approach will inspire focused investigation into the role of molecules, neurons, and circuits in regulating behavior within a broader evolutionary context.”
About this research in Neuroscience News
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“Regarding the origin of appetite: GLWamide in jellyfish represents an inherited satiety neuropeptide.Written by Hiromu Tanimoto et al. PNAS
Regarding the origin of appetite: GLWamide in jellyfish represents an inherited satiety neuropeptide.
Food intake is regulated by the internal state. This function is mediated by hormones and neuropeptides, which are better characterized in common model species. However, the evolutionary origins of such feeding-regulating neuropeptides are poorly understood. We used jellyfish cladonema to address this question.
Our combined transcriptomic, behavioral, and anatomical approaches identified GLWamide as a feeding-suppressing peptide that selectively inhibits tentacle contraction in this jellyfish. I
n Drosophila Drosophila, muscle inhibitory peptide (MIP) is a satiety-binding peptide. Surprisingly, we found that GLWamide and MIP were completely interchangeable in these evolutionarily distant species for feeding inhibition.
Our results indicate that the satiation signaling systems of diverse animals share an ancient origin.
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