Sponges provide insights into nervous system evolution!

Debarati Basu, Makaut WB

The brain is the most unique and vital organ of the human body. It is composed of nearly 86 billion neurons that help in communication through synapses. These neurons help in performing various body functions that include vision, movement, understanding, consciousness, and so on. Thus it helps in performing the most important functions of our body. The brain contains the cortex which is the outermost layer of the brain. The spinal cord and the remaining part of the brain make up the brain stem.

The major functions of the brain stem are to control breathing patterns and sleep. The brain center consists of clusters called basal ganglia that perform the role of coordinating messages among various other brain areas. The back part of the brain is the cerebellum that is responsible for maintaining the balance of our body. Though we know the importance of the brain in performing body functions the origin of the brain is still not known. It is known that the first animal brain is supposed to appear a few hundreds of millions of years ago. In recent times only the aquatic animals i.e. that form the primitive species of animals lack brains. Contradictorily these primitive animal species might play a significant role in solving the mystery behind the evolution of the brain and neurons.

Neurons in the brain individually communicate through synapses. Neurons play a key role in performing brain functions that are regulated by various genes. Although sponges lack synapses synaptic genes are still encoded by their genome. Scientists of the European Molecular Biology Laboratory (EMBL) were curious about the behavior of the sponges. They have published their findings regarding this in the journal ‘Science’. 

Significance of the study

Detlev Arendt said that it is a known fact that synaptic genes are associated with the functions of the neurons in higher animals. He is the senior scientist and the group leader of EMBL Heidelberg. But primitive species lack brains yet they have these functions which raise questions about the role of genes in these primitive animals. He further said though it seems easy findings the answers were harder as they lack the technologies required.

More details about the study:

The Arendt lab applied the microfluidic and genomic technologies to Spongilla lacustris which is the freshwater sponge to study the function of the synaptic genes in freshwater sponges. These techniques were utilized by the scientists in capturing individual cells obtained from various sponges present inside the microfluidic droplets and then characterizing individual cells’ genetic activity.

Jacob Musser is the Research scientist in the Arendt group and also the lead author of this study. According to him, a few specific cells present in the digestive chambers of the sponges are responsible for activating the synaptic responses. Thus in primitive animal species, the activation of the synaptic genes is done by some specific part of the body.

In the case of sponges, they utilize their digestive chambers for filtering out the food from the water. This also helps them in interacting with the microorganisms present in the surroundings. The Arendt group collaborated with six EMBL in Europe and worldwide for understanding the reason behind the cells that express synaptic genes. A new correlated imaging technique was developed by Yannick Schwab’s team and Thomas Schneider’s group and EMBL’s Electron Microscopy Core Facility. According to Dr. Schwab combination of electron microscopy and X-ray imaging on beamline which is synchrotron in nature were used. It helped visualize the cellular behaviors.

Conclusion:

The three-dimensional snapshots were captured by the scientists that showed the cells crawled across the digestive chamber. They crawl the chambers for clearing out any kind of bacterial attackers. It also helps them in preventing the long arms to enwrap the feeding apparatus of particular digestive cells. This behavior associates a targeted cell-cell communication as it might happen across synapses that are present between neuronal cells present in the human brain.

According to Dr. Musser, the results of their study are suggestive that cells play a major role in regulating feeding and controlling the surrounding microbial environment. They also act as precursors of evolution for the first animal brains.

Also read: COVID-19 vaccine for children: Pfizer shows progress!

Reference:

1. Musser, J. M., Schippers, K. J., Nickel, M., Mizzon, G., Kohn, A. B., Pape, C., Ronchi, P., Papadopoulos, N., Tarashansky, A. J., Hammel, J. U., Wolf, F., Liang, C., Hernández-Plaza, A., Cantalapiedra, C. P., Achim, K., Schieber, N. L., Pan, L., Ruperti, F., Francis, W. R., … Arendt, D. (2021). Profiling cellular diversity in sponges informs animal cell type and nervous system evolution. Science, 374(6568), 717–723. https://doi.org/10.1126/science.abj2949

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