"Evolution of the Sympathetic Nervous System in Early Vertebrates"
In a groundbreaking study, a team of scientists has uncovered a remarkable revelation about the origins of the sympathetic nervous system - the key driver behind the fight-or-flight response in vertebrates. Traditionally, this complex system was thought to be a feature exclusive to jawed vertebrates. However, the latest findings published in Nature suggest that the fundamental building blocks and developmental regulators of the sympathetic nervous system were already present in one of the earliest known vertebrates - the jawless sea lamprey.
This discovery, led by Edens and colleagues, represents a major milestone in our understanding of the evolutionary history of the vertebrate nervous system. By employing advanced techniques like in situ hybridization chain reaction, the researchers were able to meticulously map the expression of key transcription factors and functional signature genes that are hallmarks of sympathetic neurons across different vertebrate species, from sea lampreys to mammals.
The sea lamprey, a jawless fish considered a living fossil, was found to possess the same characteristic molecular and developmental 'fingerprint' present in the noradrenaline-producing sympathetic neurons of other vertebrates. This includes the co-expression of genes encoding critical transcription factors like Ascl1, Phox2, and Hand, as well as enzymes involved in the synthesis of the neurotransmitter noradrenaline.
Remarkably, the researchers also identified the migratory population of neural crest-derived cells that give rise to the sympathetic neurons in sea lampreys, tracing their origins to the spinal cord and their subsequent differentiation into a nerve cord between the intestine and the notochord. Further analysis revealed a gene expression profile in these cells that is strikingly similar to the pattern seen in mouse sympathetic neurons.
One of the intriguing aspects of this discovery is the stark contrast in the developmental timeline of sympathetic neuron maturation between sea lampreys and their jawed vertebrate counterparts. While the initial noradrenergic and neuronal differentiation occurs rapidly and in parallel in mice and birds, the process is surprisingly slow and asynchronous in sea lampreys, bearing similarities to the delayed development of sympathetic ganglia in zebrafish.
This evolutionary conservation of key developmental processes offers exciting opportunities for further study, particularly in the context of neuroblastoma, a type of tumor that arises from sympathetic neurons. The zebrafish, with its accessible model system, could provide valuable insights into the underlying mechanisms and potentially pave the way for the development of novel anticancer therapies.
Moreover, the findings of Edens and colleagues suggest a remarkable diversification of sympathetic neuron populations across vertebrate species, with the discovery of a sea lamprey neuron population that is comparable to an abundant noradrenergic subtype in mice, known as the NA3 population. This population is associated with the regulation of blood vessel diameter and resistance, highlighting the crucial role of the sympathetic nervous system in thermoregulation and other physiological functions.
As the scientific community grapples with the implications of this groundbreaking discovery, many questions remain to be answered. For instance, the precise anatomical targets and functional roles of the sympathetic neurons in sea lampreys are yet to be determined. Additionally, the regulation of the late acquisition of neuronal characteristics and proliferative activity in the neural crest-derived cells warrants further investigation.
This study not only revises our understanding of the evolutionary origins of the vertebrate autonomic nervous system but also opens up new avenues for exploring the fundamental mechanisms that shape the development and organization of the sympathetic circuitry across the tree of life. As the world faces the challenges of a changing climate, the insights gained from this research may also shed light on how the sympathetic nervous system might adapt to meet the physiological demands of the future.
Source: https://www.nature.com/articles/d41586-024-01017-4
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