Scientists from the RIKEN Evolutionary Morphology lab have published a study in the journal Nature titled “Evidence from cyclostomes for complex regionalization of the ancestral vertebrate brain” detailing the fact that the brains of jawless fish may be similar in structure to those of humans than previously believed.
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The researchers use hagfish and lamprey for their study – the only jawless fish remaining today – but lacking two distinguishing features that could have been them similar to those of other vertebrates.
Researchers think vertebrates developed jaws during the Paleozoic era. According to Shigeru Kuratani who led the RIKEN team, a neural tube divided into several sections informed brain development in vertebrates – and each section is controlled by certain genes which make their appearance at specific locations and moments known as genoarchitecture.
Lampreys – a type of jawless fish – appear to lack two brain regions common to jawed vertebrates – the cerebellum and a region called the medial ganglionic eminence, or MGE, from which the pallidum and cortical interneurons originate. Similarly, although hagfish do not have a true cerebellum, the team was able to identify a clear rhombic lip region that expresses Pax6.
"The problem was that lampreys had not yet been shown to have a similar patterning," Kuratani explained. "The shared pattern of brain development between hagfish and jawed vertebrates raised the possibility that the apparently primitive brain of the lamprey is simply a lamprey-unique characteristic."
The researchers further revealed that the patterning of jawed vertebrates is similar to that of hagfish than to lampreys, and that this could have occurred as a result of secondary evolutionary changes in the evolution of lamprey and not to changes peculiar to vertebrates.
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That is not all, Kuratani concluded that "With these new findings from hagfish and lampreys, we have shown that both of the extant jawless-fish species have a rhombic lip and an MGE – the sources of the cerebellum, pallidum, and GABAergic interneurons in jawed vertebrates. This firmly places the development of these genoarchitectural patterns back to a common ancestor shared by jawless and jawed vertebrates."