Birds and mammals build advanced brain circuits using different developmental mechanisms
The area in the brain responsible for complex cognitive functions have different origin in different species such as mammals, birds, and reptiles new research show. These findings indicate that these structures and circuits are not homologous, but rather the result of convergent evolution.
Chicken embryo. Photographer: Fernando Garcia Moreno
“Our study shows that they have arrived at these essential neural circuits through different evolutionary paths”, says Marco Grillo, researcher at Stockholm University and SciLifeLab.
Essential for cognitive functions
The pallium is the brain region where the neocortex forms in mammals—the area responsible for complex cognitive functions and one of the main factors distinguishing humans from other species. The pallium has traditionally been considered a comparable structure across amniotes, including mammals, birds, and reptiles, differing only in complexity but housing similar neuronal types with equivalent circuits for sensory and cognitive processing. This functional and morphological conservation had led researchers to assume a common evolutionary origin for pallial structures across amniotes.
Different evolutionary origins
A recently published study in the journal Science has however challenged this view. Comparing the development and molecular signatures of neurons involved in the sensory circuits of the different brains, the authors concluded that, while these circuits exert similar functions, their embryonic development is radically different, suggesting an independent evolutionary origin.
Cutting-edge technology
The authors used a combination of recently developed techniques, BirthSeq and NeurogenesISS (co-developed with Marco Grillo in Mats Nilsson’s team at SciLifeLab), that allow to record, together with the molecular identity of a cell, also the time and place the cell was originated at.
These techniques work by attaching a “timestamp” to the DNA of cells that were born at a specific moment of embryonic development, and to posteriorly read that timestamp together with the molecular content of a cell (using single-cell or in-situ sequencing respectively). This allows researchers to understand the unfolding of embryonic development integrating time, space and molecular identity in a single assay.
Wings of different origins
“These new tools allowed us to explore whether cells involved in circuits with similar functions have similar molecular profiles, and whether they are originated at equivalent developmental times and from equivalent embryonic regions in different species, which turned out not to be the case. Although the end products look functionally similar, as in the case for birds and bats’ wings, the way to get there from an embryological standpoint was radically different”, says Marco Grillo.
Our work is focused on the development of novel molecular analysis concepts for research and diagnostics, focused on infectious and cancer diagnostics. Our approach is interdisciplinary, spanning from physics to clinical research, with the goal of providing industrial products available to the scientific community and hospital laboratories.
