Reelin mRNA expression during embryonic brain development in the turtle Emys orbicularis

Area of Science:

• Neuroscience
• Developmental Biology
• Evolutionary Biology

Background:

• Reelin is a crucial signaling molecule in brain development, particularly for neuronal migration and cortical lamination.
• Understanding reelin expression across different species provides insights into the evolution of brain structures.

Purpose of the Study:

• To investigate the expression patterns of reelin mRNA during embryonic brain development in the turtle (Emys orbicularis).
• To compare reelin expression in turtles with that in mammals to understand evolutionary changes in cortical development.

Main Methods:

• Radioactive in situ hybridization was employed to detect reelin mRNA.
• Analysis focused on various brain regions including the olfactory bulb, cortex, diencephalon, tectum, cerebellum, and spinal cord.

Main Results:

• High reelin mRNA expression was observed in the olfactory bulb, certain cortical neurons, diencephalon nuclei, tectum, and cerebellar granule cells.
• Moderate expression was found in the septal nuclei, striatum, retina, and hypothalamus.
• Notably, the developing turtle cortex showed significantly less reelin expression in subpial Cajal-Retzius cells compared to mammals.

Conclusions:

• Reelin expression patterns are largely conserved between turtles and mammals, indicating an evolutionarily stable role.
• The reduced reelin expression in the turtle's cortical marginal zone suggests that increased reelin signaling may have been a key factor in the evolution of the highly laminated mammalian cerebral cortex.