Evolutionary origin of Tbr2-expressing precursor cells and the subventricular zone in the developing cortex

Area of Science:

• Developmental Neuroscience
• Evolutionary Biology
• Comparative Neuroanatomy

Background:

• The subventricular zone (SVZ) is crucial for generating neurons in mammals, particularly in species with complex brains.
• Tbr2-expressing cells are key intermediate progenitor cells in the mammalian SVZ, producing neocortical excitatory neurons.
• The presence and organization of the SVZ in non-mammalian vertebrates, like reptiles, remain poorly understood.

Purpose of the Study:

• To investigate the evolutionary origins of SVZ neural precursor cells in the prenatal cerebral cortex.
• To determine the presence and distribution of Tbr2-expressing cells in reptilian and avian species.
• To understand the conserved mechanisms of SVZ organization across vertebrate evolution.

Main Methods:

• Examined the prenatal cerebral cortex of various reptilian (lizard, turtle) and avian (chicken, dove) species.
• Utilized immunohistochemistry to detect and map Tbr2-expressing cells.
• Assessed the cellular organization and anatomical location of Tbr2(+) cells.

Main Results:

• Mitotic Tbr2-expressing cells were identified in the prenatal cortex of lizards, turtles, chickens, and doves.
• A distinct SVZ composed of Tbr2(+) cells was observed in the dorsal ventricular ridge of turtles and the cortices of chickens and doves.
• These findings suggest Tbr2(+) neural precursor cells were present in the common ancestor of mammals and reptiles.

Conclusions:

• Tbr2(+) neural precursor cells and a distinct SVZ organization are conserved across mammals, reptiles, and birds.
• The data support the hypothesis that Tbr2(+) cells were present in the common ancestor of mammals and reptiles.
• Tbr2 expression serves as a reliable marker for identifying and defining the boundaries of the SVZ in developing vertebrate cortices.