Changes in cortical interneuron migration contribute to the evolution of the neocortex

Area of Science:

• Neuroscience
• Evolutionary Biology
• Developmental Biology

Background:

• Neocortex evolution is linked to excitatory neuron progenitors.
• The role of inhibitory interneurons, originating outside the neocortex, remains unclear.
• Understanding interneuron migration is key to neocortex establishment.

Purpose of the Study:

• To investigate the evolutionary role of inhibitory interneuron migration in neocortex development.
• To compare the migratory behavior of medial ganglionic eminence (MGE) cells from different species within the embryonic mouse neocortex.
• To determine if the neocortical cortical plate (CP) is permissive for non-mammalian interneuron development.

Main Methods:

• Transplantation of medial ganglionic eminence (MGE) cells from chicken, turtle, mouse, and marmoset into embryonic mouse MGE in utero.
• Observation and comparison of migratory pathways and target invasion within the mouse neocortex.
• In utero transplantation of chicken MGE cells directly into the neocortical cortical plate (CP).

Main Results:

• MGE cells from all species migrated through the mouse neocortical subventricular zone.
• Mouse and marmoset MGE cells successfully invaded the neocortical CP.
• Chicken and turtle MGE cells largely bypassed the neocortical CP but invaded archicortex and paleocortex.
• Chicken MGE cells survived and matured when transplanted directly into the neocortical CP, indicating its permissiveness.

Conclusions:

• Proper targeting of the neocortical CP by MGE-derived interneurons is a mammalian-specific evolutionary adaptation.
• Evolutionary changes in inhibitory interneuron migratory behavior contributed to neocortex establishment.
• The neocortical CP environment supports the postmigratory development of interneurons, even from non-mammalian species.