Correlated gene expression and target specificity demonstrate excitatory projection neuron diversity

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• The neocortex comprises diverse excitatory neuron populations.
• These neurons are organized by cortical layer and projection targets.
• Understanding neuron class diversity is crucial for brain function.

Purpose of the Study:

• To systematically identify molecular markers for specific projection neuron classes.
• To investigate the relationship between gene expression and projection targets in the mouse primary somatosensory cortex (S1).

Main Methods:

• Utilized in situ hybridization (ISH) data mining.
• Performed marker gene colocalization studies.
• Combined retrograde labeling with ISH for layer-specific markers.

Main Results:

• Identified layer-specific genes with heterogeneous expression patterns.
• Found covariation between gene expression and projection target specificity in layers 2/3, 5, and 6.
• Demonstrated that individual genes label neurons projecting to specific target subsets.

Conclusions:

• The neocortex exhibits a high diversity of projection neuron classes, potentially exceeding that of GABAergic interneurons.
• Gene expression and projection target specificity are covariant, suggesting discrete and genetically specified neuron classes.
• This study provides a framework for understanding the molecular basis of cortical circuitry.