Identity of neocortical layer 4 neurons is specified through correct positioning into the cortex

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Abstract
Many cell-intrinsic mechanisms have been shown to regulate neuronal subtype specification in the mammalian neocortex. However, how much cell environment is crucial for subtype determination still remained unclear. Here, we show that knockdown of Protocadherin20 (Pcdh20), which is expressed in post-migratory neurons of layer 4 (L4) lineage, caused the cells to localize in L2/3. The ectopically positioned “future L4 neurons” lost their L4 characteristics but acquired L2/3 characteristics. Knockdown of a cytoskeletal protein in the future L4 neurons, which caused random disruption of positioning, also showed that those accidentally located in L4 acquired the L4 characteristics. Moreover, restoration of positioning of the Pcdh20-knockdown neurons into L4 rescued the specification failure. We further suggest that the thalamocortical axons provide a positional cue to specify L4 identity. These results suggest that the L4 identity is not completely determined at the time of birth but ensured by the surrounding environment after appropriate positioning.
Funding Information
  • Ministry of Education, Culture, Sports, Science, and Technology (15H02355, 22111004, 25640039, 15H01586, 19700295, 21700356)
  • Takeda Science Foundation
  • Strategic Research Program for Brain Sciences (Understanding of molecular and environmental bases for brain health)
  • Terumo Life Science Foundation
  • Life Science Foundation of Japan
  • Keio University (Keio Gijuku Fukuzawa Memorial Fund for the Advancement of Education and Research)
  • Keio University (Keio Gijuku Academic Development Funds)
  • Naito Foundation

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