Mef2c Controls Postnatal Callosal Axon Targeting by Regulating Sensitivity to Ephrin Repulsion

Area of Science:

• Neuroscience
• Developmental Biology
• Molecular Biology

Background:

• Cortical connectivity relies on precise neuron subtype development and axon projection.
• Mechanisms governing intracortical axon targeting, especially for callosal projections, remain incompletely understood.

Purpose of the Study:

• To investigate the role of the transcription factor Myocyte enhancer factor 2-c (Mef2c) in cortical development.
• To elucidate Mef2c's function in the specification of somatosensory cortical (S1) neurons and the targeting of layer 2/3 callosal projection neurons (L2/3 CPNs).

Main Methods:

• Utilized genetic manipulation to study Mef2c function in developing cortical neurons.
• Investigated the interplay between Mef2c and EphA-EphrinA signaling pathways.
• Analyzed axon targeting of L2/3 CPNs in Mef2c-mutant models.

Main Results:

• Mef2c directs the development of S1 layer 4 and 5 pyramidal neurons during embryogenesis.
• Postnatally, Mef2c expression shifts to L2/3 CPNs, where it mediates targeting to homotopic contralateral cortical regions.
• Mef2c downregulates EphA6 expression, desensitizing S1-L2/3 CPN axons to EphrinA5-mediated repulsion.

Conclusions:

• Mef2c exhibits dual roles in cortical development: regulating neuronal subtype specification and directing postnatal callosal axon targeting.
• This study reveals a novel mechanism for Mef2c in guiding long-range axon projections via modulation of Ephrin signaling.