The Role of Notch, ERK, and SHH Signaling Pathways in the Fate Determination of Cortical Glial Cells and Olfactory Bulb Interneurons

Academic Background

During cortical development, neurogenesis and gliogenesis are two closely connected stages. Neurogenesis primarily generates neurons, while gliogenesis produces glial cells, including astrocytes and oligodendrocytes. In the human cerebral cortex, the number of glial cells is three times that of neurons, indicating their critical role in brain function. However, the molecular mechanisms underlying the transition from cortical neurogenesis to gliogenesis, as well as the regulatory mechanisms governing glial cell fate determination, remain incompletely understood. Previous studies have shown that the Notch, ERK (extracellular signal-regulated kinase), and SHH (Sonic Hedgehog) signaling pathways play crucial roles in neural development, but how they specifically regulate glial cell fate determination requires further exploration.

Source of the Paper

This paper was completed by a research team from the Department of Neurology at Zhongshan Hospital affiliated with Fudan University, the Department of Molecular, Cellular, and Developmental Biology at the University of California, Santa Cruz, and the Department of Neurosurgery at West China Hospital, Sichuan University. The paper was published on February 25, 2025, in PNAS (Proceedings of the National Academy of Sciences of the United States of America), titled “Notch, ERK, and SHH signaling respectively control the fate determination of cortical glia and olfactory bulb interneurons.”

Research Workflow and Results

1. Research Workflow

The study was divided into several key steps:

a) The Role of ERK Signaling in Cortical Gliogenesis

• Experimental Subjects: Using a mouse model, the core genes MAP2K1 and MAP2K2 of the ERK signaling pathway were deleted through genetic editing to construct an ERK signaling-deficient mouse model (emx1-cre; map2k1/2-dcko).
  
• Experimental Methods: Fluorescent markers (Flashtag) were injected at embryonic day E18.5 to label cortical progenitor cells, followed by single-cell RNA sequencing (scRNA-seq) analysis of the gene expression profiles of cortical cells.
  
• Experimental Results: The absence of ERK signaling led to a significant reduction in the number of cortical radial glial cells (RGCs) and failed to generate tripotential intermediate progenitor cells (tri-IPCs), thereby blocking the generation of astrocytes, oligodendrocytes, and olfactory bulb interneurons.
  

b) The Role of Notch Signaling in Astrocyte Fate Determination

• Experimental Subjects: The core transcription factor RBPJ of the Notch signaling pathway was deleted through genetic editing to construct a Notch signaling-deficient mouse model (hgfap-cre; rbpjf/f).
  
• Experimental Methods: Immunohistochemistry was used to detect the expression of markers for cortical progenitor cells and glial cells.
  
• Experimental Results: The absence of Notch signaling significantly reduced the generation of astrocytes while increasing the generation of oligodendrocytes, indicating that Notch signaling plays a critical role in astrocyte fate determination.
  

c) The Role of SHH Signaling in Olfactory Bulb Interneuron Fate Determination

• Experimental Subjects: The core gene SMO of the SHH signaling pathway was deleted through genetic editing to construct an SHH signaling-deficient mouse model (hgfap-cre; smof/f).
  
• Experimental Methods: Key genes of the SHH signaling pathway (e.g., Gli2a) were overexpressed using in utero electroporation, and the gene expression profiles of cortical progenitor cells were analyzed.
  
• Experimental Results: The absence of SHH signaling blocked the generation of olfactory bulb interneurons, while overexpression of Gli2a significantly promoted their generation.
  

2. Main Results

• ERK Signaling: ERK signaling plays a critical role in cortical gliogenesis. Its absence blocks gliogenesis and prevents cortical progenitor cells from generating tri-IPCs.
  
• Notch Signaling: Notch signaling plays a critical role in astrocyte fate determination. Its absence reduces astrocyte generation while increasing oligodendrocyte generation.
  
• SHH Signaling: SHH signaling plays a critical role in olfactory bulb interneuron fate determination. Its absence blocks the generation of olfactory bulb interneurons.
  

3. Conclusions and Significance

This study reveals the critical roles of the Notch, ERK, and SHH signaling pathways in the fate determination of cortical glial cells and olfactory bulb interneurons, elucidating the molecular mechanisms underlying the transition from cortical neurogenesis to gliogenesis. The findings not only deepen our understanding of cortical development but also provide potential therapeutic targets for related neurological disorders.

4. Highlights of the Study

• Key Discoveries: This study systematically elucidates the specific roles of the Notch, ERK, and SHH signaling pathways in cortical glial cell fate determination for the first time.
  
• Methodological Innovation: By combining genetic editing techniques and single-cell RNA sequencing, the differentiation process of cortical progenitor cells was precisely analyzed.
  
• Application Value: The results offer new insights into the treatment of neurological disorders, particularly strategies for treating glial cell-related diseases such as gliomas.
  

5. Other Valuable Information

This study found that the molecular mechanisms of cortical gliogenesis are highly conserved between humans and mice, indicating the universality of this mechanism in mammalian evolution. Additionally, the study revealed the interaction between SHH and ERK signaling during cortical development, providing a new perspective for understanding the cooperative regulation of signaling pathways.

Summary

By systematically analyzing the roles of the Notch, ERK, and SHH signaling pathways in the fate determination of cortical glial cells, this study uncovers the molecular mechanisms of cortical development and provides important theoretical support for the research and treatment of neurological disorders. The innovation and application value of the study make it a significant advancement in the field of neural development.