Role of morphogens in brain growth

Area of Science:

• Developmental biology
• Neuroscience
• Evolutionary biology

Background:

• Early forebrain and midbrain vesicle expansion in chick embryos depends on the axial (notochordal) mesoderm.
• Separation from the notochord leads to midbrain and forebrain (telencephalic) vesicle collapse and neural epithelium folding.

Purpose of the Study:

• To review experiments on chick embryo brain development.
• To contextualize findings within broader studies of abnormal brain morphogenesis.
• To speculate on the role of signaling pathways in vertebrate brain evolution.

Main Methods:

• Review of historical and recent experimental data on chick embryo brain development.
• Analysis of the role of Sonic Hedgehog (Shh) signaling.
• Examination of molecular and cellular processes affecting neural epithelium.

Main Results:

• Transient separation of the midbrain from the notochord causes vesicle collapse.
• Defective Sonic Hedgehog (Shh) signaling from the notochord and floor plate is a cause of vesicle collapse.
• Loss of ventral Shh expression leads to reduced proliferation, increased cell death, and vesicle collapse.

Conclusions:

• The notochord is crucial for normal brain vesicle expansion through signaling pathways like Shh.
• Perturbations in molecular and cellular processes can lead to abnormal brain morphogenesis.
• Variations in signaling pathway regulation, such as Hedgehog, may drive vertebrate brain evolution.