Patterning of brain precursors in ascidian embryos

Area of Science:

• Developmental biology
• Neuroscience
• Chordate embryology

Background:

• Ascidian central nervous system (CNS) development involves distinct germ layer origins for anterior (ectoderm) and posterior (mesoderm) regions.
• The anterior CNS, including the sensory vesicle (brain), arises from ectodermal lineages via neuro-epidermal fate decisions.
• The posterior CNS development involves neuro-mesodermal fate decisions.

Purpose of the Study:

• To investigate the molecular mechanisms patterning anterior brain precursors along the medial-lateral axis during neural plate stages.
• To elucidate the roles of Nodal and Delta-like/Notch signaling in establishing gene expression patterns in the developing ascidian brain.

Main Methods:

• Functional studies were employed to analyze gene expression patterns.
• Investigated the roles of Nodal signaling in the induction of lateral genes such as Delta-like, Snail, Msxb, and Trp.
• Examined the effects of Delta-like/Notch signaling on intermediate (Gsx) and medial (Meis) gene expression.
• Assessed the combinatorial action of Snail and Msxb in regulating Gsx expression in lateral cells.

Main Results:

• Nodal signaling is essential for inducing lateral gene expression, including Delta-like, Snail, Msxb, and Trp.
• Delta-like/Notch signaling promotes intermediate Gsx gene expression over medial Meis gene expression.
• The combined activity of Snail and Msxb inhibits Gsx expression in lateral neural precursors.

Conclusions:

• Despite differing embryonic origins of the anterior and posterior CNS in ascidians, the underlying neural precursor patterning mechanisms are highly conserved.
• Nodal and Delta-like/Notch signaling pathways play critical roles in establishing medial-lateral patterning within the anterior brain precursors.