Early Forebrain Neurons and Scaffold Fibers in Human Embryos.

Area of Science:

• Developmental Neuroscience
• Human Embryology
• Neurobiology

Background:

• Early forebrain development, including neural progenitor proliferation, neuronal migration, areal organization, and pioneer axon wiring, is crucial but not fully understood in humans.
• Understanding these processes is vital for insights into human brain formation and potential developmental disorders.

Purpose of the Study:

• To investigate early human forebrain development from 5 to 8 postconceptional weeks (WPC5-8).
• To compare human forebrain organization and pioneer axon guidance mechanisms with those in mice.

Main Methods:

• Analysis of human embryonic forebrain tissues at WPC5-8, covering neuroepithelium, early marginal zone, telencephalic preplate, and incipient cortical plate stages.
• Comparative analysis of cellular differentiation, areal organization, and axon tract formation between human and mouse embryos.

Main Results:

• Early telencephalic neurons form at the neuroepithelial stage, originating from local neuroepithelium and potentially the olfactory placode.
• Human and mouse forebrain organization, Cajal-Retzius cells, pioneer neurons, and axons show similarities at the preplate stage.
• Pioneer neuron axons form scaffolds across key boundaries (diencephalon-telencephalon, pallial-subpallial) in human embryos, mirroring mouse development and potentially guiding later axon growth.

Conclusions:

• Human forebrain development shares organizational and axon guidance principles with mice.
• Pioneer neurons establish crucial axonal scaffolds early in human development.
• The molecules CELSR3 and FZD3 are implicated in forming these guidance scaffolds, similar to their role in mouse development.