A 5-week-old embryo is examined during a developmental biology practical. At this stage, the notochord is primarily involved in which of the following developmental processes?

Explanation

## Notochord Function in Early Embryogenesis The notochord is a transient mesodermal structure that plays two critical roles during early embryonic development: ### Primary Functions: 1. **Neural Induction**: The notochord secretes signaling molecules (particularly sonic hedgehog) that induce the overlying ectoderm to form the neural plate, which subsequently differentiates into the neural tube and brain. 2. **Vertebral Column Formation**: The notochord induces the surrounding paraxial mesoderm (somites) to differentiate into sclerotomes, which give rise to the vertebral bodies and intervertebral discs. ### Key Point: **The notochord is the primary organizer** of the dorsal midline structures during weeks 3–8 of development. It regresses by week 8 but leaves behind the nucleus pulposus of the intervertebral discs. ### Clinical Pearl: Notochord remnants can persist and give rise to chordomas (rare malignant tumors of the sacrococcygeal or skull base regions), underscoring the embryological significance of this structure.