Notochord action on spinal development. A histologic and morphometric investigation

Area of Science:

• Embryology
• Developmental Biology
• Histology

Background:

• The notochord plays a crucial role in early embryonic development.
• Its precise influence on spinal segmentation and intervertebral disc formation remains debated.
• Previous theories suggested notochordal cell migration into intervertebral spaces.

Purpose of the Study:

• To investigate the notochord's role in human spinal development and segmentation.
• To histologically and histomorphometrically examine early human embryos and fetuses.
• To clarify the cellular mechanisms behind notochordal cell reduction during development.

Main Methods:

• Histological analysis of 47 human embryos/fetuses (5-13 weeks gestational age).
• Histomorphometric evaluation to quantify cellular changes.
• Comparative analysis of notochordal tissue and surrounding spinal structures.

Main Results:

• Spinal segmentation initiated in tissues surrounding the notochord, not within it.
• Notochordal development lagged behind surrounding tissues in the cranial region.
• Reduced notochordal cell numbers in later stages were attributed to degeneration, not migration.

Conclusions:

• The notochord is not the primary initiator of spinal segmentation.
• Notochordal cell loss occurs via degeneration, contradicting the cell migration theory for intervertebral disc development.
• This study challenges established hypotheses regarding the notochord's contribution to intervertebral disc formation.