Surface ectoderm is necessary for the morphogenesis of somites

Area of Science:

• Developmental biology
• Embryogenesis
• Cell biology

Background:

• Somitogenesis, the formation of somites from paraxial mesoderm, involves segmentation, elongation, and epithelialization.
• The autonomous versus non-autonomous nature of these processes has been investigated.

Purpose of the Study:

• To determine if somite segmentation, elongation, and epithelialization are autonomous processes within the paraxial mesoderm.
• To identify the specific roles of adjacent tissues, particularly surface ectoderm, in somitogenesis.

Main Methods:

• In vitro culture of mouse embryonic presomitic mesoderm with and without adjacent tissues.
• Recombination experiments using ectoderm from different embryonic regions.
• Analysis of gene expression, including Dll1, Notch1, and Paraxis.

Main Results:

• Somite segmentation occurred autonomously in presomitic mesoderm, independent of neural tube, notochord, gut, or surface ectoderm.
• Presomitic mesoderm fragments segmented autonomously.
• Surface ectoderm is required for mesoderm elongation and somite epithelialization.
• Ectoderm-induced epithelialization correlated with Paraxis expression, but trunk ectoderm induced epithelialization without strong Paraxis expression.

Conclusions:

• Somitogenesis involves autonomous segmentation regulated by Notch signaling.
• Mesoderm elongation and epithelialization are non-autonomous processes induced by specific surface ectoderm interactions.