Ancient vertebrate dermal armor evolved from trunk neural crest.

Area of Science:

• Evolutionary developmental biology
• Vertebrate paleontology
• Skeletal biology

Background:

• Bone is a defining vertebrate innovation, likely originating in ancestral dermal armor.
• The developmental origin of this early bone (mesoderm vs. neural crest) remains debated.

Purpose of the Study:

• To investigate the developmental origin of bony dermal armor in nonteleost ray-finned fish.
• To trace the lineage of osteoblasts in sterlet sturgeon scutes.

Main Methods:

• In vivo lineage tracing in sterlet sturgeon (Acipenser ruthenus).
• Transcriptional profiling of scutes and scales.
• Histological and microCT analyses of ray-finned fish dermal armor.

Main Results:

• Sterlet trunk neural crest cells were definitively shown to generate osteoblasts in scutes.
• A neural crest gene signature was identified in sterlet scutes and bichir scales.
• Ray-finned fish dermal armor comprises bone, dentin, and mineralized tissues, resembling early vertebrate armor.

Conclusions:

• Supports a primitive, body-wide skeletogenic role for neural crest cells in early vertebrates.
• Suggests neural crest contribution to dermal armor was progressively restricted to the head during evolution.
• Highlights neural crest as a key evolutionary driver for dermal armor diversification.