Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Amphibian Anatomy

Background:

• Direct development, common in amphibians, omits the aquatic larval stage.
• Evolution of direct development in Eleutherodactylus frogs correlates with significant embryonic cranial pattern modifications.
• Understanding cranial neural crest cell roles is key to explaining these evolutionary changes.

Purpose of the Study:

• To investigate the emergence and early migration of cranial neural crest cells in Eleutherodactylus coqui using SEM.
• To assess the potential role of neural crest cells in mediating evolutionary changes associated with direct development.

Main Methods:

• Scanning electron microscopy (SEM) was employed to visualize cranial neural crest cell development.
• Observed cell emergence timing relative to neural fold closure.
• Analyzed the formation and migration patterns of three distinct neural crest cell streams.

Main Results:

• Cranial neural crest cells emerge before neural fold closure, forming rostral, otic, and caudal streams.
• These streams contribute to specific facial and arch structures, similar to metamorphosing frogs.
• No significant alterations in basic neural crest emergence or early migration patterns were observed in Eleutherodactylus coqui.

Conclusions:

• The evolution of direct development in Eleutherodactylus frogs does not appear to significantly alter early cranial neural crest cell emergence or migration.
• Evolutionary modifications in cranial patterning likely involve later stages of neural crest cell migration, behavior, commitment, or gene expression.
• Further research is needed to elucidate the precise mechanisms by which neural crest cells mediate evolutionary changes in direct development.