Embryonic motor activity and implications for regulating motoneuron axonal pathfinding in zebrafish.

Area of Science:

• Developmental biology
• Neuroscience
• Genetics

Background:

• Zebrafish embryos display spontaneous muscle contractions initiated by central nervous system activity.
• The narrowminded (nrd) mutant zebrafish exhibits motor deficits and developmental defects.

Purpose of the Study:

• To investigate the role of the narrowminded mutation in embryonic motor output and motoneuron development.
• To identify the underlying cellular and molecular mechanisms of motor defects in nrd mutant zebrafish.

Main Methods:

• Observation of nrd mutant zebrafish embryos at various developmental stages.
• Anatomical analysis of neural crest, muscle, and Rohon-Beard (RB) neurons.
• Assessment of motoneuron axonal pathfinding.
• Manipulation of embryonic activity using high potassium [K(+)] and tricaine.

Main Results:

• nrd(-/-) embryos lack normal embryonic motor output and possess defects in neural crest, slow muscle, and RB neurons.
• Motoneuron axonal pathfinding errors in nrd(-/-) embryos were reversed by high [K(+)] treatment.
• Blocking neural activity in wild-type embryos phenocopied the motoneuron defects observed in nrd(-/-) embryos.

Conclusions:

• Early embryonic neural activity, alongside other factors, is essential for normal motoneuron development.
• The narrowminded mutation disrupts early neural activity, leading to subsequent motor and axonal pathfinding defects.