In vivo labeling of zebrafish motor neurons using an mnx1 enhancer and Gal4/UAS.

The zebrafish spinal cord primary motor neurons are commonly used as an experimental model to study the molecular mechanisms that regulate axonal pathfinding and neuromuscular junction formation, and for the modeling of human neurodegenerative disorders. This study characterized a 125-bp mnx1 enhancer to direct gene expression in spinal cord motor neurons. A promoter containing three copies of the 125-bp mnx1 enhancer was generated in a Tol2 vector and used to drive enhanced green fluorescent protein (EGFP) expression either directly or in combination with the Gal4/UAS transcriptional activation system. Both methods induced protein expression for up to 5 days after fertilization, allowing the observation of the dendritic tree and axonal arborization of single motor neurons within a somitic segment in fixed and live animals. The use of the 125-bp mnx1 promoter for transient transgenic expression or for the generation of stable transgenic fish lines will facilitate the study of motor neuron development and neurodegenerative processes.