Moving cell bodies: understanding the migratory mechanism of facial motor neurons

Facial branchiomotor (FBM) neurons innervate facial musculature to control facial and jaw movement, which is crucial for facial expressions, speaking, and eating. FBM neurons are one of the largest populations among cranial motor neuronal class forming distinct nucleus in the hindbrain. To construct functional FBM neuronal system, a variety of cellular and molecular mechanisms play a role during embryonic development and thereby present a good framework for understanding the principles of neural development. Over the past decade, genetic approaches in mice and zebrafish have provided a better understanding of molecular pathways for FBM neuron development. This review will focus on regulatory mechanisms for cell body movement of FBM neurons, one of the unique features of FBM neuronal development. First, I will describe the basic anatomy of hindbrain, organization of cranial motor neurons, and developmental sequence of FBM neurons in vertebrates. Next, I will focus on the migratory process of FBM neurons in detail in conjunction with recent genetic evidence for underlying regulatory mechanisms, candidate environmental signals, and transcription factors for FBM neuronal development.