Specification of sensory neurons occurs through diverse developmental programs functioning in the brain and spinal cord

Background: Vertebrates possess two populations of sensory neurons located within the central nervous system: Rohon‐Beard (RB) and mesencephalic trigeminal nucleus (MTN) neurons. RB neurons are transient spinal cord neurons whilst MTN neurons are the proprioceptive cells that innervate the jaw muscles. It has been suggested that MTN and RB neurons share similarities and may have a common developmental program, but it is unclear how similar or different their development is. Results: We have dissected RB and MTN neuronal specification in zebrafish. We find that RB and MTN neurons express a core set of genes indicative of sensory neurons, but find these are also expressed by adjacent diencephalic neurons. Unlike RB neurons, our evidence argues against a role for the neural crest during MTN development. We additionally find that neurogenin1 function is dispensable for MTN differentiation, unlike RB cells and all other sensory neurons. Finally, we demonstrate that, although Notch signalling is involved in RB development, it is not involved in the generation of MTN cells. Conclusions: Our work reveals fundamental differences between the development of MTN and RB neurons and suggests that these populations are non‐homologous and thus have distinct developmental and, probably, evolutionary origins. Developmental Dynamics 243:1429–1439, 2014. © 2014 Wiley Periodicals, Inc. Key Findings The two sensory neuronal populations in the vertebrate central nervous system, Mesencephalic Trigeminal Nucleus (MTN) neurons and Rohon‐Beard (RB) neurons, do not show an exclusive gene expression signature that distinguishes sensory neurons. MTN neurons in zebrafish are not derived from neural crest and neither MTN or RB neurons require sox10 for their development Neither MTN nor adjacent posterior diencephalon neurons require neurogenin1 function or Notch signalling for their development.