The homeodomain transcription factor drg11 is expressed in primary sensory neurons and their putative CNS targets during embryonic development of the zebrafish

The drg11 gene is a member of the vertebrate aristaless-related gene family and encodes a paired homeodomain transcription factor. Its expression is largely restricted to PNS neurons subserving somatosensory functions and their CNS targets in rodents. The phenotype of drg11 null mice suggests that it is crucial for the proper development in the embryo of nociceptive circuits. To allow functional studies in the zebrafish, a simple vertebrate model organism, we have cloned the homologous gene and studied its expression throughout embryonic development. drg11 transcripts are first detected at neurula stage in the developing trigeminal ganglion, where it persists throughout development. This is followed by transient expression in spinal cord mechanosensory Rohon-Beard neurons shortly before axogenesis. Expression is later evident in neuronal populations of the dorsal spinal cord and in the dorsal root ganglia. In the developing brain, drg11 expression is mainly restricted to sensory neuron populations of the midbrain and hindbrain, in cranial sensory ganglia and in the habenula. Unlike rodents, however, trochlear motor neurons transiently express drg11. Our results suggest that drg11 expression in the developing zebrafish is, in common with its mammalian homologous gene, predominantly localised to neurons in sensory processing areas of the embryonic nervous system and is both spatially and temporally regulated.