Evolutionarily well-conserved Ca2+/calmodulin-dependent protein kinase (CaMK) proteins are known for their role as Ca2+ signaling mediators. 1G5 encodes a CaMK like protein, which belongs to a calmodulin (CaM) kinase gene family. Here, we report the isolation of zebrafish homologue of mammalian 1G5, which we named 1G5z. 1G5z is composed of three major domains: (1) an N-terminal serine/threonine kinase domain, (2) a central calmodulin-binding domain, and (3) a C-terminal alanine-rich domain, the 1G5z-specific domain. 1G5z shares 83∼84% homology with other vertebrate 1G5 proteins. Spatiotemporal expression studies found that 1G5z is expressed by means of zygotic transcription and appears in various neuronal tissues from the 20-somite stage. 1G5z transcripts are more regionalized in the brain and spinal cord at 24 hr postfertilization (hpf). At 35 hpf, 1G5z transcripts are exclusively present in the anterior trunk spinal cord as well as in the hindbrain, tegmentum, hypothalamus, and telencephalon. This expression pattern lasts until 48 hpf but ceases in the trunk. At 72 hpf, 1G5z is abundantly transcribed particularly in the specific region of the tectum and eye. We further observed that the number of 1G5z-positive cells is dramatically increased in the mindbomb mutant embryos but abolished in the trigeminal ganglion and caudal trunk sensory neuron of the neurogenin1 morphant at 24 hpf. In addition, bromodeoxyuridine staining further confirmed that the 1G5z-positive cells were postmitotic sensory and interneurons. Developmental Dynamics 235:835–842, 2006. © 2006 Wiley-Liss, Inc.