Expression of protocadherin-19 in the nervous system of the embryonic zebrafish.

We have analyzed the expression pattern of protocadherin-19, a member of the delta2-protocadherins, in the nervous system of developing zebrafish using in situ hybridization methods. mRNA encoding protocadherin-19 (Pcdh19) began to be expressed at about 12 hours post fertilization (hpf) showing a segmental expression pattern in the anterior 1/3 of the neural keel, with strong expression in the presumptive forebrain, cerebellum/rhombomere 1 and rhombomere 4. Pcdh19 expression in the posterior neural keel was continuous and confined to the midline region. By 24 hpf, Pcdh19 was expressed widely in the brain and spinal cord, with higher expression levels in the ventral telencephalon, dorsal and central thalamus, optic tectum, central tegmentum, cerebellum and dorsolateral regions of the hindbrain. As development proceeded, Pcdh19 expression domains became restricted to the dorsal and/or lateral regions of the central nervous system, and Pcdh19 expression was not detected in the spinal cord of two- and three-day old embryos. Pcdh19 was also expressed by the eye primordium, developing retina, lens and otic vesicle. Similar to its expression in the brain, Pcdh19 expression in the eye and ear was also spatially and temporally regulated.