Prominent transcription of zebrafish N-myc (nmyc1) in tectal and retinal growth zones during embryonic and early larval development.

Because of its oncogenic capacity and expression restricted to embryonic and newborn tissues, the N-myc proto-oncogene is suggested to play a key role in vertebrate organogenesis as well as in the control of cell proliferation and differentiation. To further approach the developmental function of N-myc, we cloned full-length zebrafish N-myc (nmyc1) and analyzed its expression in the embryo and early larva. nmyc1 transcription is initiated at the mid-blastula stage. At somitogenesis stages, its expression was detected in the retina, midbrain, posterior hindbrain and presumptive spinal cord. nmyc1 was also transcribed in the endoderm and its derivatives as well as in branchial arches. At later developmental stages, posterior neural expression of nmyc1 was switched off, but expression remained intense in the brain, mainly in the optic tectum, cerebellar plate and dorsal rhombomere 2. Comparison of nmyc1 transcription with proliferation zones using a M phase mitotic marker revealed that nmyc1 expression is specifically associated with mitosis in the optic tectum and the retina. This result contrasts with previous studies in other vertebrates where N-myc expression can persist in differentiating cells.

Cloning and expression pattern of vat-1 homolog gene in zebrafish.

The VAT-1 protein is present in the electric organ of marine rays where it is suggested to play a central role in nerve signal transmission. VAT-1 homolog protein was also identified in mouse and human but its function remains to be determined. We have investigated VAT-1 homolog in zebrafish Danio rerio since it is an excellent model amenable to the combination of genetic, molecular and embryological studies. Amino acid sequence analysis shows that the zebrafish VAT-1 homolog shares approximately 51-61% identity with the electric ray, mouse, and human counterparts. By in situ hybridization, vat-1 homolog mRNA is first observed in the trigeminal nuclei at the 8-somite stage. At 20-somite stage, vat-1 homolog is detected in the brain, namely in primary clusters of neurons, in the epiphysis and in the hindbrain. vat-1 homolog is also present in the neural tube but this expression disappears after 72 h post-fertilization. At 24 h post-fertilization, vat-1 homolog starts to be expressed in the developing gut. At later stages, vat-1 homolog is present throughout the brain, appears in the maturing retina and the pharyngeal cavity.