Differential expression of two zebrafish emx homeoprotein mRNAs in the developing brain.

The complete amino-acid sequences of two zebrafish emx homeoproteins containing a homeodomain homologous to that of the Drosophila empty spiracles head gap gene product have been determined by cloning and sequencing of cDNAs. The zebrafish emx1 and emx2 homeoproteins consist of 233 and 247 amino acids, respectively. The zebrafish emx1 and emx2 mRNAs are present at 12 h after fertilization, when the presumptive brain is in a simple tubular structure, and before first primary neurons appear. During brain development, the emx1 mRNA is localized in the dorsal telencephalon, whereas the emx2 mRNA is distributed in the dorsal telencephalon, parts of the diencephalon and the otocyst. The differential expression patterns of the two emx homeoprotein mRNAs may define the subdivisions of the zebrafish telencephalon.