Localization and characterization of kal 1.a and kal 1.b in the brain of adult zebrafish (Danio rerio).

The gene underlying the X-chromosome-linked Kallmann syndrome KAL-1 has been identified for several years, yet its role is still poorly understood. During previous research, the KAL.1 orthologs, kal 1.a and kal 1.b, were isolated in zebrafish. In the present study, in situ hybridization was used to localize and compare the expression of kal 1.a and kal 1.b in the adult zebrafish brain (Danio rerio). The kal 1.a and kal 1.b transcription products have a similar distribution, both being localized in the olfactory bulb, in the ventral and posterior zones of the telencephalic area, hypothalamus, thalamus nuclei, corpus cerebelli, and many other nuclei, such as the posterior tuberal, the periventricular gray zone of the optic tectum, the periglomerular nucleus, the entopeduncular nucleus, parvocellular preoptic nucleus, habenular nucleus suprachiasmatic nucleus, magnocellular preoptic nucleus, griseum centrale, periventricular nucleus of the posterior tuberculum and the lobus caudallis cerebelli. In addition, by double approach of in situ hybridization and immunolabeling, it was found that, in telencephalon, the two genes are expressed in neurons and oligodendrocytes but they are not astrocytes. Finally, by using a proliferation marker, BrdU, kal 1.a and kal 1.b transcripts were shown to be clearly detected in a region previously described as an area of adult neurogenesis, suggesting that they may be involved in the process. Overall, our data provide a consolidated map of expression of kal 1.a and kal 1.b and suggest a distinct function of these genes, especially neurogenesis, in an adult context.