Adult Expression Outlines Ventralized Derivatives Along Zebrafish Neuraxis.

Signals issued by dorsal roof and ventral floor plates, respectively, underlie the major patterning process of dorsalization and ventralization during vertebrate neural tube development. The ventrally produced morphogen Sonic hedgehog (SHH) is crucial for vertebrate hindbrain and spinal motor neuron development. One diagnostic gene for motor neurons is the LIM/homeodomain gene , which has additional ventral expression domains extending into mid- and forebrain. In order to corroborate motor neuron development and, in particular, to improve on the identification of poorly documented zebrafish forebrain populations, we studied adult brains of transgenic -GFP zebrafish (3 and 6 months). This molecular neuroanatomical analysis was supported by immunostaining these brains for tyrosine hydroxylase (TH) or choline acetyltransferase (ChAT), respectively, revealing zebrafish catecholaminergic and cholinergic neurons. The present analysis of ChAT and -GFP label confirms ongoing adult expression of in zebrafish (basal plate) midbrain, hindbrain, and spinal motor neurons. In contrast, non-motor cholinergic systems lack expression. Additional presumed basal plate positive systems are described in detail, aided by TH staining which is particularly informative in the diencephalon. Finally, alar plate zebrafish forebrain systems with expression are described (i.e., thalamus, preoptic region, and subpallium). We conclude that adult zebrafish continue to express in the same brain systems as in the larva. Further, pending functional confirmation we hypothesize that the larval expression of () might causally underlie much of adult expression because it explains findings beyond ventrally located systems, for example regarding expression in the zona limitans intrathalamica and correlated -GFP expression in the thalamus.