TRANSCRIPTION OF A NEW ZINC-FINGER GENE, RKRL, IS LOCALIZED TO SUBTYPES OF NEURONS IN THE ADULT-RAT CNS

Proteins which share zinc finger DNA binding motifs comprise one of th e main families of transcription factors. We have previously described rKr1, a new rat Cys(2)/Hys(2) zinc finger gene of the Kruppel gene fa mily. This gene is predominantly expressed in the nervous system, with highest abundance in neurons and with lower abundance in developing o ligodendrocytes of the CNS. Here, we have undertaken a detailed anatom ical analysis of rKr1 expression in the adult brain of the rat using i n situ hybridization. Our results show that rKr1 is expressed in a spe cific manner in defined subpopulations of neurons in many regions of t he adult brain. Moderate levels of rKr1 mRNA were detectable in some s tructures of the telencephalon (e.g. cerebral cortex and hippocampus) and a few nuclei of the thalamus. The highest degree of labelling was seen in both upper and lower motor neurons of the mesencephalon and rh ombencephalon (e.g. red nucleus, gigantocellular reticular nuclei, mot or nuclei of the cranial nerves). High levels of rKrl expression were also present in spinal motoneurons and dorsal root ganglion cells. In order to determine if rKrl gene expression can be regulated, we have e xamined the expression pattern of rKrl in the facial nucleus in respon se to facial nerve lesion. The expression of rKrl in the facial nucleu s showed a differential downregulation, reaching lowest levels 1 week after transection of the facial nerve. By 3 weeks after lesion, expres sion of rKrl on the operated side of the brain reached normal levels a nd was identical to that of the unoperated side. These data suggest th at rKrl could be involved in the maintenance of the phenotypic differe ntiation of specific neuronal subtypes including motoneurons.