BASAL EXPRESSION OF THE INDUCIBLE TRANSCRIPTION FACTORS C-JUN, JUNB, JUND, C-FOS, FOSB, AND KROX-24 IN THE ADULT-RAT BRAIN

Jun, Fos, and Krox proteins are inducible transcription factors contri buting to the control of gene expression. The elucidation of their ind ividual expression patterns in the nervous system provides new insight s into the ability of neurons to react with changes of gene expression to external stimulation under physiological or pathological condition s. The expression of c-jun, JunB, JunD, c-Fos, FosB, and Krox-24 was i nvestigated in the brain of untreated male Sprague-Dawley and female B DIX rats by immunocytochemistry using specific antibodies. JunD immuno reactivity (IR) labeled the highest number of neurons, being present i n almost all neurons of the brain. JunD was expressed at high levels i n those areas that also exhibit c-jun, JunB, c-Fos, and FosB-IR, such as locus coeruleus, periolivary nuclei (nd.), pontine and central gray , lateral lemniscal ncl., inferior and superior colliculi, leaflet of geniculate ncl., midline nuclei of thalamus, dorsomedial and paraventr icular ncl. of hypothalamus, ncl. supraopticus, dorsolateral part of c audate putamen and lateral septal ncl. In contrast to the high number of JunD-positive neurons, c-Jun, JunB, c-Fos, and FosB proteins were d etected in rather low numbers of neurons in these brain areas; the ran k of the number of immunopositive neurons was c-Fos > JunB > c-Jun > F osB. Particularly high levels of expression were observed for c-Jun in medullary motoneurons, medial geniculate ncl., arcuate ncl., and dent ate gyrus, and for JunB in the CA-1 area of the hippocampus and island s of Calleja. The zinc finger protein Krox-24 was expressed in many ne urons of these brain areas, with only discrete Jun- and Fos-IR; additi onally, many intensely labeled nuclei were present in spinal ncl. of t he trigeminal ventromedial nd. of the hypothalamus and the CA-1 area o f the hippocampus. In the cerebellum, nuclear labeling was detected on ly for c-Jun, JunD, and Krox-24 in granule cells. JunD-IR was also fou nd in glial cells of gray matter and fiber tracts, whereas glial c-Jun -IR was observed only in fiber tracts. Apart from a weak JunD-IR, some areas did not express Jun, Fos, and Krox proteins such as cuneate and gracile ncl., venterobasal complex of thalamus, globus pallidum, and Purkinje cells of the cerebellum. Our data indicate that inducible tra nscription factors of the fos, jun, and krox gene families show patter ns of individual expression in untreated animals, thereby reflecting d ifferent mechanisms and/or thresholds for induction under physiologica l conditions. (C) 1995 Wiley-Liss, Inc.