ORIGINAL PAPER Yin Yang 1 Expression in the Adult Rodent Brain Marcin Rylski Æ Renata Amborska Æ Katarzyna Zybura Æ Filip A. Konopacki Æ Grzegorz M. Wilczynski Æ Leszek Kaczmarek Accepted: 19 May 2008 Ó Springer Science+Business Media, LLC 2008 Abstract Yin Yang 1 (YY1) is a ubiquitous transcription factor belonging to Polycomb group proteins. Its expression patterns in the adult brain have not been before clearly elucidated. Using immunohistochemical stainings, we show a distribution of YY1 protein throughout the adult rodent brain. Furthermore, we characterize a cellular localization of YY1 protein and mRNA in the adult rat hippocampus. We have found that YY1 is expressed in all major brain regions, although not ubiquitously in all cells, and its expression levels vary significantly depending on the brain structure. In most of the regions YY1 is not very abundant, but in the olfactory bulb, cerebellar cortex, hippocampus, cerebral cortex, wall of the lateral ventricle and rostral migratory stream intense YY1 staining is observed. In the rat hippocampus, YY1 protein and mRNA are very strongly expressed in neurons, and to a lesser extent in oligoden- droglia and microglia. In contrast, we have not detected YY1 protein in astrocytes, which are the most abundant component of hippocampal glia. Moreover, we show that in the adult rodent brain, YY1 is expressed exclusively in the cell nuclei, except of a molecular layer of cerebellar cortex, where it is also present in the cytoplasm. Interestingly, YY1 staining is accumulated in a form of granules in cell nuclei of different types of brain cells. Thus, our data demonstrate that in the adult rodent brain YY1 is predominantly local- ized to neurons. Keywords YY1 Á Hippocampus Á Expression Á Brain Á Neuron Á Astrocyte Introduction YY1 is a ubiquitously expressed transcription factor con- taining four C-terminal zinc finger motifs of the Cys2–His2 class in its DNA-binding domain [1]. It is highly conserved both structurally and functionally from Xenopus to mam- mals [2] and it has also its homolog in Drosophila– Polycomb group protein Pleiohomeotic [3]. YY1 can either activate, or repress, or initiate transcrip- tion, depending upon cell type, biologically relevant stimuli and/or promoter context [4]. YY1 regulates gene expression during such diverse phenomena as cell growth and prolif- eration, differentiation, development, apoptosis, oncogenic transformation, genomic imprinting and X-chromosome inactivation [2, 5, 6]. Intriguingly, YY1 functions also as a Polycomb group protein in Drosophila as well as in mam- mals [7, 8]. Polycomb proteins are implicated in a formation and maintenance of a long-term cellular memory as epige- netic regulators exerting long-lasting transcriptional repression working in multimeric protein complexes which display diverse enzymatic activities transforming chromatin into compacted, regulatory inaccessible structures [9–11]. Special issue article in honor of Dr. Anna Maria Giuffrida-Stella. M. Rylski (&) Á R. Amborska Á K. Zybura Á F. A. Konopacki Á L. Kaczmarek (&) Department of Molecular and Cellular Neurobiology, Nencki Institute of Experimental Biology, ul. Pasteura 3, 02-093 Warsaw, Poland e-mail: mrylski@nencki.gov.pl L. Kaczmarek e-mail: L.Kaczmarek@nencki.gov.pl F. A. Konopacki Á G. M. Wilczynski Department of Neurophysiology, Nencki Institute of Experimental Biology, 02-093 Warsaw, Poland F. A. Konopacki Postgraduate School of Molecular Medicine, 02-093 Warsaw, Poland 123 Neurochem Res DOI 10.1007/s11064-008-9757-y