ELSEVIER Molecular Brain Research 26 (1994) 189-196 MOLECULAR BRAIN RESEARCH Research Report Differential expression of sgk mRNA, a member of the Ser/Thr protein kinase gene family, in rat brain after CNS injury K. Imaizumi a,c,., M. Tsuda a,c, A. Wanaka b, M. Tohyama b, T. Takagi a a Department of Molecular Neurobiology, 'Tanabe, b Department of Anatomy and Neuroscience, Osaka University Medical School, Osaka, Japan c Research Laboratory of Applied biochemistry, Tanabe Seiyaku Co. Ltd, Osaka, Japan Accepted 24 May 1994 Abstract We cloned genes the expression of which were induced 3 days after cortical injury of rat brain by a differential display technique, and four novel and known sequences were isolated. Among these sequences, the sgk gene which was recently identified as a novel member of the serine/threonine protein kinase gene family, was selected for analysis of its expression patterns in rat brain by northern blotting and in situ hybridization, because hybridization signals were strong at the lesion sites. Expression of sgk mRNA was induced within 3 days after injury, and was maintained at a high level for at least 14 days. The cells which strongly expressed the sgk gene were in the deep layers of the cortex and in the corpus callosum. In situ hybridization analysis for sgk and myelin proteolipid protein mRNA using serial sections showed that the distribution of both signals was very similar at the damaged regions. Therefore, it is likely that the sgk transcript is expressed by oligodendrocytes after brain injury. Investigation of the developmental expression of the sgk gene showed that neurons in layers I and II of the cortex, lateroposterior and laterodorsal thalamic nucleus, and ventral posterolateral and posteromedial thalamic nucleus strongly expressed sgk mRNA at postnatal day 1 and day 7, but these neurons showed no expression in fetal or adult brain. These results suggest that the induction of sgk gene may be associated with a series of axonal regenerations after brain injury, and in addition, the sgk gene may also play important roles in the development of particular groups of neurons in the postnatal brain. Keywords: sgk; Brain injury; Oligodendrocyte; Differential display; Transcriptional regulation 1. Introduction Injury of the central nervous system (CNS) leads to histopathological reactions including invasion of macrophages, proliferation of glial cells and sprouting of neural fibers [5,8,22]. In the regenerative events following CNS injury, a number of molecules have been shown to be differentially expressed. For exam- ple, expression of basic fibroblast growth factor, a neurotrophic factor, is increased associated with brain injury. It is released into the lesion site from damaged or dying cells and from invading macrophage cells, and plays an important role in neuronal sprouting and survival [11,12]. Other mRNAs and proteins which * Corresponding author. Department of Molecular Neurobiology, 'Tanabe', Osaka University Medical School, 2-2 Yamadaoka, Suita, Osaka 565, Japan. Fax: (81) 6-879-3648. 0169-328X/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0169-328X(94)00118-X show elevated levels during brain damage have been identified, and include early-regulated genes [7,14] and some other growth factors [9,13]. In addition, other molecules may be regulated through signaling cascades mediated by the above mRNAs and proteins. The collective delivery of these molecules to the lesion presumably promotes wound healing. However, the molecular events underlying neuronal regeneration re- main unclear, and other novel molecules which re- spond to brain injury and are transcriptionally regu- lated are likely to exist. We attempted to clone genes induced after brain injury using the differential display technique. The differential display technique is an effective method to identify and isolate genes that are differen- tially expressed in various cells or under altered condi- tions [19,20]. In the present study using this method, we compared the expression patterns of mRNAs be- tween intact and injured rat cortex, and isolated sev-