Gene expression profiling of neuropeptides in mouse cerebellum, hippocampus, and retina Kiyotaka Akiyama, Ph.D.*, Setsuko Nakanishi, Ph.D., Nozomu H. Nakamura, Ph.D., and Takayuki Naito, Ph.D. Molecular Neuroscience Unit, Okinawa Institute of Science and Technology, Okinawa, Japan Manuscript received June 11, 2008; accepted June 13, 2008. Abstract Objective: We examined gene expression profiling in single neuron types and small regions of the nervous system. Methods: The RNAs were extracted from mouse cerebellar Purkinje cells, granule cell layer, hippocampal CA1 and CA3 pyramidal cell layers, and three layers of the retina (outer nuclear layer, inner nuclear layer, and ganglion cell layer) were dissected by laser capture microdissection. The gene expression profiling of each sample was examined by Affymetrix GeneChip and real-time reverse transcription polymerase chain reaction. We studied the gene expression of 62 neuropeptide and hormone genes and 387 G-protein– coupled receptor (GPCR) genes. Results: Among them, cholecystokinin and neuropeptide Y genes were the most widely expressed. The gene expression of cholecystokinin was very high in the hippocampus, suggesting that chole- cystokinin transcripts might have unknown roles in the hippocampus. More than 10 neuropeptide genes were expressed in the ganglion cell layer of the retina, whereas the outer nuclear layer of the retina did not express a considerable amount of neuropeptide mRNAs. In total 12 GPCR genes were found in all tissues examined, and half were orphans (6 of 12). Conclusion: The high ratio of orphan GPCR genes suggests our limited knowledge of the ligand-receptor system in the nervous system. These results provide basic information for studying the function of neuropeptides. © 2008 Published by Elsevier Inc. Keywords: Gene expression profile; Neuropeptide; Purkinje cell; Hippocampus; Retina Introduction Brain functions remain unknown at the molecular level [1]. In a gene-based approach to the study of brain func- tions, our major research themes are the study of activity- dependent gene expression in the brain and identification of neuron types by genes expressed within them. “Activity- dependent gene expression” refers to the modulation of gene expression occurring in individual cells as a result of various stimuli, and it is believed to be correlated with self-organizing activities of the brain such as neuronal plas- ticity. The first step of this research is to obtain gene ex- pression profiling of single-type neurons and small regions of the nervous system. We designed a combinational method. The combined method, including laser capture microdissection (LCM), DNA microarray, and real-time reverse transcription polymerase chain reaction (RT-PCR), provides us with quantitative and spatial gene expression data with high sensitivity. Mouse cer- ebellum, hippocampus, and retina were used for this experi- ment due to their simple cytoarchitecture. Neuropeptides and their receptors (most are G-protein– coupled receptors [GPCRs]) [2] have characteristic expressions in different neu- rons, and they are believed to be involved in the activity- dependent gene expression system. Therefore, they are inter- esting targets for the study of activity-dependent gene expression in the brain and identification of neuron types by genes expressed within them. In this report, the gene expres- sion profile of neuropeptides and their receptors in these tissues are discussed. * Corresponding author. Tel.: +81-98-929-1352; fax: +81-98-929- 0592. E-mail address: kakiyama@oist.jp (K. Akiyama). Nutrition 24 (2008) 918 –923 www.elsevier.com/locate/nut 0899-9007/08/$ – see front matter © 2008 Published by Elsevier Inc. doi:10.1016/j.nut.2008.06.018