Serial analysis of gene expression predicts structural differences in hippocampus of long attack latency and short attack latency mice

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Abstract
The genetically selected long attack latency (LAL) and short attack latency (SAL) mice differ in a wide variety of behavioural traits and display differences in the serotonergic system and the hypothalamus‐pituitary‐adrenocortical (HPA)‐axis. Serial analysis of gene expression (SAGE) was used to generate a hippocampal expression profile of almost 30 000 genes in LAL and SAL mice. Using SAGE, we found differential expression of 191 genes. Among these were genes involved in growth, signal transduction, and cell metabolism. The SAGE study was supported by GeneChip analysis (Affymetrix). Strikingly, both SAGE and GeneChips showed a higher expression of numerous cytoskeleton genes, such as cofilin and several tubulin isotypes in LAL mice. LAL mice also showed a higher expression of several calmodulin‐related genes and genes encoding components of a MAPK cascade, namely raf‐related oncogene and ERK2. The findings were confirmed by in situ hybridization. Our results of differential expression of cytoskeleton and signal transduction genes therefore suggest differential regulation of the raf/ERK pathway that may be related to structural differences in the hippocampus of LAL and SAL mice. As stress‐related disorders, such as depression, are also linked to differential regulation of the HPA‐axis and the serotonergic system and are associated with altered hippocampal morphology, differential regulation of these genes may be involved in the pathogenesis of these diseases.