Microglia in Culture: What Genes Do They Express?

The cell culture model utilized in this study represents one of the most widely used paradigms of microglia in vitro. After 14 days, microglia harvested from the neonatal rat brain are considered ‘mature’. However, it is clear that this represents a somewhat arbitrary definition. In this paper, we provide a transcriptome definition of such microglial cells. More than 7,000 known genes and 1,000 expressed sequence tag clusters were analysed. ‘Microglia genes’ were defined as sequences consistently expressed in all microglia samples tested. Accordingly, 388 genes were identified as microglia genes. Another 1,440 sequences were detected in a subset of the cultures. Genes consistently expressed by microglia included genes known to be involved in the cellular immune response, brain tissue surveillance, microglial migration as well as proliferation. The expression profile reported here provides a baseline against which changes of microglia in vitro can be examined. Importantly, expression profiling of normal microglia will help to provide the presently purely operational definition of ‘microglial activation’ with a molecular biological correlate. Furthermore, the data reported here add to our understanding of microglia biology and allow projections as to what functions microglia may exert in vivo, as well as in vitro.