Gene expression in astrocytes, neurons, and oligodendrocytes

In order to gather data on the gene expression characteristics of the brain, Cahoy et al purified cell suspensions of astrocytes, neurons, and oligodendrocyte lineage cells. They then used dChip software (here) to determine the gene expression of each cell type at various days postnatal.  Here’s a dendogram showing the hierarchical clustering of cell types based on gene expression:

similarity of gene expression between cell types shown via the vertical distances of each branch; doi:10.1523/JNEUROSCI.4178-07.2008

Two take aways from this are that 1) astrocytes are just as dissimilar to oligodendrocytes as they are to neurons, meaning that the concept of glial cells is outdated and 2) maturing cell gene expression is closer to mature expression than it is to immature expression in any given cell.

Here are the top 40 genes whose expression is particularly upregulated in neurons:

doi:10.1523/JNEUROSCI.4178-07.2008

The top ones are neurod6 which is involved in cell differentation during nervous system devo, glycine receptor subunit-2, nov which codes for a protein that might be in cell adhesion signaling, prdm8 which is important in developing cell morphology, and sla which is apparently involved in T cell receptor signaling. The function of most of these genes has yet to be elucidated much.

Here are the top 40 genes particularly upregulated in astrocytes:

doi:10.1523/JNEUROSCI.4178-07.2008

Genes involved in a number of metabolic pathways are upregulated in astrocytes, such as amino acid (especially glutamate) synthesis and glycolysis. Many genes involved in phagocytotic pathways are also upregulated, suggesting astrocyte roles in breaking down apoptotic cells and in axon pruning. These two roles are presumably interrelated.

Reference

Cahoy JD, et al. 2008 A Transcriptome Database for Astrocytes, Neurons, and Oligodendrocytes: A New Resource for Understanding Brain Development and Function. J Neuro doi:10.1523/JNEUROSCI.4178-07.2008