Efficient removal of glutamate from the synaptic cleft is essential to end synaptic transmission protecting neurons from excitotoxicity. This is achieved by excitatory amino acid transporters (EAAT), which belong to the Solute Carrier Family 1 (SLC1) gene family. Besides glutamate and associated cation transport, EAATs induce a chloride conductance upon glutamate binding.
Phylogenetic analysis of the SLC1 gene family revealed duplication and deletion events during evolution leading to varying number of SLC1 genes in different species. While the zebrafish genome contains thirteen SLC1 genes, amphibians have retained nine and mice and humans only seven SLC1 genes.
In this study, we compare expression and function of selected vertebrate SLC1 genes across species (Zebrafish, Xenopus, anole lizard, chicken and mouse) in the retina. Retinal expression of SLC1 RNA provides an ideal system to compare the abundance of SLC1s in different vertebrate species, identifying potential sub-, non or neofunctionalization events. In fact we found striking differences in RNA expression between different species.
For further examination of these differences, we elaborate the biophysical properties of the SLC1 family members by expression of the transporters in Xenopus oocytes and subsequent two electrode voltage clamp recordings. This allows us to correlate expression and function across species and thereby to follow the evolutionary history of the SLC1 gene family.