Excitatory amino acid transporters in the zebrafish: Letter to “Expression and functional analysis of Na-dependent glutamate transporters from zebrafish brain” from Rico et al.

Excitatory amino acid transporters (EAATs) represent a group of high affinity glutamate transporters that are involved in the regulation of extracellular glutamate levels at glutamatergic synapses. EAAT proteins have been found on neurons as well as on glia cells where they act synergistically to remove the released glutamate. In issue 81 of the Brain Research Bulletin, Rico et al. reported the identification and functional analysis of zebrafish eaat's. While this publication described several previously unpublished zebrafish eaat's, we simultaneously published a study analyzing the phylogeny of the slc1/eaat subfamily of glutamate transporters across vertebrate species. Our study revealed several additional EAAT family members as well as differences in the phylogenetic grouping of EAATs. We identified two additional eaat subfamilies, now called eaat6 and eaat7. In the present report, we now provide evidence that the eaat1c gene described by Rico et al. may rather be an eaat4 homolog. Phylogenetic analyses as well as exon alignments demonstrate that eaat1c shares characteristics with mammalian eaat4. In addition, comparison of expression of eaat1/eaat4 family members localized eaat1a and eaat1b predominantly to glia cells whereas eaat1c transcripts described by Rico et al. are as postulated for eaat4 transcripts enriched in neurons.