The team also found homologs of ENaC in a single-celled organism, the Naegleria gruberi. Although N. gruberi is a eukaryote and shares a common ancestor with Metazoans, it is located on a different branch of the eukaryotic family tree, among the Excavates. At first glance it might make sense to assume that both Metazoans and Excavates got their ENaC from their common eukaryotic ancestor, but ENaC is absent in all other branches of the eukaryotic tree.
Dr. Rossier said that although it is possible that the genes for ENaC originated in the common ancestor of eukaryotes and were lost in all branches except the Metazoa and the Excavates, there is another possibility. There could have been a lateral transfer of genes between N. gruberi and a Metazoan ancestor, one that lived between the last common ancestor of all eukaryotes and the first Metazoans.
Whether a Metazoan transferred the genes for ENaC to N. gruberi or the other way around, Dr. Rossier is not sure. Either way, the fact that ENaC gene family appeared just before the emergence of Metazoans suggests it is somehow linked to the development of multi-celled organisms, he said.
|Contact: Donna Krupa|
American Physiological Society