Wednesday, 16 November 2011

Evolution of NaK-ATPase and ENaC: Part II: ENaC/Degenerin evolution in Metazoan


The ENaC is a channel homologous to the ASIC channel, both belonging to the ENaC/Degenerin family. The full complex is composed by three subunits (different or similar) and a single subunit is composed by two membrane segments and a long loop.
Author: NEUROtiker
In the kidney, it transports the sodium from the lumen to the cell. It is based in the apical side of the cell. In the basolateral side, we find the Na,K-ATPase pump.

We applied the same phylogenetic procedure than for the Na,K-ATPase.

It was known that the ENaC/Degenerin family is present in Vertebrates, Insects, Nematodes and other bilaterian organisms (such as Aplysia kurodai, a mollusk), and we extended this knowledge to the most basal animals such as sponges, Trichoplax (a "blob" that looks like nothing) or Cnidaria. In the vertebrate ancestor, ENaC and ASIC were already present. The two rounds of whole-genome duplication gave rise to four ENaC genes (α, β, γ and δ) and four ASIC genes (and another fifth ASIC (BLINaC) that came from older time). These new and diversified copies inside the same organism allowed differential expression and multiple variation of the trimere. For example, we found ENaC in the kidney, but also in the brain or on the tongue.

Along with the Na,K-ATPase, the presence of ENaC/Degenerin in the Urmetazoan provides a tool to make polarised cells and to build its first internal milieu.

Another importance of the EnaC/Degenerin family in Metazoan could have a link to cell movement and global contraction. I recently saw videos of Sponges and Trichoplax movements (see video below). It is well know that some members of the ENaC/Degenerin family are playing a role in the sensory mechanotransduction in Nematodes or in salt perception in flies or rodents. I am wondering if they could have a similar role in most basal animals.

video 
 Copyright by M. Nickel (http://www.porifera.net)

video
 Copyright by M. Nickel (http://www.porifera.net)

Oh, did I say the ENaC/Degenerin is exclusively restricted to Metazoan? It's maybe not entirely true as we found a dozen of exemplars in the genome of Naegleria gruberi, a protozoan. But I will keep this story for tomorrow.

RAS


Studer, R.A., Person, E., Robinson-Rechavi, M., & Rossier, B.C. (2011). Evolution of the epithelial sodium channel and the sodium pump as limiting factors of aldosterone action on sodium transport Physiological Genomics, 43 (13), 844-854 DOI: 10.1152/physiolgenomics.00002.2011

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