Evolution of the Cation Chloride Cotransporter Family: Ancient Origins, Gene Losses, and Subfunctionalization through Duplication

Abstract

The cation chloride cotransporter (CCCs) family comprises of four subfamilies-K(+)-Cl(-) cotransporters (KCCs), Na(+)-K(+)-2Cl(-) cotransporters (NKCCs), and Na(+)-Cl(-) cotransporters (NCCs)-and possibly two additional members-CCC interacting protein (CIP1) and polyamine transporters (CCC9)-as well. Altogether, CCCs can play essential physiological roles in transepithelial ion reabsorption and secretion, cell volume regulation, and inhibitory neurotransmission and so are present across all domains of life. To gain insight into the evolution of this family, we performed a comprehensive phylogenetic analysis using publically available genomic information. Our results clearly support CIP1 as being a true CCC based on shared evolutionary history. By contrast, the status of CCC9 in this regard remains equivocal. We also reveal the existence of a single ancestral CCC gene present in Archaea, from which numerous duplication events at the base of archaeans and eukaryotes lead to the divergence and subsequent neofunctionalization of the paralogous CCC subfamilies. A diversity of ensuing gene-loss events resulted in the complex distribution of CCCs present across the different taxa. Importantly, the occurrence of KCCs in "basal" metazoan taxa like sponges would allow an early formation of fast hyperpolarizing neurotransmission in metazoans. Gene duplications within the CCC subfamilies in vertebrates (in particular, KCCs, NKCCs, and NCCs) lend further evidence to the 2R hypothesis of two rounds of genome duplication at the base of the vertebrate lineage, especially in concert with our syntenic cluster analyses. This increased number of KCCs, NKCCs, and NCCs isoforms facilitates their further, important subfunctionalization in the vertebrate lineage.

K-Cl cotransporters, cell volume homeostasis, and neurological disease

“…Evolution of KCCs, which first appeared in basal metazoan taxa, such as sponges, likely enabled fast hyperpolarizing neurotransmission via their establishment of low neuronal [Cl − ] i [103]. The evolution of organismal multicellularity likely necessitated the ability to precisely regulate the ionic and osmotic composition of fluid compartments separated by epithelia.…”

Differences in molecular mechanisms of K+ clearance in the auditory sensory epithelium of birds and mammals

“…In chicks, connexins 26 and 30 were shown to be expressed in supporting cells of the basilar papilla. In contrast, birds have lost the gene Slc12a6 encoding KCC3 and amphibians and lizards are devoid of Slc12a7 encoding KCC4 (Gagnon and Delpire, 2013;Hartmann et al, 2014), suggesting differences in the K + circulation system in tetrapod inner ears. To clarify this issue, we examined the expression of avian orthologs of the mammalian toolkit.…”

Plasma Membrane Targeting of Endogenous NKCC2 in COS7 Cells Bypasses Functional Golgi Cisternae and Complex N-Glycosylation

“…These symporters belong to the Slc12a family of solute carriers, which comprise at least eight homologous genes: Slc12a1 (NKCC2), Slc12a2 (NKCC1), Slc12a3 (Na + -Cl − co-transporter, NCC), Slc12a4-7 (K + -Cl − co-transporters, KCC1-4), and Slc12a9 (Hartmann et al, 2014). NKCCs and NCCs actively accumulate Cl − in cells, using the energy stored in the sum of the Na + , K + , and Cl − chemical potential gradients, whereas KCCs mediate active Cl − extrusion driven by the sum of the K + and Cl − chemical potential gradients.…”