Hypothesis--origin of parietal cells: transfer of the H+K+-ATPase gene from parasitic microorganisms to Cnidaria?
Parietal cells present in the stomach and terminal ileum secrete a highly-concentrated hydrochloric acid into the lumen. The cells are characterized by the enzyme P-type H+K+-ATPase, which has an alpha-subunit with a high homology (>85%) for the amino acid sequences of frog, mouse and pig stomachs. Gastric H+K+-ATPase also exhibits a high homology to H+-ATPase in yeast and Na+K+-ATPase in many tissues, suggesting origination from a common ancestral ATPase. It is known that parietal cells first appeared in fish and were later expressed in evolutionarily-higher organisms. Primitive organisms, such as Cnidaria and Ctenophora, that possessed digestive organs, but not parietal cells, were abundant in the ocean more than 600 million years ago (Pre-Cambrian period). The author thus hypothesized that the genes of either H+-ATPase or H+K+-ATPase that were present in parasitic microorganisms, such as yeast, were transferred to the interstitial cells of host organisms, such as Cnidaria, eventually leading to the evolution of parietal cells. It appears that although parietal cells in the stomach developed by chance, such cells have greatly contributed to the evolution of advanced organisms, including humans, by affording safe ingestion of a large volume of various foods.
Okabe
S
S
Department of Applied Pharmacology, Kyoto Pharmaceutical University, Yamashina, Japan. okabe@mb.kyoto-phu.ac.jp
D000818:Animals; D003063:Cnidaria / Q000235:genetics*; D019143:Evolution, Molecular; D017506:H(+)-K(+)-Exchanging ATPase / Q000235:genetics*; D006801:Humans; D010271:Parasites / Q000235:genetics; D010295:Parietal Cells, Gastric / Q000201:enzymology*; D015003:Yeasts / Q000235:genetics
D017506:H(+)-K(+)-Exchanging ATPase