[From a biologist colleague:] Ross and Pawlina’s histology textbook (2006; ISBN 0781750563) demonstrates a remarkable ignorance of genetics (it’s otherwise a good text) in its discussion of the parietal cells in the stomach (which are the cells that make hydrochloric acid):
“Recently, it has been hypothesized that parietal cells may have originated from a bacterium called Neurospora crassa (TJ: it’s actually a fungus) that previously existed in a symbiotic relationship with the cells of the human stomach. The basis for this hypothesis is that the human proton pump (H+/K+ ATPas) found in parietal cells bears a strong genetic similarity to proton pumps found in this bacterium. The bacterial DNA is thought to have been translocated and subsequently incorporated into the nucleus of the stem cells, probably with the help of a virus.”
This seemed awfully bizarre, so I found the abstract for the original article, pasted below. Such a scenario seems to be impossible. It’s one thing for a microorganism to exist in a symbiotic relationship with the host organism. However, for such a horizontal gene transfer to take place, the DNA would have to be transferred to the gonads if the gene would be passed along to subsequent generations.
I guess that’s what happens when you assume that sequence similarity automatically means a common ancestry (of the gene). A more likely scenario is that both cells require a protein with the same function so they have a similar sequence by design.
Once again, an ID perspective seems much closer to reality than the Darwinian (Lamarckian?) just-so stories.
J Clin Gastroenterol. 1997;25 Suppl 1:S141-8
Hypothesis–origin of the parietal cell: microorganism?
Department of Applied Pharmacology, Kyoto Pharmaceutical University, Japan.
ABSTRACT: Parietal cells, which exist in the stomach and in Meckel’s diverticulum of the ileum, secrete hydrochloric acid by means of H+,K(+)-ATPase (alpha- and beta-subunits) in the human body. Although parietal cells are generated from progenitor cells (stem cells), their lifespan (approximately 150-200 days) is dis tinctly longer than that of surface epithelial cells (4 days), which are also derived from stem cells. Microorganisms, including bacteria (both aerobic and anaerobic), are able to pump H+ out by means of H(+)-ATPase. Of interest is that 19% of the human H+,K(+)-ATPase (alpha-subunit) comprises amino acid residues identical to those of the H(+)-ATPase found in Neurospora crassa. In addition, the amino acid sequence in the ATP binding sites of animal Na+,K(+)-ATPase and yeast H(+)-ATPase with phosphorylated intermediates is highly conserved. These data appear to indicate that the parietal cell might have originated from a microorganism that was parabiosed in a separate origin, having digestive organs, that was later incorporated into a stem cell. Thereafter, the gene encoding H+,K(+)-ATPase, or those encoding GATA DNA binding proteins (transcriptional regulators of the gastric H+,K(+)-ATPase gene), or both were translocated into the nuclei, most probably with the aid of a viru s and/or a transposon under unusual circumstances. This type of gene translocation most probably occurred during the Cambrian era when Prochordata and Chordata, which have no parietal cells, were abundant. This suggests that in the process of evolution, the stem cells in the digestive organs of the Cordata might have differentiated into two cell types, i.e., surface epithelial cells and parietal cells, before the appearance of fish (which possess parietal cells with H+,K(+)-ATPase).