Human chromosomes 11 and 12, which have parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) on their respective short arms, are known to have arisen through an ancient gene duplication event.1 Every species from sharks through to man has at least one of each of the genes for PTH and PTHrP. In some of the fish species, multiple genes for both PTH and PTHrP have been identified. The phylogenetic analysis indicates that in the elephant shark (Callorhinchus milii) the point where the duplication resulting in these genes took place is close. There were two copies of the PTH gene in elephant sharks and these have not persisted in higher vertebrates indicating that one of these PTH genes has accumulated a number of deleterious mutations and has been lost in the process. The recent sequencing of the Japanese lamprey genome (Lethenteron japonicum)2 is instructive. Jawless fish (lampreys and hagfish) have a pivotal position in evolutionary history, having undergone two whole genome duplications when compared with invertebrates. Like sharks, they have a cartilaginous skeleton but have the ability to move from seawater to freshwater. Whole genome duplications affect the animals entire set of genes simultaneously and after the duplication one copy of the gene may be lost or acquire a new function. The Japanese lamprey genome database has been interrogated for the presence of PTH and PTHrP. Also tissues from the Japanese lamprey were examined for the expression of these genes. Certainly two receptors for PTH and PTHrP (pth1r and pth2r) are present in agnathan genome (Petromyzon marinus).3 Two PTH receptors have also been identified in invertebrates (Ciona intestinalis) but the ligands have not been found.4 The evolutionary history of PTH and PTHrP might indicate which of these genes was the original gene and what possible novel roles each of the proteins/hormones may have.
Disclosure: The authors declared no competing interests.
1. Comings. Nature 1972 238 455.
2. Mehta et al. Proc Natl Acad Sci U S A2013 110 16044.
3. Pinheiro et al. BMC Evol Biol 2012 12 110.
4. Kamesh et al. BMC Evol Biol 2008 8 129.