Baleen whales have remnants of tooth genes

One of the major components of teeth is enamel. Enamel caps teeth and is the hardest known substance in the human body, an understandable feature considering the amount of grinding that teeth are used for.

Blausen_0863_ToothAnatomy_02

Several genes are crucial for enamel development, including some that encode proteins that build a scaffold for the deposition of mineralized enamel and others that breakdown these proteins.

Baleen whales, which lack teeth entirely, are thought to be derived from ancestors that possessed enamel-capped teeth, as demonstrated by evidence from the fossil record and their genetic relationships to other toothed mammals. This leads to the prediction that genes important for enamel formation have become nonfunctional in baleen whales and preserved as pseudogenes.

Sure enough, Demere et al. [1] discovered that the enamel genes ENAM (enamelin) and AMBN (ameloblastin) are inactivated in baleen whales while remaining functional in other toothed mammals, including toothed whales. Meredith et al. [2] also demonstrated that the pygmy and dwarf sperm whales, two toothed whale species that lack enamel, have shared mutations in ENAM. Another paper by Meredith et al. [3] discovered that the enamel gene MMP20 (enamelysin) has been disrupted by an inactivating retrotransposon (“jumping gene”) shared in all baleen whales, suggesting that enamel formation was likely inactivated in the last common ancestor of baleen whales.

F2.large

A figure from Meredith et al. [3] showing a summary of enamel gene mutations across a whale phylogeny and transitions from toothed to toothless species incorporating the fossil record. Nodes that are black denote toothed species, gray are enamelless but toothed species, and white are toothless.

Questions for Creationists

Why would God create nonfunctional enamel genes in whales that completely lack teeth? Is it a coincidence that all baleen whales and pygmy and dwarf sperm whales have shared inactivating mutations, respectively? Is it a coincidence that the presence of tooth pseudogenes was predicted by molecular phylogenetics and the fossil record?

References

1. Deméré, T. A., McGowen, M. R., Berta, A., & Gatesy, J. (2008). Morphological and molecular evidence for a stepwise evolutionary transition from teeth to baleen in mysticete whales. Systematic Biology57(1), 15-37.

2. Meredith, R. W., Gatesy, J., Murphy, W. J., Ryder, O. A., & Springer, M. S. (2009). Molecular decay of the tooth gene enamelin (ENAM) mirrors the loss of enamel in the fossil record of placental mammals. PLoS genetics5(9), e1000634.

3. Meredith, R. W., Gatesy, J., Cheng, J., & Springer, M. S. (2010). Pseudogenization of the tooth gene enamelysin (MMP20) in the common ancestor of extant baleen whales. Proceedings of the Royal Society B: Biological Sciences, rspb20101280.

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6 thoughts on “Baleen whales have remnants of tooth genes

  1. Pingback: Ontogeny recapitulates phylogeny: Baby baleen whales have teeth (before they lose them) | Evolution For Skeptics

  2. Pingback: Pseudogenes: Enamelless mammals and toothless turtles and birds have enamel gene remnants | Evolution For Skeptics

  3. Pingback: Pseudogenes: Enamelless/toothless vertebrates have enamel gene remnants | Evolution For Skeptics

    1. Excellent question! There are multiple ways to get at this, and for obvious reasons, tooth genes have been extremely well characterized. One way is to find where these genes are expressed (i.e., turned on) and when, and examining developing mice is an excellent way to find out. We know that these various genes are turned on during tooth development, and we know enough details that we have a very good understanding of what each tooth gene is doing. For example, some of them produce a protein scaffold that allows for tooth crystals to form, and others break down the protein scaffold once the crystals are in place.

      But this doesn’t answer your question for the potential of multifunctionality. Indeed, many genes have multiple functions and losing them could potentially have disastrous consequences. In fact, for some tooth genes that we know are involved in other functions (e.g., bone function), toothless mammals still retain them as fully functional. Again this is where mouse models come in handy. Various studies have shown that if you knock out these tooth genes in mice, their teeth do not develop properly but their bodies are otherwise healthy. Additionally, these same tooth genes are associated with tooth diseases in humans (e.g., amelogenesis imperfecta), and besides dental issues, which can be quite severe, the diseased humans are otherwise asymptomatic.

      On top of that, researchers have discovered that not only have these genes accumulated deleterious mutations in the toothless baleen whales, which I describe here, but they’re also nonfunctional in toothless birds, toothless turtles, toothless anteaters and toothless pangolins. The enamel specific genes are also nonfunctional in enamelless species such as sloths, armadillos, narwhals, pygmy sperm whales, and aardvarks. I describe some examples here: https://evolutionforskeptics.wordpress.com/2014/11/08/pseudogenes-enamelless-mammals-and-toothless-turtles-and-birds-have-enamel-gene-remnants/

  4. Pingback: When whales walked: Fossils document the rise of the largest animals on earth – Evolution For Skeptics

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