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The Genetics of Hairless Dogs:Dental Phenotype and Archaeological Records By Carrie Faber

Most people have either seen or heard of a hairless dog breed at least once in their lives. Hairlessness and its uniqueness in the mammal world is easily recognizable, but why does it occur? How long have we had these hairless dog breeds for and what are the genetic components? We will explore the archeological findings of these ancient breeds from different parts of the world, as well as the genetic correlation with a unique dental phenotype.

The lack of hair and abnormal tooth morphology in hairless breeds exhibit canine ectodermal dysplasia (CED). A study published in 2017, found a gene shared by 3 hairless breeds: the Chinese Crested, Peruvian, and Mexican Hairless. FOXI3 is expressed in the development of teeth and hair. “This has been attributed to a semi-dominant 7-base-pair duplication in the first exon of the forkhead box I3 gene (FOXI3)...we identified this FOXI3 variant in a historical museum sample of pedigreed hairless dog skulls by using ancient DNA extraction and present the associated dental phenotype” (Kupczik, et al., 2017).

Another study analyzed the CED mutation in the same 3 breeds, concluding that it is “inherited as a monogenic autosomal semidominant trait.” They mapped the mutation to a “102-kilo-base pair interval on chromosome 17…analysis revealed a frameshift mutation within the FOXI3 coding sequence in hairless dogs. Thus we have identified FOXI3 as a regulator of ectodermal development” (Drögemüller, et al. 2008). The underlying mutation yields a “frameshift that produces a premature stop codon and loss of 95% of the normal protein” (Parker, et al., 2017).

Despite having such diverse origins from around the globe, the dominance of this phenotype has helped it strive through history. Even evolutionary biologist Charles Darwin took interest with dental surgeon, Charles Sissmore Tomes who exchanged letters back and forth describing “naked Turkish dogs, extremely deficient in [their] teeth” (Darwin Correspondence Project, 2022).

It has been discovered that all hairless breeds share the same type of mutation, even though the Chinese Cresteds have more tufts of fur on their head and tail than many of the South American breeds. “The lack of homozygotes in either breed suggests that the mutation is embryonic lethal, perhaps due to other functions of the gene” (Parker, et al., 2017).

With a more dominant mutation, it is easy to detect the phenotype when crossbred with others, creating many different sizes and body shapes. There are varieties of hairless breeds around the world including the Abyssinian Sand Terriers, American Hairless Terriers, African Hairless, Peruvian Inca Orchid, Ecuadorian Hairless, Argentine Pila dog and the Hairless Khala. Not only were they worshiped in most native cultures as guides into the afterlife, but many travelers also ventured with these dogs to help with maintaining warmth and controlling rodent populations. With the help of migrating humans, these hairless dog breeds have had additional help to continue spreading their genes throughout history, becoming extremely recognizable today (Bolton, 2020).

In comparison, coated dogs do not show to have nearly as many missing teeth as hairless breeds, making it easier to identify and categorize the breed types in certain historical dog remains. “The hairless dogs were characterized in both the mandibular and maxillary dentition by a loss of the permanent canines, premolars and to some extent incisors…the deciduous fourth premolars and permanent first and second molars consistently lacked the distal and lingual cusps; this resulted in only a single enlarged cusp in the basin-like heel (talonid in lower molars, talon in upper molars)” (Kupczik, 2017).

Interestingly, they have also found the same dental phenotype on the molars of fossil carnivorans and Creodonta. Creodonts were a hypercarnivorous species that varied in sizes from ten to hundreds of pounds; this extinct species resembled that of a cat, bear, and dog mixed together (Smith, 2000). This study concluded with a heavy suggestion that the gene FOXI3, is involved in this unique dental characteristic of molar cusps developing “within and across mammalian lineages including the hominids which are known to exhibit marked variability in the presence of lingual cusps” (Kupczik, 2017).

There are historical and archeological records found in Mexico of ancient hairless breeds like the Xoloitzcuintle (Mexican Hairless), dating back to the 16th century CE. Additional, older dog skeletons have also been found with abnormal-shaped or missing teeth, inspiring researchers to explore the idea of using these morphological and genetic hints as evidence to identify hairless breeds. After categorizing remains as potential hairless dogs, this study applied “ancient mitochondrial DNA analyses along with radiocarbon dating to eight archaeological dog mandibles from Tizayuca, Basin of Mexico” (Manin, 2018). Out of the 8 archeological dogs, dating to have been alive between 1620 and 370 years BP, they found 4 “different mitochondrial haplotypes including two novel haplotypes.” Discovering haplotypes shared between the archeological dogs with our modern hairless dogs further proves their common maternal ancestry.

With such a dramatic phenotypic difference, it is no wonder humans have always been fascinated by hairless dogs throughout history. Dogs are amazing creatures that have accompanied us through so much evolution to modern society. It is even more amazing that we can identify if an archaeological dog was missing hair based on the number and shape of their teeth, thanks to a semi-dominant gene, FOXI3.

References

  1. Bolton, Maggie. “We Need to Talk about the Dog! Explorations of Human–Canine Relations and Community Hybridity in Bolivia.” The Journal of Latin American and Caribbean Anthropology, vol. 25, no. 1, 21 Apr. 2020, pp. 28–47., https://doi.org/10.1111/jlca.12463.

  2. Darwin Correspondence Project, “Letter no. 9195,” accessed on 3 December 2022

  3. Drögemüller, Cord, et al. “A Mutation in Hairless Dogs Implicates foxi3 in Ectodermal Development.” Science, vol. 321, no. 5895, 2008, pp. 1462–1462., https://doi.org/10.1126/science.1162525.

  4. Kupczik, Kornelius, et al. “The Dental Phenotype of Hairless Dogs with foxi3 Haploinsufficiency.” Scientific Reports, vol. 7, no. 1, 2017, https://doi.org/10.1038/s41598-017-05764-5.

  5. Manin, Aurélie, et al. “Can We Identify the Mexican Hairless Dog in the Archaeological Record? Morphological and Genetic Insights from Tizayuca, Basin of Mexico.” Journal of Archaeological Science, vol. 98, 2018, pp. 128–136., https://doi.org/10.1016/j.jas.2018.08.008.

  6. Parker, Heidi G., et al. “The Bald and the Beautiful: Hairlessness in Domestic Dog Breeds.” Philosophical Transactions of the Royal Society B: Biological Sciences, vol. 372, no. 1713, 2017, p. 20150488., https://doi.org/10.1098/rstb.2015.0488.

  7. Smith, Thierry. “Mammals from the Paleocene—Eocene Transition in Belgium (Tienen Formation, MP7): Palaeobiogeographical and Biostratigraphical Implications.” GFF, vol. 122, no. 1, 2000, pp. 148–149., https://doi.org/10.1080/11035890001221148.



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