Scientific research on sesame coat colour genetics in the Shiba Inu

Sesame is the rarest and most debated coat colour of the Shiba Inu — and the least understood from a genetic point of view. Until 2022, the tests available were unable to distinguish a sesame dog from a red sesame one at the genetic level: two phenotypically different variants that were identical to the diagnostic tools. The study “ASIP Promoter Variants Predict the Sesame Coat Color in Shiba Inu Dogs”, published in MDPI Veterinary Sciences and indexed on PubMed, resolved this enigma — and the Shinjukawa kennel contributed biological samples and genealogical data from its own breeding dogs. Andrea Fedele is cited among the contributors in the acknowledgements of the publication.

One hair, several colours — what sesame really is

Contrary to what many believe — and, unfortunately, to what some official descriptions also report — the sesame coat is not a mix of white, red and black hairs distributed across the body. It is something far more refined: every single hair of a sesame coat carries several colours within itself, arranged in alternating bands along the shaft. Typically three bands, but there can be more: a dark tip, an intermediate red band and a base that can vary.

This phenomenon is called banding and it is the expression of the Agouti gene — the same mechanism that produces the “wild type” coat in many mammalian species, from wolves to wild mice. It is not exclusive to the Shiba: it is also found in other canine breeds with a “wolf sable” coat. But in the Shiba Inu it takes on a unique complexity, because it exists in three variants recognised by the standard — sesame, black sesame and red sesame — which differ from one another in the proportions and distribution of the bands.

The molecular competition that decides the colour

The colour of each hair band is the result of a molecular competition that takes place in the hair follicle, at the scale of melanocytes — the cells that produce the pigment.

On the surface of every melanocyte there is a receptor called MC1R. Two molecules compete to bind to this receptor, and their relative concentration determines which pigment the melanocyte produces at any given moment:

The hormone α-MSH (melanocyte-stimulating hormone), when it binds to the MC1R receptor, makes the melanocyte produce eumelanin — the dark pigment, responsible for the black or brown bands of the hair.

The Agouti protein, produced by the hair follicle cells, binds to the same MC1R receptor and blocks its response to α-MSH. When Agouti prevails, the melanocyte “switches tracks” and produces pheomelanin — the red-yellow pigment, responsible for the light bands.

It is not a simple on/off switch. As the foundational studies by Lu et al. (1994, Nature) and Ollmann et al. (1998, Genes & Development) demonstrated, Agouti and α-MSH are two independent ligands that inhibit each other reciprocally and transmit opposing signals through the same receptor. It is a dynamic competition — a molecular pendulum that oscillates during hair growth.

The pendulum: what makes one or the other prevail

The Shiba’s hair grows in phases (the hair cycle), and the colour is built up layer by layer during the active growth phase (anagen). At the base of each follicle there is a structure called the dermal papilla, which releases molecular signals that change over time and regulate hair growth.

The Agouti gene has two promoters — like two independent switches that turn it on at different times and in different areas of the body:

The ventral promoter (VP) is always active on the belly and the lower areas of the body. This is why the urajiro — the typical light areas of the Shiba — is permanently light: the concentration of Agouti is constantly high, the melanocyte produces pheomelanin and the hair stays red or cream.

The hair cycle promoter (HCP) acts on the dorsal surface of the body, and its activity oscillates. At the start of hair growth, the HCP is still silent: the concentration of Agouti is low, α-MSH prevails, and the melanocyte produces eumelanin — the tip of the hair is coloured dark. At a certain point in anagen, the HCP switches on: the concentration of Agouti rises, the pendulum inverts, and the melanocyte shifts to producing pheomelanin — the red band is formed. When HCP activity subsides, eumelanin returns and another dark band appears.

The exact mechanism that triggers HCP activation — the precise molecular “trigger” — is still being studied. What is known is that it is linked to the hair growth cycle and to the signals from the dermal papilla, but the specific trigger remains one of the open frontiers of coat colour genetics in mammals. What recent research has clarified is that different HCP variants exist, each with a different strength — and this is where the story of red sesame becomes clear.

The discovery: red sesame is genetically different

Before this study, the genetic tests available could not distinguish a red dog from a red sesame one. A breeder who had their breeding dogs tested got the same result for both — making it impossible to select specifically for red sesame.

The study, analysing 57 Shiba Inu (42 red, 11 red sesame and 3 sesame) with buccal swabs sent in by owners and breeders — Shinjukawa among them — demonstrated that red sesame has a specific genotype that was until then invisible to traditional tests: the Ays/at combination, where Ays is a variant of the HCP1 promoter and at is a non-functional variant (HCP3).

In simple terms: red sesame is a dog that has inherited one copy of a “strong” promoter (which pushes towards red) and one copy of a “switched off” promoter (which on its own would produce black and tan). A single copy of the strong promoter is not powerful enough to keep the concentration of Agouti as high as two copies would — the result is a pendulum that oscillates in an intermediate way, producing that characteristic dark overlay on a red base with the typical red sesame mask.

It is a matter of gene dosage:

The study confirmed this model by also identifying a rare Ays/Ays specimen, whose coat was consistent with the prediction: similar to red sesame but with significantly more red.

An evolutionary clue in puppies

There is a fascinating aspect that links the genetics to the evolutionary history of the Shiba. Sesame puppies at birth do not fully express their colour, they are dark, very similar in colour to red puppies, one of the visible differences is in the urajiro, which follows the black and tan pattern rather than that of the red. The true sesame coat only begins to emerge after a few days, when the HCP promoter begins to oscillate, producing the characteristic coloured bands.

A possible explanation may lie in the puppy’s coat. Shorter and with a different growth cycle, it simply would not give the promoter time to activate the Agouti oscillation mechanism, which only begins to be expressed after a few days, to give the puppy the mimetic protection of sesame when it will need it most, when leaving the den.

This is not a scientific certainty but a hypothesis consistent with what we observe daily in breeding, and with what evolutionary biology tells us about the protective function of colour in the first period of a mammal’s life.

What it means for breeders — and for those choosing a puppy

Before this study, selecting for red sesame was a shot in the dark: you mated known carriers and hoped. Now a genetic test exists that identifies the ASIP promoter variants and makes it possible to know in advance whether a mating has the potential to produce red sesame puppies.

For Shinjukawa, having contributed to this research with the biological samples and genealogical data of our breeding dogs is not a decorative fact. It is proof that our approach to selection goes beyond empirical experience — it integrates scientific understanding of the breed at a level that very few kennels in the world can offer.

Scientific references:

References

• Belyakin S.N. et al. (2022). “ASIP Promoter Variants Predict the Sesame Coat Color in Shiba Inu Dogs.” Veterinary Sciences, 9(5), 222. MDPI. [Link to the publication: URL_MDPI] — [PubMed: URL_PUBMED]
• Lu D. et al. (1994). “Agouti protein is an antagonist of the melanocyte-stimulating-hormone receptor.” Nature, 371, 799–802.
• Ollmann M.M. et al. (1998). “Interaction of Agouti protein with the melanocortin 1 receptor in vitro and in vivo.” Genes & Development, 12, 316–330.
• Bannasch D.L. et al. (2021). “Dog colour patterns explained by modular promoters of ancient canid origin.” Nature Ecology & Evolution, 5, 1415–1423.