In the 20th century Siamese cats (Felis catus), previously being native only to Thailand (formerly known as Siam), became one of the most popular breeds in Europe and North America. Siamese cats are well known for their unique appearance, which is one of the main reasons for their popularity among the pet owners. It was previously noted that Siamese cats fur is darker in the cooler parts of the skin (extremities), such as ears, nose, tail and paws. Conversely, warmer parts of the body were associated with white- or light grey-colored fur.

Moreover, Siamese cats have a highly recognized ‘mask’ on their face for the same reason. Similar type of partial albinism has been recognized in rabbits and mice. However, the scientifically based explanation of such coat pattern began to emerge only in the early 21st century. The secret was residing in the biochemistry of the skin.

The outermost layer of the skin is known as the epidermis. Epidermis is the natural barrier protecting us against the mechanical, chemical and biological damage. Epidermis is mainly composed of specialized, keratin-producing cells, known as keratinocytes. These cells are crucial for the wound healing and coping with the minor skin injuries.

Under the layer of keratin-producing cells there are many melanin-producing cells, known as melanocytes. Melanin is the natural pigment that is responsible for our hair and skin color. Furthermore, melanin is responsible for the protection against intensive light, such as UV. When sunbathing, melanin-producing cells take the responsibility for the keratinocytes, which are unable to protect themselves. However, sometimes normal melanin production fails. The reason for this resides deep in the nuclei of the melanocytes.

Nucleus is the place, where all the information about the proteins is stored. This information is chemically encoded in the double helix of DNA. However, as the information in hard disk can sometimes go wrong, the same thing can happen in the cells. Such failings are called mutations and they can be the reason for serious disorders, such as cancer or sickle-cell anemia. When the information changes, the structure of the protein must also change. That is the reason, why mutations can end up in serious malfunctions.

Special protein (enzyme), called tyrosinase, is the main workhorse in the production of the melanin. A research team from the University of California, USA, led by L. A. Lyons, found that Siamese cats have tyrosinase that has mutated because of the changes in the DNA helix. Such mutant enzyme, as previous research papers have shown, is temperature-sensitive. It means that increasing the temperature decreases the activity of the tyrosinase. That is the reason, why cat’s warm parts of the body are coated with white, melanin-lacking hair. Tyrosinase is inactive in these parts and melanin is not produced – hair is white-colored. Conversely, in cooler extremities the enzyme is active and the melanin is produced – hair has dark color.

Such molecular mechanism of the fur color indicates that Siamese cats living in the cool weather regions should have darker pattern. The scientifically based explanation is further validated by such observation – Siamese cats in the warmth-lacking environments are really darker than those living in the warm areas.

Another research team, led by Lutz B. Giebel from the University of Wisconsin, Madison, published a research paper in the Journal of Clinical Investigation, arguing that not only Siamese cats are the victims of tyrosinase mutation. The same mechanism proves to be true for people diagnosed with temperature-related albino pigmentation. The researchers identified that the specific mutation in TYR gene is the cause of temperature-sensitive oculocutaneous albinism (OCA 1b TS) in the family of Caucasian origins. It proves that molecular mechanisms among mammals have high degree of similarity.

“The identification of feline coat color variants should enhance the understanding of mammalian physiology, support the cat as a model for human diseases and traits, and be immediately applicable for improvement and management of cat breeds and populations,” – the U.S. research team concluded in their research paper.

Written by Edvinas Stankunas

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