WhY aren’t all BLACK bears
?
I n mammals, pigment, or melanin, is produced by melanocyte skin cells. There are two types of mela- nin: eumelanin is black or brown, and pheomelanin is red or yellow. Different levels of eumelanin and pheomelanin can produce a wide array of colors in animals. In addition, mutations in melanin biosynthe- sis underlie several conditions associated with im- paired fitness or disease or unusual color morphs of large animals that are specifically targeted for trophy hunting. HudsonAlpha faculty investigator Greg Barsh, MD, PhD , is an expert in morphological variation. He and his lab use color and color variation as an experimental platform to study cellular and molecular pathways that are involved in different processes throughout the body. Barsh and collaborators from the University of Memphis and the University of Pennsylvania recently set out to study the genetics behind an interesting group of black bears 1 . In Yellowstone National Park, black bears outnumber their brownish-colored grizzly bear
GENE VARIANT RESPONSIBLE FOR CINNAMON MORPH BLACK BEAR
Barsh and his colleagues set out to determine when, where, and how the U. americanus cinnamon morph arose. With help from partners in state, provincial, and federal wildlife agencies, and university partners in North Ameri- ca, the team collected hundreds of DNA and hair samples from North American bears. It is widely accepted that genetic variation in melanin biosynthesis gives rise to differences in hair, eye, and skin color. By studying photos of bears and chemically ana- lyzing their corresponding hair samples, the team deter- mined that in both bear species, light-colored hair is due to reduced amounts of eumelanin. Genome sequence analysis of nearly 200 bears uncovered different missense mutations in the gene Tyrosinase-related protein 1 (TYRP1) : cinnamon-col- ored black bears have a mutation called
TYRP1 R153C , while most (but not all) grizzly bears have a mutation called TYRP1 R114C . The TYRP1 gene produces an enzyme within melanocytes that helps produce eumelanin, so it makes sense that the cinnamon and grizzly bears have less eumelanin. Furthermore, functional studies determined that the TYRP1 R153C and TYRP1 R114C mutations interfere with melanin synthesis and distribution. When the team looked at other species,
cousins, and in coastal areas of the Pacific Northwest, if someone says “brown bear,” they mean grizzly bear. But not all brown bears are grizzly bears. American black bears ( Ursus americanus ), which one would logically assume are black, actually come in a wide range of colors, including brown (also known as cinnamon), blond, or bluish-grey. Others have coats that are a mixture of several colors. So, how do you tell a cinnamon-colored Ursus
cinnamon-colored black bear
they were surprised to find the TYRP1 R153C variant responsible for cinnamon U. americanus is identical to one previously described as a cause of oculocutaneous albi- nism (OCA3) in humans. OCA3 is often observed in people of African or Puerto Rican ancestry and is characterized by reddish skin and hair and frequent visual abnormalities. According to Emily Puckett, PhD, the lead author of the manuscript, bears with TYRP1 mutations have normal skin and can see just fine.
americanus from its brown (grizzly) Ursus arctos cousin? Differences in body shape and size can be subtle. One hypothesis for the cinnamon color of Ursus americanus is that it mimics the appearance of a grizzly bear, helping with camouflage or defense. Barsh, along with other researchers at HudsonAlpha, the University of Memphis, and the University of Pennsyl- vania, have discovered what causes the cinnamon color, shedding some light on this color confusion.
HUDSONALPHA INSTITUTE FOR BIOTECHNOLOGY
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