The genome sequencing of an albino Western lowland gorilla reveals inbreeding in the wild [OpenAccess]
The only known albino gorilla named Snowflake was a male wild-born Western lowland gorilla (Gorilla gorilla gorilla) from Equatorial Guinea. He was brought to the Barcelona Zoo in 1966 at young age, where he gained popularity worldwide. Snowflake presented the typical properties of albinism as seen in humans: white hair, pink skin, blue eyes, reduced visual acuity and photophobia. Given his lack of pigmentation and thus reduced protection from UV light, the aged albino gorilla developed squamous-cell carcinoma that led to his euthanasia in 2003.
Snowflake was diagnosed with non-syndromic albinism (Oculocutaneous Albinism, OCA). This is a group of Mendelian recessive disorders characterized by the generalized reduction of pigmentation in skin, hair, and eyes. Pigmentation is determined by melanin compounds, which are produced in melanocytes and are transported via melanosomes into keratinocytes of the epidermis and hair follicles. It has been widely studied in humans and four genes are found to be causative of this disorder: (i) OCA1A/B (MIM 203100,606952) are caused by mutations in the gene TYR(Tyrosinase) (ii) mutations in the OCA2 gene (previously known as P-gene) can cause OCA2 phenotype (MIM 203200) (iii) mutations in TYRP1 cause OCA3 (MIM 203290) and (iv) OCA4 (MIM 606574) is caused by mutations in SLC45A2 (formerly known as MATP and AIM1). Tyrosinase and TYRP1 are critical in the melanin synthesis pathway whereas P protein (OCA2) and SLC45A2 are involved in melanocytes maintenance or formation.
A previous study tried to assess whether the causative mutation of Snowflake’s albinism was located in the TYR gene but no causative mutation was found. Here, we make use of whole genome sequencing to provide a better characterization of all known genes related to albinism to try to ascertain the genetic component causing this phenotype and to study genome wide patterns that can help the field of conservation genetics. Most of the knowledge about ecology, population dynamics, demography and social behavior about gorillas has been collected from mountain gorillas (Gorilla beringei beringei) and until recently this has not expanded to Western lowland gorillas. This effort has been extremely helpful to improve our knowledge and conservation of this endangered species. With the development of conservation genetics we have gained insights into population genetics, demographic history and group relationships through the usage of both microsatellites and mitochondrial markers. The main difficulty of these studies is that non-invasive samples such as hair or feces cannot provide DNA of high quality.
Here, using high quality DNA and next-generation sequencing, we have studied for the first time the whole genome of a wild born Western lowland gorilla. It is important to stress that previous whole-genome sequencing projects of Western lowland gorillas, involved captive-born individuals, Kamilah and Kwan, individuals that do not belong to a wild population as it has been recently studied with microsatellite markers. Studying this unique albino gorilla, we find the first evidence of inbreeding in wild Western lowland gorillas.