# Phenotype of White Sika Deer Due to SCF Gene Structural Variation
## 1 Introduction  
Sika deer (_Cervus nippon_) is an important livestock in China that has great economic value, as most parts of its body can be used in the field of medicine and health products. The sika deer has a unique coat color phenotype that is typically brown in the summer, with white spots on the sides of the body and black backs of the ears. There are also some individuals that have a black dorsal line running from the head and neck to the tail. As winter arrives, the coat color deepens to gray, and the white spots become blurred. It is difficult to find a sika deer with any other coat color, especially white, despite the large number of sika deer in the world, both wild and captive. The white sika deer has been a symbol of good luck since ancient times in China and has great ornamental value. Precisely because of this rarity, it is very difficult to obtain samples of white sika deer to figure out why they appear; thus, the genetic mechanism of coat color in sika deer still remains unclear. In contrast, about 5% of German red deer (_Cervus canadensis_) have white fur. [PERSON] found that in the 291 st amino acid of the YYR (tyrosinase) protein, glycine was replaced by arginine in these white red deer through genome-wide resequencing [1]. YTR is a key synthase involved in pigment synthesis, which can catalyze the oxidation of tyrosine to form dopa and dopaquinone, as well as participate in the subsequent reactions of pigment synthesis. Although [PERSON] [1] confirmed that the causes of these white red deer appearingin the German red deer population were related to TYR mutation, verifying the causes of the white phenotype's appearance in other red deer populations is still needed. Studies show that the \(MCIR\) (melanocortin 1 receptor) gene may regulate coat color in the white fallow deer [2], and that mutation of this gene (NM_174108.2:c.143T>C) results in an amino-acid exchange in the MC1R protein (NP_776533.1:p.L48P). MC1R is a G-protein-coupled receptor of melanocytes, which is involved in regulating the expression of MITF (microphthalmia-related transcription factor) by binding with the ligand \(\alpha\)-MSH(\(\alpha\)-melanocyte-stimulating hormone)or ASIP (application-specific instruction set processor). MITF can regulate the synthesis of pigment synthase and membrane transporters in a pigment synthesis reaction, ultimately affecting melanin synthesis [3]. There is a coat color trait called the roan phenotype, which is related toSCF in some ruminants, such as cattle and sheep [4; 5]. Functional mutations in the _SCF_ gene can cause the roan phenotype in ruminants and melanocyte defects in mice [6]. Individuals with the roan phenotype are usually heterozygous in genotype, while homozygous individuals have a white color covering their fur. Sheep with the homozygous genotype die at the newborn stage due to anemia and digestive disorders [7], and very few homozygous cows have abnormalities in the reproductive tract [8]. Mutations in this gene can also cause human familial progressive hyper- and hypopigmentation (FPHH), a condition in which people who carry the mutated _SCF_ gene have not been found in homozygous mutations. Histology reveals fewer pigment granules in the skin in light-colored spots and more pigment granules in darker spots [9]. The _SCF_ gene encodes a transmembrane protein that is synthesized and secreted by keratinocytes. It has two isomers, a soluble isomer and a membrane-bound isomer. The soluble isomer is mainly involved in the synthesis of melanin in melanocytes, while the membrane-bound isomer is mainly involved in the development and migration of melanocytes. Both isomers act by binding with the KIT (receptor tyrosine kinase) [10; 11]. Soluble isomer precursors are transported to the cell membrane and cut by chymotrypsin [12], before being released into the extracellular space, while transmembrane isomers remain on the membrane because they do not encode hydrolysis sites [13].