# Phenotype of White Sika Deer Due to SCF Gene Structural Variation
## 4 Discussion
The exon sequence of the _SCF_ gene was extracted from the sika deer genome, and the structure of the SCF protein was predicted using online software ([[https://services.healthtech.dtu.dk/service.php?TMHMM-2.0](https://services.healthtech.dtu.dk/service.php?TMHMM-2.0)]([https://services.healthtech.dtu.dk/service.php?TMHMM-2.0](https://services.healthtech.dtu.dk/service.php?TMHMM-2.0)), accessed on 20 January 2023) after sequence translation (Figure S1). The mutation position was located in the transmembrane region and part of the intramembrane region of the _SCF_ protein. Surprisingly, a similar _SCF_ gene mutation was identified in SLD (Steel-Dickie) mice [30]. This kind of mouse has black eyes and a white coat color, and its features are also caused by structural variation in the _SCF_ gene. Mutation caused a deletion of 4.0 kb in the _SCF_ gene sequence, resulting in keratinocytes only encoding a soluble isomer lacking transmembrane and cytoplasmic domains [31]. The membrane-bound isoform cannot be encoded after mutations in the _SCF_ gene, which plays a major role in melanocyte development and migration. This can guide cells to move along the correct route by mediating adhesion [30]. Although the mutant _SCF_ gene may still retain the ability to encode soluble isomers, neural crest cells that did not differentiate into melanocytes during embryonic development cannot transfer to the epidermal basal layer and follicles due to the migration disorder of melanocytes. Although these SNPs can reflect the polymorphism of genes related to the sika deer's coat color to a certain degree, this polymorphism has little to do with the extreme change in coat color since the change in coat color tends to be triggered by the change in protein function. The skin tissue of the body loses the ability to synthesize melanin because of the lack of melanocytes. Genotyping further confirmed the correlation between the white phenotype of sika deer and the _SCF_ gene. Among the four primers used for genotyping, SCF-1 was designed on the basis of the mutant _SCF_ gene sequence, which could amplify about 294 bp bands at both ends of the deleted fragment. The normal _SCF_ gene could not amplify SCF-1 because it retained the deleted fragment of 10.099 kb. SCF-2, SCF-3, and SCF-4 were located in the deleted fragments, and the mutant _SCF_ gene could not amplify the bands because of the loss of the deleted fragments. Genotyping showed that the male parent, female parent, and grandfather of white sika deer with white spots on their faces all carried the mutated SCF gene, and it was indicated that the white spots on their faces were also related to SCF gene mutation. The DNA of white sika deer only amplified the band of SCF-1; hence, it did not carry the normal SCF gene. The genotype and phenotype of the family members were completely matched. Studies have shown that the SCF gene also controls the white phenotype in Belgian blue cattle and short-horned cattle. The coding sequence of the SCF gene in both kinds of cattle has a base substitution at 654 bp, which leads to the substitution of Ala by Asp [9]. Belgian blue cattle have three coat color phenotypes: black spots, blue and white, and blue as a mixture of black and white. The coat color of short-horned cattle has similar phenotypes: black, black-red, and white [4]. The coat color phenotype of homozygous mutant Belgian blue cattle and short-horned cattle is all white, and whereas heterozygous cattle have blue or black-red coats. Similarly, the homozygous mutation phenotype in sika deer is white, while the heterozygous individual phenotype features white spots on the face; the inheritance mode of coat color is also single-gene dominant inheritance.