Genetic analysis of platelet-derived growth factor receptor-like gene (<i>PDGFRL</i>) polymorphism and melanin traits in Lanping black-boned sheep (<i>Ovis aries</i>)

Abstract

In the intricate tapestry of Yunnan Province's biodiversity, the Lanping black-boned sheep (LPBB) emerges as a captivating enigma, distinguished by its profound melanin pigmentation adorning both its skin and its internal organs. Initially cataloged in the 1950s within the confines of Lanping County, this exceptional mammalian species presents a scarcity and uniqueness that extends beyond its geographic origins. Here, we collected 100 blood samples from Lanping black-boned sheep along with 50 samples each from Lanping normal sheep (LPN) and Huize normal sheep (HZN), all sourced from Yunnan Province. Our investigation focused on the association between the platelet-derived growth factor receptor-like gene (PDGFRL) polymorphism and the distinctive melanin characteristics observed in Lanping black-boned sheep. Utilizing UV–visible spectrophotometry, we assessed the melanin indexes present, such as tyrosinase activity and true melanin in the sheep blood, and the results demonstrated a significant elevation in melanin indexes for Lanping black-boned sheep compared to the control group (P<0.05). We also identified three synonymous mutation sites within a partial 1128 bp exon fragment of the gene-encoding PDGFRL (EX2-G408A, EX5-T184C, and EX5-G222T). Notably, Lanping black-boned sheep, harboring genotypes GG, TT, and GG at these specific sites, showcased a pronounced surge in tyrosinase activity, eumelanin / total melanin ratios, and plasma colorimetric values when contrasted with the control group (P<0.05). The discernment of GG, TT, and GG as the prevailing genotypes at their respective genetic loci in Lanping black-boned sheep heralds a breakthrough in our understanding of the genetic markers associated with black pigmentation. However, all three loci are silent mutations and do not alter the phenotypic changes. Whether they affect changes in melanin content through other metabolic pathways requires further study. In conclusion, the PDGFRL gene was silenced by mutations in our study and affected blood melanin levels. However, the gene did not undergo a missense mutation that altered the phenotypic changes, and the exact channel through which the changes in melanin content were affected needs to be further verified.