Unique insertion/deletion polymorphisms within histidine-rich region of histidine-rich glycoprotein in Thoroughbred horses

Abstract

Histidine-rich glycoproteins (HRG) are abundant plasma protein with various effects on angiogenesis, coagulation, and immune responses. Previously, we identified the base and amino acid sequences of equine HRG (eHRG) and revealed that eHRG regulates neutrophil functions. In this study, we first conducted a large-scale gene analysis with DNA samples extracted form 1,700 Thoroughbred horses and identified unique insertion/deletion polymorphisms in the histidine-rich region (HRR) of eHRG. Here we report two types of polymorphisms (deletion type 1 [D1] and deletion type 2 [D2]) containing either a 45 bp or 90 bp deletion in the HRR of eHRG, and five genotypes of eHRG (insertion/insertion [II], ID1, ID2, D1D1, and D1D2) in Thoroughbred horses. The incidence of each genotype was 23.4%, 46.2%, 3.6%, 23.1%, and 3.7%, respectively. We also examined the molecular weight of plasma eHRG originated from each insertion/deletion mutant eHRG genes and eHRG proteins were detected as bands with different sizes. Furthermore, nickel-binding affinity of eHRG with D1 or D2 deletion was reduced. As HRG possesses a variety of biological and immunological activities in vivo and HRR is the active center of HRG, genetic polymorphisms in eHRG may participate in performance, productivity, and susceptibility to infectious diseases in Thoroughbred horses.