An ordered BAC contig map of the equine major histocompatibility complex

Area of Science:

• Genomics
• Immunogenetics
• Comparative Genomics

Background:

• The horse major histocompatibility complex (MHC) organization is poorly understood.
• Comparative analysis with other species can guide MHC mapping efforts.

Purpose of the Study:

• To construct a physical map of the equine MHC.
• To determine the genetic organization and gene content of the horse MHC.

Main Methods:

• Designed overgo probes from conserved MHC gene sequences of various species.
• Screened an equine bacterial artificial chromosome (BAC) library.
• Assembled BAC contigs and determined gene order.
• Used fluorescence in situ hybridization (FISH) for physical mapping and orientation.

Main Results:

• Assembled 238 BAC clones into two contigs covering the horse MHC.
• Identified a ~800 kb contig with the MHC class II region (≥20 genes).
• Identified a ~1.6 Mb contig with the MHC class III/I region (≥34 genes).
• FISH localized the MHC to ECA20q21 and oriented class I, III, and II regions relative to the centromere.

Conclusions:

• The equine MHC is a single, gene-dense region organized similarly to the human MHC.
• Unlike ruminants and pigs, the equine MHC structure is not disrupted.
• Provides a foundational map for future equine immunogenetic studies.