A complete DNA sequence map of the ovine major histocompatibility complex

Area of Science:

• Genomics
• Immunogenetics
• Comparative Genomics

Background:

• The ovine Major Histocompatibility Complex (MHC) is crucial for disease resistance but lacks comprehensive sequence data.
• Previous work established a physical map of the ovine MHC, but a complete DNA sequence was unavailable.

Purpose of the Study:

• To assemble a complete DNA sequence map of the ovine MHC.
• To identify novel genes and regulatory elements within the ovine MHC.
• To facilitate comparative genomic studies with other mammalian species.

Main Methods:

• Shotgun sequencing of 26 overlapping bacterial artificial chromosome (BAC) clones covering the ovine MHC.
• Bioinformatic assembly and gene annotation of the sequenced DNA.
• Comparative sequence analysis with human and cattle MHC regions.

Main Results:

• A complete ovine MHC DNA sequence map of approximately 2.43 Mb was assembled.
• 177 protein-coding genes/ORFs were identified, including 145 novel ovine genes and 10 species-specific genes.
• Comparative analysis revealed conserved MHC structure with a distinct class II subregion organization in ruminants and identified 18 novel microRNAs.

Conclusions:

• The assembled ovine MHC sequence map provides the second complete ruminant MHC sequence, enabling evolutionary and functional research.
• Comparative analyses support a chromosomal inversion model for ruminant MHC evolution.
• The discovery of numerous microRNAs suggests their active role in regulating ovine MHC gene expression and function.