Expression of multiple DQB genes in Bos indicus cattle

Area of Science:

• Veterinary Science
• Immunogenetics
• Animal Breeding

Background:

• The bovine major histocompatibility complex (MHC) plays a crucial role in immune responses.
• Polymorphism within MHC genes, particularly DQB, influences disease resistance and herd productivity.
• Understanding MHC gene structure and expression in diverse cattle breeds like Boran (Bos indicus) is vital for genetic improvement.

Purpose of the Study:

• To investigate the polymorphism and identify potential gene duplications of expressed bovine MHC class II DQB genes.
• To analyze the sequence variation within DQB second exon fragments in homozygous Kenya Boran cattle.
• To assess the implications of observed DQB gene duplications on MHC haplotype distribution in Boran cattle.

Main Methods:

• Total mononuclear cell RNA was extracted from nine MHC-homozygous Kenya Boran cattle.
• DQB second exon fragments were amplified using reverse transcription-polymerase chain reaction (RT-PCR).
• Amplified fragments were cloned and sequenced to identify distinct DQB sequences and potential gene duplications.

Main Results:

• Sequence analysis revealed the expression of duplicated DQB genes in some animals, indicated by the presence of two distinct DQB exon 2 sequences.
• Two distinct pairs of duplicated DQB genes were identified among the homozygous Boran cattle.
• Sequence analysis confirmed that both duplicated gene pairs contained distinct DQB alleles, suggesting functional diversity.

Conclusions:

• The study identified DQB gene duplications in Boran cattle, indicating a more complex MHC structure than previously assumed.
• One duplication was observed in related animals sharing an MHC haplotype, while another was found in unrelated animals with shared DRB3 and DQB alleles.
• These findings suggest that a specific DR/DQ haplotype, potentially including duplicated DQB genes, may be widespread in the Boran cattle population.