Transcriptomic profiling of milk fat globules in cows with different β-casein genotypes.

Area of Science:

• Dairy Science
• Genomics
• Molecular Biology

Background:

• Growing interest in A2 β-casein milk for potential health benefits.
• Selective breeding for A2A2 genotype cows is increasing globally.
• The impact of β-casein genotype on mammary gland gene expression is largely unknown.

Purpose of the Study:

• To investigate gene expression differences in the milk fat globule (MFG) transcriptome between A1A1 and A2A2 β-casein genotype cows.
• To determine if β-casein genotype influences milk synthesis or composition through transcriptomic changes.
• To provide insights for selective breeding strategies focused on A2A2 milk production.

Main Methods:

• RNA sequencing (RNA-seq) was performed on MFG from 14 cows with distinct β-casein genotypes (A1A1 vs. A2A2).
• Functional enrichment analysis identified key processes in MFG, including protein synthesis, milk fat secretion, and energy metabolism.
• Differential gene expression analysis was conducted using DESeq2 and EdgeR.

Main Results:

• Highly expressed transcripts in MFG included CSN1S1, PAEP/BLG, CSN2, GLYCAM1, COX1, COX3, and CSN3.
• Minimal gene-level differences were observed between A1A1 and A2A2 groups, with only two genes significantly altered.
• NADH dehydrogenase subunit 6 (ND6) and 16S mitochondrial rRNA (16S Mt-rRNA) were down-regulated in A2A2 cows, suggesting potential minor impacts on mitochondrial activity.

Conclusions:

• The β-casein genotype (A1A1 vs. A2A2) shows no strong association with significant gene-level transcriptomic differences in the bovine mammary gland.
• The findings support the current selective breeding strategies for A2A2 genotype cows.
• Further research into post-transcriptional regulatory mechanisms is recommended to fully understand genotype-phenotype relationships.