Identification and characterization of alternative splicing variants of buffalo LXR α expressed in mammary gland

Liver X receptor α (LXR α ) is a ligand-dependent transcription factor and plays an important role in the regulation of cholesterol homeostasis, fatty acid biosynthesis and glucose metabolism. In this study, transcripts of LXRα gene were cloned and characterized from buffalo mammary gland, and three alternative splicing transcripts of buffalo LXRα gene were identified, named LXRα1 , LXRα 2 and LXRα 3. The structure of the LXRα transcripts of buffalo and cattle was highly similar. Bioinformatics analysis showed that LXR α 1 contains two complete functional domains of LXR α , one is the DNA-binding domain (NR_DBD_LXR) and the other is the ligand-binding domain (NR_LBD_LXR). The reading frame of LXRα2 is altered due to the skipping of exon 9, which truncates its encoding protein prematurely at the 400th amino acid residue, making it contain a complete DNA-binding domain and part of a ligand-binding domain. Due to the deletion of exon 4, the protein encoded by LXRα3 lacks 89 amino acid residues and contains only a complete ligand-binding domain, which makes it lose its transcriptional regulation function. In addition, motifs and conserved domains of three LXR α variants of buffalo were highly consistent with those of corresponding transcripts from other mammal species. Subcellular localization analysis showed that LXR α 1 plays a functional role in the nucleus of buffalo mammary epithelial cells, while LXR α 2 and LXR α 3 are distributed in the nucleus and cytoplasm. Compared with non-lactating period, the mRNA abundance of the three LXRα transcripts in the mammary gland tissue of buffalo increased during lactating period, revealing that they play a key role in the synthesis of buffalo milk fat. Among the three LXR α transcripts, LXRα1 has the highest expression in the mammary gland, indicating that it is the major transcript in the mammary gland and has important regulatory functions, while LXR α 2 and LXR α 3 may have regulatory effects on the function of LXR α 1. This study highlights the key role of LXR α alternative splicing in the post-transcriptional regulation of buffalo lactation.