Novel isoforms of the bovine Nuclear factor I/X (CCAAT‐binding transcription factor) transcript products and their diverse expression profiles

The aim of this study was to detect splicing variants of the bovine NFIX gene and determine their expression regulations. Through bioinformatics analysis, we predicted five isoforms of the bovine NFIX transcript product and validated their existence using cDNA pool and sequencing methods. The five isoforms had a common 5′‐terminal sequence and various 3′‐terminal sequences. Nuclear factor I family genes can activate or repress transcription by a highly variable C‐terminal region. Thus, the five isoform products from a single gene may function differently. Quantitative PCR results showed that NFIX had highest expression in brain; medial expression in lung and muscle; and lower expression in spleen, kidney, liver and heart of both embryo and adult cattle. However, the expression levels NFIX in adult tissues were significantly decreased, and the diversity of its alternative splicing events was lower. Each isoform was expressed differently in different tissues at the embryo and adult stages. One of the isoforms (Nfix2) was not detected in tissues of adult cattle. In brain, another of the isoforms (Nfix3) was not detected, whereas the other four isoforms were highly expressed. In the embryo, of the five isoforms, the profile of the one labeled Nfix4 was the most similar to that of total Nfix, and we proved that it was the major isoform. This study is the first that has detected five novel isoforms of the bovine NFIX transcript products and that has examined their profiles at spatial and temporal levels, which will provide essential information for better understanding the bovine NFIX gene.