Paired box gene 5 isoforms A and B have different functions in transcriptional regulation of B cell development-related genes in immature B cells.

The transcription factor paired box gene 5 (Pax5) is essential for B cell development. In this study, complementation analyses in Pax5-deficient DT40 cells showed that three Pax5 isoforms Pax5A, Pax5B and Pax5BΔEx8 (another spliced isoform of Pax5B lacking exon 8) exhibit distinct roles in transcriptional regulation of six B cell development-related genes (activation-induced cytidine deaminase, Aiolos, BTB and CNC homology 2, B cell lymphoma-6, early B cell factor 1, origin binding factor-1 genes), transcriptions of which are remarkably down-regulated by Pax5-deficiency. Moreover, ectopic expression study shows that these Pax5 isoforms may regulate themselves and each other at the transcriptional level.