PAX9 and atrial fibrillation: Since there were no significant changes in Sox9 mRNA levels, and no increase in those of Pax9, in the control vs. the Pax1-silenced AF pellets under chondrogenic conditions, reduced Pax1 expression could ultimately lead to augmented transcriptional activity of SOX trio (SOX5, 6, 9) complexes, which drive robust Acan expression.