Abstract 2167: Conditional Knockout of Nkx2.5 in Anterior Heart Field Results in Cardiac Looping Arrest
Background: Recent advances in cardiovascular genetics have improved our understanding of congenital heart disease and arrhythmias. Developmental biology and molecular genetics studies have clarified the role of various gene products in cardiac development. Nkx2.5 is an evolutionary conserved transcription factor that contributes to cardiogenesis from early embryonic stages. Nkx2.5 mutations have been associated in humans with disorders such as atrial septal defect, ventricular septal defect, tetralogy of Fallot and mitral valve abnormalities. Early embryonic lethality of the global knockout of Nkx2.5 precludes the interrogation of its function in later stages of development and in specific cell types. In order to learn more about its role in anterior heart field and nodal formation, we conditionally ablated Nkx2.5 in cells derived from anterior heart field.
Methods: Using myocyte enhancing factor 2C (Mef2C)-Cre transgenic mouse line and floxed allele of Nkx2.5, we conditionally knocked out Nkx2.5 in anterior heart field. The contribution of Mef2C and Nkx2.5-expressing cells to different components of the heart and conduction system was evaluated by lineage analyses using the cross of Mef2C-Cre and Nkx2.5-Cre with ROSA26R reporter mice.
Results: We noticed early lethality between embryonic days 9.5–11 in conditional knockout embryos with smaller body size compared to wild type littermates and prominent pericardial effusion. Evaluation of embryos revealed arrested cardiac looping at embryonic day 9.5. Lineage analysis showed that Mef2C has limited expression in sinoatrial and atrioventricular nodes. In addition Nkx2.5 does not express in the sinoatrial node until later stages of embryonic development at day 15.5. Therefore, it is unlikely that cardiac conduction defect has contributed to the observed early lethality.
Conclusion: Our results for the first time show that Nkx2.5 is not expressed in early conductive cells and limited ablation of Nkx2.5 in anterior heart field prevents normal cardiac looping.