Primary cilia are small organelles projecting from the cell surface of various cell types. They play a crucial role in the regulation of various signaling pathway. In this study, we investigated the importance of cilia for heart development by conditionally deleting intraflagellar transport protein Ift88 using the col3.6-cre mouse. Analysis of col3.6;Ift88 offspring showed a wide spectrum of cardiovascular defects including Double Outlet Right Ventricle and Atrioventricular Septal Defects. In addition, we found that in the majority of specimens the pulmonary veins did not properly connect to the developing left atrium. The abnormal connections found resemble those seen in patients with Total Anomalous Pulmonary Venous Return. Analysis of mutant hearts at early stages of development revealed abnormal development of the dorsal mesocardium, a second heart field-derived structure at the venous pole intrinsically related to the development of the pulmonary veins. Data presented support a crucial role for primary cilia in outflow tract development and atrioventricular septation and their significance for the formation of the second heart field derived tissues at the venous pole including the dorsal mesocardium. Furthermore, the results of this study indicate that proper formation of the dorsal mesocardium is critically important for the development of the pulmonary veins.

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