A Novel Mouse Model for Cilia‐Associated Cardiovascular Anomalies with a High Penetrance of Total Anomalous Pulmonary Venous Return

Abstract

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.

Sites of Cre-recombinase activity in mouse lines targeting skeletal cells

“…Additional sites of Cre mTmG/LacZ activity in the rat 3.6kb‐Col1a1‐Cre line include the neural tube, ectoderm, neuroepithelium, hindlimb buds, foregut endoderm, walls of the dorsal aortae, and virtually all cell layers constituting the future heart (E8.5). ( 132,236 ) Germline transmission was observed in both lines. Another rat 3.6kb‐Col1a1‐Cre line generated by Zha et al ( 133 ) showed Cre LacZ activity in calvaria, trabecular bone, and osteocytes (P10).…”

“…Tables 1–6 list the Cre lines discussed and include references of documents describing Cre activity in bone and off‐target sites, and original articles reporting the lines (knock‐in–based Cre lines in these tables are labeled with an asterisk). ( 22‐213 )…”

Functions of cilia in cardiac development and disease

“…Loss of function mutants of IFT genes also display cardiac malformations. For example, Ift88 mutant mice show defects in cardiac OFT septation, ventricular trabeculation, AVSD, and cardiac cushion EMT, with no localization of the Hh pathway transcription factor Gli2 in cardiac cilia (Burns et al, 2019;Clement et al, 2009;Willaredt et al, 2012). In a previous study, Washington Smoak et al (2005) reported that Shh deletion results in abnormal migration of neural crest cells, contributing to arch artery and OFT septation defects.…”

Sox9 Expression in the Second Heart Field; A Morphological Assessment of the Importance to Cardiac Development with Emphasis on Atrioventricular Septation

“…In recent years, the insight into the pathogenesis of AVSDs has significantly changed. Studies from a number of different groups have implicated abnormal development of the SHF-derived DMP in the pathogenesis of pASDs, i.e., the most common single septal defect in virtually all forms of AVSDs [2][3][4]10,13,14,[21][22][23]. Understanding of the molecular mechanisms that govern DMP development has steadily developed over the last 10 years.…”