Cardiac conduction system malformations in heterotaxy result from dysregulated Pitx2 expression
Kunihiko Joo, Ryohei Matsuoka, Keiko Kitajima, Kenta Yashiro, Akira Shiose, Ryuji Tominaga, Michael M. Shen, Shinya Oki, Chikara Meno
Kunihiko Joo, Ryohei Matsuoka, Keiko Kitajima, Kenta Yashiro, Akira Shiose, Ryuji Tominaga, Michael M. Shen, Shinya Oki, Chikara Meno
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Research Article Cardiology Development

Cardiac conduction system malformations in heterotaxy result from dysregulated Pitx2 expression

Abstract

The cardiac conduction system (CCS) develops asymmetrically along the body axes. In heterotaxy syndrome — resulting from aberrant left-right axis formation — atrial and atrioventricular conduction defects can cause life-threatening arrhythmias. However, the developmental mechanisms regulating the atrioventricular conduction system (AVCS) disposition and integrity remain unclear. To investigate the etiology of AVCS malformations in laterality defects, we analyzed CCS development and function in mouse mutants for Cryptic and Lefty1, which are key regulators of Pitx2 in the left-right axis formation. Cryptic–/– embryos exhibited bilateral sinoatrial nodes and an ectopic anterior AV node and bundle accompanied by reduced Pitx2 expression. In contrast, Lefty1–/– embryos showed a hypoplastic sinoatrial node and AV node–bundle dissociation with ectopic Pitx2 expression. Single-cell transcriptomic analysis of Pitx2–/– hearts revealed expansion of AV node and bundle populations, consistent with a repressive role of Pitx2 in AVCS specification. Genetic lineage tracing indicated that Pitx2-expressing cells from the left lateral plate mesoderm populate cranioventral cardiac regions, where AVCS development is suppressed. Together, these findings clarify how global left-right axis information is locally integrated to shape AVCS disposition and integrity, providing a mechanistic model for AVCS abnormalities in laterality-associated congenital heart disease.

Authors

Kunihiko Joo, Ryohei Matsuoka, Keiko Kitajima, Kenta Yashiro, Akira Shiose, Ryuji Tominaga, Michael M. Shen, Shinya Oki, Chikara Meno

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Figure 3

Pitx2 expression domains in the cardiac conduction system and its cell lineages.

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Pitx2 expression domains in the cardiac conduction system and its cell ...
(A–N) Transverse sections of hearts from WT (A–H) and Cryptic–/– (I–N) embryos stained by in situ hybridization at E14.5 (A–F and I–M), E12.5 (G and H), and E18.5 (N) for Pitx2 (A, C, E, G–I, K, and M), Tbx3 (B, D, J, L, and N), and Myl7 (F). The arrows indicate Pitx2 or Tbx3 expression in the septal branch (A, B, I, and J) and in the cranioventral side of the AV rings (K). The asterisks in C, D, K, and L indicate the AV bundle, whereas those in E and F denote the AV node. The arrowheads indicate loss of Pitx2 expression in the atrium (I) and left AV ring (M). The dashed rectangle in G indicates Pitx2+ superior AV canal myocardium, including AV rings. The arrows in I and K show residual expression of Pitx2 in the septal branch and AV rings, respectively. (O and P) X-gal staining of a Pitx2 17-Cre CAG-CAT-LacZ heart at E12.0. Coronal sections are shown. The arrow indicates the septal branch. Scale bars: 200 μm. The scale bars in A, G, and O apply to A–F and I–M, G and H, and O and P, respectively. Abbreviations are the same as in Figure 1, except for AS, atrial septum; CAVV, common atrioventricular valve; (i/s)AVC, (inferior/superior) atrioventricular cushion; L, left; MV, mitral valve; R, right; TV, tricuspid valve.