# Patterning Defects in Mice with Defective Ventricular Wall Maturation and Cardiomyopathy

## TL;DR

This study compares gene expression patterns in mouse and human heart development, highlighting differences and their implications for cardiomyopathy.

## Contribution

The study identifies a transitional cardiomyocyte lineage in mice and shows how disrupted gene expression patterns may lead to cardiomyopathy.

## Key findings

- Mouse ventricular walls show less complex regional gene expression compared to human fetal hearts.
- In LVNC models, altered spatial gene expression suggests a link to ventricular wall maturation defects.
- Endocardial and coronary endothelial cell markers differ in expression patterns between mice and humans.

## Abstract

Ventricular chamber development involves the coordinated maturation of diverse cardiomyocyte cell populations. In the human fetal heart, single-cell and single-nucleus RNA sequencing technologies and spatial transcriptomics reveal marked regional gene expression differences. In contrast, the mouse ventricular wall appears more homogeneous, except for a transient hybrid cardiomyocyte population co-expressing compact (Hey2) and trabecular (Irx3, Nppa, Bmp10) markers, indicating a transitional lineage state. To further investigate this, we used in situ hybridization (ISH) to examine the expression of a selected set of cardiomyocyte markers in normal and left ventricular non-compaction cardiomyopathy (LVNC) mouse models. In developing mouse ventricles, the expression of key marker genes was largely restricted to two wide myocardial domains, compact and trabecular myocardium, suggesting a less complex regional organization than the human fetal heart. Other markers labeled endocardial and coronary endothelial cells rather than cardiomyocytes, differing from patterns observed in the human heart. In the LVNC model, various markers exhibited altered spatial expression, indicating that the precise regional organization of gene expression is critical for normal ventricular wall maturation. These findings underscore the critical role of spatially regulated gene programs in ventricular chamber development and point to their potential involvement in cardiomyopathy pathogenesis.