As Heart Month unfolds, the laboratory of researcher Rubén Marín Juez unveils the first comprehensive atlas of coronary vessel development in the zebrafish. Led by student Muhammad Abdul Rouf, this large‑scale work traces—with unprecedented single‑cell resolution—how vessels form and interact with the cardiac muscle, culminating several years of meticulous analysis.

Revealing the Architecture

Published in Development, the study combines 3D imaging with genetic zebrafish lines to determine where, when, and how coronary vessels establish themselves and guide the maturation of cardiac muscle cells.

“For a long time, vessels were viewed simply as conduits that transport blood. Today, we show that they orchestrate the growth of the cardiac muscle, starting from the earliest stages of heart formation,” says Rubén Marín Juez, researcher at the Centre de recherche Azrieli du CHU Sainte‑Justine and professor at the Université de Montréal.

This idea emerged from the lab’s work on cardiac regeneration: in adult zebrafish, coronary vessels form a kind of scaffold that enables the muscle to rebuild after an injury. This observation led the team to trace development back to the embryo to understand how these interactions arise from the very beginning of life.
 

Image 1 : This view of the zebrafish ventricle reveals the emergence of future coronary vessels, made visible thanks to two fluorescent lines: one labels the coronary endothelial cells, and the other labels the coronary arteries.
Image 2 : Using different fluorescent markers, this image simultaneously shows nascent coronary vessels, cardiomyocytes, and proliferating cells, illustrating the synchronized growth of the vascular network and the cardiac muscle.
Image 3 : This view highlights the parallel progression of the developing coronary vessels and the growing cardiac muscle tissue, each marked with a distinct fluorescent color that allows their coordinated maturation to be followed.
© Courtesy of Rubén Marín Juez's Laboratory

A Unique Window Into the Forming Heart

A model of choice in developmental biology, the zebrafish develops a functioning heart just 24 hours after fertilization. With direct access to embryos and larvae—and cellular labeling made easier by their natural transparency—the team can observe structures that remain invisible in mammals at this early stage.

By analyzing vascular development micrometre by micrometre, starting at a body length of 7mm, the team produced remarkably precise 3D images. This approach made it possible to follow the formation of the coronary network: the emergence of the first vascular sprouts, their anchoring, growth, branching and maturation into a fully functional network.

Comparing different zebrafish models also revealed the exact moment when development goes awry, highlighting defects that arise when a key gene is altered.

In parallel, the team performed RNA sequencing on more than 37,000 cells, identifying the various cell types involved, as well as new markers and molecular signatures associated with key stages of coronary development. This atlas thus offers a complete anatomical and genomic portrait of how the coronary network takes shape.

A Resource for Understanding Pediatric Heart Disease

Beyond fundamental insights, this atlas opens new avenues for understanding several congenital heart diseases. Increasing evidence suggests that an insufficient or disorganized coronary network very early in development can compromise normal heart formation. By mapping these steps with such precision, the study now enables researchers to explore these hypotheses at an unprecedented level.

In species capable of regenerating their hearts, such as the zebrafish, several developmental programs are reactivated after injury. Understanding these mechanisms at the embryonic stage could therefore inspire future therapeutic approaches, particularly in pediatrics.

By combining cutting‑edge imaging, genetics and single‑cell analyses, this study highlights the strength of collaboration between scientific teams and technological platforms—a partnership that is transforming our understanding of the heart from its very first beats. 

Left, Muhammad Abdul Rouf and right, Rubén Marín Juez. © CHU Sainte-Justine (Véronique Lavoie)