Abstract
Despite our increasing understanding of zebrafish heart development and regeneration, there is limited information about the distribution of endothelial cells (ECs) in the adult zebrafish heart. Here, we investigate and compare the distribution of cardiac ECs (cECs) in adult mouse and zebrafish ventricles. Surprisingly, we find that (i) active coronary vessel growth is present in adult zebrafish, (ii) ~37 and ~39% of cells in the zebrafish heart are ECs and cardiomyocytes, respectively, a composition similar to that seen in mouse. However, we find that in zebrafish, ~36% of the ventricular tissue is covered with ECs, i.e., a substantially larger proportion than in mouse. Capitalising on the high abundance of cECs in zebrafish, we established a protocol to isolate them with high purity using fluorescent transgenic lines. Our approach eliminates side-effects due to antibody utilisation. Moreover, the isolated cECs maintained a high proliferation index even after three passages and were amenable to pharmacological treatments to study cEC migration in vitro. Such primary cultures will be a useful tool for supplementary in vitro studies on the accumulating zebrafish mutant lines as well as the screening of small molecule libraries on cardiac specific endothelial cells.
Highlights
The morphological diversity and cell surface protein heterogeneity of endothelial cells (ECs) in different organs of the body is known since the early 1990s1, 2
Using tissue specific reporter lines, flow cytometry, EdU incorporation assay and immunohistochemical analysis we show that (i) coronary vessels continuously grow in adult zebrafish, (ii) the relative surface area of the ventricle covered by ECs is larger in zebrafish than in mouse, (iii) ~37 and ~39% of cells
Harrison et al suggested that coronary vessel density in adult zebrafish continues to increase[17]
Summary
The morphological diversity and cell surface protein heterogeneity of endothelial cells (ECs) in different organs of the body is known since the early 1990s1, 2. In the brain microvasculature, well-developed tight junctions between ECs ensure the selective transport between the blood and central nervous system[1]. This EC specialization takes place in the microenvironments of the different organs during their development[9]. A few attempts towards this direction have utilised immunomagnetic cell enrichment to isolate endothelial cells from mammalian organs for in vitro studies[2, 10], but not from zebrafish, an important in vivo model for studying organ development and regeneration. In the zebrafish heart are ECs and CMs, respectively, (iv) highly pure primary cEC cultures can be obtained from isolated hearts, and (v) cECs are highly proliferative and responsive to small molecules in vitro
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