Transcriptome Profile of the Sinoatrial Ring Reveals Conserved and Novel Genetic Programs of the Zebrafish Pacemaker

Abstract

Background: Sinoatrial Node (SAN) is part of the cardiac conduction system, which controls the rhythmic contraction of the vertebrate heart. The SAN consists of a specialized pacemaker cell population that has the potential to generate electrical impulses. Although the SAN pacemaker has been extensively studied in mammalian and teleost models, including the zebrafish, their molecular nature remains inadequately comprehended. Results: To characterize the molecular profile of the SAR and elucidate the mechanism of pacemaker function, we utilized the zebrafish transgenic line sqet33mi59BEt to isolate cells of the sinoatrial ring (SAR) of developing zebrafish embryos and profiled their transcriptome. Our analyses identified novel candidate genes and well-known conserved signaling pathways involved in pacemaker development. We show that, compared to the rest of the heart, the zebrafish SAR overexpresses several mammalian SAN pacemaker signature genes, which include hcn4 as well as those encoding calcium- and potassium-gated channels. Moreover, genes encoding components of the BMP and Wnt signaling pathways, as well as members of the Tbx family, which have previously been implicated in pacemaker development, were also overexpressed in the SAR. Among SAR-overexpressed genes, 24 had human homologues implicated in 104 different ClinVar phenotype entries related to various forms of congenital heart diseases, which suggest the relevance of our transcriptomics resource to studying human heart conditions. Finally, functional analyses of three SAR-overexpressed genes, pard6a, prom2, and atp1a1a.2, uncovered their novel role in heart development and physiology. Conclusion: Our results established conserved aspects between zebrafish and mammalian pacemaker function and revealed novel factors implicated in maintaining cardiac rhythm. The transcriptome data generated in this study represents a unique and valuable resource for the study of pacemaker function and associated heart diseases.

Genomic and physiological analyses of the zebrafish atrioventricular canal reveal molecular building blocks of the secondary pacemaker region

“…The differences in the inherent activation rates of the SAR and AVC regions of the zebrafish heart led us to question the molecular nature underlying their distinct properties. We compared the transcriptome of the AVC with that of the SAR [40] to identify differentially enriched genes. Intersection between the two transcriptomes obtained a total of 1516 AVC-unique, 701 SAR-unique, and 450 common genes (S9 Table ).…”

“…The transgenic line sqet33mi59BEt, in which the enhancer trap was inserted close by the fhf2 gene locus, expresses EGFP in the SAR [39]. Recently, we completed the analysis of the transcriptome of these cells [40]. Comparisons between the SAR and AVC transcriptomes revealed differences reflected in expression profiles of ion channels and connexins implicated in pacemaker function.…”