Fig. 1

Asymmetric expression of atrial-specific transcription factor genes in adult zebrafish.

(a) Comparison of different vertebrate hearts showing the emergence of distinct left and right chamber identities and atrial septation. (b) Schematic representation of the workflow for the identification of cardiac chamber-specific transcription factor gene expression. (c) Atrial gene expression level (signal intensity) and chamber-specific enrichment in the atrium (fold change >0) or ventricle (fold change <0). Red line marks 2.5 (log₂) fold cutoff. Highly enriched atrial transcription factor genes (blue), ventricular (myh7l) and atrial (myh6) chamber-specific myosin genes (orange) are shown. (d) Atrial enriched transcription factor genes (log₂ fold change >2.5). (e–f) Whole-mount in situ hybridization on adult zebrafish hearts; myh6 expression covers the entire atrium while meis2b expression is restricted to the left side of the atrium. (g–h) In situ hybridization on adult cardiac sections; myl7 is expressed in all cardiomyocytes while meis2b is expressed on the left side of the atrium in the wall and trabeculae (see Figure 1—figure Supplement 1a for higher magnification). (i–i’) Brightfield and fluorescence images of a 4 mpf Tg(meis2b-reporter) zebrafish atrium. (j–j’) High-magnification confocal projections of a 4 mpf Tg(meis2b-reporter) heart showing expression of the Tg(meis2b-reporter) in the myocardium (Tg(meis2b-reporter)+/MF20+/Fli cells) but not the endocardium (Tg(meis2b-reporter)-/MF20-/Fli1+cells). (e–f, i–i’) Red and white dotted lines delineate the atrium; (i’) yellow line delineates Tg(meis2b-reporter) expression. Scale bars: (e–i) 1 mm, (j’) 50 µm.