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Semaphorin3f as a cardiomyocyte derived regulator of heart chamber development
Rami Halabi1, Paula Bernice Cechmanek1, Carrie Lynn Hehr1
1Hotchkiss Brain Institute, Alberta Children's Hospital Research Institute, Department of Cell Biology and Anatomy, University of Calgary, 3330 Hospital Dr., NW, Calgary, AB, T2N 4N1, Canada.
Insights
Loss of secreted semaphorin Sema3fb impairs zebrafish heart development, causing smaller chambers and defective chamber-specific gene expression. This suggests Sema3fb signaling is crucial for establishing distinct atrial and ventricular borders for a functional heart.
Area of Science:
- Cardiovascular Biology
- Developmental Biology
- Genetics
Background:
- Heart development involves forming distinct atrial and ventricular chambers with specific properties.
- Congenital heart defects arise from deviations in normal chamber development, highlighting the need to understand cardiomyocyte differentiation.
- Understanding the molecular mechanisms of chamber-specific cardiomyocyte differentiation is crucial due to numerous genes involved in congenital heart defects.
Purpose of the Study:
- To investigate the role of the secreted semaphorin Sema3fb in zebrafish heart development.
- To identify the consequences of Sema3fb loss on heart chamber formation and differentiation.
Main Methods:
- Utilized CRISPR technology to create two sema3fb mutant zebrafish alleles.
- Employed in situ hybridization and immunohistochemistry to analyze gene and protein expression.
- Conducted functional analyses to assess heart development and chamber properties in mutants.
Main Results:
- Sema3fb mRNA is broadly expressed in cardiomyocytes, while its receptor Plxna3 shows preferential ventricular expression.
- Zebrafish mutants lacking Sema3fb exhibit smaller atrial and ventricular chambers due to reduced cell size.
- Defects in chamber-specific gene expression and failure to restrict cardiomyocyte markers were observed at chamber borders and the atrioventricular canal.
Conclusions:
- Propose a model where secreted Sema3fb, acting via spatially restricted receptor expression, signals in a ventricular-specific manner.
- This signaling establishes a critical border between atrial and ventricular chambers.
- Proper chamber bordering mediated by Sema3fb signaling is essential for a fully functional heart.
Background:
During development a pool of precursors form a heart with atrial and ventricular chambers that exhibit distinct transcriptional and electrophysiological properties. Normal development of these chambers is essential for full term survival of the fetus, and deviations result in congenital heart defects. The large number of genes that may cause congenital heart defects when mutated, and the genetic variability and penetrance of the ensuing phenotypes, reveals a need to understand the molecular mechanisms that allow for the formation of chamber-specific cardiomyocyte differentiation.
Methods:
We used in situ hybridization, immunohistochemistry and functional analyses to identify the consequences of the loss of the secreted semaphorin, Sema3fb, in the development of the zebrafish heart by using two sema3fb CRISPR mutant alleles.
Results:
We find that in the developing zebrafish heart sema3fb mRNA is expressed by all cardiomyocytes, whereas mRNA for a known receptor Plexina3 (Plxna3) is expressed preferentially by ventricular cardiomyocytes. In sema3fb CRISPR zebrafish mutants, heart chamber development is impaired; the atria and ventricles of mutants are smaller in size than their wild type siblings, apparently because of differences in cell size and not cell numbers. Analysis of chamber differentiation indicates defects in chamber specific gene expression at the border between the ventricular and atrial chambers, with spillage of ventricular chamber genes into the atrium, and vice versa, and a failure to restrict specialized cardiomyocyte markers to the atrioventricular canal (AVC). The hypoplastic heart chambers are associated with decreased cardiac output and heart edema.
Conclusions:
Based on our data we propose a model whereby cardiomyocytes secrete a Sema cue that, because of spatially restricted expression of the receptor, signals in a ventricular chamber-specific manner to establish a distinct border between atrial and ventricular chambers that is important to produce a fully functional heart. Video abstract.
