Retinoic Acid Directs Cardiac Laterality and the Expression of Early Markers of Precardiac Asymmetry

Abstract

Formation of the left/right body axis is a critical early step in embryogenesis. The heart loop is one of the first clearly recognizable morphological asymmetries, and the molecular pathway which dictates this laterality is now beginning to be understood. We report here that the left and right precardiac fields of chick differ in their sensitivity to retinoic acid (RA); while RA applied to the right precardiac field at gastrulation randomizes heart looping, left side treatment induces situs inversus only at high RA concentrations. We identified two extracellular matrix proteins, the heart-specific lectin-associated matrix protein-1 (hLAMP1) and the fibrillin-related protein recognized by the antibody JB3, which are distributed asymmetrically within the precardiac fields at the head process stage. In normal embryos, JB3 expression is enhanced within the right precardiac field, and hLAMP-1 is enriched within the left. RA treatment predictably altered the expression of these proteins in a manner consistent with subsequent heart laterality: RA treatments which randomize heart loop direction also equalized or reversed the left/right JB3 and hLAMP-1 distribution prior to heart tube fusion. The existence of asymmetrically expressed extracellular matrix proteins within precardiac regions suggests that interactions between cardiocytes and their environment may contribute to heart laterality determination and looping.

Retinoic acid administration is associated with changes in the extracellular matrix and cardiac mesenchyme within the endocardial cushion

“…These mRNAs include activin receptor IIa (cAct-RIIa), Sonic hedgehog (Shh), the transcription factor HFN3␤, and the chicken nodal-related gene cNR-1 (Levin et al, 1995). Finally, two extracellular matrix molecules, hLAMP-1 and JB-3 have asymmetric distribution along the left-right axis in early stage chick embryo (Smith et al, 1997). In normal development, at stage 5-7, hLAMP-1 is more abundant in the left heartforming region whereas greater amounts of JB-3 can be found in the right heart field.…”

“…RA treatment caused their expressions either to be equalized or reversed. The disturbance in the asymmetry of these proteins resulted in randomization of early heart looping and concomitant cardiac defects (Smith et al, 1997). The randomization of left-right orientation such as reversals and isomerism in the heart and the viscera are also seen in genetic mutants (Seo et al, 1992;Metzler et al, 1994).…”

“…This molecule has been shown to be present at Henson's node in stage 4 and early stage 5 chick embryos (Smith et al, 1997). hLAMP-1 is next seen in the lateral plate mesoderm anterior to Henson's node and becomes enriched in the left precardiac and ventral foregut regions of the embryo (Smith et al, 1997). In the heart, at stage 15-16 when endothelial transformation is taking place, hLAMP-1 was localized to the expanded myocardial basement membrane with limited staining at the endothelial or myocardial layers (Sinning and Hewitt, 1996).…”

“…The latter is a 283-kDa protein that was identified using a monoclonal antibody developed from the SBA positive fraction of the particulate matrix (Sinning and Hewitt, 1996). This molecule has been shown to be present at Henson's node in stage 4 and early stage 5 chick embryos (Smith et al, 1997). hLAMP-1 is next seen in the lateral plate mesoderm anterior to Henson's node and becomes enriched in the left precardiac and ventral foregut regions of the embryo (Smith et al, 1997).…”

“…In the heart, at stage 15-16 when endothelial transformation is taking place, hLAMP-1 was localized to the expanded myocardial basement membrane with limited staining at the endothelial or myocardial layers (Sinning and Hewitt, 1996). Finally hLAMP-1 is responsive to retinoic acid (RA) treatment suggesting that the cause of cardiac defects seen in RA teratogenesis may involve the production of the particulate matrix (Smith et al, 1997;Yan et al, 2000).…”