Relationship between fibronectin expression during gastrulation and heart formation in the rat embryo

Authors

  • Hiroaki R. Suzuki,

    Corresponding author
    1. Department of Biological Sciences, University of Iowa, Iowa City, Iowa 52242
    Current affiliation:
    1. Department of Anatomy, Medical College of Georgia, Augusta, GA 912-2000
    • Department of Anatomy, Medical College of Georgia, Augusta, GA 30912-2000
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  • Dr. Michael Solursh,

    1. Department of Biological Sciences, University of Iowa, Iowa City, Iowa 52242
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    • In memory of Dr. Michael Solursh. The authors also express appreciation to the late Dr. Reiji Hirakow and his work.

  • H. Scott Baldwin

    1. Division of Pediatric Cardiology, Children's Hospital of Philadelphia/University of Pennsylvania Medical School, Philadelphia, Pennsylvania 19104
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Abstract

By utilizing myosin immunostaining, we were able to identify early rat myocardium as a thin epithelial sheet and realized that its cohesive movement toward the midline leads to the straight heart tube formation. Localization study of fibronectin mRNA and protein was, therefore, carried out to investigate its tissue origin and possible roles in facilitating mesoderm migration and heart formation. Fibronectin mRNAs were first detected throughout the mesoderm during the early primitive streak stage, suggesting that the mesoderm is the source of fibronectin. By pre-head fold (pre-somite) and head fold (early somite) stages, the mesoderm became largely down-regulated for fibronectin mRNAs, while it was also at these stages when myosin-positive myocardium formed itself into the epithelium and was subsequently folding toward the midline. Thus, there appears to be little fibronectin synthesis during and directly relevant to early heart tube formation. Later, during the early straight heart tube stage (5 somite and older), endocardium became highly positive for fibronectin mRNAs, suggesting that the endocardium is the major source of fibronectin for the cardiac jelly. Based on the results, we present a map for the early mammalian heart in which the heart is a single crescentic band lying in front of the prechordal plate. We also suggest a process for heart tube formation based on the cohesive movement of the myocardial epithelium. During heart tube formation, fibronectin protein had been deposited previously by the mesoderm and was found uniformly in the ECM and not newly produced by any adjacent tissue. The data contradict the endodermal guidance of heart migration by fibronectin gradient and suggest, instead, a permissive role for the fibronectin substrate. © 1995 wiley-Liss, Inc.

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