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A Role for BMP Signalling in Heart Looping Morphogenesis in Xenopus

Summary: A Role for BMP Signalling in Heart Looping
Morphogenesis in Xenopus
Ross A. Breckenridge,* Tim J. Mohun, and Enrique Amaya*,1
*Wellcome/CRC Institute, Department of Zoology, University of Cambridge, Tennis Court
Road, Cambridge CB2 1QR, United Kingdom; and National Institute for Medical Research,
The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom
The heart develops from a linear tubular precursor, which loops to the right and undergoes terminal differentiation to form
the multichambered heart. Heart looping is the earliest manifestation of left­right asymmetry and determines the eventual
heart situs. The signalling processes that impart laterality to the unlooped heart tube and thus allow the developing organ
to interpret the left­right axis of the embryo are poorly understood. Recent experiments in zebrafish led to the suggestion
that bone morphogenetic protein 4 (BMP4) may impart laterality to the developing heart tube. Here we show that in
Xenopus, as in zebrafish, BMP4 is expressed predominantly on the left of the linear heart tube. Furthermore we demonstrate
that ectopic expression of Xenopus nodal-related protein 1 (Xnr1) RNA affects BMP4 expression in the heart, linking
asymmetric BMP4 expression to the left­right axis. We show that transgenic embryos overexpressing BMP4 bilaterally in
the heart tube tend towards a randomisation of heart situs in an otherwise intact left­right axis. Additionally, inhibition of
BMP signalling by expressing noggin or a truncated, dominant negative BMP receptor prevents heart looping but allows the
initial events of chamber specification and anteroposterior morphogenesis to occur. Thus in Xenopus asymmetric BMP4
expression links heart development to the left­right axis, by being both controlled by Xnr1 expression and necessary for
heart looping morphogenesis. © 2001 Academic Press
Key Words: bone morphogenetic protein; heart; left­right axis; Xenopus; transgenics.


Source: Amaya, Enrique - Healing Foundation Centre & Developmental Biology, Faculty of Life Sciences, University of Manchester
Chin-Sang, Ian - Department of Biology, Queen's University (Kingston)


Collections: Biology and Medicine