Neuregulin-1 is essential for nerve plexus formation during
a, b, #
, Leigh Ann Samsa
a, c, #
, Cade Ito
, Hong Ma
, Karla Batres
, Rima Arnaout
, Jiandong Liu
McAllister Heart Institute, University of North Carolina, Chapel Hill, NC, USA
Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, NC, USA
Department of Cell Biology and Physiology, University of North Carolina, Chapel Hill, NC, USA
Department of Medicine, Division of Cardiology, Cardiovascular Research Institute, University of California, San Francisco, CA,
Received: June 27, 2017; Accepted: August 30, 2017
The Neuregulin-1 (Nrg1)/ErbB pathway plays multiple, critical roles in early cardiac and nervous system development and has been implicated
in both heart and nerve repair processes. However, the early embryonic lethality of mouse Nrg1 mutants precludes an analysis of Nrg1’s func-
tion in later cardiac development and homeostasis. In this study, we generated a novel nrg1 null allele targeting all known isoforms of nrg1 in
zebraﬁsh and examined cardiac structural and functional parameters throughout development. We found that zebraﬁsh nrg1 mutants instead
survived until young adult stages when they exhibited reduced survivorship. This coincided with structural and functional defects in the develop-
ing juvenile and young adult hearts, as demonstrated by reduced intracardiac myocardial density, cardiomyocyte cell number, swimming perfor-
mance and dysregulated heartbeat. Interestingly, nrg1 mutant hearts were missing long axons on the ventricle surface by standard length (SL)
5 mm, which preceded juvenile and adult cardiac defects. Given that the autonomic nervous system normally exerts ﬁne control of cardiac out-
put through this nerve plexus, these data suggest that Nrg1 may play a critical role in establishing the cardiac nerve plexus such that inadequate
innervation leads to deﬁcits in cardiac maturation, function and survival.
While heart development is known to require coordination between
multiple cell types , the complex genetic interactions governing
coordination between the nervous system and the developing heart
 are largely unknown and understudied. Obtaining a greater under-
standing of when and how Neuregulin-1 (Nrg1)/ErbB signalling
directs cardiac development and homeostasis will allow scientists
and clinicians to harness this pathway for cardiovascular therapies.
The Nrg1/ErbB2 signalling pathway has been strongly implicated in
multiple aspects of development, homeostasis and disease in both
cardiac and nervous systems [3–6]. Canonically, transmembrane
pro-Neuregulin-1 (Nrg1) is cleaved to release Nrg1 ligands that inter-
act with ErbB2/ErbB4 or ErbB2/ErbB3 receptor heterodimers, leading
to tyrosine kinase phosphorylation events that promote downstream
signalling with broad effects [4, 7]. Several rodent studies have
demonstrated that each component of the Nrg1/ErbB pathway is
essential for cardiac chamber maturation during embryogenesis [3,
8–11], and while embryos appear to die in utero from cardiovascular
failure, these defects are coincident with defects in the developing
nervous system [8, 10, 11]. The zebraﬁsh, Danio rerio, represents a
premier model organism for studying the molecular and genetic regu-
lation of the heart development, given their rapid external develop-
ment, optical clarity and ease of genetic manipulation .
Furthermore, although mammalian embryos rapidly deteriorate from
cardiovascular defects, zebraﬁsh are relatively hypoxia tolerant .
Notably, heart development in zebraﬁsh is not completed at embry-
onic or larval stages. For example, zebraﬁsh hearts develop a critical
outer layer of cortical myocardium about 6–8 weeks post-fertilization,
as young adults . Additionally, trabeculae continue developing
through adulthood, and the adult myocardium is comprised primarily
of an expanded and remodelled meshwork of trabeculae .
Nrg1 growth factors are known to be necessary for both central
and peripheral nervous system development . With respect to
These authors contributed equally to this work.
*Correspondence to: Jiandong LIU
ª 2017 The Authors.
Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use,
distribution and reproduction in any medium, provided the original work is properly cited.
J. Cell. Mol. Med. Vol 22, No 3, 2018 pp. 2007-2017