Congress Abstracts - Society for Developmental Biology

Congenital outflow tract (OFT) malformations (e.g. conotruncal defects) are significant causes of newborn morbidity and mortality in
the US and worldwide. In mammals, the embryonic OFT and primitive right ventricle arise by accretion of newly differentiated cells
to the arterial pole of the heart tube from multi-potent progenitors residing in the anterior second heart field (SHF). While severe SHF
deficiencies cause embryonic lethality, intermediate defects cause misalignment of the outflow tract relative to the ventricles, a
defining feature of double outlet right ventricle (DORV) and Tetralogy of Fallot (TOF). In 2011, the Burns Laboratory reported that
zebrafish cardiogenesis relies on LTBP3-mediated TGFβ signaling (Zhou 2011). Using microarray profiling followed by in situ
analyses, we learned that transcriptional regulator, fos-like antigen 2 (fosl2), is expressed in a pattern overlapping with nkx2.5 in the
heart field prior to becoming restricted to the junction between the myocardium and SHF at linear heart tube stages. Like ltbp3
morphants that show a SHF deficiency, morpholino-mediated fosl2 knock-down results in embryos with severe arterial pole defects
characterised by reductions in the number of ventricular cardiomyocytes and multi-lineage loss of the outflow tract (OFT) derivatives.
However, unlike ltbp3 morphants that fail to maintain a SHF progenitor pool, fosl2 morphants show a dramatic accumulation of SHF
progenitor cells. Using photoconvertible reporter transgenic lines, we learned that the build-up of undifferentiated second heart field
cells was due to defective myocardial accretion and differentiation in fosl2 morphants. In addition, using RNA-seq, we have shown
that markers of differentiated myocardium are downregulated in fosl2 morphants. Furthermore, we report our findings on the genetic
interactions between fosl2 and ltbp3 in second heart field development.
Program/Abstract # 368
Cadm4 restricts the production of cardiac outflow tract progenitor cells
Zeng, Xin-Xin I.; Yelon, Deborah (University of California, San Diego, USA)
Proper development of the cardiac outflow tract (OFT) is essential for connecting the heart to the vasculature, and abnormal OFT
growth or morphogenesis can cause congenital heart defects. Given the importance of appropriate OFT assembly, the embryonic
origins of OFT progenitor cells are of great interest. A variety of recent studies have illustrated that the heart is built through two
major sources of progenitors: first heart field (FHF) and second heart field (SHF) progenitors, which differ in their timing of
differentiation and in their contributions to specific regions of the heart. Notably, the OFT is built by the addition of latedifferentiating,
SHF-derived cardiomyocytes to the arterial pole of the primitive heart tube. We have identified an intriguing gene, cell
adhesion molecule 4 (cadm4), that is expressed in a region near the arterial pole where the SHF-derived OFT progenitor cells reside.
Strikingly, loss of cadm4 function causes a dramatic enlargement of OFT size: a surplus of SHF-derived cells aggregates around the
arterial pole and ultimately results in the addition of nearly twice the normal number of OFT cardiomyocytes. Conversely,
overexpression of cadm4 reduces the size of the OFT by decreasing the number of OFT progenitor cells clustered at the arterial pole.
Analyses of the dynamics of cell division and differentiation suggest that cadm4 influences the proliferation and maintenance of OFT
progenitor cells before they migrate into the heart tube and contribute to the OFT myocardium. Together, our data support a novel
model in which Cadm4 activity limits the production of OFT progenitor cells, potentially through an adhesion-based mechanism for
the regulation of cardiomyocyte differentiation.
Program/Abstract # 369
Mutant Shp2 from Noonan Syndrome and LEOPARD Syndrome induced similar defects during early heart development.
Bonetti, Monica (Hubrecht Institute, Netherlands)
Germline mutations in the human gene PTPN11, encoding Shp2, cause Noonan syndrome (NS) and LEOPARD syndrome (LS), two
multisymptomatic developmental disorders that are characterized by cardiac defects, short stature, craniofacial defects and mental
retardation. Interestingly, Shp2 catalytic activity is enhanced by NS mutations and reduced by LS mutations. The heart defects appear
to be distinct between NS and LS patients, in that NS patients usually develop pulmonary stenosis and hyperthrophic cardiomyopathy
is observed more in LS patients. We generated the most common NS/LS Shp2 mutations and expressed these in zebrafish embryos to
analyse their function in vivo . The resulting embryos were shorter than control wild-type Shp2-expressing embryos and they
displayed cardiac and craniofacial defects, reminiscent of human symptoms. In this study, we investigated the cardiac defects that
were induced by expression of mutant Shp2. We found that the developing heart in NS/LS embryos failed to undergo looping
morphogenesis. These defects were indistinguishable between NS and LS during early embryogenesis. Expression of NS and LS
mutants induced MAPK hyperactivation at bud stage, which may explain why the early developmental defects were indistinguishable.
The cardiac anomalies occured during the elongation of the heart tube and consisted of reduced cardiomyocyte migration, coupled
with a reduced heart rotation. Furthermore, the expression of specific laterality markers was randomized in NS/LS embryos, which
might be caused by defective ciliogenesis that we observed at early developmental stages. These results indicate a direct correlation
between NS and LS mutations and their ability to cause defects in early heart development.
Program/Abstract # 370
The androgen receptor is differentially expressed in the atrium and ventricle tissue of mouse embryo.
De Ita Ley, Marlon; Pedernera Astegiano, Enrique Antonio; Meneses Morales, Iván; Gómora Herrera, María José; Méndez Herrera,
María del Carmen (UNAM, Mexico)
The androgen receptor is differentially expressed in the atrium and ventricle tissue of mouse embryo De Ita Ley, M; Pedernera
Astegiano, E; Meneses Morales, I; Gómora Herrera MJ; Méndez Herrera, MC. The presence of androgen receptor (AR) was
described in the heart of adult and neonatal mice; however the pattern of expression of this receptor during the prenatal heart
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