This document summarizes a study analyzing mouse embryos with a point mutation in the non-muscle myosin heavy chain II-B gene (Myh10) using high resolution 3D imaging. Mice homozygous for the R709C Myh10 mutation exhibited all features of Pentalogy of Cantrell (POC), a rare birth defect affecting the abdominal wall and heart. Heterozygous mice showed variable phenotypes. Micro-CT scans of E14.5 embryos found cardiac defects in homozygous mice consistent with POC, including double outlet right ventricle and ventricular septal defects. The homozygous mutation was embryonic lethal by E14.5 due to cardiac failure. Future studies aim

1. Poster produced by Faculty & Curriculum Support (FACS), Georgetown University School of Medicine
Detailed analysis of the morphology of mouse embryos with a point mutation
in non-muscle myosin heavy chain II-B using high resolution 3D imaging
Zachary M. Weisner1,2
; Xuefei Ma Ph.D.2
; and Robert S. Adelstein M.D.2
Abstract
1
Georgetown University Medical Center, Department of Biochemistry and Molecular Biology, Washington, DC
2
National Institutes of Health, National Heart, Lung, and Blood Institute, Laboratory of Molecular Cardiology,
Bethesda, Maryland
Introduction
Methods & Materials
Conclusions
Future Directions
References
Acknowledgments
Mutations of the Myh10 gene, encoding nonmuscle myosin
heavy chain II-B (NMHC II-B), are proposed to be one of the
causative genetic links to Pentaology of Cantrell (POC). POC
is a developmental defect causing inadequate closure of the
ventral body wall often resulting in ectopia cordis and an
omphalocele in 63% of all cases. POC presents with a set of
five phenotypes including: (1) anterior diaphragm deficiency,
(2) midline supraumbilical wall defect, (3) diaphragmatic
pericardium defect, (4) intracardiac abnormalities such as
double outlet right ventricle (DORV) and ventral septal defect
(VSD), and (5) lower sternum defect (Ma and Adelstein). POC
is a very rare congenital defect that affects up to 1 in 200,000
live births (Harmath, Hajdu and Hauzman). Males are generally
affected more than females with a predominance of 2.7:1
(Pakdaman, Woodward and Kennedy). In efforts to better
understand the phenotypic development over time, our lab
utilized a mouse model with a point mutation at R709C on
NMHC II-B. This study performed whole body micro-
computerized topography scans on mice at embryonic day
(E)14.5, allowing characterization of the defects. Hearts were
then dissected and a detailed CT scan was performed.
Preliminary results reveal that mice homozygous for the
R709C mutation contain all the fore- mentioned defects.
Heterozygous mice for the R709C mutation vary in their
phenotype expression.
Review of Nonmuscle Myosin II-B:
I would like to sincerely thank Dr. Xuefei Ma and Dr. Robert S.
Adelstein for their guidance and instruction throughout this project.
A special thanks to Dr. Mary Anne Conti for a review of this poster.
Additionally, I would like to express gratitude to Danielle Donahue
of the Mouse Imaging Facility for her guidance with the CT
programing. Finally, I would like to thank Milton Williams and
Mohamed Elshazzly for their support.
Figure 1: Non-muscle myosin II-B
Genotyping: Confirming Mutant Mice
Figure 5: Results of Genotyping
Figure 5 displays the genotyping results conducted for the E14.5 embryos.
Embryos included MA-134, 1-8, for each respective lane. Lanes 1 and 2
were mutant, Lane 3 was wild type, and Lanes 4 thru 8 were heterozygous.
• NM-II is hypothesized to be a genetic link to POC
• Homozygous NM II-B R709C mice exhibit a phenotype consistent
with all aspects of POC
• Homozygous mutation is embryonic lethal for mice at E14.5 due to
cardiac failure
• Heterozygous mice vary in their phenotype expression. Some mice
do not display defects suggesting other compensatory mechanisms.
• Most common heart defects include double outlet right ventricle
(DORV) and ventral septal defects (VSD).
• Some studies suggest that the cardiac defects occur in order to
promote survival in utero in efforts to adapt to the disease.
Figure 6: Microscope Evaluation of Embryos:
Figure 6: All the above specimens are at E14.5. 1 and 2 are mutant, 3 is
a wild type and the rest are heterozygous. Current studies show that a
mutation in NM II-B is embryonic lethal by E14.5.
Understanding Pentalogy of Cantrell:
Identifying the Time Line of Defects: Mouse Model
Figure 2: POC Clinical Development
Figure 2: On the left is a normal heart. In the middle, the visual defects of
POC are displayed. Ectopia cordis is present. An omphalocele is
present in 63% of all cases. The five clinical phenotypes include: (1)
anterior diaphragm deficiency, (2) midline supraumbilical wall defect, (3)
diaphragmatic pericardium defect, (4) intracardiac abnormalities such as
double outlet right ventricle (DORV) and ventral septal defect (VSD), and
(5) lower sternum defect. On the right are cartoon displays of the DORV
and VSD defects associated with the heart.
Results
Results
Figure 1: There are three isoforms of nonmuscle myosin II (NM II),
including: A, B, and C. Myosin interacts with actin in order to facilitate
cell division, cell-cell adhesion, and cell migration. The N-terminal makes
up the globular domain and the C-terminal makes up the coiled-coil end
of the myosin heavy chain. Two sets of light chains bind near the
globular domain. These two pairs of light chains are essential for
function and regulation. Myh10 is the gene encoding NMHC II-B. NM II-
B is shown to be essential for cardiac development. Mutations in the
Myh10 gene are hypothesized to be related to POC.
Figure 3: Mouse Embryonic Development Diagram
Figure 4: Cardiac Development in Mouse Embryos
Figure 3: The embryonic development of mice occurs within 18-21 days
of gestation. A zygote undergoes gastrulation and turning and eventually
organogenesis followed by birth. Lifespan averages about 867 days.
Figure 4: The cardiac development of the heart starts around E7.5 with
the formation of the cardiac crescent. The heart tube and looping heart
form by E8.5. The chamber formation is defined by E10.5 and the
tissues become defined by E15. NM II-B Mice which phenocopy POC,
die at E14.5 due to cardiac failure.
Micro-Computerized Topography:
Figure 7: Micro-CT Scans with a sagittal plane view:
Histology and Immunohistochemistry:
Figure 8: H&E staining on Cardiac Structures
Figure 9: Immunofluorescence Confocal Microscopy
Figure 8 displays cardiac histology of a wild type E14.5 embryo. On the
left side is the 10x view of the heart and on the left is a 40x view, focused
on the cardiac myocytes of the myocardium.
Figure 7: A full body CT was performed on the fore-mentioned samples.
Three fields of view were included. Red arrows indicate the heart.
Figure 9: E14.5 mouse sagittal view of the heart. Top row, NM II-A
(green), E-cadherin (red), and DAPI stains nuclei (blue). Bottom row,
NM II-B (green), desmin (red), and DAPI stains nuclei (blue). Images
were obtained with confocal microscopy. Z stacks were obtained with
heart tissue and cells. The cell images were taken at 63x and the
tissues were viewed at 20x both with confocal microscopy.
• Complete micro-CT scanning for mouse embryos. Our group plans
to analyze mice from E10 to E14. The goal is to determine a time
line of defects.
• Continue heart dissection of the embryos and perform detailed
scans of the heart to better characterize the cardiac defects.
• Determine the mechanism behind POC and any related cellular
pathways.
• Determine other causative genetic links with POC.
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Morphological Characterization:
Mouse Model: A mixture of SV129 and C57BL/6J mouse models
contained a mutation in the Myh10 gene. Point mutation in R709C of NM
II-B.
Genotyping: Samples were obtained from embryos and lysed. PCR was
performed. Samples were run on a 1.0% gel and photos were taken on a
UV-transilluminator.
Micro-Computerized Topography: Embryos were incubated in contrast
solution (25% lugol and 5% iodine) for 48 hours. Samples then were
placed in a Sky Scan 1172. Reconstruction, analysis, and histogram was
adjusted using Sky Scan programs. Resolution went as low as 13 microns
for full body scans and 4 microns for detailed heart scans.
Histology and Immunofluroescence: Tissues were fixed in 4%
paraformaldehyde, embedded in paraffin and sectioned (preformed
previously by XM). Samples were dewaxed and antigen retrieval was
performed. Blocking buffer was 1% BSA/10% normal goat serum in PBS.
Samples were blocked for 1 hour and primary antibody was incubated at
4˚C overnight. Secondary Ab was incubated for an hour at room
temperature. Primary Abs: NM II-A with E-cadherin, and NM II-B with
desmin. Images were taken on Zeiss 780 inverted confocal microscope.
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Harmath, Agnes, et al. "Surgical and Dysmorphological Aspects of Abdominal Wall Defects." Donald School Journal of Ultrasound in Obstetrics and Gynecology (2009): 38-47. Document.
Harmath, Agnes, et al. "Surgical and Dysmorphological Aspects of Abdominal Wall Defects." Donald School Journal of Ultrasound in Obstetrics and Gynecology (2009): 38-47. Document.
DORV
VSD