iBet uBet web content aggregator. Adding the entire web to your favor.
iBet uBet web content aggregator. Adding the entire web to your favor.



Link to original content: https://www.ncbi.nlm.nih.gov/pubmed/28526751
A new hypothesis for foregut and heart tube formation based on differential growth and actomyosin contraction - PubMed Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2017 Jul 1;144(13):2381-2391.
doi: 10.1242/dev.145193. Epub 2017 May 19.

A new hypothesis for foregut and heart tube formation based on differential growth and actomyosin contraction

Hadi S Hosseini  1   2 , Kara E Garcia  1 , Larry A Taber  3
Affiliations

A new hypothesis for foregut and heart tube formation based on differential growth and actomyosin contraction

Hadi S Hosseini et al. Development. .

Abstract

For decades, it was commonly thought that the bilateral heart fields in the early embryo fold directly towards the midline, where they meet and fuse to create the primitive heart tube. Recent studies have challenged this view, however, suggesting that the heart fields fold diagonally. As early foregut and heart tube morphogenesis are intimately related, this finding also raises questions concerning the traditional view of foregut formation. Here, we combine experiments on chick embryos with computational modeling to explore a new hypothesis for the physical mechanisms of heart tube and foregut formation. According to our hypothesis, differential anisotropic growth between mesoderm and endoderm drives diagonal folding. Then, active contraction along the anterior intestinal portal generates tension to elongate the foregut and heart tube. We test this hypothesis using biochemical perturbations of cell proliferation and contractility, as well as computational modeling based on nonlinear elasticity theory including growth and contraction. The present results generally support the view that differential growth and actomyosin contraction drive formation of the foregut and heart tube in the early chick embryo.

Keywords: Biomechanics; Computational model; Contraction; Growth; Morphogenesis.

PubMed Disclaimer

Conflict of interest statement

Competing interestsThe authors declare no competing or financial interests.

Figures

Fig. 1.
Fig. 1.
Morphology of foregut and heart tube formation in chick embryo (stages HH5-HH10). (A-E) Brightfield images of embryo (ventral view). Scale bar: 150 μm (for all images). (A′-E′) Schematics illustrating folding of heart fields (HFs). Lateral regions (blue) and medial regions (red) become inflow and outflow regions of the HT (E′). (A″-E″) Schematics of cross-sections indicated by dashed yellow lines in A-E. Red dashed lines indicate HFs in A and anterior intestinal portal (AIP) in B-E. CC, cardiac crescent; CJ, cardiac jelly; FG, foregut; HT, heart tube; iSPL, oSPL, inner, outer splanchnopleure; N, notochord; OV, omphalomesenteric vein. Schematics in A′-E′ are reprinted, with permission, from Kirby (2007); those in A″-E″ are based on drawings by Kirby (2007).
Fig. 2.
Fig. 2.
Effects of inhibiting cell proliferation. (A) Representative chick embryo cultured in normal media for 30 h from stage HH5 (ventral view). Folding of the splanchnopleura (SPL) creates the foregut as the anterior intestinal portal (AIP, yellow dashed line) descends progressively. After 30 h, the heart tube (HT; red dashed line) is looped towards the right. Scale bar: 250 μm. (B) Embryo cultured for 5 h in media containing the mitotic inhibitor aphidicolin (50 μM) shows negligible folding. After washout and continued culture, folding and AIP descension began. At the end of the incubation period, an abnormal HT had formed. (C) Embryo cultured in media containing aphidicolin (50 μM) for 21 h from stage HH8. Plot of relative oSPL length L/L0 (mean±s.d.) shows that exposure to aphidicolin (n=7) decreased the rate of AIP descension relative to controls (n=4). For this embryo, the treatment resulted in the formation of two heart tubes (HT, right). These results suggest that inhibiting cell proliferation blocks initial folding of the SPL and slows downward motion of the AIP at later stages.
Fig. 3.
Fig. 3.
Effects of inhibiting contraction. (Aa-Ah) Representative chick embryo cultured for 15 h from stage HH6 (ventral view). Yellow dashed lines indicate anterior intestinal portal (AIP). (Aa-Ad) Embryo cultured for 7.5 h to HH7+ in media containing the myosin inhibitor blebbistatin (75 μM). Initial folding of splanchnopleure (SPL) occurred, but after 5 h downward movement of the AIP slowed to nearly a stop. (Ae-Ah) After washout at 7.5 h, AIP descension resumed as heart tube (HT) formed (dashed white lines). (B) Normalized length of oSPL (L/L0; mean±s.d.) as a function of incubation time for control embryos (n=4) and blebbistatin-treated embryos (n=4). AIP descension rate slowed until washout, then returned to approximately normal. These results suggest that, after initial folding, contraction is required for normal elongation of the SPL and downward motion of the AIP. Scale bar: 150 μm.
Fig. 4.
Fig. 4.
Effects of blebbistatin exposure on growth of the SPL during Phase 1. (A,B) Embryo with attached beads at HH5 and after 3 h of culture. Two representative triangles used to compute tissue strains are indicated. Analyzed beads were taken from the regions marked by red ovals. (C) Growth ratios Gx and Gy computed from strain and stress data (see supplementary Materials and Methods). Results are shown for control embryos (n=8) and blebbistatin-treated embryos (n=7) (two-way ANOVA, *P<0.01). Blebbistatin exposure slowed but did not stop growth in both the x and y directions.
Fig. 5.
Fig. 5.
Finite-element model for foregut and heart tube formation in initial configuration (HH5). (A) The model for the inner splanchnopleure (iSPL) is a flat plate consisting of two layers representing the mesoderm and endoderm. Because of bilateral symmetry, only half of the iSPL is modeled with the y-axis representing the embryonic midline. Roller boundary conditions are indicated; other surfaces are free. (B,C) Ventral views of mesoderm and endoderm layers. Black circles indicate roller boundary conditions. Red and green denote regions representing the heart field (HF) and presumptive anterior intestinal portal (AIP), respectively. (D) The spatial pattern of growth rate (formula image, see Eqn S6) is the same for both layers during Phase 1, when diagonal folding of iSPL occurs. Growth rate is normalized to the maximum rate in each layer, but actual growth rates are higher in mesoderm (see supplementary Materials and Methods). Arrows indicate directions of increasing (Inc.) growth rate.
Fig. 6.
Fig. 6.
Results from computational model for folding of inner splanchnopleure (iSPL). Top row: Ventral view of the model at stages HH5-10, divided into three phases. Phase 1: differential growth between SPL layers; Phase 2: contraction along anterior intestinal portal (AIP, green); Phase 3: growth of heart field (HF, red). Middle row: Cross-sections from the model at locations indicated by the dashed black lines. Bottom row: Schematics of the same cross-sections [based on drawings from Kirby (2007)]. Although there are some morphological differences, the model captures the evolving shapes of the foregut (FG) and heart tube (HT) reasonably well.
Fig. 7.
Fig. 7.
Comparison of HH10 heart shapes: experiment and model (ventral view). (A) Scanning electron microscopy image [reproduced, with permission, from Männer (2000)]. (B) Model at HH10. Modeled half of embryo is combined with its mirror image to aid visualization. Yellow dashed lines represent outline of heart tube (HT) and omphalomesenteric veins (OVs); white dashed line in B indicates fused heart-field region in the model. OVs represent posterior regions of inner splanchnopleure (iSPL) that have not yet fused. (C,D) Transverse cross-sections of HH10 chick embryo and model at locations indicated by white/black lines in A and B, respectively. Thin green lines in model sections 3 and 4 are the contracting AIP border region. [Experimental sections are reproduced, with permission, from De Jong et al. (1990).] AIP, anterior intestinal portal; FG, foregut; NT, neural tube.
Fig. 8.
Fig. 8.
Simulation of growth inhibition experiment. (A) Ventral view of model during stages HH7+ to HH10 with growth turned off. Green and red regions represent anterior intestinal portal region and heart field, respectively. Compare with model for control embryo in Fig. 6. (B) Plot of normalized oSPL length (L/L0) versus stage. Experimental results for control embryos (n=4) and embryos exposed to aphidicolin (n=7, mean±s.d.; beginning at HH7+) are compared with model predictions for normal growth and no growth, respectively.
Fig. 9.
Fig. 9.
Deformation rate around AIP during heart tube formation. (A) Tungsten beads (black dots) were injected into an embryo at HH7 (ventral view). Scale bar: 100 μm. (B) The same embryo after 2 h of culture. Dashed yellow curves show a representative pair of beads used for calculations. (C) Comparison of experimental (n=11) and model-predicted deformation rate averaged over the region indicated by arrows in A. For experiments, mean±s.d. are plotted versus stage. Deformation rate DT was computed tangent to the AIP in the current configuration. Blue dashed line indicates results computed from data given in Ramasubramanian et al. (2006).
Fig. 10.
Fig. 10.
Tension in foregut. (A,A′) Representative HH8 embryo immediately before and after punching a circular hole (ventral view). (A″) Ellipse (dashed line) was fit to the wound opening (expanded view of yellow box in A′). (A‴) Finite-element model at HH8 with circular hole in inner splanchnopleure (iSPL) introduced at HH5. (A″″) Ellipse was fit to the model wound opening (expanded view of pink box in A‴). (B,B′) OCT images of transverse and longitudinal cross-sections, respectively, for the embryo shown in A′. A pipette was used to punch holes though oSPL, head ectoderm (HE) and foregut (FG, iSPL). Lengths a and b correspond to minor and major axes of elliptical wound in FG floor. (C) Experimental and model-predicted results for elastic stretch ratios (formula image, formula image; d=pipette diameter) at stages HH8 (n=6) and HH9 (n=5) (two-way ANOVA, *P<0.01). (D) Experimental elastic stretch ratios in the FG for stage HH8+ embryos cultured from stage HH8 onwards in control media (n=7) and media containing 50 μM aphidicolin (n=8). Inhibition of cell proliferation resulted in increased FG tension in the axial direction during Phase 2 (two-way ANOVA, *P<0.01). AIP, anterior intestinal portal; NT, neural tube. Scale bars: 50 μm (A″); 100 μm (B); 200 μm (A′,B′).
Fig. 11.
Fig. 11.
Tension in anterior intestinal portal (AIP) and heart tube (HT). (A) HH8 embryo immediately after a linear cut at the medial point of the AIP. White dashed curve outlines AIP with cut. [Reproduced, with permission, from Varner and Taber (2012a).] The opening angle α characterizes the magnitude of tension tangential to AIP. (A′) Finite-element model for an AIP cut at HH8. (A″) Comparison of experimental (mean±s.d.) and model results at different stages of development. Experimental data for stage HH8 are reproduced, with permission, from Varner and Taber (2012a); data for stages HH9 and HH10 are reproduced, with permission, from Shi et al. (2014). (B) HH10 heart with circumferential cut. Cut opens to indicate longitudinal tension (dashed ellipse) [reproduced, with permission, from Shi et al. (2014)]. (B′) Model at HH10 with horizontal cut in heart. (B″) Enlarged view of the black box in B′. (B‴) Experimental (n=6) and model-predicted results for cut aspect ratio (a/b). Experimental data are from Shi et al. (2014).
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Abu-Issa R. (2014). Heart fields: spatial polarity and temporal dynamics. Anat. Rec. 297, 175-182. 10.1002/ar.22831 - DOI - PubMed
    1. Abu-Issa R. and Kirby M. L. (2007). Heart field: from mesoderm to heart tube. Rev. Cell Dev. Biol. 23, 45-68. 10.1146/annurev.cellbio.23.090506.123331 - DOI - PubMed
    1. Abu-Issa R. and Kirby M. L. (2008). Patterning of the heart field in the chick. Dev. Biol. 319, 223-233. 10.1016/j.ydbio.2008.04.014 - DOI - PMC - PubMed
    1. Aegerter-Wilmsen T., Smith A. C., Christen A. J., Aegerter C. M., Hafen E. and Basler K. (2010). Exploring the effects of mechanical feedback on epithelial topology. Development 137, 499-506. 10.1242/dev.041731 - DOI - PubMed
    1. Aleksandrova A., Czirok A., Kosa E., Galkin O., Cheuvront T. J. and Rongish B. J. (2015). The endoderm and myocardium join forces to drive early heart tube assembly. Dev. Biol. 404, 40-54. 10.1016/j.ydbio.2015.04.016 - DOI - PMC - PubMed

Publication types