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Chapter 8: Molecular and Cellular Development of the Heart

Which of the following is not true about the specification of cardiac precursors during gastrulation?

A. Cardiac precursors are derived from mesoderm following gastrulation

B. The fates of cardiac progenitor cells are already determined at the epiblast stage

C. The fates of progenitor cells are determined by the sequence and intensity of external signals encountered during gastrulation

D. A precursor cell’s position within the epiblast determines the complement of external signals it receives

E. Mesoderm is the result of epithelial-to-mesenchymal transition (EMT) in the epiblast

The answer is B. (Hurst’s The Heart, 14th Edition, Chap. 8) After gastrulation, the cardiogenic area, containing cardiac precursors, is formed by early gastrulating mesoderm (option A). It is located within the mesodermal component of the splanchnopleural layer of the anteriormost lateral plate.1,2 Mesoderm itself is formed by EMT of cells at the central-posterior position in the epiblast (option E).3 Although different regions of the epiblast give rise to specific cell types, the fates of the precursor cells themselves at this stage are not yet determined (option B).4 Transplantation studies have shown, for example, that epiblast regions fated to produce brain transplanted to the cardiac-forming region will form the heart, and vice versa. Ultimately, the history of external signals cells receive during their journey through gastrulation determines the differentiation pathway of precursor cells (option C). The sequence of signals received is determined by the location of precursor cells within the epiblast (option D).3

Which of the following is true about the specification of mesoderm that gives rise to cardiac cells?

A. Cells that migrate from the anterior primitive streak give rise to lateral mesoderm

B. Cardiac progenitors are found in the lateral plate mesoderm

C. The heart and liver are the last mesoderm to be produced by the embryo

D. Retinoic acid gradients are important for separating cardiac and forelimb fields, but they do not have a role in determining whether cardiac precursors give rise to atrial cells or ventricular cells

E. The first cardiac cells formed in the lateral plate mesoderm are atrial cells

The answer is B. (Hurst’s The Heart, 14th Edition, Chap. 8) Cells migrate out of the primitive streak, such that the anteriormost cells form the axial mesoderm and the posterior cells form the lateral mesoderm (option A). The cardiac fields are found in the lateral plate mesoderm, ...

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