Easton, Heather Shannon; (1991) Migration and differentiation of precardiac mesoderm in the chick embryo. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Two regions of precardiac mesoderm initially situated in a cardiogenic crescent, migrate in an anterio-medial direction early in the development of the embryo to form the primitive heart. The movement of the precardiac cells over the underlying endoderm is termed "directional migration", and is thought to involve an intimate association between the precardiac cells and the extracellular matrix that exists at the mesoderm-endoderm interface. The role of the extracellular matrix in the migration of the cells has been studied by treating early chick embryos with Monensin, a sodium ionophore which disrupts secretion. The range of anomalies - a reduction in embryo length, underdeveloped hearts and irregularly spaced and sized somites - is interpreted as evidence for the importance of the extracellular matrix in precardiac cell migration. Directional migration of the precardiac mesoderm in the chick embryo has been studied by culturing together explants 'in tandem' and 'abutting', from the precardiac area of both chick and quail embryos. These were examined histologically to ascertain the direction in which the cells had migrated, thereby testing whether chemotaxis was playing a role in the directional migration. Precardiac cells did not alter their direction of migration toward the putative chemotactic source. The idea that chemotaxis is involved is therefore rejected. The interaction of the precardiac tissues has been studied by microsurgery. Mesoderm from the anterior and posterior precardiac region of quail embryos was grafted into the posterior or anterior precardiac region of chick embryos to form chimeras. Grafts from the posterior region inserted into the anterior region lead to failure of heart looping, but grafts from the anterior region inserted into the anterior region never had this effect. It is suggested that a special function of the posterior precardiac mesoderm (a morphogen?) inhibits looping.

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