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Surgical induction of cardia bifida in 1-day-old
Gallus domesticus embryos
Anisha Chandra and Marielena Vélez
Swarthmore College, 2004
Most embryos undergo both mosaic and regulative development at some point during embryogenesis. However, specific organs and areas may undergo one, the other, or a combination of the two types of development at different times across species. Previous studies and current literature suggest that the avian heart undergoes regulative development in that two primordia develop independently and then fuse. The heart fields of eleven one-day old chick embryos were bisected in an attempt to determine whether the chicken heart undergoes regulative development. Three embryos were successfully operated such that each developed with two functional hearts. This data supports the current understanding of avian heart formation and provides an experimental model for organ regeneration or tissue culture for the purpose of transplantation.


Organogenesis is the period of embryogenesis during which the three germ layers formed during gastrulation are further organized into tissues and organs. This process often requires the rearrangement and interaction of disparate and distant cells. These cells must frequently migrate from their original positions to their final locations. Most organs are formed through the interaction of two or more germ layers. (Gilbert, 2003). Such is the case for the Gallus domesticus heart.

The heart is the first functional organ to form in the amniote vertebrate. In chicks, presumptive heart cells migrate through the primitive streak and form two groups of mesodermal cells lateral to and level with Hensen’s node (Gilbert, 2003). These cells are collectively referred to as the cardiogenic mesoderm and form from the lateral plate mesoderm. The cardiogenic mesoderm layer is specified by the underlying anterior endoderm through BMP and FGF signalling pathways. These signals direct the two groups of cells to differentiate independently while they migrate anteriorly toward the gut tube. The two endocardial tubes fuse when the infolding of a superficial layer called the splanchnic (or ventral) mesoderm brings them together. Migration and fusion seem to be directed, respectively, by a fibronectin gradient in the foregut endoderm, and the selective expression of N-cadherin on the apices of the migrating bilateral primordial. These two clusters will go on to form atrial, ventricular musculature, cushion cells of valves, the Purkinje conducting fibers, and endothelial lining of heart (Gilbert, 2003).

There are two modes of development common to most species in the animal kingdom. Virtually all embryos undergo both mosaic and regulative development at some point during their growth. Regulative development generally occurs in early gastrulation when cells are induced to form different structures according to the cell-cell signalling interactions in a specific area of the embryo that lead to the conditional specification of a cell’s fate. A cell undergoing regulative development can be transplanted to another part of the embryo and form whatever structure belongs in that area instead of the structure that it would have originally formed because it is competent to receive the different signals from the new cells around it.

The second mode of development is mosaic development. Mosaic development results from the autonomous specification of a cell’s fate. These cells, instead of depending on cell-cell interactions, are determined by cytoplasmic factors contained within the cell itself. These cells will form a given structure even if they are moved to a new location and are exposed to cell-cell interactions and signals that differ from their original position. Most organisms contain different types of tissues, each of which may undergo one of these developmental mechanisms at a given time (Gilbert, 2003).

The developmental pattern of the avian heart was studied by bisecting the heart primordial field and observing the subsequent development of the heart, if present. If the heart were to develop using an autonomous mechanism, the cells would develop normally even if the two sides were not in physical contact with one another. This would lead to half a heart growing on either side of the incision. However, if instead the heart developed using a regulative mechanism, then the cells on the two sides would compensate for the perceived absence of the other cells. This would lead to the development of two distinct, and perhaps functional, hearts (Hamburger, 1960).

©Cebra-Thomas, 2000

Last Modified: May 2nd 2004

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