Cell Population Growth and Area Expansion in Early Chick Embryos During Normal and Abnormal Morphogenesis in vitro:...

The exponential growth and cell population during the early embryogenesis of chick, cultured in vitro correlates with a linear increase in the blastoderm area. To understand the relationship between these parameters and normal morphogenesis, we have used a known teratogen, trypan blue, as a probe. A method is developed in which each new embryonic structure is assigned a rank value of 1 and the total number of ranks allows quantification of development and establishment of a numerical relationship between the size of the cell population, blastoderm area and the morphological development. The teratogen inhibits cell population growth, morphogenetic movements and shaping of organ primordia, but not the epiboly and differentiation of cells which have already invaginated and positioned during primitive streak formation. In contrast, the cell population growth, but not the blastoderm area-expansion, is correlated with the extent of abnormal development. A graphic analysis of the rank order, log cell number and blastoderm area reveals that these three parameters coordinately regulate morphogenesis. It is suggested that head fold formation is the key event regulating the progress of early morphogenesis.