Morphological differentiation of mitochondria in the early chick embryo: a stereological analysis.

The morphological evolution of mitochondria in three cell types of chick embryo in neurulation was analyzed by stereological methods. Mitochondria, showing a random distribution, were characterized by moderate electron-dense matrices and normal cristae. The numerical density of mitochondria significantly increased in the neuroectoderm and epiblastic cells while their volume density remained unchanged. The mitochondria in mesoderm cells were ellipsoidal (axial ratio 2:1) at stages 5 and 8 although they underwent an elongation in neuroectoderm and epiblastic cells (axial ratio from 2:1 to 1.6:1). The individual size of "average mitochondria" in the mesoderm cells was smaller than in other cell types. The total V/S (volume/surface) ratio of mitochondria decreased during neurulation. These morphological changes have been discussed emphasizing the possible metabolical role of mitochondria during morphogenesis.