Mitochondrial differentiation during the early development of the amphibian embryo

Sammanfattning: Mitochondria from Xenopus laevis and Ambystoma mexica- num embryos between fertilization and the beginning of feeding were studied: the former with respect to metabolic behaviour, enzyme pattern and carrier activity, and the latter with respect to morphological parameters.The metabolic behaviour of mitochondria was studied by assessing the rates of oxygen uptake in presence of various substrates. The rates of oxidation of most substrates change during development. The only substrate to be readily metabolized is glutamate (in presence of malate), whose rate of oxidation presents a peak during gastrulation and declines during larval development. The high rate of oxidation of glutamate and a high aspartate aminotransferase activity indicate that the glutamate- aspartate cycle may be predominant in early embryonic mitochondria.The activity of enzymes from the matrix, the inner membrane and the outer membrane were studied. During early development activities of enzymes in the various compartments change independently of each other. Furthermore, enzymes within one compartment may vary independently. Measurements of carrier activity reveal that the carrier for dicarboxylic acids displays a high activity before gastrulation and decreases thereafter, while the tricarboxylic acid, pyruvate and glutamate/OH carriers show the opposite pattern of change, their activities being low or undetectable during early development.This implies that a mitochondrial differentiation takes place ' during development, beginning at gastrulation when the first differentiated cells appear. In order to correlate mitochondrial and cellular differentiation, morphological parameters of mitochondria from undifferentiated and differentiated cells - Ruffini cells and epidermal cells - were analyzed. Mitochondria from the differentiated cells are significantly different from those in undifferentiated cells. Thus the processes of cell differentiation are accompanied by morphological and biochemical differentiation of the mitochondria.