Mitochondrial respiratory chain complex assembly and function during human fetal development.

Oxidative phosphorylation (OXPHOS) deficiency may have early antenatal manifestations, probably related to the time course and/or tissue specificity of the disease gene expression during the embryo-fetal period. This feature hampers a fully reliable prenatal enzymological diagnosis of OXPHOS deficiency. We have studied OXPHOS in various human fetal tissues from 9 to 17 weeks of gestation. We found that the fetal respiratory chain complexes are fully assembled and functional at early stages of development in heart, liver, muscle, brain and kidney. We also observed a marked increase of respiratory chain activities and mitochondria content in postnatal compared to prenatal tissues. However, we were not able to detect obvious modification in the size, composition or activity of the various OXPHOS complexes during the second trimester of pregnancy that could account for the variations we observed in a pathological context. Therefore, we suggest that the time-dependent expression of respiratory chain deficiency either during fetal life or after birth could be related to the differential expression or regulation of the mutant proteins.