ULTRASTRUCTURAL-STUDY OF MITOCHONDRIA AND THEIR CRISTAE IN EMBRYONIC RATS AND PRIMATE (N-NEMISTRINA)

Information on the morphology of mitochondria during embryogenesis is scattered in the Literature but there appears to be a developmental pa ttern characterized by vesiculation of the mitochondrial cristae. Duri ng early organogenesis, the embryo is in a relative state of hypoxia a nd this is associated with decrease of terminal electron transport sys tem activity and a marked increase in glycolysis. Ultrastructural stud ies of a 14 somite monkey embryo, and day 10 and 12 rat embryos, along with a review of the literature led us to determine that this hypoxic stage is characterized by vesiculation of the mitochondrial cristae. Starting in the late morula stage and continuing during early postimpl antation embryogenesis the cristae increase and appear tubular or vesi cular. After the end of neurulation, and with onset of vascular perfus ion, the cristae gradually become lamellated and by the limb bud stage appear more mature. We suggest that new cristae form from blebs of th e inner mitochondrial membrane and that subsequently with maturation t hese blebs collapse giving them a lamelliform appearance. The delamell ated state of the cristae may protect the embryo from toxic respirator y end-products of oxidative respiration which could accumulate in an e mbryo lacking vascular perfusion. In the heart of monkey and rat embry os, the mitochondria had diameters which were approximately twice thos e found in skin and neural tube. Anat. Rec. 252:383-392, 1998. (C) 199 8 Wiley-Liss, Inc.