Mitochondrial origin of centrioles and cilia in some human endocrine neoplasms

Fine structural investigation of surgically removed human pituitary and parathyroid adenomas, pheochromocytomas and bronchial carcinoids revealed a hitherto undetected sequence of events in the formation of centrioles and cilia indicating that mitochondria may serve as their progenitors. The first steps seem to be the disappearance of mitochondrial cristae and a polar accumulation of a fibrillar-granular material with a subsequent increase of electron density of the double mitochondrial membranes and deposition of more electron opaque substance within and around these procentriolar bodies. This process is followed by the disintegration of the double membranes and an asymmetrical division of the electron dense aggregate. The larger part seems to be the precursor of the primary centriole (basal body) whereas the smaller one that of the secondary centriole. Formation of centrioleand rudimentary cilium-like structures was disclosed within the unaltered mitochondrial membranes of oncocytic cells present in two pituitary adenomas and in one pheochromocytoma. Accumulation of procentriolar bodies and mature centrioles, noted in some tumors, may be due to a defect in the process of centriolo- and ciliogenesis. It is conceivable that the mitochondrial genome plays an important role in formation of centrioles and cilia.