CENTRIOLE REPLICATION DURING CILIOGENESIS IN CHICK TRACHEAL EPITHELIUM

Morphological aspects of centriole replication as displayed in tracheal epithelial cells of 15 to 19-day-old chick embryos during ciliogenesis were examined by electron microscopy. It was found that centriole replication and development take place in a finely fibrous region around the two mature centrioles of the diplosome. Procentrioles in early stages of development are observed in clusters. The core of each cluster is occupied by one or more cylindrical structures which gradually disappear as the procentrioles mature. Some of the procentriolar clusters are attached directly to the walls of the diplosomal centrioles by the cylindrical cores. This observation suggests that all of the clusters may form initially in close association with the diplosomal centrioles. The earliest recognizable procentrioles are short, cylindrical structures that have no microtubules. Later microtubules appear, first as singlets, then doublets and finally as triplets. The singlet becomes the innermost microtubule of the triplet. Following the assembly of the nine triplets, the procentrioles separate from the clusters, elongate to their mature length and acquire rootlets, ciliary vesicles and cilia. The observation that all the procentrioles in each cell are in the same stage of development indicates that all the centrioles or presumptive basal bodies required by this cell are produced at the same time. © 1969 Springer-Verlag.