Journal of Cell Science, Vol 6, 629-653, Copyright © 1970 by Company of Biologists

Submitted on August 21, 1969

Formation of Centriole and Centriole-Like Structures During Meiosis and Mitosis In LABYRINTHULA Sp. (Rhizopodea, Labyrinthulida)

An Electron-Microscope Study

¹ Virginia Institute of Marine Science, Gloucester Point, Virginia 23062, U.S.A.

The fine structure of mitosis in vegetative cells of the marine protist Labyrinthula was found to involve formation of two approximately spherical, electron-dense aggregates (termed protocentrioles) 200-300nm in diameter. Spindle microtubules were directly attached to the structures. The aggregates contained centrally located cartwheel structures but no microtubular elements in the form of a centriole-like cylinder. In non-sporulating cells the aggregates occurred only during mitosis or possibly in late interphase cells. During meiotic zoosporulation de novo centriole formation was observed. Vegetative spindle cells, which contained no centrioles, procentrioles, or centriolar plaques, aggregated then changed into approximately round or oval presporangia within sori. Two protocentrioles were formed in the cytoplasm a few hundred nanometres from each nucleus. Microtubules, oriented in astral ray patterns, were attached directly to each of the protocentrioles. Following migration to opposite sides of the nucleus, each of the protocentrioles differentiated into two centrioles attached at the cartwheel or proximal ends in a longitudinally continuous orientation. Binary fission of the paired centrioles (termed bicentrioles) and reorientation yielded a diplosome or an approximate orthogonal orientation of the organelles. Each mature centriole consisted of the usual cylinder of 9 triplet microtubular blades with a cartwheel complex at the proximal end consisting of 5 or 6 tiers of cartwheels. Further centriole replication appeared to occur by orthogonal budding from mature centrioles.

Note:

Contribution No.324, Virginia Institute of Marine Science.