Flagellar Elongation Research Articles

Spermatid differentiation in the blowfly Sarcophaga bullata with particular reference to flagellar morphogenesis

Young spermatids of Sarcophaga possess a single centriole apposed to the nuclear envelope and surrounded by a dense centriole adjunct. Concomitant with nuclear condensation and flagellar elongation, the centriole adjunct disappears and the centriole dedifferentiates from its normal triplet microtubule grouping. The triplet organization is retained only in the most proximal 500 Å of the centriole while subfiber C of each group becomes centrifugally displaced and is continuous with the 9 accessory tubules that extend the length of the mature axoneme. Flagellar axoneme morphogenesis is first apparent as a ring of 9 single microtubules, or the A subfibers of the presumptive doublets. This is followed by the appearance of the radial linkage along each A subfiber, the B subfiber of each doublet from a projection off subfiber A, the paired arms along subfiber A, the central tubules and sheath, the accessory tubules from a projection off the B subfibers, and finally the outer coarse fibers. Occurring at the same time as axoneme assembly is the elongation of the 2 adjacent mitochondrial derivatives and the formation of their crystalloids. In addition, the acrosome of mature spermatids shows a paracrystalline organization as revealed by negative staining.

Flagellar regeneration in protozoan flagellates.

The flagella of populations of three protozoan species (Ochromonas, Euglena, and Astasia) were amputated and allowed to regenerate. The kinetics of regeneration in all species were characterized by a lag phase during which there was no apparent flagellar elongation; this phase was followed by elongation at a rate which constantly decelerated as the original length was regained. Inhibition by cycloheximide applied at the time of flagellar amputation showed that flagellar regeneration was dependent upon de novo protein synthesis. This was supported by evidence showing that a greater amount of leucine was incorporated into the proteins of regenerating than nonregenerating flagella. The degree of inhibition of flagellar elongation observed with cycloheximide depended on how soon after flagellar amputation it was applied: when applied to cells immediately following amputation, elongation was almost completely inhibited, but its application at various times thereafter permitted considerable elongation to occur prior to complete inhibition of flagellar elongation. Hence, a sufficient number of precursors were synthesized and accumulated prior to addition of cycloheximide so that their assembly (elongation) could occur for a time under conditions in which protein synthesis had been inhibited. Evidence that the site of this assembly may be at the tip of the elongating flagellum was obtained from radioautographic studies in which the flagella of Ochromonas were permitted to regenerate part way in the absence of labeled leucine and to complete their regeneration in the presence of the isotope. Possible mechanisms which may be operating to control flagellar regeneration are discussed in light of these and other observations.