How is the flagellar length of mature sperm determined?: III. Comparison of initial growth rate of flagella in spermatids from Cynops and Xenopus in the presence and absence of cycloheximide

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Previous studies [1, 2] on flagellar growth in round spermatids from Cynops and Xenopus in vitro have shown that the period and rate of flagellar growth are greater in Cynops than in Xenopus. The present study shows, however, that during the initial phase of flagellar growth (for the first 12 h following the second meiotic division), the growth rate is very similar in both Cynops and Xenopus (0.5–0.6 μm/h at 22 °C). The difference in the growth rate between Cynops and Xenopus was observed beyond 12 h following the second meiotic division. When round spermatids in both species were inoculated with 10 μ M cycloheximide, flagella grew at the same rate as in the absence of cycloheximide for the first 12 h following the second meiotic division. Beyond 12 h, however, cycloheximide suppressed flagellar growth in round spermatids in both species. These results indicate that the initial flagellar growth in round spermatids is provided for by flagellar protein pools which were present just after the second meiotic division; the growth beyond 12 h in round spermatids is contributed by newly synthesized flagellar proteins.