Cytology of lepidoptera VIII. Acetylation of ?-tubulin in mitotic and meiotic spindles of two Lepidoptera species,Ephestia kuehniella (Pyralidae) andPieris brassicae (Pieridae)

Abstract

The microtubular spindle in spermatocytes of Lepidoptera is unconventional in that the bulk of the microtubules (MTs) ends relatively abrupt about halfway between the spindle equator and the centrosomes from late prometaphase through early anaphase. Membranous elements separate the MT ends from the centrosomes. In the present study, the question is addressed whether MTs in meiotic spindles of male Lepidoptera are — as typical of spindle MTs in other systems — highly dynamic or whether they represent a more stable MT population. To this end, primary spermatocytes of two Lepidoptera species,Ephestia kuehniella (Pyralidae) andPieris brassicae (Pieridae), were probed with a widely used antibody, 6–11B-1, directed against acetylated α-tubulin. Tubulin acetylation is believed to indicate the presence of long-lived MTs. In late telophase spermatocytes of both species, spindle MTs were highly acetylated. This is in keeping with observations in other systems: MT dynamics decreases towards telophase. The labeling intensity in younger spermatocytes differed, however, between both species. InE. kuehniella only flagella were labeled, whereas inP. brassicae also the kinetochore MTs and small MT arrays around the centrosomes were detected by the antibody against acetylated α-tubullin. The findings are compatible with the suggestion that spindle MTs are dynamic in prometaphase to anaphase spermatocytes ofE. kuehniella. In fact, treatment with taxol, a MT-stabilizing drug, leads to high acetylation of α-tubulin throughout spindle MTs ofE. kuehniella in this period. Meiotic spindles inP. brassicae are longer by a factor of 1.3 than those ofE. kuehniella. The shorter MTs inE. kuehniella may turnover completely and cannot accumulate acetylated portions, whereas segments of MTs in the longer spindles ofP. brassicae persist and become post-translationally acetylated. Spermatogonial mitosis was also studied in both species and spindle MTs were found highly acetylated throughout mitosis. Thus, mitotic and meiotic spindles in males of Lepidoptera differ with respect to MT turnover.