Cytology of Lepidoptera. V. The microtubule cytoskeleton in eupyrene spermatocytes of Ephestia kuehniella (Pyralidae), Inachis io (Nymphalidae), and Orgyia antiqua (Lymantriidae).

The structural transformations of the microtubule cytoskeleton during eupyrene meiosis were characterized in the Mediterranean mealmoth, Ephestia kuehniella. Anti-tubulin immunofluorescence was used in two strains, L and Sbr, of this species. In addition, living primary eupyrene spermatocytes from strain L were observed with phase-contrast light microscopy, and metaphase I spermatocytes were studied with the electron microscope. The analysis did not reveal strain-specific differences in the behavior of the chromatin and the microtubule cytoskeleton in eupyrene meiosis. The general pattern of the two subsequent meiotic divisions in Ephestia kuehniella did not deviate from that observed during nuclear division in other species. A bipolar spindle developed during prophase, chromatin migrated towards the poles in anaphase, and spindle elongation occurred in telophase. Spindle development and behavior were qualitatively almost identical in primary and secondary spermatocytes. The assembly of the second meiotic spindle was initiated during the depolymerization of interzone microtubules of the first division. The relationship between spindle microtubules and centrosomes, however, showed some particularities in the moth. While microtubules radiated out from the spindle poles in late prophase, most microtubules ended about half-way between the equatorial plane and the spindle poles from late prometaphase to early anaphase. The termination of most microtubules distant from the poles was confirmed using electron microscopy in Ephestia kuehniella and using anti-tubulin immunofluorescence in two other Lepidoptera species, Inachis io and Orgyia antiqua. The microtubules were oriented parallel to the pole-to-pole axis of the spindle and were confined to an area laterally sheath by membrane layers. The spindle portions between the pole-proximal termini of the microtubules and the spindle poles contained irregularly shaped membrane elements. In late anaphase, microtubules reform between the migrating chromatin plates and the spindle poles. Concomitantly with the migration of the chromosomes towards the spindle poles, interzone microtubules are assembled. The origin of most of them appears to be at the pole-distal face of the chromatin masses.