Cytology of lepidoptera. VI. Immunolocalization of microtubules in detergent-extracted apyrene spermatocytes of Ephestia kuehniella Z.

Apyrene meiosis was studied in two wild-type strains, L and Sbr, of the Mediterranean mealmoth, Ephestia kuehniella, using anti-tubulin immunofluorescence. The observations were supplemented by phase-contrast light microscopy of living spermatocytes from strain L. The study revealed that nuclear envelope breakdown, centrosome separation, migration of chromatin elements towards the poles, and spindle elongation also occur in apyrene spermatocytes. However, a conventional metaphase plate is never formed, and chromatin segregation is irregular and delayed. Chromosome laggards are frequent. As a rule, apyrene spindles have a low microtubule content. The two strains, L and Sbr, differ regarding the chromatin behavior during meiosis. In strain L, the developing spindles contain numerous small chromatin clumps which segregate asynchronously. The resulting daughter cells possess about the same amount of chromatin. In contrast, large chromatin clumps exist in strain Sbr at the onset of spindle formation. The chromatin blocks transiently occupy an equatorial position and elongate subsequently parallel to the spindle axis. These elongated chromatin bodies often divide highly unequally. As a consequence, secondary spermatocytes in strain Sbr differ greatly in chromatin content. Subjective assessment shows that the size of the microtubular cytoskeleton is positively correlated with the chromatin content of the cell. Hence, it is hypothesized that the chromatin content determines spindle size. This possibly comes about the number of available kinetochores which are exposed and able to stabilize microtubules of centrosomal origin attached with the kinetochores. However, a direct bearing of chromatin on spindle size is similarly conceivable. Other Lepidoptera species examined so far are compatible with a 'type L' or a 'type Sbr' pattern of apyrene meiosis.