Cytology of Lepidoptera

Abstract

Using ultrathin sections and electron microscopy, the structure of prophase I spermatocytes is described in the mothEphestia kuehniella Z. Some stages were also examined using light microscopy and antitubulin immunofluorescence microscopy. Changes in the mitochondrial inventory, the endomembranes, and the nuclear content during the progression of meiosis from pachytene to diakinesis have a bearing on the structure of prometaphase and metaphase I spermatocytes. In late diplotene, a short-lived system of cytoplasmic microtubules forms independently of the flagellar bases. Possibly mediated by these microtubules, mitochondria gather in a portion of the cell and fusion of individual mitochondria occurs. The clustering of mitochondria, which persists until the meiotic spindle has developed, may be the prerequisite for the bipartition of the chondriome during cytokinesis. After late pachytene, the mass of perinuclear endoplasmic reticulum and the number and size of the Golgi stacks also increase. These endomembranes give rise to the multi-layered membraneous envelope around the meiotic spindle and probably to the intraspindle membrane system. After late pachytene, the number of nuclear pores also increases and material export from the nucleus is apparent. The exchange is interpreted as an indicator for transcriptional activity in the late prophase I nucleus when the chromatin is transiently decondensed (diffuse stage). In the course of chromatin recondensation, the bivalents assume a speckled appearance in ultrathin sections. Metaphase I bivalents possess lighter staining equatorial material. This material is not stained with a DNA-specific fluorescent dye or with acetic orcein, which preferentially binds to chromatin. It is hypothesized that less dense core material becomes interspersed with chromatin during the diffuse stage and is involved in the maintenance of bivalent structure until the onset of anaphase I.