SPERMATOGENESIS IN TENEBRIO-MOLITOR (TENEBRIONIDAE, COLEOPTERA) - A FINE-STRUCTURE AND ANTITUBULIN IMMUNOFLUORESCENCE STUDY

Spermatogonia and both generations of spermatocytes of Tenebrio molito r possess conventional bipolar spindles with only few aster MTs. Spind les in metaphase spermatogonia are surrounded by fenestrated two-layer ed cisternae and do not contain intraspindle membranes. In metaphase s permatocytes, a spindle envelope is missing, but intraspindle membrane s are abundant. Mitochondria form long threads lateral to the nucleus in prophase I of meiosis. The elongated mitochondria also align parall el to the spindle apparatus in prometaphase I. As a consequence, the s pindles reside in a cage formed of mitochondria. This arrangement may guarantee proper bisection of the chondriome during division. Cells ar e tightly packed during spermatogonial divisions and in prophase I, bu t large intercellular spaces develop when the first meiotic spindle as sembles. Then, cytoplasmic bridges which persist between the cells as a result of incomplete cytokinesis appear as slender tubes. Anti-tubul in immunofluorescence using an antibody against acetylated alpha-tubul in revealed intense acetylation throughout spermatogonial mitosis but a low degree of alpha-tubulin acetylation in meiotic spindles prior to telophase. This may indicate a high microtubule turnover in meiosis.