ACETYLATION OF ALPHA-TUBULIN IN MALE MEIOTIC SPINDLES OF PYRRHOCORIS APTERUS, AN INSECT WITH HOLOKINETIC CHROMOSOMES

摘要

Kinetochore structure was examined in metaphase sper matogonia and primary spermatocytes of the red firebug, Pyrrhocoris apterus (Pyrrhocoridae, Hemiptera). Chromosome spreads were analysed using light microscopy and serial sections through spindles were studied using electron microscopy. Mitotic chromosomes were rod-shaped bodies and did not possess primary constrictions. Trilaminar kinetochores occurred throughout about 72% of the chromosomal length. Numerous microtubules (MTs) were connected with the outer plates of the kinetochores and interactions between MTs and the remainder of the chromosomal surface were rare. The bivalents formed dumbbell-shaped bodies in metaphase I spermatocytes. At that stage, MTs were found in contact with the entire poleward surface of the chromosomes. Distinct kinetochore material was, however, not detectable and some MTs penetrated deeply into the chromatin. Mitotic and meiotic chromosomes of P. apterus are holokinetic and consequently the number of kinetochore MTs is expected to be relatively high. In the second part of the study, the question whether holokinetic chromosomes affect spindle MT dynamics is addressed. To this end, primary spermatocytes of P. apterus were labelled with a widely used antibody, 6-11B-1, directed against acetylated alpha-tubulin, The acetylation of alpha-tubulin is believed to indicate the presence of long-lived MTs. MT bundles were labelled in metaphase and anaphase I spindles, while prophase and prometaphase I spermatocytes did not contain acetylated MTs. MTs in early and mid telophase spindles were not acetylated. Only late telophase I spindles pos sessed small amounts of acetylated alpha-tubulin. The acetylated MT bundles of metaphase and anaphase I spindles probably represent kinetochore MTs stabilized by their association with the holokinetic chromosomes at one end and the spindle poles at the opposite end. [References: 53]