The structure of condensed chromosomes in mitosis and meiosis of insects

This article revolves around the structure of condensed mitotic and meiotic chromosomes in insects. In the first section, the potential of cytological approaches in the field of chromosome biology is described. Emphasis is on immunolabeling, and transmission and scanning electron microscopy. In particular, the latter technology revealed a series of unusual components in association with the chromosomes, such as membranes and non-chromatin material, which is presumably responsible for the formation of achiasmatic bivalents. Virus-like particles were found scattered throughout the chromatin in a Lepidoptera species. This association is possibly responsible for the transmission of the particles into the next generation. Then, the cytology and the molecular make-up of the key components of insect chromosomes are described. These are the centromeres, telomeres, and nucleoli. In any case, the situation in insects is compared briefly with that in mammals. The general structure of the centromeres in terms of centromere-specific repetitive DNA and proteins is similar in insects and mammals. This applies also to telomeres of most insect orders, but the chromosome ends of Diptera species differ from those in mammals. Fine structure observations raise also the possibility that insect nucleoli have a specific architecture. Chromosomal proteins-and emphasis is on histone acetylation-are addressed in an individual section. Evidence is accumulating that histone H4 acetylation plays a role in dosage compensation and is a cytogenetic marker of constitutive heterochromatin in insects. In the final section, the characteristics of holokinetic chromosomes are listed. A series of insect orders, where direct or indirect evidence points to chromosomes with relatively large centromeres, is presented. These are Lepidoptera, Trichoptera, Hemiptera, Homoptera, Odonata, and Dermaptera. Copyright (C) 1996 Elsevier Science Ltd.