Ultrastructure of cytoplasmic nucleolus-like bodies and nuclear RNP particles in late prophase of tipulid spermatocytes.

Abstract

Late prophase stages of Pales ferruginea (Tipulidae) spermatocytes were examined by means of conventional electron microscopic section technique, combined with cytochemical methods. The cytoplasm of cells in diakinesis contains nucleolus-like bodies (NLB) 1 mum in diameter which are formed in diplotene at the pores of the nuclear membrane. They are compound structures consisting of fibro-granular RNP material which is associated wth one or two electron-dense gobules. The RNP material has a hollow core which contains polyribosomes. The NLBs possibly indicate rRNA gene amplification. At diakinesis the nucleus contains numerous electron-dense RNP particles scattered throughout the chromatin-free karyoplasm, and associated with the condensed chromosomes. The diameter of the chromation associated particles is markedly higher (mean 630 A) than that of the free particles (mean 540 A). The RNP particles seem to be aggregates of 200 A subunits. They are regarded as transcription products of chromosomal genes.