Morphogenesis of the giant sperm axoneme in Asphondylia ruebsaameni Kertesz (Diptera, Cecidomyiidae)

The formation of the sperm giant axoneme of the gall-midge fly Asphondylia ruebsaameni is described here. The axoneme consists of a great number of mi crotubular doublets (up to 2500) arranged in a double spiral wrapping aroun d an axial cluster of mitochondria. Each microtubular doublet is provided w ith an outer arm only. In the early spermatid the occurrence of a large sys tem of curved multi-layered filamentous material associated with membranous cisternae has been observed in the perinuclear region. Such a system exten ds throughout the cytoplasm to contact the plasma membrane. The filamentous material appears to act as a nucleating centre for the assembly of the mic rotubular doublets, which initially have a submembranous location and later are distributed in the interior of the cell. After their assembly, microtu bular doublets are associated pairwise and are arranged in a single microtu bular row with a zig-zag configuration, This configuration changes during s permiogenesis as a consequence both of a rotation of the microtubular doubl et pairs and a compaction of the axonemal complex due to the elimination of the excess cytoplasm, As a result of this process, a double parallel spira l of microtubular doublets is formed. (C) 2000 Harcourt Publishers Ltd.