Chromatin condensation involving lamellar strands in spermiogenesis of Goniobasis proxima

A birefringence, electron microscopy, and histochemical survey of chromosomal structure in the sperm nuclei of an echinothurid sea urchin, Araeosoma owstoni

The mature sperm head of Araeosoma owstoni, an echinothurid sea urchin, showed positive birefringence reflecting that the overall orientation of DNA molecules was semiperpendicular toward the nuclear axis of the sperm head. Transmission electron microscopical observation of sperm in this species revealed a highly electron-dense cylindrical coil with an empty central core extending along the major axis of the sperm head. This coil had seven to eight turns along its entire length of 3.5 micron. The maximum width was 0.35 micron near the distal end of the nucleus, and the minimum width was 0.17 micron near the apical end. Lamellar substructures were also present in the sperm nucleus, appearing at the periphery of the electron-dense cylinder in a radial manner. Staining with Feulgen's reaction and acid-orcein indicated that the coil was probably composed of sperm chromosomes.

Ultrastructure of Euspermatozoa of cerithiacean gastropods (Prosobranchia: Mesogastropoda)

Euspermatozoa of selected cerithiacean gastropods have been studied using transmission electron microscopy and the results compared (primarily) with previous studies of mesogastropod and neogastropod euspermatozoa. Cerithiacean euspermatozoa each possess a well-defined acrosome (extremely varied in shape), a short (2.25-3 μm), very electron-dense nucleus, an elongate midpiece, and an elongate glycogen piece. A dense ring structure associated with the plasma membrane occurs at the junction of the midpiece and glycogen piece. While features such as the dense ring structure and the systematic periaxonemal arrangement of "glycogen" granules can be understood from a purely functional standpoint, it is suggested that euspermatozoon features also provide information of taxonomic and phylogenetic relevance. On the basis of euspermatozoon midpiece structure, true cerithiaceans can be easily distinguished from other mesogastropods and from neogastropods and are divided tentatively into two groups: Group 1 (Turritellidae, Cerithiidae, Australaba (family uncertain), Planaxidae, Potamididae (subfamily Batillariinae)), and Group 2 (Potamididae (subfamily Potamidinae), Modulidae, Obtortio (family uncertain)). Using midpiece and acrosomal features, group 1 can be further subdivided into two subgroups: Subgroup 1(i) (Turritellidae, Cerithiidae, Australaba) and Subgroup 1(ii) (Planaxidae, Potamididae (subfamily Batillariinae)). It is suggested that the pronounced differences existing between the two subfamilies of the Potamididae may indicate the necessity for a separate family for the Batillariinae.

Chromatin model calculations: Arrays of spherical nu bodies

Chromatin fibers consists of globular nucleohistone particles (designated nu bodies) along the length of the chromatin DNA with approximately 6-to7-fold compaction of the DNA within the nu bodies. We have calculated theoretical small-angle x-ray scattering curves and have compared these with experimental data in the literature. Several models predict maxima at the correct angles. The first maximum (approximately 110 degrees A) results from interparticle interference, while both the spatial arrangement and the structure factor the nu bodies can contribute to the additional small-angle maxima. These calculations suggest models which can account for the electron microscopic observation that chromatin is seen as either approximately 100-or approximately 200-to 250 degrees A-diameter fibers, depending on the solvent conditions. They also account for the limited orientability of the x-ray pattern from pulled chromatin fibers.