6 research outputs found
Analysis of the cytoskeleton organization and its possible functions in male earthworm germ-line cysts equipped with a cytophore
We studied the organization of F-actin and the microtubular
cytoskeleton in male germ-line cysts in the seminal
vesicles of the earthworm Dendrobaena veneta using light,
fluorescent and electron microscopy along with both chemically
fixed tissue and life cell imaging. Additionally, in order
to follow the functioning of the cytoskeleton, we incubated the
cysts in colchicine, nocodazole, cytochalasin D and
latrunculin A. The male germ-line cells of D. veneta are interconnected
via stable intercellular bridges (IB), and form syncytial
cysts. Each germ cell has only one IB that connects it to
the anuclear central cytoplasmic mass, the cytophore. During
the studies, we analyzed the cytoskeleton in spermatogonial,
spermatocytic and spermatid cysts. F-actin was detected in the
cortical cytoplasm and forms distinct rings in the IBs. The arrangement
of the microtubules changed dynamically during
spermatogenesis. The microtubules are distributed evenly in
whole spermatogonial and spermatocytic cysts; however, they
primarily accumulate within the IBs in spermatogonia. In early
spermatids, microtubules pass through the IBs and are present
in whole cysts. During spermatid elongation, the microtubules
form a manchette while they are absent in the cytophore and in
the IBs. Use of cytoskeletal drugs did not alter the general
morphology of the cysts. Detectable effects—the occurrence
of nuclei in the late spermatids and manchette fragments in
the cytophore—were observed only after incubation in
nocodazole. Our results suggest that the microtubules are responsible
for cytoplasmic/organelle transfer between the germ
cells and the cytophore during spermatogenesis and for the
positioning of the spermatid nuclei
Serial block face SEM visualization of unusual plant nuclear tubular extensions in a carnivorous plant (Utricularia, Lentibulariaceae)
Background and Aims In Utricularia nelumbifolia, the nuclei of placental nutritive tissue possess unusually shaped projections not known to occur in any other flowering plant. The main aim of the study was to document the morphology and ultrastructure of these unusual nuclei. In addition, the literature was searched to find examples of nuclear tubular projections in other plant groups, and the nuclei of closely related species of Utricularia (i.e. sects Iperua, Orchidioides, Foliosa and Utricularia) were examined.
Methods To visualize the complexity of the nuclear structures, transmission electron microscopy (TEM) was used, and 3-D ultrastructural reconstructions were made using the serial block face scanning electron microscopy (SBEM) technique. The nuclei of 11 Utricularia species, i.e. U. nelumbifolia, U. reniformis, U. cornigera, U. nephrophylla (sect. Iperua), U. asplundii, U. alpina, U. quelchii (sect. Orchidioides), U. longifolia (sect. Foliosa), U. intermedia, U. minor and U. gibba (sect. Utricularia) were examined.
Key Results Of the 11 Utricularia species examined, the spindle-like tubular projections (approx. 5 \mu m long) emanating from resident nuclei located in placental nutritive tissues were observed only in U. nelumbifolia. These tubular nuclear extensions contained chromatin distributed along hexagonally shaped tubules. The apices of the projections extended into the cell plasma membrane, and in many cases also made contact at the two opposing cellular poles, and with plasmodesmata via a short cisterna of the cortical endoplasmic reticulum. Images from the SBEM provide some evidence that the nuclear projections are making contact with those of neighbouring cells.
Conclusions The term chromatubules (chromatin-filled tubules) for the nuclear projections of U. nelumbifolia placental tissue was proposed here. Due to the apparent association with the plasma membrane and plasmodesmata, it was also speculated that chromatubules are involved in nucleus-cell-cell communication. However, further experimental evidence is required before any functional hypothesis can be entertained
Morphology of Mitochondria in Syncytial Annelid Female Germ-Line Cyst Visualized by Serial Block-Face SEM
Mitochondria change their morphology and distribution depending on the metabolism and functional state of a cell. Here, we
analyzed the mitochondria and selected structures in female germ-line cysts in a representative of clitellate annelids – the white
worm Enchytraeus albidus in which each germ cell has one cytoplasmic bridge that connects it to a common cytoplasmic mass.
Using serial block-face scanning electron microscopy (SBEM), we prepared three-dimensional ultrastructural reconstructions of the
entire selected compartments of a cyst at the advanced stage of oogenesis, i.e. the nurse cell, cytophore, and cytoplasmic bridges of all
16 cells (15 nurse cells and oocyte). We revealed extensive mitochondrial networks in the nurse cells, cytophore and mitochondria
that pass through the cytoplasmic bridges, which indicates that a mitochondrial network can extend throughout the entire cyst.
e dynamic hyperfusion state was suggested for such mitochondrial aggregations. We measured the mitochondria distribution
and revealed their polarized distribution in the nurse cells and more abundant accumulation within the cytophore compared to the
nurse cell. A close association of mitochondrial networks with dispersed nuage material, which seems to be the structural equivalent
of a Balbiani body, not described in clitellate annelids so far, was also revealed