A novel adhering junction in the apical ciliary apparatus of the rotifer Brachionus plicatilis (Rotifera, Monogononta)
ABSTRACT Cultures of the rotifer Brachionus plicatilis were examined with regard to their interepithelial junctions after infiltration with the extracellular tracer lanthanum, freeze-fracturing or quick-freeze deep-etching. The lateral borders between ciliated cells have an unusual apical adhering junction. This apical part of their intercellular cleft looks desmosome-like, but it is characterized by unusual intramembranous E-face clusters of particles. Deep-etching reveals that these are packed together in short rows which lie parallel to one another in orderly arrays. The true membrane surface in these areas features filaments in the form of short ribbons; these are produced by projections, possibly part of the glycocalyx, emerging from the membranes, between which the electron-dense tracer lanthanum permeates. These projections appear to overlap with each other in the centre of the intercellular cleft; this would provide a particularly flexible adaptation to maintain cell-cell contact and coordination as a consequence. The filamentous ribbons may be held in position by the intramembranous particle arrays since both have a similar size and distribution. These contacts are quite different from desmosomes and appear to represent a distinct new category of adhesive cell-cell junction. Beneath these novel structures, conventional pleated septate junctions are found, exhibiting the undulating intercellular ribbons typical of this junctional type, as well as the usual parallel alignments of intramembranous rows of EF grooves and PF particles. Below these are found gap junctions as close-packed plaques of intramembranous particles on either the P-face or E-face. After freeze-fracturing, the complementary fracture face to the particles shows pits, usually on the P-face, arrayed with a very precise hexagonal pattern.
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ABSTRACT: Thin sections of cartilage from the chondrocranium of cuttle fish and octopus were examined using the transmission electron microscope. It was found that cephalopod chondrocytes differed considerably from the chondrocytes of vertebrate cartilage; in particular they possessed many long and ramifying cytoplasmic processes and had an ultrastructure typical of protein-secreting cells. They did not, however, contain secretory granules; while vesicles and rough endoplasmic reticulum cisternae seemed to open directly to the cell surface. The cell body and processes contained cytoskeletal structures: microtubules were easily recognized, but intermediate and thin filaments were difficult to make out as they were frequently clumped into bundles. Some chondrocytes contained conspicuous accumulations of hemocyanin. The cytoplasmic processes possessed intercellular contacts similar to gap junctions. Also present on processes and the cell body were cell-extracellular matrix focal adhesions. The chondrocytes were not polarized or arranged in any preferential spatial order, however, with their processes they formed a three-dimensional network throughout the cartilage tissue. Ultrastructural findings are discussed in relation to the singular morphofunctional characteristics of cephalopod cartilage which shares features with both the cartilage and bone of vertebrates.Tissue and Cell 06/1998; 30(3-30):340-351. DOI:10.1016/S0040-8166(98)80047-5 · 1.25 Impact Factor
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ABSTRACT: Middle Pleistocene warm periods are particularly useful for comparison with our present warm period. One of them, Marine Isotope Stage (MIS) 11, has been considered a potential analogue for the Holocene, whereas older interglacials, e.g. MIS 13, are distinctly different. However, terrestrial Middle Pleistocene sites, other than the Holsteinian, and quantitative climate reconstructions for this period are very rare in Europe. A unique terrestrial site in North Central Europe is known from Bilshausen, Germany. The sediments are varved and indicate that this interglacial lasted ∼25,000 years, more than twice as long as the Holocene so far. The warm period probably correlates to MIS 11, or possibly to MIS 13. A new palynological investigation with large pollen counts is presented which forms the basis for quantitative temperature reconstructions based on the probabilistic indicator taxa approach (the so-called pdf-method).The range of tree species that formed the vegetation during the Bilshausen warm period is reminiscent of the Holocene, but the vegetational as well as the reconstructed climatic development shows distinct differences. No pronounced initial successional phase is recorded in the pollen stratigraphy from Bilshausen. In addition, a mesocratic or optimum phase of forest development as in the Holocene is unclear in the Bilshausen sequence. Reconstructed temperature values are several °C lower than Holocene temperatures for most of the Bilshausen interglacial. Only for several millennia in the late phase of the Bilshausen interglacial were July temperatures higher than the Holocene July temperatures. Seasonality was much stronger during the Bilshausen interglacial and the temperature trends differ between the two interglacials. Likely reasons for the pronounced differences are, on one hand, global temperature, insolation changes and atmospheric circulation. On the other hand, more regional factors such as the configuration of the North Sea basin may also be responsible for the colder winter temperatures and stronger seasonality during the Bilshausen interglacial compared to the Holocene. Reliable absolute dating of the Bilshausen interglacial is needed, which would allow a more detailed evaluation of the forcing factors that determined the climate during the Bilshausen interglacial.Quaternary Science Reviews 12/2010; 29(27):3736-3749. DOI:10.1016/j.quascirev.2010.08.006 · 4.57 Impact Factor