Thecal designs in isorophinid edrioasteroids

A study of functional morphology in the edrioasteroid suborder Isorophina reveals three major thecal designs: domal, pyrgate, and clavate. Pyrgate forms are characterized by specialized morphologic features that facilitate extension of the theca well above the substrate and contraction of the theca to a low, streamlined, domal profile. Domal forms have a low, domal thecal profile capable of little shape change. Clavate forms are characterized by modifications to the pyrgate theca to facilitate higher-level suspension feeding. Pyrgate species are generalized edrioasteroids that inhabited a variety of nearshore open-marine environments. Domal species are small specialized edrioasteroids that inhabited shallow-marine to intertidal environments. Clavate species inhabited offshore, open-marine environments. The size reduction of the peripheral rim and the modifications to the pedunculate zone are adaptations allowing clavate edrioasteroids to compete for small attachment sites while maintaining the ability to extend the theca for higher-level suspension feeding and respiration. A phylogenetic analysis of well-known isorophinid edrioasteroids to determine the relationships between the three designs indicates that domal species are a monophyletic group within the Isorophinidae, clavate species are a monophyletic group within the Agelacrinitidae, and isorophinid pyrgate species are a paraphyletic group ancestral to both domal and clavate forms. □ Edrioasteroidea, Echinodermata, functional morphology, phylogeny.     

The Proximal Development and Thecal Structure of the Ordovician Graptolites Tylograptus and Sinograptus

A study of pyritic and three-dimensional specimens of sinograptids from the early Middle Ordovician Ningkuo Formation of western Zhejiang Province, south-east China, indicates that the proximal development of both TylograptusSinograptus is of modified isograptid type. The thecal apertures of the two genera are reconstructed and display a complex morphology more typical of stratigraphically younger graptoloids. Because of differences in its prothecal folds and thecal apertures Tylograptus is distinguished from Holmograptus and regarded as a valid genus. In Sinograptus, a tongue-shaped structure, and constriction of the thecal tube after the metathecal fold, are illustrated for the first time. The proximal development and thecal structures of TylograptusSinograptus imply a possible origin of sinograptids from earlier didymograptids or sigmagraptids. Four species, Tylograptus intermediusT. globiformisSinograptus typicalisS. rastritoides, are revised.     

Cellulosomes-structure and ultrastructure

The cellulosome is a macromolecular machine, whose components interact in a synergistic manner to catalyze the efficient degradation of cellulose. The cellulosome complex is composed of numerous kinds of cellulases and related enzyme subunits, which are assembled into the complex by virtue of a unique type of scaffolding subunit (scaffoldin). Each of the cellulosomal subunits consists of a multiple set of modules, two classes of which (dockerin domains on the enzymes and cohesin domains on scaffoldin) govern the incorporation of the enzymatic subunits into the cellulosome complex. Another scaffoldin module-the cellulose-binding domain-is responsible for binding to the substrate. Some cellulosomes appear to be tethered to the cell envelope via similarly intricate, multiple-domain anchoring proteins. The assemblage is organized into dynamic polycellulosomal organelles, which adorn the cell surface. The cellulosome dictates both the binding of the cell to the substrate and its extracellular decomposition to soluble sugars, which are then taken up and assimilated by normal cellular processes.     

Studies of adrenocortical ultrastructure

Summary The ultrastructural features of interrenal cells derived from the normal domestic fowl are described. The interrenal cells, like other steroid-producing cells, contain more smoothsurfaced endoplasmic reticulum than the granular variety, and accommodate mitochondria with tubular inner structure. Other cytoplasmic structures are lipid droplets, dense bodies and the Golgi apparatus. The following structures were demonstrated for the first time in the avian adrenocortical cell:intramitochondrial crystallized tubules and intramatrical lipid-like droplets, cytoplasmic microtubules and filaments, cilia, both free and intracytoplasmic; nuclear bodies and intranuclear lipid-like inclusions; and attachment devices, often combined with mortisetenon joints. Likewise, this study demonstrated for the first time the polarity of the interrenal cells of the fowl. These rest on a basal lamina and accommodate the majority of lipid droplets at the basal (vascular) pole, and the Golgi apparatus, dense bodies and attachment devices at the apical pole. Due to the uniform fixation of the entire organ obtained in this investigation, the present work has provided a useful base line for subsequent investigations concerning adrenal physiology and pathology (Kjaerheim, 1968b, c).

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Zusammenfassung Die Ultrastruktur der Interrenalzellen des Huhns wird beschrieben. Die interrenalen Zellen enthalten, wie andere Steroid-produzierende Zellen, mehr glattes endoplasmatisches Reticulum als die granuläre Form und Mitochondrien mit tubulärer Innenstruktur. Andere zytoplasmatische Strukturen sind Lipidtropfen, Dense Bodies und Golgi-Apparat. Folgende Strukturen wurden erstmals in der Vogelnebenniere nachgewiesen: Intramitochondriale kristallisierte Tubuli und Lipid-ähnliche Tröpfchen in der Mitochondrienmatrix, zytoplasmatische Mikrotubuli, Filamente und Zilien, sowohl frei als auch intrazytoplasmatisch gelegen, ferner Sphäridien und intranukleäre Lipid-ähnliche Einschlüsse sowie Haftapparate, oft kombiniert mit komplizierten zytoplasmatischen Ein- und Ausstülpungen. Ebenfalls erstmalig zeigt diese Arbeit die Polarität der Interrenalzellen des Huhns. Diese befinden sich auf einer Basalmembran und enthalten die meisten Fetttröpfchen am basalen (vaskulären) Pol und Golgi-Apparat, Dense Bodies und Haftapparate am apikalen Pol. Dank der gleichmäßigen Fixation des gesamten Organs wurde eine Grundlage für spätere Untersuchungen der Physiologie und Pathologie der Nebenniere geliefert.

     

Surface ultrastructure of trypsin-banded chromosomes

The surface ultrastructure of trypsin-banded chromosomes has been examined by electron microscopy. Trypsin pretreatment removed cellular debris and produced banding patterns recognizable with the electron microscope as ridges in platinum-carbon replicas. The ridges observed in replicas of trypsin-treated chromosomes corresponds to Giemsa-stained bands observed by light microscopy. The bands appeared as an area of tightly compacted fibrils on the surface of the chromosomes. Prolonged treatment in trypsin resulted in collapsed chromosomes and loss of ridges in the replicas. Interchromosomal fibers were also noted and in some preparations appeared to be localized to banded regions.     

The ultrastructure of R-banded chromosomes

Electron microscopy has been used to study the fine structural organization of R-banded chromosomes prepared by treatment of the chromosomes with a hot NaH₂PO₄ solution. The results indicate that there is a structural basis for R-banding with this technique. In comparison to untreated control chromosomes, the R-banded chromosomes had a greatly reduced electron density, suggesting that the heat treatment has a general adverse effect on chromosome structure. Chromatin fibers formed a coarse, irregular network throughout the chromosome and were often enlarged, probably as a result of the fusion of two or more native fibers. The chromatin fibers were more aggregated and had an increased electron density in the R-band regions of the chromosome than in the interbands. This indicates that the treatment has a differential effect on the structure of bands and interbands. A comparison of the ultrastructure of R- and G-banded chromosomes demonstrated that the distribution of aggregated chromatin was reversed by these two types of banding techniques; however, the treatments producing R-banding appeared to induce less extreme differences in the degree of chromatin condensation in band and interband regions than those giving rise to G-banding. It is suggested that alterations of DNA-protein interactions may arise from the differential denaturation of proteins and/or DNA in R-band and interband regions during the heat pretreatment. Such differential alterations in DNA-protein interactions may induce localized changes in the organization of chromatin and may account for the subtle morphological differences observed between the band and interband regions.     

Caveolae--from ultrastructure to molecular mechanisms

Almost 50 years after the first sighting of small pits that covered the surface of mammalian cells, investigators are now getting to grips with the detailed workings of these enigmatic structures that we now know as caveolae.     

The ultrastructure of Prototheca wickerhamii

Two clinical isolates of Prototheca wickerhamii were freeze-dried, fixed and studied by electron microscopy and were also examined growing in culture medium by phase contrast light microscopy. Resting spores placed on fresh medium developed cytoplasmic extensions which sequestrated before proliferation occurred. In the presence of adequate nutrients vegetative spores grew and subdivided to form up to 12 endospores within large sporangia which ruptured to release free spores every 5–6 hours. These proliferating or vegetative spores contained much more endoplasmic reticulum and mitochondria than the resting spores which contained more lipid, and often starch granules as well, but relatively few membranous organelles.