Morphology and histology of the digestive tract of Nautilus pompilius and Nautilus macromphalus (Cephalopoda, Tetrabranchiata)

 This study presents histological and scanning electron microscopical findings on the structural differentiation, and the nervous and vascular supply of the digestive tracts of Nautilus pompilius and N. macromphalus, including the foregut, stomach, vestibulum, caecum, midgut and rectum. The stereoscopic reconstruction of the vestibulocaecal complex gives an idea how the digestive cycle between the stomach, vestibulum, caecum and proximal midgut could possibly proceed. All parts of the digestive tract are covered luminally by a columnar epithelium which contains numerous goblet cells. The epithelium is ciliated in the vestibulum, caecum, proximal midgut and the longitudinal groove of the rectum. On this lamina epithelialis mucosae borders the lamina propria mucosae, which consists of connective tissue and some muscle cells. In the stomach it is differentiated, forming a special bolster-like layer. The lamina propria mucosae is followed by the tunica muscularis, which consists of a stratum circulare and a stratum longitudinale in the foregut, vestibulum, caecum, midgut and rectum. In the stomach, midgut and rectum, the tunica adventitia, which consists of a thin layer of connective tissue, is located between the tunica muscularis and the cuboidal tunica serosa. Accepted: 4 August 1997     

Origin of jurassic ammonite concretions assemblages at Alfeld,Germany: a biogenic alternative

The ecology of macrofossils in ammonite-rich concretions and in coeval host sediments from Lower Bajocian mudstones in N.W. Germany indicates a predominantly epifaunal suspensionfeeding community living at maximally 50–90 m on a firm mud bottom during a hiatus or reduced sedimentation. Concretions are lined below with shell debris and contain numerous dimorphicStephanoceras [Ammonitina]. The dimorphs, however, are not a corresponding pair, showing instead extreme and uniquely inverse dimorphic ratios. Distribution of fossils and other debris within the concretions and the host sediments suggests the ammonite shells were swept by currents into subcircular depressions, lined with shell debris. We propose a biogenic alternative to the current/wave scour hypothesis for the origin of the depressions, which are essential to the accumulation of concretion assemblages: the pits were produced by rays feeding on the benthic fauna. Extant rays (Elasmobranchia) excavate such subcircular pits by jetting water through the gills (or mouth) for winnowing of the fauna from the sediment. The ammonite shells were transported post-mortem into the pits by moderate bottom currents. Rapid burial occurred by either a mudflow or renewal of strong sedimentation. Concretion growth was initiated by decomposition of organic matter within the mud.     

Species delimitation of the liquorice tribe (Leguminosae: Glycyrrhizeae) based on phylogenomic and machine learning analyses

The liquorice tribe Glycyrrhizeae is a leguminous herbaceous group of plants comprised of the genera Glycyrrhiza and Glycyrrhizopsis. Some Glycyrrhiza taxa contain glycyrrhizin, a pharmacologically significant sweet substance that also has applications in crafting industrial materials. Here, we utilized an expanded taxon sampling of Glycyrrhizeae to reconstruct the phylogenetic relationships in the tribe based on genome skimming data, including whole chloroplast genomes, nuclear ribosomal DNA, and low-copy nuclear DNA. We also launched machine learning analysis (MLA) for one species pair with controversial taxonomic boundary. The integrated results indicated Glycyrrhizopsis should be split from Glycyrrhiza, while the former genus Meristotropis should be treated as part of Glycyrrhiza. Glycyrrhizopsis includes two species, Glycyrrhizopsis asymmetrica and Glycyrrhizopsis flavescens, and we recognize 13 species in Glycyrrhiza: Glycyrrhiza acanthocarpa, Glycyrrhiza astragalina, Glycyrrhiza bucharica, Glycyrrhiza echinata, Glycyrrhiza foetida, Glycyrrhiza glabra, Glycyrrhiza gontscharovii, Glycyrrhiza lepidota, Glycyrrhiza macedonica, Glycyrrhiza pallidiflora, Glycyrrhiza squamulosa, Glycyrrhiza triphylla, and Glycyrrhiza yunnanensis. We propose a broader G. glabra that includes former Glycyrrhiza aspera, G. glabra s.s., Glycyrrhiza inflata, and Glycyrrhiza uralensis, and represents the glycyrrhizin-contained medicinal group. Our ancestral state inferences show the ancestor of Glycyrrhiza lacked glycyrrhizin, and the presence of glycyrrhizin evolved twice within Glycyrrhiza during the last one million years. Our integrative phylogenomics-MLA study not only provides new insights into long-standing taxonomic controversies of Glycyrrhizeae, but also represents a useful approach for future taxonomic studies on other plant taxa.     

New observations on the rodlet cell (Rhabdospora thelohani) in the white sucker Catostomus commersoni (Lacépède): LM and EM studies

Light and electron microscopic studies of the morphological features of immature and mature rodlet cells in Catostomus commersoni are presented emphasizing the cells' association with epithelial tissues. The peripheral fibrillar layer is lacking from the apex and from the base of the cell. A cytoplasmic extension from the base may be a feeding mechanism whereby the rodlet cell obtains nutrient at the expense of adjacent cells leaving intercellular spaces often containing myelin figures. RNAase digestion studies demonstrate the presence of RNA in the electron dense rodlet core.
The structure and histochemistry of the rodlets which do not appear to disintegrate upon expulsion from the cell are compared to the cytoplasmic inclusions of both normal fish cells and protozoan parasites. The possible association of the rodlet cell with various pathological conditions is briefly reviewed and the authors conclude that it is premature to disregard the possibility that this cell could be a parasite or infective agent.     

Rearrangements of integral membrane components during in vitro aging of sheep erythrocyte membranes

In vitro aged sheep erythrocytes and sheep erythrocyte ghosts spontaneously release vesicles that consist of long protrusions affixed to flattened headlike structures. The intramembranous particles seen on the protoplasmic face of freeze fracture electron micrographs of vesicle protrusions are arranged in paired particle rows. On the equivalent fracture face of headlike structures, the particle density is low; if particles are present, they are clustered along the rim of the flattened headlike structure and at the junction with the protrusion. The released vesicles are depleted of the intramembranous particles seen on the exoplasmic face of ghost but retain almost exclusively particles of the protoplasmic face. Correspondingly, the exoplasmic face of ghosts that have released vesicles reveals a 28 percent higher density of intramembranous particles than that of fresh ghosts. Purified vesicles are depleted of spectrin but retain integral membrane proteins, with one of an apparent mol wt of 160,000 accounting for nearly 50 percent of the total protein (Lutz, H.U.,R. Barber, and R.F. McGuire. 1976. J. Biol. Chem. 251:3500-3510). When vesicles are modified with the cleavable cross-linking reagent [(35)S]dithiobis (succinimidyl propionate)at 0 degrees C, the 160,000 mol wt protein is rapidly converted to disulfide-linked dimers and higher oligomers. Exposure of intact ghosts to the reagent in the same way fails to yield equivalent polymers. A comparison of the morphological and biochemical aspects of ghosts and vesicles suggest that a marked rearrangement of membrane proteins accompanies the supramolecular redistribution of intramembranous particles during spontaneous vesiculation. The results also suggest that the paired particles of the protoplasmic face of vesicle protrusions are arranged in paired helices and contain the 160,000 mol wt protein as dimers.     

Cross-linking of Met-tRNAf to eIF-2 beta and to the ribosomal proteins S3a and S6 within the eukaryotic inhibition complex, eIF-2 .GMPPCP.Met-tRNAf.small ribosomal subunit.

In the quaternary initiation complex, eIF-2.GMPPCP.Met-tRNAf.40S ribosomal subunit, the Met-tRNAf can be cross-linked to the beta subunit of initiation factor eIF-2 as well as to ribosomal proteins S3a and S6 by treatment with the bifunctional reagent, diepoxybutane. Using 40S subunits, modified in advance with the heterobifunctional reagent, methyl-rho-azido-benzoylaminoacetimidate, Met-tRNAf is covalently bound to the same ribosomal proteins (S3a and S6) upon irradiation of the complex with ultraviolet light. Under both conditions proteins S3a and S6, together with a limited number of other ribosomal proteins, are covalently bound to 18S ribosomal RNA.     

Pathways shaping the mitochondrial inner membrane

Mitochondria are complex organelles with two membranes. Their architecture is determined by characteristic folds of the inner membrane, termed cristae. Recent studies in yeast and other organisms led to the identification of four major pathways that cooperate to shape cristae membranes. These include dimer formation of the mitochondrial ATP synthase, assembly of the mitochondrial contact site and cristae organizing system (MICOS), inner membrane remodelling by a dynamin-related GTPase (Mgm1/OPA1), and modulation of the mitochondrial lipid composition. In this review, we describe the function of the evolutionarily conserved machineries involved in mitochondrial cristae biogenesis with a focus on yeast and present current models to explain how their coordinated activities establish mitochondrial membrane architecture.     

SNAREpins are functionally resistant to disruption by NSF and alphaSNAP

SNARE (SNAP [soluble NSF {N-ethylmaleimide–sensitive fusion protein} attachment protein] receptor) proteins are required for many fusion processes, and recent studies of isolated SNARE proteins reveal that they are inherently capable of fusing lipid bilayers. Cis-SNARE complexes (formed when vesicle SNAREs [v-SNAREs] and target membrane SNAREs [t-SNAREs] combine in the same membrane) are disrupted by the action of the abundant cytoplasmic ATPase NSF, which is necessary to maintain a supply of uncombined v- and t-SNAREs for fusion in cells. Fusion is mediated by these same SNARE proteins, forming trans-SNARE complexes between membranes. This raises an important question: why doesn''t NSF disrupt these SNARE complexes as well, preventing fusion from occurring at all? Here, we report several lines of evidence that demonstrate that SNAREpins (trans-SNARE complexes) are in fact functionally resistant to NSF, and they become so at the moment they form and commit to fusion. This elegant design allows fusion to proceed locally in the face of an overall environment that massively favors SNARE disruption.     

Hemocyanin re-uptake in the renal and branchial heart appendages of the coleoid cephalopod Sepia officinalis

The renal and branchial heart appendages of Sepia officinalis L. were investigated in order to elucidate a possible involvement of their excretory epithelia in hemocyanin metabolism. Immunocytochemical findings and tracer experiments indicate that after passing the barrier of ultrafiltration the hemocyanin molecules are taken up by the epithelial cells of the renal and branchial heart appendages and are subsequently carried back to the circulatory system, suggesting a mechanism of hemocyanin recycling. Apart from a function in maintaining constant hemocyanin levels, the present study indicates that the renal and branchial heart appendages are also sites of temporary hemocyanin storage.