Characterization and significance of nine novel mutations in exon 16 of the neurofibromatosis type 1 (NF1) gene

Nine novel mutations have been characterized as the result of screening exon 16 of the human NF1 gene in 465 unrelated neurofibromatosis type 1 patients. These lesions include three nonsense and two missense mutations, two deletions, one duplication, and one mutation in the 5′ splice site of intron 16. Although exon 16 is the largest NF1 exon, no mutations have so far been reported in this region. This apparent paucity of lesions may be due either to a reduced functional importance of exon 16 or a screening bias or both. However, consideration of the mutability of exon 16 in comparison with other exons suggests that, at least for single base pair substitutions, no such factors need be invoked. Any previous lack of exon 16 mutations in this category would be explicable in terms of a lower propensity to mutate for codons in this gene region. Received: 1 November 1996 / Revised: 5 December 1996     

Aspects of the Natural History of the Arboreal Harvestman <Emphasis Type="Italic">Cynorta marginalis</Emphasis> (Opiliones: Cosmetidae) Inhabiting a Costa Rican Forest

Relatively little is known about the natural history of the cosmetid harvestmen that inhabit the forests of Central America. The primary objective of this study was to investigate habitat use among adult Cynorta marginalis. In the field, we established 15 transects (40 m in length) and sampled them repeatedly in the morning (0830–1100 h) and evening (1800–2300 h). During 45 morning and 35 evening surveys, we captured and marked 146 males and 112 females. Only three individuals (all females) were recaptured over the course of the study, indicating that the population size at this field site was relatively large. Heavy rains significantly reduced the surface activity of adults (1.1 individuals per transect during heavy rain vs. 3.7 individuals per transect during light or no rain). Harvestmen most commonly used leaves (65% of captures) or tree trunks (31%) as perches, and rarely occupied branches or the leaf litter. Only 18 adults were observed with leg injuries, with two individuals having damage to multiple legs. Perch height was significantly lower during the evening (110.9 cm at night vs. 155.1 cm during the day). Adults were most commonly found alone (85%), however, we observed several harvestmen in male-female pairs (8%), same sex pairs (4%) and heterosexual groups (3%). Although we did not observe reproductive or aggressive behaviors in the field, we observed intraspecific interactions under laboratory conditions and found that some individuals (15%) engaged in courtship suggesting that the sharing of perches by male-female pairs may be related to reproductive activity.     

The Structure of Mytilus Smooth Muscle and the Electrical Constants of the Resting Muscle

The individual muscle fibers of the anterior byssus retractor muscle (ABRM) of Mytilus edulis L. are uninucleate, 1.2–1.8 mm in length, 5 µm in diameter, and organized into bundles 100–200 µm in diameter, surrounded by connective tissue. Some bundles run the length of the whole muscle. Adjacent muscle cell membranes are interconnected by nexuses at frequent intervals. Specialized attachments exist between muscle fibers and connective tissue. Electrical constants of the resting muscle membrane were measured with intracellular recording electrodes and both extracellular and intracellular current-passing electrodes. With an intracellular current-passing electrode, the time constant τ, was 4.3 ± 1.5 ms. With current delivered via an extracellular electrode τ was 68.3 ± 15 ms. The space constant, λ, was 1.8 mm ± 0.4. The membrane input resistance, R_eff, ranged from 23 to 51 MΩ. The observations that values of τ depend on the method of passing current, and that the value of λ is large relative to fiber length and diameter are considered evidence that the individual muscle fibers are electrically interconnected within bundles in a three-dimensional network. Estimations are made of the membrane resistance, R_m, to compare the values to fast and slow striated muscle fibers and mammalian smooth muscles. The implications of this study in reinterpreting previous mechanical and electrical studies are discussed.     

Microscopic localization of cholinesterases in the nervous systems of the lobsters, Panulirus argus and Homarus americanus

Using acetylthiocholine as substrate, microscopically localizable cholinesterase (ChE) activity is demonstrated in neural and glial elements of central and peripheral nervous systems of the lobsters, Panulirus argus and Homarus americanus. Moderate to very intense ChE activity occurs in all synaptic regions of the central ganglia and stomatogastric ganglion, in glial sheaths around neuron somata and peripheral nerve axons, and in cytoplasm of a few nerve cell bodies. Axons, identified as motor, contain extremely little ChE. The principal reaction in peripheral nerves occurs in sheath elements of sensory fibres; in most cases, much of the reaction is lost as the nerves lose the sheaths at the point of entry into brain.     

Effect of interleukin-1 on intracellular concentration of sodium, calcium, and potassium in 70Z/3 cells

The cytokine interleukin-1 (IL-1) has been shown to induce the differentiation of a murine pre-B like cell line 70Z/3. An early intracellular event caused by exposure to IL-1 is an amiloride-sensitive progressive rise in the total concentration of intracellular sodium ([Na]i), caused by influx of Na+ from outside, and a transient fall in total intracellular calcium. The results suggest that IL-1-induced influx of Na+ into 70Z/3 occurs via stimulation of the Na+/H+ antiport. IL-1-induced differentiation is also blocked by amiloride suggesting that stimulation of Na+/H+ exchange may play a role in IL-1-induced differentiation.     

Human alveolar macrophage fibronectin: synthesis, secretion, and ultrastructural localization during gelatin-coated latex particle binding

Human pulmonary alveolar macrophages synthesized and secreted several characteristic high molecular weight proteins for at least 7 d in vitro. Immunoprecipitates of medium and cell lysates from metabolically labeled cultures with specific anti-human plasma fibronectin IgG contained one major labeled polypeptide of molecular weight 440,000 (unreduced) or 220,000 (reduced). An identical polypeptide in conditioned medium from radiolabeled macrophages bound specifically to gelatin-Sepharose, demonstrating that alveolar macrophages synthesized and secreted a molecule immunologically and functionally similar to fibronectin. Fibronectin was the major newly synthesized and secreted polypeptide of freshly harvested alveolar macrophages. Pulse-chase experiments revealed that newly synthesized fibronectin was rapidly secreted into medium, approximately 50 percent appearing by 1 h and 80 percent by 8 h. Immunoperoxidase staining using antifibronectin F(ab’)(2)-peroxidase conjugates revealed the majority of immunoreactive fibronectin to be intracellular, localized to endoplasmic reticulum and Golgi apparatus. No extracellular matrix fibronectin was visualized, and cell surface staining was rarely seen, usually appearing only at sites where cells were closely apposed and not at sites of macrophage-substrate attachment. Similar immunostaining of fibroblast cultures revealed cell surface-associated fibrillar fibronectin. Ultrastructural localization of fibronectin during binding and phagocytosis of gelatin-coated and plain latex particles revealed fibronectin only on gelatin-latex beads and at their cell binding sites. Neigher plain latex beads nor their cell membrane binding sites stained for fibronectin. These results demonstrate that fibronectin is a major product of human alveolar macrophages, is rapidly secreted, and is localized at cell membrane binding sites for gelatin-coated particles. In view of the known binding properties of fibronectin, it may serve as an endogenous opsonic factor promoting the binding of staphylococcus, denatured collagen, fibrin, or other macromolecules to macrophages in the lower respiratory tract.