The isolation of a soluble type III collagen precursor from rat skin

A soluble form of type III collagen has been isolated from the 1.0 M NaCl neutral salt soluble extract of rat skin. This component has a molecular weight of 350,000 and is converted by reduction and alkylation to three identical α-chains with molecular weight 118,000. Segment-long-spacing precipitates produced from the renatured disulfide-linked component are about 300 Å longer than collagen with extensions at both the amino and carboxyl terminal ends. Pepsin treatment removes both amino and carboxyl terminal extensions. These and radioisotope incorporation data lead to the conclusion that this component is a precursor of the [αl(III)₃] collagen.     

Effect of protease inhibitors on mitogen stimulation of hamster lymphoid cells

Hamster lymph node and spleen cells can be stimulated to incorporate tritiated thymidine ([³H]TdR) in vitro under serum-free conditions by the proteases trypsin and chymotrypsin. Under similar conditions, thymocytes could be stimulated by concanavalin A (ConA) but not lipopolysaccharide (LPS) or the proteases. The subpopulation of cells responding to the proteases correlated with the cells responding to LPS on fractionation of spleen and lymph node cells on discontinuous bovine serum albumin (BSA) gradients or on nylon-wool columns. The stimulation induced by trypsin was completely blocked by soybean trypsin inhibitor (SBTI) while that induced by chymotrypsin was only partially blocked. The inhibition by SBTI of protease activation was not effective when added 24 h after initiation of stimulation. On the other hand, addition of clarified isologous serum to protease activated cultures after 24 h still lead to greater than 50% inhibition of [³H]TdR incorporation.     

Practising Conservation Biology in a Virtual Rainforest World

The interdisciplinary science of conservation biology provides undergraduate biology students with the opportunity to connect the biological sciences with disciplines including economics, social science and philosophy to address challenging conservation issues. Because of its complexity, students do not often have the opportunity to practise conservation biology. To increase exposure to this science, this paper describes a virtual rainforest island on which students collect data related to forest carbon storage, while also confronting ethical issues. Students are asked to independently make decisions, collect data and explore the island before writing a research report with recommendations for the future management of the island’s forests. The ethics of decision-making are addressed in the students’ research reports and are reinforced through guided class discussion. Students will complete this activity with increased ethical awareness, as well as a better understanding of the challenges associated with the practise of conservation biology.     

Lichens and mosses promote alternate stable plant communities in the New Jersey Pinelands

Severely burned areas in the pitch pine-dominated forests of the New Jersey Pinelands may remain open and only vegetated with mats of lichens and mosses and sparse, scattered vascular plants for many decades. We hypothesize that climate-driven alternation between moss and lichen domination of the cryptogam mats may foster and inhibit, respectively, vascular plant development. We propose that these processes are mediated by the inhibitory effects of lichens on seed germination and seedling establishment versus a facilitating effect of mosses. We tested the hypothesis by 1) detailed surveys of the composition of cryptogam mats and their association with vascular plants, 2) experimental studies of the effects of tissue leachates on seed germination, 3) observations of mycorrhizal infection in field-collected plants, and 4) experimental tests of seedling emergence from mats. Lichen dominance in the mats was correlated with low densities of vascular plants (graminoids and ericoid shrubs), thin organic horizons on the soil, and high levels of light availability; moss dominance was correlated with higher vascular plant densities, thicker organic horizons, and lower light. Tissue extracts of lichens strongly inhibited seed germination, while moss extracts had no effect. Similarly, mycorrhizal infection by both ecto- and endomycorrhizae was lower in plants growing within lichen mats than in moss mats or in bare soil. However, thick mats of both types of cryptogam inhibited seedling emergence. We observed that moss-dominated patches became overgrown with lichens during a series of very dry, hot summers during the study. These observations all support the hypothesis that fluctuating warm and dry versus cool and moist conditions allow alternative stable states (open cryptogam mats vs succession to pine forest) to develop.     

Localization of the actin-binding protein fesselin in chicken smooth muscle

This report compares cellular localization of fesselin in chicken smooth, skeletal and cardiac muscle tissues using affinity purified polyclonal fesselin antibodies. Western blot analyses revealed large amounts of fesselin in gizzard smooth muscle with lower amounts in skeletal and cardiac muscle. In gizzard, fesselin was detected by immunofluorescence as discrete cytoplasmic structures. Fesselin did not co-localize with talin, vinculin or caveolin indicating that fesselin is not associated with dense plaques or caveolar regions of the cell membrane. Immunoelectron microscopy established localization of fesselin within dense bodies. Since dense bodies function as anchorage points for actin and desmin in smooth muscle cells, fesselin may be involved in establishing cytoskeletal structure in this tissue. In skeletal muscle, fesselin was associated with desmin in regularly spaced bands distributed along the length of muscle fibers suggesting localization to the Z-line. Infrequently, this banding pattern was observed in heart tissue as well. Localization at the Z-line of skeletal and cardiac muscle suggests a role in contraction of these tissues.     

DLG1: Chromosome Location of the Closest Human Homologue of the Drosophila Discs Large Tumor Suppressor Gene

The Drosophila discs large tumor suppressor protein, Dlg, is the prototype of a newly discovered family of proteins termed MAGUKs (membrane-associated guanylate kinase homologues). MAGUKs are localized at the membrane-cytoskeleton interface, usually at cell-cell junctions, where they appear to have both structural and signaling roles. They contain several distinct domains, including a modified guanylate kinase domain, an SH3 motif, and one or three copies of the DHR (GLGF/PDZ) domain. Recessive lethal mutations in the discs large tumor suppressor gene interfere with the formation of septate junctions (thought to be the arthropod equivalent of tight junctions) between epithelial cells, and they cause neoplastic overgrowth of imaginal discs, suggesting a role for cell junctions in proliferation control. A homologue of the Dlg protein, named Hdlg, has been isolated from human B lymphocytes. It shows 65-79% identity to Dlg in the different domains, and it binds to the cytoskeletal protein 4.1. Here, we report that the gene for lymphocyte Hdlg, named DLG1, is located at chromosome band 3q29. This finding identifies a novel site for a candidate tumor suppressor on chromosome 3.     

Genetic monogamy in blue-headed vireos and a comparison with a sympatric vireo with extrapair paternity

Based on the breeding synchrony hypothesis, we predicted, intwo congeners that nest in simiilar habitat but differ in nestingsynchrony, that blue-headed vireos (Vireo solitarius) wouldhave fewer extrapair fertilizations (EPFs) thaii red-eyed vireos(V. olivaceus EPFs were rare in blue-headed vireos (1/37 nestlings),but common in red-eyed vireos (11/19 nestlings). We studiedthe behavior of blue-headed vireos to determine what factorscould promote genetic monogamy. We found no evidence that malesmate guarded to prevent extrapair copulations from occurring.Males did not follow fertile mates closely when mates left thenest (14–25% of female departures) and, during the egg-layingperiod, males were often alone on the nest (22.3 mm/h). Femaleblue-headed vireos, but not red-eyed vireos, obtain direct benefitsfrom social mates such as nest building and incubation (49.1%of the total), and they assess male quality long before becomingfertile. Female blue-headed vireos spent more time incubatingwhen their mates had low incubation effort. Furthermore, maleincubation effort was positively correlated with nest survivalduring incubation. We discuss the evolution of genetic monogamyand sex role convergence in blue-headed vireos in relation toasynchronous breeding.