Lateral segregation of neutrophil chemotactic receptors into actin- and fodrin-rich plasma membrane microdomains depleted in guanyl nucleotide regulatory proteins

Subcellular fractions were prepared from human neutrophils desensitized at 15 degrees C with stimulatory doses of the photoaffinity derivative F-Met-Leu-Phe-N epsilon-(2-(rho-azido[125I]salicylamido)ethyl-1,3'- dithio-propionyl)-Lys. The covalently labeled receptors were found in a membrane fraction of higher density than those from cells preexposed to ligand at 4 degrees C but not desensitized. The denser fraction (rho approximately equal to 1.155 g/cc) was the cellular locus of the membrane associated cytoskeletal proteins, actin, and fodrin, as detected immunologically on western blots. The light fraction (rho approximately equal to 1.135), cosedimented with neutrophil plasma membrane markers, plasma membrane guanyl nucleotide regulatory proteins, and several characteristic polypeptides identified by SDS-PAGE, including a major 72-kD species. The photoaffinity-labeled species in either case showed the same mobility on SDS-PAGE (Mr = 50,000-70,000) corresponding to previously reported values for N-formyl chemotactic receptors. These labeled receptors were sensitive to proteolysis after exposure of the intact photoaffinity-labeled cells to papain at 4 degrees C. We conclude that (a) the fractions isolated are probably derived from different lateral microdomains of the surface of human neutrophils; (b) the higher density fraction contains occupied N-formyl-chemotactic receptors previously shown to have been converted, to a high affinity, slowly dissociating form coisolating with neutrophil cytoskeleton and implicated in the termination of formyl peptide-induced neutrophil activation; and (c) the translocation of receptors to these microdomains may serve to compartmentalize receptors and perhaps regulate the interaction of the receptor/G-protein transduction pair.     

Chironomidae (Diptera) of peatlands in northwestern Ontario, Canada

Eighty-four species of Chironomidae were collected, using emergence traps, from three poor fens located in the Experimental Lakes Area (ELA) of northwestern Ontario. Of these, 37 were considered to be true peatland fauna. The majority (23) of the peatland species are new North American or Canadian records and, of these, 10 are previously undescribed. Numbers m⁻² yr⁻¹ emerging from the fens were similar to neighbouring lakes but biomass (mg) m⁻² yr⁻¹ emerging was much less, indicating the small average size of the fen chironomids. Emergence began in early May and was virtually completed by late July-early August in all three years of the study. Most of the emergence occurred early in the season. Eight species accounted for ≥90% of the emergence. Five of these, Gymnometriocnemus (R.) acigus Saeth., Doithrix villosa Saeth. and Subl., Pseudorthocladius (s.s.) destitutus Saeth. and Subl., P. (s.s.) curtistylus (Goetgh.), and Paramerina nr. smithae (Subl.) had univoltine life cycles and relatively stichronous emergences. Pseudosmittia forcipata (Goetgh.) was bivoltine, and Limnophyes minimus (Meig.) and Smittia nr. nudipennis Geotgh. had protracted emergence periods that made voltinism difficult to determine. Characteristic features of the chironomid fauna of peatlands at ELA are discussed. The general applicability of these features to peatlands, and needs for further research in these neglected but extensive Canadian habitats are considered.     

Effects of spring and autumn fires on the composition of Chionochloa rigida tussock grassland,New Zealand

Two areas of Chionochloa rigida tussock grassland on Flagstaff Hill were burnt in autumn and spring 1976, respectively. Plant species cover and frequency were recorded in 1977 and 1985. Initially, plant cover and frequency were lower, and the area of bare ground was greater, on the autumn burnt site. After nine years, cover and frequency values were similar for most species, and bare ground was rare, on both sites. Over this period, recovery in size of indigenous tussock-forming physiognomic dominants resulted in suppression of intertussock sub-shrubs, herbs and grasses that were initially favoured by reduction of competition after fire. Plant species most tolerant of fire have features that protect the meristem, for instance an underground perennating organ or dense tillering.     

Antigenic mapping of a human λ light chain: Correlation with three dimensional structure

Although the amino acid sequence and three-dimensional structure of human immunoglobulin light chains have been known for more than 15 years, the location of antigenic markers characteristic of chains has not been determined. Here, we use a set of synthetic overlapping peptides to completely model the sequence of the chain Mcg and test these for the binding or rabbit and goat antisera specific for chain determinants. We assess peptide contributions to -antigenic reactivity and also to identify a portion of C-region where conformational factors contribute to the antigenicity. Specific determinants occur both in the constant and variable (first and third framework) domains of the molecule. The fourth framework of the variable region, a segment specified by the joining gene, is also recognized and cross-reacts antigenically with the homologous region of T cell receptor chains. Major specific determinants are localized in the N- and C-terminal segments, which are linear and devoid of major conformational folding. Other segments that are strongly antigenic, such as the third framework of the V region (residue 78–93) and a segment of the constant region (residues 177–192), show strong conformational dependence in antigenicity.     

Modulation of differentiation markers in human choriocarcinoma cells by extracellular matrix: on the role of a three-dimensional matrix structure

Abstract. During spontaneous or chemically induced differentiation human choriocarcinoma cells express typical characteristics of the normal differentiating trophoblast: 1) increased production of peptide and steroid hormones (chorionic gonadotropin, placental lactogen, estrogens, progesterone); 2) increased activity of cellular alkaline phosphatase; 3) morphological transition from cytotrophoblast to syncytiotrophoblast-like cells; and 4) arrested cell proliferation. Since the extracellular matrix is known to control gene expression we have examined the effects of different substrates composed of matrix macromolecules on the differentiation of BeWo choriocarcinoma cells. Matrices tested were; fibronectin, laminin, collagens type I and type IV, the basement membrane-like complex matrix Matrigel, and a complex matrix extracted from human term placenta. Irrespective of the type of molecule(s), it was consistently found that, whenever the matrix molecules were presented as threedimensional structures (as opposed to protein coatings on tissue culture plastic) the response of affected differentiation markers monitored was highly pronounced. Morphology was changed from monolayers to rounded colonies, cell proliferation was reduced, and the secretion of chorionic gonadotropin was increased up to tenfold. Heterogeneous effects were observed on progesterone secretion and on the activity of cellular alkaline phosphatase. Cell adhesion to matrix molecules, however, did not depend on the structure of the matrix. This study demonstrates that gene expression in these tumor cells can be modified by extracellular matrix and highlights that not only the presence of effector molecules in the matrix but also the three-dimensional structure of the matrix is important for the induction of differentiation.     

A review and update of animal toxicoses associated with fumonisin-contaminated feeds and production of fumonisins by Fusarium isolates

During the 1989 corn harvest season, numerous reports of equine leukoencephalomalacia (ELEM) outbreaks and a pulmonary edema (PPE) syndrome in swine from several regions of the United States were received by the National Veterinary Services Laboratories (NVSL), Ames, Iowa. Previous and concurrent research linked Fusarium moniliforme and fumonisin-contaminated feeds to both diseases. Chemical and mycological investigations revealed fumonisin B₁ (FB₁) concentrations of 20 to 360 ppm in suspect swine feeds and 8 to 117 ppm in suspect equine feeds. Nonproblem feeds contained concentrations below 8 ppm. Fusarium moniliforme and Fusarium proliferatum were isolated from both problem and nonproblem equine and swine feeds. When cultured on autoclaved corn, the F. moniliforme and F. proliferatum isolates produced respective FB₁ and fumonisin B₂ (FB₂) that range from less than 5 to more than 2450 ppm and less than 5 to more than 1000 ppm, respectively. Isolates from both problem and nonproblem feeds produced high levels (greater than 500 ppm) in culture. Reported here is a review of chemical and mycological data resulting from the study of several cases of PPE and ELEM.     

The effect of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus

Synopsis The effects of constant and diurnally fluctuating levels of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus, were examined under controlled laboratory conditions. Fish were exposed for either 10 or 11 weeks to constant levels of 6.7 (high) and 2.2 (low) mg l^–1, and a diurnal fluctuation, ranging from 2.5 to 6.4 mg 0₂l^–1. Growth rates, calculated for both standard length and weight, for fish exposed to low and diurnally fluctuating levels were significantly reduced (p < 0.001) as compared to those for fish exposed to the high level. Growth rates of fish exposed to the high level were over twice those of fish held under low oxygen conditions. Under fluctuating conditions, fish grew at intermediate rates. Following these exposures, all fish were subsequently held at 7.2 mg Oz l^–1 for five weeks. Growth rates increased over two and a half times for fish previously exposed to the low oxygen level and were significantly (p < 0.001) higher than for the other two groups.