Three Approaches to the Study of Language and Gender

Gender across Languages: The Linguistic Representation of Women and Men. Vol. 2. Marlis Hellinger and Hadumod Bußmann eds. Amsterdam: John Benjamins, 2002. 348 pp.
Gender Identity and Discourse Analysis. Lia Litosseliti and Jane Sunderland eds. Amsterdam: John Benjamins, 2002. 335 pp.
Talking Gender and Sexuality. Paul McIlvenny. ed. Amsterdam: John Benjamins, 2002. 327 pp.     

Waddington redux: models and explanation in stem cell and systems biology

Stem cell biology and systems biology are two prominent new approaches to studying cell development. In stem cell biology, the predominant method is experimental manipulation of concrete cells and tissues. Systems biology, in contrast, emphasizes mathematical modeling of cellular systems. For scientists and philosophers interested in development, an important question arises: how should the two approaches relate? This essay proposes an answer, using the model of Waddington’s landscape to triangulate between stem cell and systems approaches. This simple abstract model represents development as an undulating surface of hills and valleys. Originally constructed by C. H. Waddington to visually explicate an integrated theory of genetics, development and evolution, the landscape model can play an updated unificatory role. I examine this model’s structure, representational assumptions, and uses in all three contexts, and argue that explanations of cell development require both mathematical models and concrete experiments. On this view, the two approaches are interdependent, with mathematical models playing a crucial but circumscribed role in explanations of cell development.     

An endonuclease from Chlamydomonas reinhardtii that cleaves the sequence TATA

An endodeoxyribonuclease, designated CreI, was purified 16,000-fold from zygotes of the eukaryote Chlamydomonas reinhardtii. CreI preferentially attacks the sequence TATA producing double strand breaks with 3'-phosphomonoester and 5'-hydroxyl termini. The endonuclease has an Mr = 27,000 and requires Ca2+ at pH 7.5 for optimal activity.     

Real-time analysis of the assembly of ligand, receptor, and G protein by quantitative fluorescence flow cytometry.

We describe a general approach for the quantitative analysis of the interaction among fluorescent peptide ligands (L), receptors (R), and G proteins (G) using fluorescence flow cytometry. The scheme depends upon the use of commercially available fluorescent microbeads as standards to calibrate the concentration of fluorescent peptides in solution and the receptor number on cells in suspension. We have characterized a family of fluoresceinated formyl peptides and analyzed both steady-state and dynamic aspects of ligand formyl peptide-receptor interactions in digitonin-permeabilized human neutrophils. Detailed receptor-binding studies were performed with the pentapeptide N-formyl-Met-Leu-Phe-Phe-Lys-fluorescein. Equilibrium studies showed that GTP [S] caused a loss of binding affinity of approximately two orders of magnitude, from approximately 0.04 nM (LRG) to approximately 3 nM (LR), respectively. Kinetic studies revealed that this change in affinity was principally due to an increase in the dissociation rate constants from approximately 1 x 10(-3) s-1 (LRG) to approximately 1 x 10(-1) s-1 (LR). In contrast, the association rate constants in the presence and absence of guanine nucleotide (approximately 3 x 10(7) s-1 M-1) were statistically indistinguishable and close to the diffusion limit. In the presence of guanine nucleotide (LR), the kinetic data were adequately fit by a single-step reversible-binding model. In the absence of guanine nucleotides, not all receptors have rapid access to G to form the LRG ternary complex. Mathematically, those R that have rapid access to G are either precoupled to R or the association of G with R is fast compared to the association of L with R. The physiological consequences of coupling heterogeneity are discussed.     

Oscillating actin polymerization/depolymerization responses in human polymorphonuclear leukocytes

Leukotriene B4 and platelet-activating factor induced a rapidly oscillating actin polymerization/depolymerization response in human polymorphonuclear leukocytes. N-Formylpeptides were deficient in the ability to induce these oscillations. Flow cytometric analysis of filamentous actin verified that all cells were synchronously responding in this cyclic manner. The hypothesis was tested that these oscillations were analogous to chemical oscillations, i.e. oscillations of intermediate species in chemical systems that are far from equilibrium (Epstein, I. R., Kustin, K., DeKepper, P., and Orban, M. (1983) Sci. Am. 248, 112). Actin polymerization/depolymerization cycles were terminated by adding receptor antagonist a few seconds after initiation of the response by agonists. Thus the oscillations did not represent chemical oscillations that hypothetically could result from a rapid jump of the intracellular milieu to a state far from equilibrium. Rather, continued occupancy of receptors and/or occupancy of new receptors was required to sustain the oscillations. This suggested that the oscillations resulted from regulated polymerization and depolymerization pathways. In simultaneous measurements of actin-associated right angle light scatter and intracellular calcium, no calcium oscillations were detected. Thus, cycles of actin polymerization/depolymerization were not regulated by calcium oscillations.     

Transient increase in phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol trisphosphate during activation of human neutrophils

We recently showed that phosphatidylinositol trisphosphate (PIP3) was present in a unique lipid fraction generated in neutrophils during activation. Here, we demonstrate that the band containing this fraction isolated from thin layer chromatography consists primarily of PIP3 and that only small amounts of radiolabeled PIP3 exist prior to activation. In addition, high performance liquid chromatography of deacylated phospholipids from stimulated cells reveals an increase in a fraction eluting ahead of glycerophosphoinositol 4,5-P2. After removal of the glycerol we found that it coeluted with inositol 1,3,4-P3 when resubjected to high performance liquid chromatography. Thus, we have detected a second, novel form of phosphatidylinositol bisphosphate in activated neutrophils, PI-(3,4)P2. The elevation of PIP3 through the formyl peptide receptor is blocked by pretreatment with pertussis toxin, implicating mediation of the increase in PIP3 by a guanosine triphosphate-binding (G) protein. The rise in PIP3 is not secondary to calcium elevation. Buffering the rise in intracellular calcium did not diminish the increase in PIP3. The elevation of PIP3 appears to occur during activation with physiological agonists, its level varying with the degree of activation. Leukotriene B4, which elicits many of the same responses as stimulation of the formyl peptide receptor but with minimal oxidant production, stimulates a much attenuated rise in PIP3. Isoproterenol, which inhibits oxidant production also reduces the rise in PIP3. Hence formation of PI(3,4)P2 and PIP3 (presumed to be PI(3,4,5)P3) correlates closely with the early events of neutrophil activation.     

Human λ light chain locus: Organization and DNA sequences of three genomicJ regions

Evidence for the genomic organization of human lambda light chain joining (J) region gene segments is presented. A mouse J probe was used in Southern hybridizations to localize joining region sequences in a cosmid clone containing the genomic cluster of six human lambda constant (C) region gene segments. The results of these hybridizations suggest the presence of at least one J gene segment upstream from each constant region gene segment. The DNA sequences indicate that the human JI, J2, and J3 gene segments have consensus nonamer and heptamer sequences, proposed to be involved in V-J joining, are capable of encoding the known amino acid sequences for the respective J peptides, and have a sequence which could give functional RNA splice site at the end of their coding regions. Our data show that a single functional J is located 1.3 or 1.6 kb upstream of each of the C gene segments known to encode the Mcg, Kern^– Oz^–, and Kern^–Oz⁺ isotypes. Therefore, the gene organization of this region of the human lambda locus is J1 CI -J2C2-J3C3. The DNA sequences ofJ 1,J 2, andJ 3 presented in this paper establish that a singleJ gene segment precedes each expressed C gene segment, and support a model for the evolution of the human JC clusters where JICI andJ2C2-J3C3. arose from different ancestral JC units.     

LTB4 induced activation signals and responses in neutrophils are short-lived compared to formylpeptide

Leukotriene B4 (LTB4) was shown to be a potent stimulator of neutrophil actin polymerization as detected by right-angle light scatter and rhodamine-phalloidin staining of F-actin. When we compared the kinetics of this neutrophil cytoskeletal response to the chemoattractants formylpeptide and LTB4, we observed that the response to LTB4 was markedly shorter-lived. To understand the basis of this result, we re-examined the kinetics of superoxide generation, elastase release, intracellular calcium elevation, and phosphoinositide metabolism in neutrophils stimulated with LTB4 and N-formylhexapeptide. LTB4 was relatively inefficient in producing superoxide and in releasing elastase. Although both responses were initiated with similar rapidity, they turned off sooner with LTB4 as compared with N-formylhexapeptide stimulation. Intracellular calcium elevation, a signal that is necessary for superoxide generation and degranulation, was of similar magnitude but of shorter duration in response to LTB4 as compared with the N-formylhexapeptide. The LTB4-induced rise of phosphatidic acid also was not sustained as long as the N-formylhexapeptide-induced increase. Prior exposure of neutrophils to LTB4 did not inhibit subsequent stimulation of superoxide generation by N-formylhexapeptide. Thus, the inability of LTB4 to stimulate superoxide generation was not due to LTB4-induced global inhibitory signals. The deficiency in LTB4-induced superoxide and elastase responses may be related to short-lived LTB4-induced activation signals and/or the number of receptors contributing to these responses.     

The response of a bumblebee goby,Brachygobius sabanus,to chemical stimuli from injured conspecifics

Synopsis Brachygobius sabanus move less often and spend less time swimming when they detect chemicals released from injured conspecifics. This resembles the alarm response found in ostariophysan fishes, darters, and at least one other gobiid. Chemicals from injured Poecilia reticulata do not induce an alarm response in B. sabanus.