Identification of regions of Ail required for the invasion and serum resistance phenotypes

Yersinia enterocolitica is an enteric pathogen that has served as a model system for the study of microbial pathogenesis. Numerous virulence gene have been identified both on the virulence plasmid and on the chromosome. One of the chromosomal genes that is highly correlated with virulence is ail, a gene identified along with inv in a screen for Y. enterocolitica genes that could confer an invasive phenotype to Escherichia coli. Ail also promotes serum resistance in both E. coli and Y. enterocolitica. Several virulence factors homologous to Ail have been identified in other pathogens, yet very little is known about what constitutes the functional domain(s) of these proteins. Proteins in this family are predicted to consist of eight transmembrane beta-sheets and four cell surface-exposed loops. We constructed and characterized a number of insertion, deletion and point mutations in the regions of ail predicted to encode the cell surface loops. The results from the analysis of these mutants indicate that cell surface loops one and four do not directly promote invasion or serum resistance, whereas mutations in loop three appear to modulate both phenotypes. Analysis of mutations in loop 2 suggests that this surface-exposed loop contains sequences required for serum resistance and invasion. In addition, a peptide derived from the sequence of loop 2 was able specifically to inhibit Ail-mediated invasion in a dose-dependent manner. These results suggest that Ail directly promotes invasion and that loop 2 contains an active site, perhaps a receptor-binding domain. Analyses of the mutations also suggest that the serum resistance and invasion phenotypes may be separable, because there are numerous mutations that affect one phenotype but not the other.     

Genomics: leprosy - a degenerative disease of the genome

Analysis of the genome of the leprosy bacillus uncovers evidence of extensive deletion and inactivation of genes. Secluded in a specialised niche, it has discarded much of its genetic heritage, though retaining just enough to be a major human pathogen.     

Crystal structure of the alpha-actinin rod reveals an extensive torsional twist

BACKGROUND: Alpha-actinin is a ubiquitously expressed protein found in numerous actin structures. It consists of an N-terminal actin binding domain, a central rod domain, and a C-terminal domain and functions as a homodimer to cross-link actin filaments. The rod domain determines the distance between cross-linked actin filaments and also serves as an interaction site for several cytoskeletal and signaling proteins. RESULTS: We report here the crystal structure of the alpha-actinin rod. The structure is a twisted antiparallel dimer that contains a conserved acidic surface. CONCLUSIONS: The novel features revealed by the structure allow prediction of the orientation of parallel and antiparallel cross-linked actin filaments in relation to alpha-actinin. The conserved acidic surface is a possible interaction site for several cytoplasmic tails of transmembrane proteins involved in the recruitment of alpha-actinin to the plasma membrane.     

Microarray profiling of gene expression patterns in bladder tumor cells treated with genistein

Microarray technology was used to gain an insight into the molecular events of tumor cell growth inhibition mediated by the soy isoflavone genistein. For this, a susceptible bladder tumor line TCCSUP was treated with the inhibitory dose (50 microM) of genistein for various periods of time, followed by mRNA isolations, cDNA probe preparations, and hybridization individually to cDNA chips containing 884 sequence-verified known human genes. After analyzing the hybridization signals with a simple quantitative method developed by this study, we detected that egr-1, whose expression has been associated with proliferation and differentiation, was transiently induced and this expression pattern was later confirmed by RT-PCR. Thus, microarray technology is a reliable and powerful tool for profiling gene expression patterns in many biological systems related to cancer. We further detected many groups of genes with distinct expression profiles and most of them encode for proteins that regulate the signal transduction or the cell cycle pathways. These genes warrant further investigation as regards their roles in the susceptibility of the tumor cell line to the antitumor drug.     

Exertion-induced fatigue and thermoregulation in the cold

Cold exposure facilitates body heat loss which can reduce body temperature, unless mitigated by enhanced heat conservation or increased heat production. When behavioral strategies inadequately defend body temperature, vasomotor and thermogenic responses are elicited, both of which are modulated if not mediated by sympathetic nervous activation. Both exercise and shivering increase metabolic heat production which helps offset body heat losses in the cold. However, exercise also increases peripheral blood flow, in turn facilitating heat loss, an effect that can persist for some time after exercise ceases. Whether exercise alleviates or exacerbates heat debt during cold exposure depends on the heat transfer coefficient of the environment, mode of activity and exercise intensity. Prolonged exhaustive exercise leading to energy substrate depletion could compromise maintenance of thermal balance in the cold simply by precluding continuation of further exercise and the associated thermogenesis. Hypoglycemia impairs shivering, but this appears to be centrally mediated, rather than a limitation to peripheral energy metabolism. Research is equivocal regarding the importance of muscle glycogen depletion in explaining shivering impairments. Recent research suggests that when acute exercise leads to fatigue without depleting energy stores, vasoconstrictor responses to cold are impaired, thus body heat conservation becomes degraded. Fatigue that was induced by chronic overexertion sustained over many weeks, appeared to delay the onset of shivering until body temperature fell lower than when subjects were rested, as well as impair vasoconstrictor responses. When heavy physical activity is coupled with underfeeding for prolonged periods, the resulting negative energy balance leads to loss of body mass, and the corresponding reduction in tissue insulation, in turn, compromises thermal balance by facilitating conductive transfer of body heat from core to shell. The possibility that impairments in thermoregulatory responses to cold associated with exertional fatigue are mediated by blunted sympathetic nervous responsiveness to cold is suggested by some experimental observations and merits further study.     

Effects of androgen deprivation on the histology of adult chimpanzee testis

Until primate sperm are exposed to the unique microenvironment of the epididymis, they are not capable of fertilization or vigorous motility. Many of the proteins that contribute to the unique microenvironment of the primate epididymis, and thus to sperm maturation, are dependent on androgens to induce their synthesis and secretion. GnRH antagonists have proved effective in suppressing LH and testosterone synthesis and secretion, and thus in maintaining a state of androgen deprivation or functional hypogonadotropism. We report here the effects of GnRH antagonist-induced androgen-deprivation on the histology of the testicular interstitium and seminiferous epithelium of the adult male chimpanzee. After only 21 days of androgen-deprivation, chimpanzee testicular tissues exhibit specific atrophic changes, including the loss of contact between developing spermatocytes and between Sertoli cells and their developing spermatids, alterations in cell development resulting in missing maturation steps (elongating Sc and structurally complete Sd2 spermatids) and inappropriate cell associations, varying degrees of cytoplasmic degradation in germ cells, Sertoli cells, and Leydig cells, and a tubular lumen obscured by masses of sloughed primary and secondary spermatocytes and what appear histologically to be Sb1 and Sd1 spermatids.