Quorum sensing is not required for twitching motility in Pseudomonas aeruginosa

It has been reported that mutations in the quorum-sensing genes lasI and rhlI in Pseudomonas aeruginosa result in, among many other things, loss of twitching motility (A. Glessner, R. S. Smith, B. H. Iglewski, and J. B. Robinson, J. Bacteriol. 181:1623-1629, 1999). We constructed knockouts of lasI and rhlI and the corresponding regulatory genes lasR and rhlR and found no effect on twitching motility. However, twitching-defective variants accumulated during culturing of lasI and rhlI mutants. Further analysis showed that the stable twitching-defective variants of lasI and rhlI mutants had arisen as a consequence of secondary mutations in vfr and algR, respectively, both of which encode key regulators affecting a variety of phenotypes, including twitching motility. In addition, when grown in shaking broth culture, lasI and rhlI mutants, but not the wild-type parent, also accumulated unstable variants that lacked both twitching motility and swimming motility and appeared to be identical in phenotype to the S1 and S2 variants that were recently reported to occur at high frequencies in P. aeruginosa strains grown as a biofilm or in static broth culture (E. Deziel, Y. Comeau, and R. Villemur, J. Bacteriol. 183:1195-1204, 2001). These results indicate that mutations in one regulatory system may create distortions that select during subsequent culturing for compensatory mutations in other regulatory genes within the cellular network. This problem may have compromised some past studies of regulatory hierarchies controlled by quorum sensing and of bacterial regulatory systems in general.

Play Preferences and Behavior of Preschool Children with Autistic Spectrum Disorder in the Clinical Environment

The play of children with autistic spectrum disorder (ASD) is a valuable medium for assessment and intervention, and its analysis has the potential to aid diagnosis. This study investigated spontaneous play behavior and play object preferences for 24 preschool children with ASD in a typical occupational therapy clinical environment. Play behavior was rated and choice of play object noted at 10-second intervals from a 15-minute video recording of unstructured play. Statistical analyses indicated that play behavior was consistent with descriptions in the literature. In addition, the children demonstrated clear preferences for play objects in the form of popular characters (e.g., Thomas the Tank Engine) and those with sensorimotor properties. We propose that the inclusion of preferred play objects in a clinical environment may increase intrinsic motivation to play, and thereby enhance assessment and intervention.

The spectrum of minimal defining sets of some Steiner systems

For a design D, define spec(D) = {\M\ \ M is a minimal defining set of D} to be the spectrum of minimal defining sets of D. In this note we give bounds on the size of an element in spec(D) when D is a Steiner system. We also show that the spectrum of minimal defining sets of the Steiner triple system given by the points and lines of PG(3,2) equals {16,17,18,19,20,21,22}, and point out some open questions concerning the Steiner triple systems associated with PG(n, 2) in general. (C) 2002 Elsevier Science B.V. All rights reserved.

Autosomal dominant hypocalcemia: A novel activating mutation (E604K) in the cysteine-rich domain of the calcium-sensing receptor

We report a novel activating mutation (E604K) of the calcium-sensing receptor in a family with autosomal dominant hypocalcemia. Whereas all affected individuals exhibited marked hypocalcemia, some cases with untreated hypocalcemia exhibited seizures in infancy, whereas others were largely asymptomatic from birth into adulthood. The missense mutation E604K (G2182A, GenBank accession no. U20759), which affects an amino acid residue in the C terminus of the cysteine-rich domain of the extracellular head, co-segregated with hypocalcemia in all seven individuals for whom DNA was available. Two unaffected, normocalcemic members of the family did not exhibit the mutation. The molecular impact of the mutation on two key components of the signaling response was assessed in HEK-293 cells transiently transfected with cDNA corresponding to either the wild-type calcium-sensing receptor or the E604K mutation derived by site-directed mutagenesis. There was a significant leftward shift in the concentration response curves for the effects of extracellular Ca2+ on both intracellular Ca2+ mobilization (determined by aequorin luminescence) and MAPK activity (determined by luciferase expression). The C terminus of the cysteine-rich domain of the extracellular head may normally act to suppress receptor activity in the presence of low extracellular Ca2+ concentrations.