Several mammalian protein families inhibit the activity of signal transducer and activator of transcription (STAT) proteins. The protein inhibitor of activated STAT (PIAS) was initially identified through its ability to interact with human STAT proteins. We isolated a gene (pisA) encoding a Dictyostelium orthologue of PIAS, Dd-PIAS, which possesses almost all the representative motifs and domains of mammalian PIAS proteins. A Dd-PIAS null mutant strain displays a normal terminal morphology but with accelerated development once cells are aggregated. In contrast, Dd-PIAS overexpressor strains demonstrate delayed aggregation, almost no slug phototaxis, impaired slug motility, and a prolonged slug migration period. This strain is a near phenocopy of the Dd-STATa null mutant, although it eventually forms a fruiting body, albeit inefficiently. The expression of several Dd-STATa-activated genes is upregulated in the Dd-PIAS null mutant and there is ectopic expression of pstAB makers. The concentration of a PIAS-green fluorescent protein (GFP) fusion protein, expressed under the PIAS promoter, is greatest in the pstO cells and gradually decreases with proximity to the tip of the slug and culminant: a pattern diametrically opposite to that of Dd-STATa. Our results suggest a functional interrelationship between Dd-PIAS and Dd-STATa that influences gene expression and development.

A Dd-STATa-null mutant, which is defective in expression of a Dictyostelium homologue of the metazoan STAT (signal transducers and activators of transcription) proteins, fails to culminate and this phenotype correlates with the loss of expression of various prestalk (pst) genes. An EST clone, SSK395, encodes a close homologue of the adducin amino-terminal head domain and harbors a putative actin-binding domain. We fused promoter fragments of the cognate gene, ahhA (adducin head homologue A), to a lacZ reporter and determined their expression pattern. The proximal promoter region is necessary for the expression of ahhA at an early (pre-aggregative) stage of development and this expression is Dd-STATa independent. The distal promoter region is necessary for expression at later stages of development in pstA cells, of the slug and in upper cup and pstAB cells during culmination. The distal region is partly Dd-STATadependent. The ahhA-null mutant develops almost normally until culmination, but it forms slanting culminants that tend to collapse on to the substratum. The mutant also occasionally forms'fruiting bodies with swollen papillae and with constrictions in the prestalk region. The AhhA protein localizes to the stalk tube entrance and also to the upper cup cells and in cells at or near to the constricted region where an F-actin ring is localized. These findings suggest that DdSTATa regulates culmination and may be necessary for straight downward elongation of the stalk, via the putative actin-binding protein AhhA.

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Detonation transition was experimentally investigated using flame jetting through the orifice of a small sub-chamber, which was equipped on the side wall near the closed end of the main channel (square inner closs section, 50 mm on a side) filled with a stoichiometric hydrogen-oxygen mixture at an initial pressure of 80 kPa. The number of sub-chambers and orifice diameters were changed as 1, 2, 4 (called as FJ1, FJ2, FJ4, respectively) and 3, 5, 7 mm, respectively, and the facing flame jets were collided with each other in FJ2 and FJ4. Two regimes of detonation transition were observed: (i) deflagration-to-detonation transition (DDT) accompanied by flame acceleration process and (ii) direction initiation of a detonation near the flame jetting section. The flame propagation distance required for detonation transition was one-half to one-third for regime (i) compared to single-spark ignition without flame jet, and below one-sixth for regime (ii). Except for the case of regime (ii), observed for an orifice diameter of 5 or 7 mm of FJ4, the detonation transition distance had no significant effect on the types of flame jetting and orifice diameters. Time-resolved schlieren recordings showed that the choked jet of combustion products drove the shock wave preceding the flame front, and induced multi-dimensional flame motion and repeated shock-flame interactions in the confinement. These behaviors enhanced flame velocity at the ignition end by a factor of 4 to 7 in FJ1 and FJ2, compared to single-spark ignition. The effect of these enhanced flame velocities on DDT distances was consistent with the semi-empirical model of flame acceleration process in a smooth tube. The schlieren recordings and pressure measurements at the closed end indicated that the possible factors for the initiation of detonation in regime (ii) were the mixing of reacted and unreacted gas induced by the repeated strong shock-flame interaction and the hot spot formed by shock-shock interaction driven by the facing flame jetting.