Functional contacts with a range of splicing proteins suggest a central role for Brr2p in the dynamic control of the order of events in spliceosomes of Saccharomyces cerevisiae

Mapping of functional protein interactions will help in understanding conformational rearrangements that occur within large complexes like spliceosomes. Because the U5 snRNP plays a central role in pre-mRNA splicing, we undertook exhaustive two-hybrid screening with Brr2p, Prp8p, and other U5 snRNP-associated proteins. DExH-box protein Brr2p interacted specifically with five splicing factors: Prp8p, DEAH-box protein Prp16p, U1 snRNP protein Snp1p, second-step factor Slu7p, and U4/U6.U5 tri-snRNP protein Snu66p, which is required for splicing at low temperatures. Co-immunoprecipitation experiments confirmed direct or indirect interactions of Prp16p, Prp8p, Snu66p, and Snp1p with Brr2p and led us to propose that Brr2p mediates the recruitment of Prp16p to the spliceosome. We provide evidence that the prp8-1 allele disrupts an interaction with Brr2p, and we propose that Prp8p modulates U4/U6 snRNA duplex unwinding through another interaction with Brr2p. The interactions of Brr2p with a wide range of proteins suggest a particular function for the C-terminal half, bringing forward the hypothesis that, apart from U4/U6 duplex unwinding, Brr2p promotes other RNA rearrangements, acting synergistically with other spliceosomal proteins, including the structurally related Prp2p and Prp16p. Overall, these protein interaction studies shed light on how splicing factors regulate the order of events in the large spliceosome complex.     

Susceptibility of Burkholderia cepacia and other pathogens of importance in cystic fibrosis to u.v. light

To investigate the potential usefulness of u.v. germicidal irradiation (UVGI) in preventing the spread of Burkholderia cepacia, an important pathogen in cystic fibrosis (CF), the in-vitro susceptibility of B. cepacia to UVGI was determined. Five strains were exposed to UVGI from a 7.2-W source. Burkholderia cepacia was less susceptible to UVGI than other important CF-related pathogens, namely Staphylococcus aureus and Pseudomonas aeruginosa, but was more susceptible than Stenotrophomonas maltophilia. No strain of B. cepacia survived longer than an 8 s exposure to UVGI, with doses required to achieve 1 log reduction in bacterial numbers ranging from 28.3 to 57.5 J m(-2).     

Genetic and physical interactions between factors involved in both cell cycle progression and pre-mRNA splicing in Saccharomyces cerevisiae

The PRP17/CDC40 gene of Saccharomyces cerevisiae functions in two different cellular processes: pre-mRNA splicing and cell cycle progression. The Prp17/Cdc40 protein participates in the second step of the splicing reaction and, in addition, prp17/cdc40 mutant cells held at the restrictive temperature arrest in the G2 phase of the cell cycle. Here we describe the identification of nine genes that, when mutated, show synthetic lethality with the prp17/cdc40Delta allele. Six of these encode known splicing factors: Prp8p, Slu7p, Prp16p, Prp22p, Slt11p, and U2 snRNA. The other three, SYF1, SYF2, and SYF3, represent genes also involved in cell cycle progression and in pre-mRNA splicing. Syf1p and Syf3p are highly conserved proteins containing several copies of a repeated motif, which we term RTPR. This newly defined motif is shared by proteins involved in RNA processing and represents a subfamily of the known TPR (tetratricopeptide repeat) motif. Using two-hybrid interaction screens and biochemical analysis, we show that the SYF gene products interact with each other and with four other proteins: Isy1p, Cef1p, Prp22p, and Ntc20p. We discuss the role played by these proteins in splicing and cell cycle progression.     

Alterations in the TGFbeta signaling pathway in myogenic progenitors with age

Myogenic progenitors in adult muscle are necessary for the repair, maintenance and hypertrophy of post-mitotic muscle fibers. With age, fat deposition and fibrosis contribute to the decline in the integrity and functional capacity of muscles. In a previous study we reported increased accumulation of lipid in myogenic progenitors obtained from aged mice, accompanied by an up-regulation of genes involved in adipogenic differentiation. The present study was designed to extend our understanding of how aging affects the fate and gene expression profile of myogenic progenitors. Affymetrix murine U74 Genechip analysis was performed using RNA extracted from myogenic progenitors isolated from adult (8-month-old) and aged (24-month-old) DBA/2JNIA mice. The cells from the aged animals exhibited major alterations in the expression level of many genes directly or indirectly involved with the TGFbeta signaling pathway. Our data indicate that with age, myogenic progenitors acquire the paradoxical phenotype of being both TGFbeta activated based on overexpression of TGFbeta-inducible genes, but resistant to the differentiation-inhibiting effects of exogenous TGFbeta. The overexpression of TGFbeta-regulated genes, such as connective tissue growth factor, may play a role in increasing fibrosis in aging muscle.     

FAK deficiency in cells contributing to the basal lamina results in cortical abnormalities resembling congenital muscular dystrophies

Targeted deletion of focal adhesion kinase (fak) in the developing dorsal forebrain resulted in local disruptions of the cortical basement membrane located between the neuroepithelium and pia-meninges. At disruption sites, clusters of neurons invaded the marginal zone. Retraction of radial glial endfeet, midline fusion of brain hemispheres, and gliosis also occurred, similar to type II cobblestone lissencephaly as seen in congenital muscular dystrophy. Interestingly, targeted deletion of fak in neurons alone did not result in cortical ectopias, indicating that fak deletion from glia is required for neuronal mislocalization. Unexpectedly, fak deletion specifically from meningeal fibroblasts elicited similar cortical ectopias in vivo and altered laminin organization in vitro. These observations provide compelling evidence that FAK plays a key signaling role in cortical basement membrane assembly and/or remodeling. In addition, FAK is required within neurons during development because neuron-specific fak deletion alters dendritic morphology in the absence of lamination defects.     

Activin-A up-regulates type I activin receptor mRNA levels in human immortalized extravillous trophoblast cells.

Activin is known to play an important regulatory role in reproduction, including pregnancy. To further examine the role and signaling mechanism of activin in regulating placental function, the steady-state level of activin type I receptor (ActRI) mRNA in immortalized extravillous trophoblasts (IEVT) cells was measured using competitive PCR (cPCR). An internal standard of ActRI cDNA for cPCR was constructed for the quantification of ActRI mRNA levels in IEVT cells. ActRI mRNA levels were increased in a dose-dependent manner by activin-A with the maximal effect observed at the dose of 10 ng/ml. Time course studies revealed that activin-A had maximal effects on ActRI mRNA levels at 6 hours after treatment. The effects of activin-A on ActRI mRNA levels was blocked by follistatin, an activin binding protein, in a dose-dependent manner. In addition, inhibin-A inhibited basal, as well as activin-A-induced ActRI mRNA levels. These findings provide evidence, for the first time, that activin-A modulates ActRI mRNA levels in human trophoblast cells.     

Identification and characterization of Prp45p and Prp46p,essential pre-mRNA splicing factors

Through exhaustive two-hybrid screens using a budding yeast genomic library, and starting with the splicing factor and DEAH-box RNA helicase Prp22p as bait, we identified yeast Prp45p and Prp46p. We show that as well as interacting in two-hybrid screens, Prp45p and Prp46p interact with each other in vitro. We demonstrate that Prp45p and Prp46p are spliceosome associated throughout the splicing process and both are essential for pre-mRNA splicing. Under nonsplicing conditions they also associate in coprecipitation assays with low levels of the U2, U5, and U6 snRNAs that may indicate their presence in endogenous activated spliceosomes or in a postsplicing snRNP complex.