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HP1 proteins are thought to be modulators of chromatin organization in all mammals, yet their exact physiological function remains unknown. In a first attempt to elucidate the function of these proteins in vivo, we disrupted the murine Cbx1 gene, which encodes the HP1-[beta] isotype, and show that the [Cbx1.sup.-/-] null mutation leads to perinatal lethality. The newborn mice succumbed to acute respiratory failure, whose likely cause is the defective development of neuromuscular junctions within the endplate of the diaphragm. We also observe aberrant cerebral cortex development in [Cbx1.sup.-/-] mutant brains, which have reduced proliferation of neuronal precursors, widespread cell death, and edema. In vitro cultures of neurospheres from [Cbx1.sup.-/-] mutant brains reveal a dramatic genomic instability. Our results demonstrate that HP1 proteins are not functionally redundant and that they are likely to regulate lineage-specific changes in hetero-chromatin organization.

Proteasome activator PA200 enhances proteasome-mediated cleavage after acidic residues in vitro; however, its role within cells is not known. Here, we show that, in response to ionizing radiation, PA200 forms hybrid proteasomes with 19S caps and 20S core proteasomes that accumulate on chromatin, leading to an increase in proteolytic activity. Unlike many other proteins that respond to DNA damage, the response of PA200 appears to be independent of Ataxia Telangiectasia Mutated and p53, but dependent on DNA-dependent protein kinase activity. Nonetheless, PA200 is critical because PA200-knockdown cells show genomic instability and reduced survival after exposure to ionizing radiation. This phenotype is reproduced by specific inhibition of postglutamyl activity of proteasomes, but combined treatment with PA200 siRNA and postglutamyl inhibitor does not show additive effects on survival. Together, these data suggest a unique role for PA200 in genomic stability that is likely mediated through its ability to enhance postglutamyl cleavage by proteasomes. ATM | chromatin | DNA-dependent protein kinase | ionizing radiation | DNA damage

Single-strand DNA (ssDNA)-binding proteins (SSBs) are ubiquitous and essential for a wide variety of DNA metabolic processes, including DNA replication, recombination, DNA damage detection and repair (1). SSBs have multiple [...]

Bladder overactivity associated with outflow obstruction is a common human condition recapitulated in the female rat by narrowing the diameter of the urethra. The goal of these studies was to evaluate the role of intercellular communication through connexin43 (Cx43)-derived gap junction channels to bladder overactivity following partial urethral outflow obstruction of 3-day to 6-wk duration. Cx43 mRNA and protein expression were barely detectable by Northern or Western blots, respectively, in the detrusor layer of normal bladders, but bands were found with both techniques after 6 wk of obstruction. Linear regression analysis of the RT-PCR data revealed a statistically significant positive correlation between the duration of obstruction (again, ranging from 3-day to 6-wk duration) and Cx43 mRNA transcript levels, such that after 6 wk of obstruction, Cx43 transcript levels were [approximately equal to] 15-fold greater than initial control values. When taking into account the approximately fivefold increase in bladder weight over this same time frame, the absolute amount of Cx43 mRNA in the bladder apparently increased by [approximately equal to] 75-fold. In that regard, as anticipated, and consistent with previous observations, 6 wk of obstruction was also associated with a significant increase in spontaneous bladder contractions between micturitions. The amplitude of these contractions was significantly reduced by heptanol given intravesically. Furthermore, carbachol-precontracted bladder strips from obstructed animals were more sensitive to heptanol-induced relaxation (100 [micro]M) than their unobstructed counterparts (n = 6; P < 0.01). When bladder strips were equivalently precontracted via electrical field stimulation (EFS; 20 Hz), similar heptanol-induced relaxation responses were observed. However, the tetrodotoxin-resistant portion of the EFS-induced contraction was greater in the obstructed than in the unobstructed animals, and this portion of the contractile response was more sensitive to heptanol-induced relaxation in obstructed than unobstructed bladders (n = 7; P < 0.01). Taken together, these observations indicate that partial outlet obstruction produces an overactive bladder that may be more dependent on intercellular communication through gap junctions for modulation of contractile responses than its normal counterpart. tissue and cellular physiology; gap junction; smooth muscle; electrical field stimulation; cystometry

Research has been conducted on the velo-cardio-facial/DiGeorge syndrome characterized by the phenotypic features such as cardiovascular defects. The cre-loxP strategy in generating the mice which are hemizygous for the deletion has been used to investigate the etiology of the cardiovascular disorder and the results are presented.

Research indicates that the 3-Mb hemizygous deletion is mediated by meiotic intrachromosomal recombination in subjects who have velo-cardio-facial syndrome. In studies using two three-generation families, haplotype analysis, genomic fingerprint analysis and physical mapping showed that 200-kb region low-copy repeats are nearly identical, implying that deletion is affected by homologous recombination.

The consequence of spinal and peripheral administration of an alpha-1 adrenoreceptor antagonist was examined in animals undergoing continuous cystometry and in vitro on isolated bladder and urethral tissues to compare the effects of noradrenergic mechanisms involved in micturition in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats. Results indicate that that bladder function in SHR differs from control rats characterized by a decrease in bladder capacity and microturition volume with an increase in nonvoiding bladder contractions.