Imputation strategies for genomic prediction using nanopore sequencing

BACKGROUND

Genomic prediction describes the use of SNP genotypes to predict complex traits and has been widely applied in humans and agricultural species. Genotyping-by-sequencing, a method which uses low-coverage sequence data paired with genotype imputation, is becoming an increasingly popular SNP genotyping method for genomic prediction. The development of Oxford Nanopore Technologies' (ONT) MinION sequencer has now made genotyping-by-sequencing portable and rapid. Here we evaluate the speed and accuracy of genomic predictions using low-coverage ONT sequence data in a population of cattle using four imputation approaches. We also investigate the effect of SNP reference panel size on imputation performance.

RESULTS

SNP array genotypes and ONT sequence data for 62 beef heifers were used to calculate genomic estimated breeding values (GEBVs) from 641 k SNP for four traits. GEBV accuracy was much higher when genome-wide flanking SNP from sequence data were used to help impute the 641 k panel used for genomic predictions. Using the imputation package QUILT, correlations between ONT and low-density SNP array genomic breeding values were greater than 0.91 and up to 0.97 for sequencing coverages as low as 0.1 × using a reference panel of 48 million SNP. Imputation time was significantly reduced by decreasing the number of flanking sequence SNP used in imputation for all methods. When compared to high-density SNP arrays, genotyping accuracy and genomic breeding value correlations at 0.5 × coverage were also found to be higher than those imputed from low-density arrays.

CONCLUSIONS

Here we demonstrated accurate genomic prediction is possible with ONT sequence data from sequencing coverages as low as 0.1 × , and imputation time can be as short as 10 min per sample. We also demonstrate that in this population, genotyping-by-sequencing at 0.1 × coverage can be more accurate than imputation from low-density SNP arrays.

Prehospital Double Sequential Defibrillation: A Matched Case-Control Study

OBJECTIVES

The goal of our study was to determine whether prehospital double sequential defibrillation (DSD) is associated with improved survival to hospital admission in the setting of refractory ventricular fibrillation/pulseless ventricular tachycardia (VF/pVT).

METHODS

This project is a matched case-control study derived from prospectively collected quality assurance/quality improvement data obtained from the San Antonio Fire Department out-of-hospital cardiac arrest (OHCA) database between January 2013 and December 2015. The cases were defined as OHCA patients with refractory VF/pVT who survived to hospital admission. The control group was defined as OHCA patients with refractory VF/pVT who did not survive to hospital admission. The primary variable in our study was prehospital DSD. The primary outcome of our study was survival to hospital admission.

RESULTS

Of 3,469 consecutive OHCA patients during the study period, 205 OHCA patients met the inclusion criterion of refractory VF/pVT. Using a predefined algorithm, two blinded researchers identified 64 unique cases and matched them with 64 unique controls. Survival to hospital admission occurred in 48.0% of DSD patients and 50.5% of the conventional therapy patients (p > 0.99; odds ratio = 0.91, 95% confidence interval = 0.40-2.1).

CONCLUSION

Our matched case-control study on the prehospital use of DSD for refractory VF/pVT found no evidence of associated improvement in survival to hospital admission. Our current protocol of considering prehospital DSD after the third conventional defibrillation in OHCA is ineffective.

Survey of Casualty Evacuation Missions Conducted by the 160th Special Operations Aviation Regiment During the Afghanistan Conflict

BACKGROUND

Historically, documentation of prehospital combat casualty care has been relatively nonexistent. Without documentation, performance improvement of prehospital care and evacuation through data collection, consolidation, and scientific analyses cannot be adequately accomplished. During recent conflicts, prehospital documentation has received increased attention for point-of-injury care as well as for care provided en route on medical evacuation platforms. However, documentation on casualty evacuation (CASEVAC) platforms is still lacking. Thus, a CASEVAC dataset was developed and maintained by the 160th Special Operations Aviation Regiment (SOAR), a nonmedical, rotary-wing aviation unit, to evaluate and review CASEVAC missions conducted by their organization.

METHODS

A retrospective review and descriptive analysis were performed on data from all documented CASEVAC missions conducted in Afghanistan by the 160th SOAR from January 2008 to May 2015. Documentation of care was originally performed in a narrative after-action review (AAR) format. Unclassified, nonpersonally identifiable data were extracted and transferred from these AARs into a database for detailed analysis. Data points included demographics, flight time, provider number and type, injury and outcome details, and medical interventions provided by ground forces and CASEVAC personnel.

RESULTS

There were 227 patients transported during 129 CASEVAC missions conducted by the 160th SOAR. Three patients had unavailable data, four had unknown injuries or illnesses, and eight were military working dogs. Remaining were 207 trauma casualties (96%) and five medical patients (2%). The mean and median times of flight from the injury scene to hospital arrival were less than 20 minutes. Of trauma casualties, most were male US and coalition forces (n = 178; 86%). From this population, injuries to the extremities (n = 139; 67%) were seen most commonly. The primary mechanisms of injury were gunshot wound (n = 89; 43%) and blast injury (n = 82; 40%). The survival rate was 85% (n = 176) for those who incurred trauma. Of those who did not survive, most died before reaching surgical care (26 of 31; 84%).

CONCLUSION

Performance improvement efforts directed toward prehospital combat casualty care can ameliorate survival on the battlefield. Because documentation of care is essential for conducting performance improvement, medical and nonmedical units must dedicate time and efforts accordingly. Capturing and analyzing data from combat missions can help refine tactics, techniques, and procedures and more accurately define wartime personnel, training, and equipment requirements. This study is an example of how performance improvement can be initiated by a nonmedical unit conducting CASEVAC missions.

Time to epinephrine in out-of-hospital cardiac arrest: A retrospective analysis of intraosseous versus intravenous access

INTRODUCTION

The 2015 advanced cardiac life support update continues to advocate administering epinephrine during cardiac arrest. The goal of our study is to determine if prehospital intraosseous (IO) access results in shorter time to epinephrine than prehospital peripheral intravenous (PIV) access.

METHODS

The out-of-hospital cardiac arrest (OHCA) database of a large, urban, fire-based emergency medical services system was searched for consecutive cases of OHCA between January 2013 and December 2015. The time to the first dose of epinephrine was calculated and compared by vascular access technique utilized (PIV or IO). Descriptive statistics were used to report first pass success and IO complications.

RESULTS

A total of 3,470 OHCA cases were treated during the study period. Of those cases, 2,656 met our inclusion criteria. There were 2,601 cases of IO usage and 55 cases of PIV usage. The mean time from arrival at the patient's side to administration of the first dose of epinephrine was 5.0 minutes (95% CI: 4.7 minutes, 5.4 minutes) for the IO group and 8.8 minutes (95% CI: 6.6 minutes, 10.9 minutes) for the PIV group (p<0.001). There were a total of 2,879 IO attempts with 2,753 IOs successfully placed in 2,601 patients. The first pass IO success rate was 95.6 percent (2,753/2,879).

CONCLUSION

In the setting of OHCA, the time to administer the first dose of epinephrine was faster in the IO access group when compared to PIV access group. The prehospital use of IO vascular access for time-dependent medical conditions is recommended.

Dual defibrillation in out-of-hospital cardiac arrest: A retrospective cohort analysis

STUDY OBJECTIVES

The goal of our study is to determine if prehospital dual defibrillation (DD) is associated with better neurologically intact survival in out-of-hospital cardiac arrest.

METHODS

This study is a retrospective cohort analysis of prospectively collected Quality Assurance/Quality Improvement data from a large urban fire based EMS system out-of-hospital cardiac arrest (OHCA) database between Jan 2013 and Dec 2015. Our inclusion criteria were administration of DD or at least four conventional 200J defibrillations for cases of recurrent and refractory ventricular fibrillation (VF). We excluded any case with incomplete data. The primary outcome for our study was neurologically intact survival (defined as Cerebral Performance Category 1 and 2).

RESULTS

A total of 3470 cases of OHCA were treated during the time period of Jan 2013 to Dec 2015. There were 302 cases of recurrent and refractory VF identified. Twenty-three cases had incomplete data. Of the remaining 279 cases, 50 were treated with DD and 229 received standard single shock 200J defibrillations. There was no statistically significant difference in the primary outcome of neurologically intact survival between the DD group (6%) and the standard defibrillation group (11.4%) (p=0.317) (OR 0.50, 95% CI 0.15-1.72).

CONCLUSION

Our retrospective cohort analysis on the prehospital use of DD in OHCA found no association with neurologically intact survival. Case-control studies are needed to further evaluate the efficacy of DD in the prehospital setting.

Operational Point-of-Care Ultrasound Review: Low-Cost Simulators and Resources for Advanced Prehospital Providers

Prehospital ultrasound use is a relatively new skill set. The military noted the clear advantages of this skill set in the deployed setting and moved forward with teaching their advanced combat trauma medics skills to perform specific examinations. The training curriculum for Special Operations-level clinical ultrasound was created and adapted from training guidelines set forth by the American College of Emergency Physicians with a focus on the examinations relevant to the Special Operations community. Once providers leave the training environment, skill sustainment can be difficult. We discuss the relevant ultrasound exams for the prehospital setting. We address opportunities to improve point-of-care ultrasound skills through hands-on experience while in a fixed medical facility. Options for simulation-based training are discussed with descriptions for creating low-cost simulation models. Finally, a list of online resources is provided to review specific ultrasound examinations.

Low-fidelity hybrid sexual assault simulation training's effect on the comfort and competency of resident physicians

BACKGROUND

Alternative training methods are needed for resident physicians to ensure that care is not compromised should they practice in settings without well-established Sexual Assault Nurse Examiner (SANE) programs.

OBJECTIVE

The purpose of this study is to determine the effectiveness of a simulation-based sexual assault response course for resident physicians at an institution without an on-site SANE program.

METHODS

Educational intervention study of 12 emergency medicine residents using a low-fidelity hybrid simulation model. The study was comprised of eight male and four female physicians at a military medical center in San Diego, CA. Assessment occurred using three separate metrics. The first was a written knowledge test. The second was a simulated interview and evidentiary examination. These metrics were given 1 month before and 3 months after an 8-h training course. The final metric was Likert-scale questionnaires surveying pre- and post-course feelings of competency and comfort.

RESULTS

The emergency medicine residents showed a 13% improvement (95% confidence interval [CI] 7-20%) in written examination scores pre and post intervention. Post-course interview and examinations reflected a 44% improvement (95% CI 24-64%) in critical action completion. Pre-course comfort and competency questionnaires were a median of 2 (interquartile range [IQR] 1-3) on a Likert Scale. Post-course survey responses were a median of 4 (IQR 2-5).

CONCLUSIONS

Low-fidelity hybrid simulation is a useful tool to train inexperienced physicians to perform evidentiary examinations and interviews without sacrificing the privacy and direct care of sexual assault victims.

Measuring arterial oxygenation in a high altitude field environment: comparing portable pulse oximetry with blood gas analysis

OBJECTIVE

High altitude environments present unique medical treatment challenges. Medical providers often use small portable pulse oximetry devices to help guide their clinical decision making. A significant body of high altitude research is based on the use of these devices to monitor hypoxia, yet there is a paucity of evidence that these devices are accurate in these environments. We studied whether these devices perform accurately and reliably under true mountain conditions.

METHODS

Healthy unacclimatized active-duty military volunteers participating in mountain warfare training at 2100 m (6900 feet) above sea level were evaluated with several different pulse oximetry devices while in a cold weather, high altitude field environment and then had arterial blood gases (ABG) drawn using an i-STAT for comparison. The pulse oximeter readings were compared with the gold standard ABG readings.

RESULTS

A total of 49 individuals completed the study. There was no statistically significant difference between any of the devices and the gold standard of ABG. The best performing device was the PalmSAT (PS) 8000SM finger probe with a mean difference of 2.17% and SD of 2.56 (95% CI, 1.42% to 2.92%). In decreasing order of performance were the PS 8000AA finger probe (mean ± SD, 2.54% ± 2.68%; 95% CI, 1.76% to 3.32%), the PS 8000Q ear probe (2.47% ± 4.36%; 95% CI, 1.21% to 3.75%), the Nonin Onyx 9500 (3.29% ± 3.12%; 95% CI, 2.39% to 4.20%), and finally the PS 8000R forehead reflectance sensor (5.15% ± 2.97%; 95% CI, 4.28% to 6.01%).

CONCLUSIONS

Based on the results of this study, results of the newer portable pulse oximeters appear to be closely correlated to that of the ABG measurements when tested in true mountain conditions.

Human herpesviruses-6 and -7 each cause significant neurological morbidity in Britain and Ireland

BACKGROUND

Primary human herpesvirus-6 and -7 (HHV-6/-7) infections cause febrile illness sometimes complicated by convulsions and rarely encephalopathy.

AIMS

To explore the extent of such HHV-6 and -7 induced disease in young children.

METHODS

In a three year prospective study in Britain and Ireland, 205 children (2-35 months old) hospitalised with suspected encephalitis and/or severe illness with fever and convulsions were reported via the British Paediatric Surveillance Unit network. Blood samples were tested for primary HHV-6 and -7 infections.

RESULTS

26/156 (17%) of children aged 2-23 months had primary infection (11 HHV-6; 13 HHV-7; two with both viruses) coinciding with the acute illness; this was much higher than the about three cases expected by chance. All 26 were pyrexial; 25 had convulsions (18 status epilepticus), 11 requiring ventilation. Median hospital stay was 7.5 days. For HHV-6 primary infection the median age was 53 weeks (range 42-94) and the distribution differed from that of uninfected children; for HHV-7, the median was 60 weeks (range 17-102) and the distribution did not differ for the uninfected. Fewer (5/15) children with primary HHV-7 infection had previously been infected with HHV-6 than expected.

CONCLUSIONS

Primary HHV-6 and HHV-7 infections accounted for a significant proportion of cases in those <2 years old of severe illness with fever and convulsions requiring hospital admission; each virus contributed equally. Predisposing factors are age for HHV-6 and no previous infection with HHV-6 for HHV-7. Children with such neurological disease should be investigated for primary HHV-6/-7 infections, especially in rare cases coinciding by chance with immunisation to exclude misdiagnosis as vaccine reactions.

RGSZ1 and Ret RGS: two of several splice variants from the gene RGS20

RGSZ1 and Ret RGS, members of the regulator of G-protein signaling (RGS) family, are GTPase-activating proteins (GAPs) with high selectivity for G alpha(z). We show here that RGSZ1 and Ret RGSZ1 are products of two of several splice variants of one gene, RGS20. RGS20 spans approximately 107 kb and contains at least seven exons. Five exons account for RGSZ1, including a single exon distinct to RGSZ1 that encodes a newly identified amino-terminal region. The previously described open reading frame (ORF) and 3' untranslated region are encoded by four downstream exons that also encode about half of Ret RGS. The 5' end of the RGSZ1 ORF contains several in-frame ATG codons (3-5 depending on the species), and multiple translational start sites may help explain the molecular weight heterogeneity of purified bovine brain RGSZ. Ret RGS replaces the 24 N-terminal amino acid residues of RGSZ1 with a large, N-terminal region that initially distinguished the bovine Ret RGS from human and mouse RGSZ1. This N-terminal domain is encoded by two distinct 5' exons that are variably combined with the four downstream exons shared with RGSZ1 to produce at least six mRNAs. They encode proteins with N termini that vary in size, hydrophobicity, and the presence of a cysteine string. At least two mRNAs that include the exon that encodes the N-terminal region unique to RGSZ1 were found in brain and a few other tissues, but not retina. RGS20 thus can account for multiple G(z)-selective GAPs in different tissues.

Binding of regulator of G protein signaling (RGS) proteins to phospholipid bilayers. Contribution of location and/or orientation to Gtpase-activating protein activity

Regulator of G protein signaling (RGS) proteins must bind membranes in an orientation that permits the protein-protein interactions necessary for regulatory activity. RGS4 binds to phospholipid surfaces in a slow, multistep process that leads to maximal GTPase-activating protein (GAP) activity. When RGS4 is added to phospholipid vesicles that contain m2 or m1 muscarinic receptor and G(i), G(z), or G(q), GAP activity increases approximately 3-fold over 4 h at 30 degrees C and more slowly at 20 degrees C. This increase in GAP activity is preceded by several other events that suggest that, after binding, optimal interaction with G protein and receptor requires reorientation of RGS4 on the membrane surface, a conformational change, or both. Binding of RGS4 is initially reversible but becomes irreversible within 5 min. Onset of irreversibility parallels initial quenching of tryptophan fluorescence (t(12) approximately 30 s). Further quenching occurs after binding has become irreversible (t(12) approximately 6 min) but is complete well before maximal GAP activity is attained. These processes all appear to be energetically driven by the amphipathic N-terminal domain of RGS4 and are accelerated by palmitoylation of cysteine residues in this region. The RGS4 N-terminal domain confers similar membrane binding behavior on the RGS domains of either RGS10 or RGSZ1.

GTPase-activating proteins for heterotrimeric G proteins: regulators of G protein signaling (RGS) and RGS-like proteins

GTPase-activating proteins (GAPs) regulate heterotrimeric G proteins by increasing the rates at which their subunits hydrolyze bound GTP and thus return to the inactive state. G protein GAPs act allosterically on G subunits, in contrast to GAPs for the Ras-like monomeric GTP-binding proteins. Although they do not contribute directly to the chemistry of GTP hydrolysis, G protein GAPs can accelerate hydrolysis >2000-fold. G protein GAPs include both effector proteins (phospholipase C-¿, p115RhoGEF) and a growing family of regulators of G protein signaling (RGS proteins) that are found throughout the animal and fungal kingdoms. GAP activity can sharpen the termination of a signal upon removal of stimulus, attenuate a signal either as a feedback inhibitor or in response to a second input, promote regulatory association of other proteins, or redirect signaling within a G protein signaling network. GAPs are regulated by various controls of their cellular concentrations, by complex interactions with G¿ or with G¿5 through an endogenous G-like domain, and by interaction with multiple other proteins.

Palmitoylation of a conserved cysteine in the regulator of G protein signaling (RGS) domain modulates the GTPase-activating activity of RGS4 and RGS10

RGS4 and RGS10 expressed in Sf9 cells are palmitoylated at a conserved Cys residue (Cys(95) in RGS4, Cys(66) in RGS10) in the regulator of G protein signaling (RGS) domain that is also autopalmitoylated when the purified proteins are incubated with palmitoyl-CoA. RGS4 also autopalmitoylates at a previously identified cellular palmitoylation site, either Cys(2) or Cys(12). The C2A/C12A mutation essentially eliminates both autopalmitoylation and cellular [(3)H]palmitate labeling of Cys(95). Membrane-bound RGS4 is palmitoylated both at Cys(95) and Cys(2/12), but cytosolic RGS4 is not palmitoylated. RGS4 and RGS10 are GTPase-activating proteins (GAPs) for the G(i) and G(q) families of G proteins. Palmitoylation of Cys(95) on RGS4 or Cys(66) on RGS10 inhibits GAP activity 80-100% toward either Galpha(i) or Galpha(z) in a single-turnover, solution-based assay. In contrast, when GAP activity was assayed as acceleration of steady-state GTPase in receptor-G protein proteoliposomes, palmitoylation of RGS10 potentiated GAP activity >/=20-fold. Palmitoylation near the N terminus of C95V RGS4 did not alter GAP activity toward soluble Galpha(z) and increased G(z) GAP activity about 2-fold in the vesicle-based assay. Dual palmitoylation of wild-type RGS4 remained inhibitory. RGS protein palmitoylation is thus multi-site, complex in its control, and either inhibitory or stimulatory depending on the RGS protein and its sites of palmitoylation.

Reciprocal signaling between heterotrimeric G proteins and the p21-stimulated protein kinase

p21-activated protein kinase (PAK)-1 phosphorylated Galpha(z), a member of the Galpha(i) family that is found in the brain, platelets, and adrenal medulla. Phosphorylation approached 1 mol of phosphate/mol of Galpha(z) in vitro. In transfected cells, Galpha(z) was phosphorylated both by wild-type PAK1 when stimulated by the GTP-binding protein Rac1 and by constitutively active PAK1 mutants. In vitro, phosphorylation occurred only at Ser(16), one of two Ser residues that are the major substrate sites for protein kinase C (PKC). PAK1 did not phosphorylate other Galpha subunits (i1, i2, i3, o, s, or q). PAK1-phosphorylated Galpha(z) was resistant both to RGSZ1, a G(z)-selective GTPase-activating protein (GAP), and to RGS4, a relatively nonselective GAP for the G(i) and G(q) families of G proteins. Phosphorylation of Ser(27) by PKC did not alter sensitivity to either GAP. The previously described inhibition of G(z) GAPs by PKC is therefore mediated by phosphorylation of Ser(16). Phosphorylation of either Ser(16) by PAK1 or Ser(27) by PKC decreased the affinity of Galpha(z) for Gbetagamma; phosphorylation of both residues by PKC caused no further effect. PAK1 thus regulates Galpha(z) function by attenuating the inhibitory effects of both GAPs and Gbetagamma. In this context, the kinase activity of PAK1 toward several protein substrates was directly inhibited by Gbetagamma, suggesting that PAK1 acts as a Gbetagamma-regulated effector protein. This inhibition of mammalian PAK1 by Gbetagamma contrasts with the stimulation of the PAK homolog Ste20p in Saccharomyces cerevisiae by the Gbetagamma homolog Ste4p/Ste18p.

Rapid GTP binding and hydrolysis by G(q) promoted by receptor and GTPase-activating proteins

Receptor-promoted GTP binding and GTPase-activating protein (GAP)-promoted GTP hydrolysis determine the onset and termination of G protein signaling; they coordinately control signal amplitude. The mechanisms whereby cells independently regulate signal kinetics and signal amplitude are therefore central to understanding G protein function. We have used quench-flow kinetic methods to measure the rates of the individual reactions of the agonist-stimulated GTPase cycle for G(q) during steady-state signaling. G(q) and m1 muscarinic cholinergic receptor were co-reconstituted into proteoliposomes with one of two GAPs: phospholipase C (PLC)-beta1, the major G(q)-regulated effector protein, and RGS4, a GAP commonly thought to be an inhibitor of G(q) signaling. In this system, the rate constant for GAP-stimulated hydrolysis of Galpha(q)-bound GTP at 30 degrees C was 9-12 s(-1) for PLC-beta1 and 22-27 s(-1) for RGS4. These rates are 1,000- to 2,000-fold faster than in the absence of a GAP and far faster than measured previously. G(q) can thus hydrolyze bound GTP with deactivation half-times of 25-75 ms at 30 degrees C, commensurate with physiological rates of signal termination. GDP/GTP exchange, which reactivates G(q), was the principal rate-limiting step for the GTPase cycle and was also faster than previously thought. At physiological concentrations of GTP, exchange was limited by the rate of dissociation of GDP from the receptor-G(q) complex, with a maximal rate of 1.8 s(-1) at 30 degrees C. Comparison of activation and deactivation rates help explain how GDP/GTP exchange balance rapid GTP hydrolysis to maintain steady-state signal amplitude.

Individualizing therapy to prevent long-term consequences of estrogen deficiency in postmenopausal women

BACKGROUND

Alendronate sodium and raloxifene hydrochloride were recently approved for the prevention of postmenopausal osteoporosis, but data on their clinical efficacy are limited. We compared these drugs with hormone replacement therapy (HRT) to help women and physicians guide postmenopausal treatment decisions.

OBJECTIVE

To help physicians understand how they can best help women choose the most beneficial therapy after menopause based on their individual risk profile.

METHODS

We developed a decision analytic Markov model to compare the effects of alendronate therapy, raloxifene therapy, and HRT on risks of hip fracture, coronary heart disease (CHD), breast cancer, and life expectancy. Regression models linked individual risk factors to future disease risks and were modified by drug effects on bone density, lipid levels, and associated breast cancer effects.

RESULTS

Hormone replacement therapy, alendronate therapy, and raloxifene therapy have similar predicted efficacies in preventing hip fractures (estimated relative risk, 0.57, 0.54, and 0.58, respectively). Hormone replacement therapy should be more than 10 times more effective than raloxifene therapy in preventing CHD, but raloxifene therapy may not induce breast cancer. Women at low risk for hip fracture, CHD, and breast cancer do not benefit significantly from any treatment. Among women at average risk, HRT was preferred unless raloxifene therapy could reduce the risk of breast cancer by at least 66%, compared with a 47% increase for HRT. Women at high risk for CHD benefit most from HRT; women at high risk for breast cancer but low risk for CHD benefit most from raloxifene therapy, but only if it lowers the risk of breast cancer.

CONCLUSION

Because of significant differences in the impact of these drugs, treatment choice depends on an individual woman's risk for hip fracture, CHD, and breast cancer.

Phospholipase C-beta1 directly accelerates GTP hydrolysis by Galphaq and acceleration is inhibited by Gbeta gamma subunits

Phospholipase C-beta, the principal effector protein regulated by Galphaq, has been shown to increase the agonist-stimulated, steady-state GTPase activity of Gq in proteoliposomes that contain both heterotrimeric Gq and m1 muscarinic receptor. We now use a moderately stable complex of R183C Galphaq bound to GTP to show that PLC-beta1 acts directly as a GTPase-activating protein (GAP) for isolated Galphaq in a membrane-free system. PLC-beta1 accelerated the hydrolysis of GalphaqR183C.GTP up to 20-fold. The Km was 1.5 nM, which is similar both to the EC50 with which R183C and wild type Galphaq activate PLC-beta1 and to the EC50 with which PLC-beta1 acts as a Gq GAP in the vesicle-based assay. The Galphaq GAP activity of RGS4 can also be quantitated by this assay; it accelerated hydrolysis of bound GTP about 100-fold. The Gq GAP activities of both PLC-beta1 and RGS4 are blocked by Gbeta gamma subunits, probably by a competitive mechanism. These data suggest either that the Gbeta gamma subunits are not continuously required for receptor-catalyzed GDP/GTP exchange during steady-state GTP hydrolysis or that GAPs, either PLC-beta or RGS proteins, can substitute for Gbeta gamma in this set of reactions.

Kinetic control of guanine nucleotide binding to soluble Galpha(q)

Binding of guanine nucleotides to heterotrimeric G proteins is controlled primarily by kinetic factors, such as the release of bound GDP, rather than by affinity alone. Detergent-solubilized Galpha(q) displays unusual guanine nucleotide binding properties in comparison with other G protein alpha subunits. Under conditions where most G proteins bind nearly stoichiometric GTPgammaS in 5-30 min at micromolar nucleotide concentrations, GTPgammaS binding to Galpha(q) is slow (>1 hr to completion), markedly substoichiometric, and dependent upon high concentrations of nucleotide (0.1 to 0.2 mM). Although the latter two properties suggest low affinity, GTPgammaS dissociation is immeasurably slow under commonly used conditions. We found that purified Galpha(q) can bind stoichiometric GTPgammaS, but that binding is controlled kinetically by a combination of factors. GDP (or IDP) dissociated slowly from Galpha(q), but the dissociation rate increased linearly with the concentration of (NH4)2SO4 up to 0.75 M (approximately 20-fold acceleration). The resulting GDP-free Galpha(q) was labile to rapid and irreversible denaturation, however (rate constant > or = 1 min(-1) at 20 degrees). Denaturation competed kinetically with relatively slow GTPgammaS association, such that stoichiometric binding was only attained at 100 microM GTPgammaS. These findings reconcile the slowly reversible binding of GTPgammaS to Galpha(q) with the other behaviors that suggested lower affinity, and point out that events subsequent to GDP dissociation can markedly influence the rates and extents of guanine nucleotide binding to G protein alpha subunits. Understanding these interactions allowed the direct, accurate quantitation of active Galpha(q) by a simple GTPgammaS binding assay in the presence of (NH4)2SO4, and similarly can prevent underestimation of the concentrations of other G proteins.

Modulation of the affinity and selectivity of RGS protein interaction with G alpha subunits by a conserved asparagine/serine residue

The crystal structure of the complex between a G protein alpha subunit (Gi alpha 1) and its GTPase-activating protein (RGS4) demonstrated that RGS4 acts predominantly by stabilization of the transition state for GTP hydrolysis [Tesmer, J. J., et al. (1997) Cell 89, 251]. However, attention was called to a conserved Asn residue (Asn128) that could play a catalytic role by interacting, directly or indirectly, with the hydrolytic water molecule. We have analyzed the effects of several disparate substitutions for Asn128 on the GAP activity of RGS4 toward four G alpha substrates (Go, Gi, Gq, and Gz) using two assay formats. The results substantiate the importance of this residue but indicate that it is largely involved in substrate binding and that its function may vary with different G alpha targets. Various mutations decreased the apparent affinity of RGS4 for substrate G alpha proteins by several orders of magnitude, but had variable and modest effects on maximal rates of GTP hydrolysis when tested with different G alpha subunits. One mutation, N128F, that differentially decreased the GAP activity toward G alpha i compared with that toward G alpha q could be partially suppressed by mutation of the nearby residue in G alpha i to that found in G alpha q (K180P). Detection of GAP activities of the mutants was enhanced in sensitivity up to 100-fold by assay at steady state in proteoliposomes that contain heterotrimeric G protein and receptor.

Fitting nutrition into the medical model: the role of decision analytic cost-effectiveness techniques

Physicians are accustomed to making decisions based on information regarding the prevalence of disease, symptoms, physical signs, laboratory test results, and the risks and benefits of alternative treatments. If nutritional assessment and therapeutics are to become more common components of medical practice, significant barriers in each of these areas must be overcome. Even rudimentary dietary assessment is often missing from physician education. Dietary assessment tools that are readily available and that have demonstrated usefulness are largely unknown. In addition, many nutritional interventions have not been formally investigated in randomized, controlled trials, and thus their cost-effectiveness remains unknown. We present one approach to these issues by discussing the construction of a decision model examining strategies for vitamin D and calcium screening. The application of medical decision making techniques to problems in clinical nutrition illustrates how findings from research studies may be used to determine the risks, benefits and costs of alternative population based health related nutrition policies which can then be applied by physicians in their daily interactions with patients.

The N-terminal domain of RGS4 confers receptor-selective inhibition of G protein signaling

Regulators of heterotrimeric G protein signaling (RGS) proteins are GTPase-activating proteins (GAPs) that accelerate GTP hydrolysis by Gq and Gi alpha subunits, thus attenuating signaling. Mechanisms that provide more precise regulatory specificity have been elusive. We report here that an N-terminal domain of RGS4 discriminated among receptor signaling complexes coupled via Gq. Accordingly, deletion of the N-terminal domain of RGS4 eliminated receptor selectivity and reduced potency by 10(4)-fold. Receptor selectivity and potency of inhibition were partially restored when the RGS4 box was added together with an N-terminal peptide. In vitro reconstitution experiments also indicated that sequences flanking the RGS4 box were essential for high potency GAP activity. Thus, RGS4 regulates Gq class signaling by the combined action of two domains: 1) the RGS box accelerates GTP hydrolysis by Galphaq and 2) the N terminus conveys high affinity and receptor-selective inhibition. These activities are each required for receptor selectivity and high potency inhibition of receptor-coupled Gq signaling.

RGSZ1, a Gz-selective RGS protein in brain. Structure, membrane association, regulation by Galphaz phosphorylation, and relationship to a Gz gtpase-activating protein subfamily

We cloned the cDNA for human RGSZ1, the major Gz-selective GTPase-activating protein (GAP) in brain (Wang, J., Tu, Y., Woodson, J., Song, X., and Ross, E. M. (1997) J. Biol. Chem. 272, 5732-5740) and a member of the RGS family of G protein GAPs. Its sequence is 83% identical to RET-RGS1 (except its N-terminal extension) and 56% identical to GAIP. Purified, recombinant RGSZ1, RET-RGS1, and GAIP each accelerated the hydrolysis of Galphaz-GTP over 400-fold with Km values of approximately 2 nM. RGSZ1 was 100-fold selective for Galphaz over Galphai, unusually specific among RGS proteins. Other enzymological properties of RGSZ1, brain Gz GAP, and RET-RGS1 were identical; GAIP differed only in Mg2+ dependence and in its slightly lower selectivity for Galphaz. RGSZ1, RET-RGS1, and GAIP thus define a subfamily of Gz GAPs within the RGS proteins. RGSZ1 has no obvious membrane-spanning region but is tightly membrane-bound in brain. Its regulatory activity in membranes depends on stable bilayer association. When co-reconstituted into phospholipid vesicles with Gz and m2 muscarinic receptors, RGSZ1 increased agonist-stimulated GTPase >15-fold with EC50 <12 nM, but RGSZ1 added to the vesicle suspension was <0.1% as active. RGSZ1, RET-RGS1, and GAIP share a cysteine string sequence, perhaps targeting them to secretory vesicles and allowing them to participate in the proposed control of secretion by Gz. Phosphorylation of Galphaz by protein kinase C inhibited the GAP activity of RGSZ1 and other RGS proteins, providing a mechanism for potentiation of Gz signaling by protein kinase C.

Dynamic regulation of RGS2 suggests a novel mechanism in G-protein signaling and neuronal plasticity

Long-term neuronal plasticity is known to be dependent on rapid de novo synthesis of mRNA and protein, and recent studies provide insight into the molecules involved in this response. Here, we demonstrate that mRNA encoding a member of the regulator of G-protein signaling (RGS) family, RGS2, is rapidly induced in neurons of the hippocampus, cortex, and striatum in response to stimuli that evoke plasticity. Although several members of the RGS family are expressed in brain with discrete neuronal localizations, RGS2 appears unique in that its expression is dynamically responsive to neuronal activity. In biochemical assays, RGS2 stimulates the GTPase activity of the alpha subunit of Gq and Gi1. The effect on Gi1 was observed only after reconstitution of the protein in phospholipid vesicles containing M2 muscarinic acetylcholine receptors. RGS2 also inhibits both Gq- and Gi-dependent responses in transfected cells. These studies suggest a novel mechanism linking neuronal activity and signal transduction.

PDZ domain proteins: scaffolds for signaling complexes

InaD, a Drosophila photoreceptor scaffolding protein, assembles multiple signal-transducing proteins at the membrane via its five PDZ domains, enhancing speed and efficiency of vision. Extensive conservation of PDZ domains suggests that these motifs have a general role in organizing diverse signaling complexes.

Inhibition of brain Gz GAP and other RGS proteins by palmitoylation of G protein alpha subunits

Palmitoylation of the alpha subunit of the guanine nucleotide-binding protein Gz inhibited by more than 90 percent its response to the guanosine triphosphatase (GTPase)-accelerating activity of Gz GAP, a Gz-selective member of the regulators of G-protein signaling (RGS) protein family of GTPase-activating proteins (GAPs). Palmitoylation both decreased the affinity of Gz GAP for the GTP-bound form of Galphaz by at least 90 percent and decreased the maximum rate of GTP hydrolysis. Inhibition was reversed by removal of the palmitoyl group by dithiothreitol. Palmitoylation of Galphaz also inhibited its response to the GAP activity of Galpha-interacting protein (GAIP), another RGS protein, and palmitoylation of Galphai1 inhibited its response to RGS4. The extent of inhibition of Gz GAP, GAIP, RGS4, and RGS10 correlated roughly with their intrinsic GAP activities for the Galpha target used in the assay. Reversible palmitoylation is thus a major determinant of Gz deactivation after its stimulation by receptors, and may be a general mechanism for prolonging or potentiating G-protein signaling.

Expression of human muscarinic cholinergic receptors in tobacco

We expressed human m1, m2 and chimeric muscarinic cholinergic receptors (MAChR) in tobacco plants and in cultured BY2 tobacco cells using Agrobacterium-mediated transformation. The membranes of most transgenic plants and calli bound muscarinic ligands with appropriate affinities, kinetics and pharmacologic specificity, as determined by direct and competitive binding measurements using the muscarinic ligand [3H]quinuclidinyl benzylate (QNB). Membranes of untransformed plants and calli or those transformed with vector alone did not bind [3H]QNB. Preliminary experiments did not suggest regulation of endogenous plant G protein signalling pathways by the recombinant receptors. Membranes from one callus clone expressed m1 MAChR at the level of 2.0-2.5 pmol [3H]QNB bound per mg membrane protein, more than the number of m1 MAChR in mammalian brain and comparable to that expressed in Sf9 insect cells using baculovirus vectors. This work demonstrates high level expression of active G protein-coupled receptors in plants, such that signaling might be genetically reconstituted by co-expression of appropriate G proteins and effectors.

Patient-specific decisions about hormone replacement therapy in postmenopausal women

OBJECTIVE

To examine the effect of hormone replacement therapy on life expectancy in postmenopausal women with different risk profiles for heart disease, breast cancer, and hip fracture.

DESIGN

Decision analysis using a Markov model. Published regression models were used to link risk factors to disease incidence and to estimate the lifetime risks of developing coronary heart disease (CHD), breast cancer, hip fracture, and endometrial cancer. The impact of hormone therapy on disease incidence was estimated from published epidemiologic studies.

SETTING

Mathematical model applicable to primary care.

INTERVENTIONS

Treatment with hormone replacement therapy or no hormone replacement therapy.

MAIN OUTCOME MEASURE

Life expectancy.

RESULTS

Hormone replacement therapy should increase life expectancy for nearly all postmenopausal women, with some gains exceeding 3 years, depending mainly on an individual's risk factors for CHD and breast cancer. For women with at least 1 risk factor for CHD, hormone therapy should extend life expectancy, even for women having first-degree relatives with breast cancer. Women without any risk factors for CHD or hip fracture, but who have 2 first-degree relatives with breast cancer, however, should not receive hormone therapy.

CONCLUSIONS

The benefit of hormone replacement therapy in reducing the likelihood of developing CHD appears to outweigh the risk of breast cancer for nearly all women in whom this treatment might be considered. Our analysis supports the broader use of hormone replacement therapy.

A Gs-selective analog of the receptor-mimetic peptide mastoparan binds to Gs alpha in a kinked helical conformation

Mastoparan, a 14-residue peptide, stimulates GDP/GTP exchange on G proteins in a manner strikingly analogous to that of agonist-bound receptors. Presumably, the peptide structurally mimics a receptor's G protein-binding domain. We previously reported that mastoparan-X binds to alpha-subunits of Gi and Go in a predominantly alpha-helical conformation [Sukumar, M., & Higashijima, T. (1992) J. Biol. Chem. 267, 21421-21424]. We have now developed an analogous peptide, INWKGIASM-alpha-aminoisobutyryl (Aib)-RQVL-NH2 (MP-S), which is a selective activator of Gs. We report the conformation of MP-S when it is bound to Gs alpha, determined from distance geometry calculations based on transferred nuclear Overhauser effects (TRNOEs). The Gs-bound conformation of MP-S is an alpha-helix that is kinked at residue 9. The conformations of MP-S when bound to Gi alpha or Go alpha are similar to the Gs alpha-bound conformation. In contrast, the lipid-bound conformation of MP-S is a straight helix. On the basis of the Gs-bound conformation of MP-S, directions for the design of Gs-selective peptidergic mimics of receptors are suggested.

A GTPase-activating protein for the G protein Galphaz. Identification, purification, and mechanism of action

A GTPase-activating protein (GAP) specific for Galphaz was identified in brain, spleen, retina, platelet, C6 glioma cells, and several other tissues and cells. Gz GAP from bovine brain is a membrane protein that is refractory to solubilization with most detergents but was solubilized with warm Triton X-100 and purified up to 50,000-fold. Activity is associated with at least two separate proteins of Mr approximately 22,000 and 28,000, both of which have similar specific activities. In an assay that measures the rate of hydrolysis of GTP pre-bound to detergent-soluble Galphaz, the GAP accelerates hydrolysis over 200-fold, from 0.014 to 3 min -1 at 15 degrees C, or to >/=20 min-1 at 30 degrees C. It does not alter rates of nucleotide association or dissociation. When co-reconstituted into phospholipid vesicles with trimeric Gz and m2 muscarinic receptor, Gz GAP accelerates agonist-stimulated steady-state GTP hydrolysis as predicted by its effect on the hydrolytic reaction. In the single turnover assay, the Km of the GAP for Galphaz-GTP is 2 nM. Its activity is inhibited by Galphaz-guanosine 5'-O-thiotriphosphate (Galphaz-GTPgammaS) or by Galphaz-GDP/AlF4 with Ki approximately 1.5 nM for both species; Galphaz-GDP does not inhibit. G protein betagamma subunits inhibit Gz GAP activity, apparently by forming a GTP-Galphazbetagamma complex that is a poor GAP substrate. Gz GAP displays little GAP activity toward Galphai1 or Galphao, but its activity with Galphaz is competitively inhibited by both Galphai1 and Galphao at nanomolar concentrations when they are bound to GTPgammaS but not to GDP. Neither phospholipase C-beta1 (a Gq GAP) nor several adenylyl cyclase isoforms display Gz GAP activity.

Carboxyl-terminal fragments of phospholipase C-beta1 with intrinsic Gq GTPase-activating protein (GAP) activity

Fragments of the approximately 50 kDa COOH-terminal region of phospholipase C-beta1 (PLC-beta1(1)), ranging in size from 14 to 38 kDa, were expressed in Escherichia coli, purified, and tested for their regulatory activities. As expected, none of the fragments had phospholipase activity. Several fragments, referred to as PLC tails, displayed GTPase-activating protein (GAP) activity for Gq, the G protein class that stimulates the PLC-betas in response to receptors. Gq GAP activity is characteristic of intact PLC-betas. In reconstituted phospholipid vesicles that contained purified Gq and m1 muscarinic cholinergic receptors, the most active tails increased agonist-stimulated, steady-state GTPase activity over 4-fold. Stimulation of steady-state GTPase by the tails depended on receptors for facilitation of GDP-GTP exchange, suggesting that the tails act by accelerating hydrolysis of bound GTP. In addition to intrinsic GAP activity, one tail with high GAP activity and others with low or minimal activity potentiated the GAP activity of intact PLC-beta1. Other tails inhibited PLC-beta1s GAP effect. Both intrinsic GAP activity and potentiation of the PLC-beta1 GAP effect were often biphasic, with maxima as low as 100 nM tail and declining activities at higher concentrations. Several tails inhibited either the phospholipase activity of PLC-beta1, its stimulation by Gq, or both. The tails thus define the region of PLC-beta1 that has Gq GAP activity and suggest a mechanism of action in which the COOH terminus of PLC-betas can interact with Gq and with other PLC-beta1 molecules.

Purification and characterization of phospholipase C-beta 1 mutants expressed in E. coli

In the M1-muscarinic receptor-Gq-phospholipase C-beta 1 (PLC-beta 1) pathway, PLC-beta 1 is both the effector regulated by Gq and acts as GTPase activating protein (GAP) for Gq. To rapidly evaluate in vitro PLC-beta 1 mutants constructed by oligonucleotide-directed mutagenesis, we established a quick expression and purification procedure. A pQE60/His6PLC-beta 1 construct was expressed in E. coli SG13009[pREP4]. Purification (approximately 160-fold) was obtained after high-salt extraction and chromatography over Ni(+)-agarose, Mono Q and Mono S columns. Several His6PLC-beta 1 mutants were equally responsive to alpha q. GTP gamma S, although the mutant His6PLC-beta 1-P57 (G758D) had only 2.5% the intrinsic PLC activity of the wild type. Also, His6PLC-beta 1 wild type and mutants acted as GAPs for Gq in a reconstitution assay. Thus, the present procedure provides a method to quickly assess phospholipase activity, alpha q-responsiveness, and GAP activity of PLC-beta 1.

Regulation of phospholipase C-beta1 by Gq and m1 muscarinic cholinergic receptor. Steady-state balance of receptor-mediated activation and GTPase-activating protein-promoted deactivation

The phospholipase C-beta1 (PLC-beta1) signaling pathway was reconstituted by addition of purified PLC to phospholipid vesicles that contained purified recombinant m1 muscarinic cholinergic receptor, Gq, and 2-4 mol % [3H]phosphatidylinositol 4,5-bisphosphate. In this system, the muscarinic agonist carbachol stimulated steady-state PLC activity up to 90-fold in the presence of GTP. Both GTP and agonist were required for PLC activation, which was observed at physiological levels of Ca2+ (10-100 nM). PLC-beta1 is also a GTPase-activating protein for Gq. It accelerated steady-state GTPase activity up to 60-fold in the presence of carbachol, which alone stimulated activity 6-10-fold, and increased the rate of hydrolysis of Gq-bound GTP by at least 100-fold. Despite this rapid hydrolysis of Gq-bound GTP, the receptor maintained >10% of the total Gq in the active GTP-bound form by catalyzing GTP binding at a rate of at least 20-25 min-1, approximately 10-fold faster than previously described. These and other kinetic data indicate that the receptor and PLC-beta1 coordinately regulate the amplitude of the PLC signal and the rates of signal initiation and termination. They also suggest a mechanism in which the receptor, Gq, and PLC form a three-protein complex in the presence of agonist and GTP (stable over multiple GTPase cycles) that is responsible for PLC signaling.

Functional importance of the amino terminus of Gq alpha

Gq alpha is palmitoylated at residues Cys9 and Cys10. Removal of palmitate from purified Gq alpha with palmitoylthioesterase in vitro failed to alter interactions of Gq alpha with phospholipase C-beta 1, the G protein beta gamma subunit complex, or m1 muscarinic cholinergic receptors. Mutants C9A, C10A, C9A/C10A, C9S/C10S, and truncated Gq alpha (removal of residues 1-6) were synthesized in Sf9 cells and purified. Loss of both Cys residues or truncation prevented palmitoylation of Gq alpha. However, truncated Gq alpha and the single Cys mutants activated phospholipase C-beta 1 normally, while the double Cys mutants were poor activators. Loss of both Cys residues impaired but did not abolish interaction of Gq alpha with m1 receptors. These Cys residues are thus important regardless of their state of palmitoylation. When expressed in HEK-293 or Sf9 cells, all of the proteins studied associated entirely or predominantly with membranes, although a minor fraction of nonpalmitoylated Gq alpha proteins accumulated in the cytosol of HEK-293 cells. When subjected to TX-114 phase partitioning, a significant fraction of all of the proteins, including those with no palmitate, was found in the detergent-rich phase. Removal of residues 1-34 of Gq alpha caused a loss of surface hydrophobicity as evidenced by complete partitioning into the aqueous phase. The Cys residues at the amino terminus of Gq alpha are thus important for its interactions with effector and receptor, and the amino terminus conveys a hydrophobic character to the protein distinct from that contributed by palmitate.

Carboxyl-terminal domains in the avian beta 1-adrenergic receptor that regulate agonist-promoted endocytosis

Most G protein-coupled receptors, including the mammalian beta 2-adrenergic receptor, are endocytosed to an intracellular, vesicular compartment upon continued exposure to agonist. The long form of the avian beta 1-adrenergic receptor, which contains a carboxyl-terminal 59-amino acid extension, does not undergo agonist-promoted endocytosis. We constructed and expressed turkey beta 1-adrenergic receptor cDNAs with regularly spaced carboxyl-terminal truncations and studied their agonist-promoted endocytosis. Removal of 34-86 amino acids from the carboxyl terminus of the turkey receptor allowed its efficient endocytosis, with optimal endocytosis observed upon removal of 59 residues. Removal of only 18 residues allowed some endocytosis. A receptor that lacks the entire carboxyl-terminal region (124 residues) was not endocytosed. We also constructed a chimeric hamster beta 2-adrenergic receptor with the added 59-residue carboxyl-terminal domain of the turkey receptor. The chimera was not significantly endocytosed. These data indicate that residues 450-465 in the carboxyl-terminal region of the beta 1-adrenergic receptor can act independently to block agonist-promoted endocytosis and that other carboxyl-terminal structures nearer to the seventh membrane span are required for endocytosis.

The carboxyl-terminal anchorage domain of the turkey beta 1-adrenergic receptor is encoded by an alternatively spliced exon

The originally described cDNA of the turkey beta 1-adrenergic receptor encodes a receptor with a carboxyl-terminal, 59-amino acid extension that was not found in several mammalian beta 1-adrenergic receptors. This extension blocks agonist-promoted endocytosis and down-regulation of the receptor. This carboxyl-terminal domain is encoded by an exon distinct from that which encodes the body of the receptor, and the originally described cDNA results from removal of an 849-nucleotide intron. Unspliced mRNA encodes a shorter open reading frame whose translated carboxyl terminus is identical with that of the mammalian beta 1-adrenergic receptors. There is no evidence for other introns in the coding region. Splicing of the intron to produce the non-endocytosing receptor is highest in fetal blood cells, is appreciable in adult brain and heart, and is detectable in other tissues. Thus, different tissues use alternative splicing to express beta-adrenergic receptors that either do or do not endocytose and down-regulate in response to agonist.

Fetal oxygenation at cordocentesis, maternal smoking and childhood neuro-development

OBJECTIVE

To assess the relationship between subsequent neuro-development and measurements in small for gestational age (SGA) fetuses, including oxygenation at cordocentesis.

DESIGN

A longitudinal study of a cohort of SGA fetuses using those with normal oxygenation as controls.

SUBJECTS

65 chromosomally normal children aged 12-66 months who, as fetuses, had been small for gestational age, had undergone cordocentesis and had been delivered after 32 weeks' gestation.

RESULTS

Griffiths' developmental quotient (DQ) was significantly associated with fetal blood pH (r = 0.41, P = 0.0008), PO2 (r = 0.25, P = 0.047) and PCO2 (r = -0.28, P = 0.027) at cordocentesis but not with the severity of growth retardation (r = 0.18, P = 0.17). However, the significant correlations between DQ and both PO2 and PCO2 were explained by their co-correlations with pH and neither remained significant after removing the effect of pH by analysis of variance. The association between DQ and pH was still significant after removing the effect of confounding variables. Maternal smoking during pregnancy was significantly associated with DQ (F to remove = 6.89, P = 0.011) even after allowing for the effects of possible confounding variables including fetal blood pH.

CONCLUSIONS

Both fetal pH at cordocentesis and maternal smoking correlate significantly with subsequent neuro-development. Further investigation into the causes of these associations is required.

Protein modification. Palmitoylation in G-protein signaling pathways

The reversible palmitoylation of G proteins and their receptors is involved both in receptor desensitization and in association and disassociation of G alpha subunits with the plasma membrane.

Childhood epilepsies--a measure of concern

Childhood epilepsies are a serious and sizeable problem, and children with epilepsy have many needs. Epidemiological studies carried out 20-30 years ago provided valuable information on the incidence and prevalence of epilepsy in children. However, the causes of epilepsies in most children still remain unidentified. Following the introduction of an international classification of epilepsies and sophisticated brain scanning techniques, new population-based studies should now be performed to determine the prevalence and long-term outcome of the various types of epilepsy in children. These studies will undoubtedly lead to a greater understanding of childhood epilepsies and should result in better management of this condition.

Chimeric muscarinic cholinergic:beta-adrenergic receptors that are functionally promiscuous among G proteins

We evaluated the G protein selectivity of chimeric M1 and M2 muscarinic cholinergic receptors in which either the third intracellular (I3) loop or the N-terminal portion of this loop (the I3N peptide) was replaced by the corresponding sequence from the beta 1-adrenergic receptor. The chimeras retained agonist-dependent G protein regulatory activity, but were completely promiscuous among potential G protein targets. When expressed in transfected cells, the chimeric receptors activated adenylyl cyclase, the major target of the beta-adrenergic receptor, and activated phospholipase C via a pertussis toxin-insensitive G protein, presumably a Gq. Gs is not a target of either muscarinic receptor, and Gq is not a cellular target of either the M2 muscarinic or beta-adrenergic receptor. When co-reconstituted into phospholipid vesicles with purified G proteins, the chimeric receptors were completely nonselective among all G proteins tested. They activated Gi, G(o), Gz, and Gs with similar efficiencies. This promiscuity was largely suppressed, both in transfected cells and in reconstituted vesicles, by the additional replacement of the second intracellular (I2) loop of the beta-adrenergic receptor. Such double substitutions created receptors specific for Gs, the target of the beta-adrenergic receptor. These findings suggest that G protein specificity depends on the proper combination of multiple regions on a receptor's cytoplasmic surface. In addition, the promiscuous receptors described here may be useful for regulating novel G proteins whose natural regulators are not yet known.

Gs regulation of endosome fusion suggests a role for signal transduction pathways in endocytosis

Work from several laboratories indicates that guanine nucleotide-binding proteins (GTP-binding proteins) are required for intracellular vesicular transport. In a previous report we presented evidence indicating that one or more heterotrimeric G proteins regulate fusion between endosomes (Colombo, M. I., Mayorga, L. S., Casey, P. J., and Stahl, P. D. (1992) Science 255, 1695-1697). We now report on experiments showing that Gs plays a role in endosome fusion. We have used several reagents known to modulate Gs function including (i) peptides corresponding to the cytoplasmic domains of G protein-coupled receptors and peptides that mimic interaction of receptors with G proteins, (ii) anti-G protein antibodies, and (iii) cholera toxin. Synthetic peptides corresponding to the third cytoplasmic loop of the beta 2-adrenergic receptor which putatively interact with G alpha s inhibited endosomal fusion. The inhibitory effect of these peptides was prevented by a short preincubation of endosomes with guanosine-5'-3-O-(thio)triphosphate or by phosphorylating the peptide with cAMP-dependent protein kinase. The involvement of Gs in endosome recognition and/or the fusion process was assessed by testing an antibody against the COOH terminus of G alpha s. Anti-G alpha s IgG completely abolished fusion between endosomes. Lastly, preincubation of endosomal vesicles with cholera toxin abrogated fusion in the presence of NAD, whereas no effect was observed in the absence of the cofactor. Taken together these findings indicate a role for Gs in either the mechanism or the regulation of fusion among endosomes. These results raise the possibility that signal transduction through cytoplasmic domains of receptors may participate in the regulation of endocytic trafficking.