Reduced fertility in patients' families is consistent with the sexual selection model of schizophrenia and schizotypy

Background

Schizophrenia is a mental disorder marked by an evolutionarily puzzling combination of high heritability, reduced reproductive success, and a remarkably stable prevalence. Recently, it has been proposed that sexual selection may be crucially involved in the evolution of schizophrenia. In the sexual selection model (SSM) of schizophrenia and schizotypy, schizophrenia represents the negative extreme of a sexually selected indicator of genetic fitness and condition. Schizotypal personality traits are hypothesized to increase the sensitivity of the fitness indicator, thus conferring mating advantages on high-fitness individuals but increasing the risk of schizophrenia in low-fitness individuals; the advantages of successful schzotypy would be mediated by enhanced courtship-related traits such as verbal creativity. Thus, schizotypy-increasing alleles would be maintained by sexual selection, and could be selectively neutral or even beneficial, at least in some populations. However, most empirical studies find that the reduction in fertility experienced by schizophrenic patients is not compensated for by increased fertility in their unaffected relatives. This finding has been interpreted as indicating strong negative selection on schizotypy-increasing alleles, and providing evidence against sexual selection on schizotypy.

Methodology

A simple mathematical model is presented, showing that reduced fertility in the families of schizophrenic patients can coexist with selective neutrality of schizotypy-increasing alleles, or even with positive selection on schizotypy in the general population. If the SSM is correct, studies of patients'' families can be expected to underestimate the true fertility associated with schizotypy.

Significance

This paper formally demonstrates that reduced fertility in the families of schizophrenic patients does not constitute evidence against sexual selection on schizotypy-increasing alleles. Futhermore, it suggests that the fertility estimates derived from extant studies may be biased to an unknown extent. These results have important implications for the evolutionary genetics of psychosis.     

Allelic subtypic determinants of hepatitis B surface antigen (i and t) that are distinct from d/y or w/r.

A monoclonal antibody (I-18) was raised against an enneapeptide representing amino acids 125 to 133 of the product of the S gene of hepatitis B virus DNA [S(125-133) segment] with a sequence of Thr-Ile-126-Pro-Ala-Gln-Gly-Thr-Ser-Met. Another monoclonal antibody (T-7) was raised against an S(125-133) segment in which Ile-126 was replaced by Thr-126. In a panel of 16 samples of hepatitis B surface antigen (HBsAg) with known S gene sequences, I-18 reacted with 5 with Ile-126. T-7 reacted with 10 HBsAg samples with Thr-126; it did not, however, react with the remaining one of subtype ayw with Thr-126 flanked by Met-125 and Thr-127. The two allelic subtypic determinants, specified by Ile-126 and Thr-126 and distinct from d/y or w/r, were named i and t after isoleucine and threonine, which regulate them. They were expressed in a mutually exclusive fashion in 216 (83%) of 260 HBsAg samples from asymptomatic carriers. They were not detected in 36 (14%) samples; the failure to detect an i or t determinant was particularly common in HBsAg samples of subtype ayw (26 [79%] of 33). A part of the S gene sequence was determined for eight HBsAg samples without a detectable i or t determinant. They had an Ile-126 or Thr-126 residue that was flanked by Thr-127, not the Pro-127 commonly possessed by HBsAg samples displaying an i or t determinant. Expression of the i/t allele, therefore, would require Pro-127. In eight (3%) of the samples, both i and t determinants were detected; the presence of i and t on the selfsame HBsAg particles was verified by sandwiching the particles between I-18 and T-7. A point mutation from thymine to cytosine at nucleotide 377 in the S gene, contributing different second letters to codon 126 (ATT for Ile and ACT for Thr), would have been responsible for the assembly of HBsAg particles with both i and t determinants by means of phenotypic mixing.     

Quantum mechanics/molecular mechanics modeling of substrate-assisted catalysis in family 18 chitinases: conformational changes and the role of Asp142 in catalysis in ChiB

Family 18 chitinases catalyze the hydrolysis of β-1,4-glycosidic bonds in chitin. The mechanism has been proposed to involve the formation of an oxazolinium ion intermediate via an unusual substrate-assisted mechanism, in which the substrate itself acts as an intramolecular nucleophile (instead of an enzyme residue). Here, we have modeled the first step of the chitin hydrolysis catalyzed by Serratia marcescens chitinase B for the first time using a combined quantum mechanics/molecular mechanics approach. The calculated reaction barriers based on multiple snapshots are 15.8-19.8 kcal mol(-1) [B3LYP/6-31+G(d)//AM1-CHARMM22], in good agreement with the activation free energy of 16.1 kcal mol(-1) derived from experiment. The enzyme significantly stabilizes the oxazolinium intermediate. Two stable conformations ((4)C(1)-chair and B(3,O)-boat) of the oxazolinium ion intermediate in subsite -1 were unexpectedly observed. The transition state structure has significant oxacarbenium ion-like character. The glycosyl residue in subsite -1 was found to follow a complex conformational pathway during the reaction ((1,4)B → [(4)H(5)/(4)E](++) → (4)C(1) ? B(3,O)), indicating complex conformational behavior in glycoside hydrolases that utilize a substrate-assisted catalytic mechanism. The D142N mutant is found to follow the same wild-type-like mechanism: the calculated barriers for reaction in this mutant (16.0-21.1 kcal mol(-1)) are higher than in the wild type, in agreement with the experiment. Asp142 is found to be important in transition state and intermediate stabilization.     

KvAP-based model of the pore region of shaker potassium channel is consistent with cadmium- and ligand-binding experiments

Potassium channels play fundamental roles in excitable cells. X-ray structures of bacterial potassium channels show that the pore-lining inner helices obstruct the cytoplasmic entrance to the closed channel KcsA, but diverge in widely open channels MthK and KvAP, suggesting a gating-hinge role for a conserved Gly in the inner helix. A different location of the gating hinge and a narrower open pore were proposed for voltage-gated Shaker potassium channels that have the Pro-473-Val-Pro motif. Two major observations back the proposal: cadmium ions lock mutant Val-476-Cys in the open state by bridging Cys-476 and His-486 in adjacent helices, and cadmium blocks the locked-open double mutant Val-474-Cys/Val-476-Cys by binding to Cys-474 residues. Here we used molecular modeling to show that the open Shaker should be as wide as KvAP to accommodate an open-channel blocker, correolide. We further built KvAP-, MthK-, and KcsA-based models of the Shaker mutants and Monte-Carlo-minimized them with constraints Cys-476-Cd(2+)-His-486. The latter were consistent with the KvAP-based model, causing a small-bend N-terminal to the Pro-473-Val-Pro motif. The constraints significantly distorted the MthK-based structure, making it similar to KvAP. The KcsA structure resisted the constraints. Two Cd(2+) ions easily block the locked-open KvAP-based model at Cys-474 residues, whereas constraining a single cadmium ion to four Cys-474 caused large conformational changes and electrostatic imbalance. Although mutual disposition of the voltage-sensor and pore domains in the KvAP x-ray structure is currently disputed, our results suggest that the pore-region domain retains a nativelike conformation in the crystal.     

N-218 MLN64, a protein with StAR-like steroidogenic activity, is folded and cleaved similarly to StAR

The steroidogenic acute regulatory protein (StAR) facilitates the movement of cholesterol from the outer to inner mitochondrial membrane in adrenal and gonadal cells, fostering steroid biosynthesis. MLN64 is a 445-amino acid protein of unknown function. When 218 amino-terminal residues of MLN-64 are deleted, the resulting N-218 MLN64 has 37% amino acid identity with StAR and 50% of StAR's steroidogenic activity in transfected cells. Antiserum to StAR cross-reacts with N-218 MLN64, indicating the presence of similar epitopes in both proteins. Western blotting shows that MLN64 is proteolytically cleaved in the placenta to a size indistinguishable from N-218 MLN64. Bacterially expressed N-218 MLN64 exerts StAR-like activity to promote the transfer of cholesterol from the outer to inner mitochondrial membrane in vitro. CD spectroscopy indicates that N-218 MLN64 is largely alpha-helical and minimally affected by changes in ionic strength or the hydrophobic character of the solvent, although glycerol increases the beta-sheet content. However, decreasing pH diminishes structure, causing aggregation. Limited proteolysis at pH 8.0 shows that the C-terminal domain of N-218 MLN64 is accessible to proteolysis whereas the 244-414 domain is resistant, suggesting it is more compactly folded. The presence of a protease-resistant domain and a protease-sensitive carboxy-terminal domain in N-218 MLN64 is similar to the organization of StAR. However, as MLN64 never enters the mitochondria, the protease-resistant domain of MLN64 cannot be a mitochondrial pause-transfer sequence, as has been proposed for StAR. Thus the protease-resistant domain of N-218 MLN64, and by inference the corresponding domain of StAR, may have direct roles in their action to foster the flux of cholesterol from the outer to the inner mitochondrial membrane.     

Binding of plasma membrane glycoproteins to the cytoskeleton during patching and capping is consistent with an entropy-enhancement model

Concentrations of concanavalin A that induced patching and capping of cell surface receptors on Dictyostelium discoideum also induce binding of the receptors to the cortical cytoskeleton, which was isolated by density-gradient centrifugation. The receptors were solubilized by deoxycholate, purified by affinity chromatography, and used to determine whether the receptors bound directly to the cytoskeletal protein, actin. As the concentration of actin was increased, many of the receptors became bound to purified filamentous rabbit muscle actin, even in the absence of concanavalin A. As in the ligation-induced binding of receptors to the cortical cytoskeleton in cells, concanavalin A induced much stronger binding of the purified receptors to filamentous actin. The results were consistent with a previously stated hypothesis that induction of receptor binding to the cytoskeleton during their patching and capping is driven by clustering the receptors, which reduces their translational entropy and by doing so enhances their avidity for the cytoskeleton.     

A method for introduction of unmarked mutations in the genome of Paracoccus denitrificans: construction of strains with multiple mutations in the genes encoding periplasmic cytochromes c550, c551i, and c553i.

A new suicide vector, pRVS1, was constructed to facilitate the site-directed introduction of unmarked mutations in the chromosome of Paracoccus denitrificans. The vector was derived from suicide vector pGRPd1, which was equipped with the lacZ gene encoding beta-galactosidase. The reporter gene was found to be a successful screening marker for the discrimination between plasmid integrant strains and mutant strains which had lost the plasmid after homologous recombination. Suicide vectors pGRPd1 and pRVS1 were used in gene replacement techniques for the construction of mutant strains with multiple mutations in the cycA, moxG, and cycB genes encoding the periplasmic cytochromes c550, c551i, and c553i, respectively. Southern analyses of the DNA and protein analyses of the resultant single, double, and triple mutant strains confirmed the correctness of the mutations. The wild type and mutant strains were all able to grow on succinate and choline chloride. In addition, all strains grew on methylamine and displayed wild-type levels of methylamine dehydrogenase activities. cycA mutant strains, however, showed a decreased maximum specific growth rate on the methylamine substrate. The wild-type strain, cycA and cycB mutant strains, and the cycA cycB double mutant strain were able to grow on methanol and showed wild-type levels of methanol dehydrogenase activities. moxG mutant strains failed to grow on methanol and had low levels of methanol dehydrogenase activities. The maximum specific growth rate of the cycA mutant strain on methanol was comparable with that of the wild-type strain. The data indicate the involvement of the soluble cytochromes c in clearly defined electron transport routes.     

N.m.r. and c.d. studies of the DNA fragments d(TATATATA) and d(TATATA) in solution

DNA fragments d(TATATATA) and d(TATATA) were studied in low-salt aqueous solutions and found to coexist in more than one conformer. 1H-n.m.r. demonstrates that single-stranded and double-stranded states are involved in the conformational coexistence. Circular dichroism spectroscopy indicates a global B-DNA stacking of bases in the fragments. 31P-n.m.r. resonances of the TpA and ApT phosphodiester bonds are substantially separated in the spectra of both d(TATATATA) and d(TATATA) duplexes to suggest an alternating architecture of their backbones. In fact, the oligonucleotide duplexes are much more alternating than the corresponding polynucleotide under the same solution conditions. The alternating character of the d(TATATATA) double helix is further enhanced in molar caesium fluoride solutions. The oligonucleotide isomerization into X-DNA is, however, accompanied by gel formation, which makes high resolution n.m.r. measurements impossible.     

Reduced calcium/calmodulin-dependent protein kinase II activity in the hippocampus is associated with impaired cognitive function in MPTP-treated mice

Parkinson's disease (PD) patients frequently reveal deficit in cognitive functions during the early stage in PD. The dopaminergic neurotoxin, MPTP-induced neurodegeneration causes an injury of the basal ganglia and is associated with PD-like behaviors. In this study, we demonstrated that deficits in cognitive functions in MPTP-treated mice were associated with reduced calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and impaired long-term potentiation (LTP) induction in the hippocampal CA1 region. Mice were injected once a day for 5days with MPTP (25mg/kg i.p.). The impaired motor coordination was observed 1 or 2week after MPTP treatment as assessed by rota-rod and beam-walking tasks. In immunoblotting analyses, the levels of tyrosine hydroxylase protein and CaMKII autophosphorylation in the striatum were significantly decreased 1week after MPTP treatment. By contrast, deficits of cognitive functions were observed 3-4weeks after MPTP treatment as assessed by novel object recognition and passive avoidance tasks but not Y-maze task. Impaired LTP in the hippocampal CA1 region was also observed in MPTP-treated mice. Concomitant with impaired LTP induction, CaMKII autophosphorylation was significantly decreased 3weeks after MPTP treatment in the hippocampal CA1 region. Finally, the reduced CaMKII autophosphorylation was closely associated with reduced AMPA-type glutamate receptor subunit 1 (GluR1; Ser-831) phosphorylation in the hippocampal CA1 region of MPTP-treated mice. Taken together, decreased CaMKII activity with concomitant impaired LTP induction in the hippocampus likely account for the learning disability observed in MPTP-treated mice.     

CD, absorption and thermodynamic analysis of repeating dinucleotide DNA, RNA and hybrid duplexes [d/r(AC)]12.[d/r(GT/U)]12 and the influence of phosphorothioate substitution.

Circular dichroism (CD) spectra and melting temperature (Tm) data for five duplexes containing phosphorothioate linkages were compared with data for four unmodified duplexes to assess the effect of phosphorothioate modification on the structure and stability of DNA. DNA and DNA.RNA duplexes. Nine duplexes were formed by mixing oligomers 24 nt long in 0.15 M K+(phosphate buffer), pH 7.0. Unmodified DNA.DNA and RNA.RNA duplexes were used as reference B-form and A-form structures. The CD spectra of the modified hybrids S-d(AC)12.r(GU)12 and r(AC)12.S-d(GT)12 differed from each other but were essentially the same as the spectra of the respective unmodified hybrids. They were more A-form than B-form in character. CD spectra of duplexes S-d(AC)12.d(GT)12 and d(AC)12.S-d(GT)12 were similar to that of d(AC)12.d(GT)12, except for a reduced long wavelength CD band. Sulfur modifications on both strands of the DNA duplex caused a pronounced effect on its CD spectrum. The order of thermal stability was: RNA.RNA > DNA.DNA > DNA.RNA > S-DNA.DNA > S-DNA. RNA > S-DNA.S-DNA. Phosphorothioation of one strand decreased the melting temperature by 7.8+/-0.6 degrees C, regardless of whether the substitution was in a hybrid or DNA duplex. Thermodynamic parameters were obtained from a multistate analysis of the thermal melting profiles. Interestingly, the destabilizing effect of the phosphorothioate substitution appears to arise from a difference in the entropy upon forming the DNA.DNA duplexes, while the destabilizing effect in the DNA.RNA hybrids appears to come from a difference in enthalpy.     

A homology model of the pore domain of a voltage-gated calcium channel is consistent with available SCAM data

In the absence of x-ray structures of calcium channels, their homology models are used to rationalize experimental data and design new experiments. The modeling relies on sequence alignments between calcium and potassium channels. Zhen et al. (2005. J. Gen. Physiol. doi:10.1085/jgp.200509292) used the substituted cysteine accessibility method (SCAM) to identify pore-lining residues in the Ca_v2.1 channel and concluded that their data are inconsistent with the symmetric architecture of the pore domain and published sequence alignments between calcium and potassium channels. Here, we have built K_v1.2-based models of the Ca_v2.1 channel with 2-(trimethylammonium)ethyl methanethiosulfonate (MTSET)-modified engineered cysteines and used Monte Carlo energy minimizations to predict their energetically optimal orientations. We found that depending on the position of an engineered cysteine in S6 and S5 helices, the ammonium group in the long flexible MTSET-modified side chain can orient into the inner pore, an interface between domains (repeats), or an interface between S5 and S6 helices. Different local environments of equivalent positions in the four repeats can lead to different SCAM results. The reported current inhibition by MTSET generally decreases with the predicted distances between the ammonium nitrogen and the pore axis. A possible explanation for outliers of this correlation is suggested. Our calculations rationalize the SCAM data, validate one of several published sequence alignments between calcium and potassium channels, and suggest similar spatial dispositions of S5 and S6 helices in voltage-gated potassium and calcium channels.     

Comparison of myeloperoxidase and hemi-myeloperoxidase with respect to catalysis, regulation, and bactericidal activity

It has been demonstrated previously (P.C. Andrews and N.I. Krinsky (1981) J. Biol. Chem. 256, 4211-4218) that human leukocyte myeloperoxidase, an alpha 2 beta 2 enzyme, can be cleaved by mild reduction and alkylation to an alpha 1 beta 1 structure that we have termed hemi-myeloperoxidase. The native enzyme and hemi-myeloperoxidase have the same specific activity in a Cl--independent peroxidase assay and identical visible spectra under either oxidized or reduced conditions. This paper compares other properties of native and hemi-myeloperoxidase. Both enzymes are inhibited by high concentrations of H2O2 in an identical fashion. Both enzymes showed identical regulation by pH and Cl-. The utilization of Cl-, as assayed by chlorination of diethanolamine, was moderately decreased in hemi-myeloperoxidase. This reduction in chlorination was not reflected in a bactericidal assay, where again, hemi-myeloperoxidase was identical in activity to native myeloperoxidase.     

Evidence that CED-9/Bcl2 and CED-4/Apaf-1 localization is not consistent with the current model for C. elegans apoptosis induction

In C. elegans, the BH3-only domain protein EGL-1, the Apaf-1 homolog CED-4 and the CED-3 caspase are required for apoptosis induction, whereas the Bcl-2 homolog CED-9 prevents apoptosis. Mammalian B-cell lymphoma 2 (Bcl-2) inhibits apoptosis by preventing the release of the Apaf-1 (apoptotic protease-activating factor 1) activator cytochrome c from mitochondria. In contrast, C. elegans CED-9 is thought to inhibit CED-4 by sequestering it at the outer mitochondrial membrane by direct binding. We show that CED-9 associates with the outer mitochondrial membrane within distinct foci that do not overlap with CED-4, which is predominantly perinuclear and does not localize to mitochondria. CED-4 further accumulates in the perinuclear space in response to proapoptotic stimuli such as ionizing radiation. This increased accumulation depends on EGL-1 and is abrogated in ced-9 gain-of-function mutants. CED-4 accumulation is not sufficient to trigger apoptosis execution, even though it may prime cells for apoptosis. Our results suggest that the cell death protection conferred by CED-9 cannot be solely explained by a direct interaction with CED-4.     

Arginine 54 in the active site of Escherichia coli aspartate transcarbamoylase is critical for catalysis: a site-specific mutagenesis, NMR, and X-ray crystallographic study.

The replacement of Arg-54 by Ala in the active site of Escherichia coli aspartate transcarbamoylase causes a 17,000-fold loss of activity but does not significantly influence the binding of substrates or substrate analogs (Stebbins, J.W., Xu, W., & Kantrowitz, E.R., 1989, Biochemistry 28, 2592-2600). In the X-ray structure of the wild-type enzyme, Arg-54 interacts with both the anhydride oxygen and a phosphate oxygen of carbamoyl phosphate (CP) (Gouaux, J.E. & Lipscomb, W.N., 1988, Proc. Natl. Acad. Sci. USA 85, 4205-4208). The Arg-54-->Ala enzyme was crystallized in the presence of the transition state analog N-phosphonacetyl-L-aspartate (PALA), data were collected to a resolution limit of 2.8 A, and the structure was solved by molecular replacement. The analysis of the refined structure (R factor = 0.18) indicates that the substitution did not cause any significant alterations to the active site, except that the side chain of the arginine was replaced by two water molecules. 31P-NMR studies indicate that the binding of CP to the wild-type catalytic subunit produces an upfield chemical shift that cannot reflect a significant change in the ionization state of the CP but rather indicates that there are perturbations in the electronic environment around the phosphate moiety when CP binds to the enzyme. The pH dependence of this upfield shift for bound CP indicates that the catalytic subunit undergoes a conformational change with a pKa approximately 7.7 upon CP binding. Furthermore, the linewidth of the 31P signal of CP bound to the Arg-54-->Ala enzyme is significantly narrower than that of CP bound to the wild-type catalytic subunit at any pH, although the change in chemical shift for the CP bound to the mutant enzyme is unaltered. 31P-NMR studies of PALA complexed to the wild-type catalytic subunit indicate that the phosphonate group of the bound PALA exists as the dianion at pH 7.0 and 8.8, whereas in the Arg-54-->Ala catalytic subunit the phosphonate group of the bound PALA exists as the monoanion at pH 7.0 and 8.8. Thus, the side chain of Arg-54 is essential for the proper ionization of the phosphonate group of PALA and by analogy the phosphate group in the transition state. These data support the previously proposed proton transfer mechanism, in which a fully ionized phosphate group in the transition state accepts a proton during catalysis.     

Synthesis of the oligodeoxyribonucleotide, d(CpTpGpGpApTpCpCpApG), and its substrate activity with the restriction endonuclease, BamHI

The synthesis of the DNA fragment, d(CpTpGpGpApTpCpCpApG), using a long-chain alkylamine-controlled pore glass bead polymer support, crystalline (9-phenyl-9-xanthenyl) nucleosides, and the bifunctional phosphorylating reagent, bis(1-benzotriazolyl)-2-chlorophenyl phosphate is described. For high coupling yields a mixed catalyst (1-methyl-imidazole + diisopropylethylamine) is required. The oligodeoxyribonucleotide shows activity with the DNA restriction endonuclease, BamHI. Kinetic parameters have been determined for the reaction.     

The Drosophila melanogaster RAD54 homolog, DmRAD54, is involved in the repair of radiation damage and recombination.

The RAD54 gene of Saccharomyces cerevisiae plays a crucial role in recombinational repair of double-strand breaks in DNA. Here the isolation and functional characterization of the RAD54 homolog of the fruit fly Drosophila melanogaster, DmRAD54, are described. The putative Dmrad54 protein displays 46 to 57% identity to its homologs from yeast and mammals. DmRAD54 RNA was detected at all stages of fly development, but an increased level was observed in early embryos and ovarian tissue. To determine the function of DmRAD54, a null mutant was isolated by random mutagenesis. DmRADS4-deficient flies develop normally, but the females are sterile. Early development appears normal, but the eggs do not hatch, indicating an essential role for DmRAD54 in development. The larvae of mutant flies are highly sensitive to X rays and methyl methanesulfonate. Moreover, this mutant is defective in X-ray-induced mitotic recombination as measured by a somatic mutation and recombination test. These phenotypes are consistent with a defect in the repair of double-strand breaks and imply that the RAD54 gene is crucial in repair and recombination in a multicellular organism. The results also indicate that the recombinational repair pathway is functionally conserved in evolution.