ALS2 regulates endosomal trafficking,postsynaptic development,and neuronal survival

Mutations in the human ALS2 gene cause recessive juvenile-onset amyotrophic lateral sclerosis and related motor neuron diseases. Although the ALS2 protein has been identified as a guanine-nucleotide exchange factor for the small GTPase Rab5, its physiological roles remain largely unknown. Here, we demonstrate that the Drosophila homologue of ALS2 (dALS2) promotes postsynaptic development by activating the Frizzled nuclear import (FNI) pathway. dALS2 loss causes structural defects in the postsynaptic subsynaptic reticulum (SSR), recapitulating the phenotypes observed in FNI pathway mutants. Consistently, these developmental phenotypes are rescued by postsynaptic expression of the signaling-competent C-terminal fragment of Drosophila Frizzled-2 (dFz2). We further demonstrate that dALS2 directs early to late endosome trafficking and that the dFz2 C terminus is cleaved in late endosomes. Finally, dALS2 loss causes age-dependent progressive defects resembling ALS, including locomotor impairment and brain neurodegeneration, independently of the FNI pathway. These findings establish novel regulatory roles for dALS2 in endosomal trafficking, synaptic development, and neuronal survival.     

Intraprotein electron transfer in inducible nitric oxide synthase holoenzyme

Intraprotein electron transfer (IET) from flavin mononucleotide (FMN) to heme is essential in NO synthesis by NO synthase (NOS). Our previous laser flash photolysis studies provided a direct determination of the kinetics of the FMN–heme IET in a truncated two-domain construct (oxyFMN) of murine inducible NOS (iNOS), in which only the oxygenase and FMN domains along with the calmodulin (CaM) binding site are present (Feng et al. J. Am. Chem. Soc. 128, 3808–3811, 2006). Here we report the kinetics of the IET in a human iNOS oxyFMN construct, a human iNOS holoenzyme, and a murine iNOS holoenzyme, using CO photolysis in comparative studies on partially reduced NOS and a NOS oxygenase construct that lacks the FMN domain. The IET rate constants for the human and murine iNOS holoenzymes are 34 ± 5 and 35 ± 3 s⁻¹, respectively, thereby providing a direct measurement of this IET between the catalytically significant redox couples of FMN and heme in the iNOS holoenzyme. These values are approximately an order of magnitude smaller than that in the corresponding iNOS oxyFMN construct, suggesting that in the holoenzyme the rate-limiting step in the IET is the conversion of the shielded electron-accepting (input) state to a new electron-donating (output) state. The fact that there is no rapid IET component in the kinetic traces obtained with the iNOS holoenzyme implies that the enzyme remains mainly in the input state. The IET rate constant value for the iNOS holoenzyme is similar to that obtained for a CaM-bound neuronal NOS holoenzyme, suggesting that CaM activation effectively removes the inhibitory effect of the unique autoregulatory insert in neuronal NOS. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Transforming growth factor-beta3 gene SfaN1 polymorphism in Korean nonsyndromic cleft lip and palate patients

The nonsyndromic cleft lip and palate (NSCL/P) is a congenital deformity of multifactorial origin with a relatively high incidence in the oriental population. Various etiologic candidate genes have been reported with conflicting results, according to race and analysis methods. Recently, the ablation of the TGF-beta3 gene function induced cleft palates in experimental animals. Also, polymorphisms in the TGF-beta3 gene have been studied in different races; however, they have not been studied in Koreans. A novel A --> G single nucleotide polymorphism (defined by the endonuclease SfaN1) was identified in intron 5 of TGF-beta3 (IVS5+104 A > G). It resulted in different genotypes, AA, AG, and GG. The objective of this study was to investigate the relationship between the SfaN1 polymorphism in TGF-beta3 and the risk of NSCL/P in the Korean population. The population of this study consisted of 28 NSCL/P patients and 41 healthy controls. The distribution of the SfaN1 genotypes was different between the cases and controls. The frequency of the G allele was significantly associated with the increased risk of NSCL/P [odds ratio (OR) = 15.92, 95% confidence interval (CI) = 6.3-41.0]. The risk for the disease increased as the G allele numbers increased (GA genotype: OR = 2.11, 95% CI = 0.38-11.68; GG genotype: OR = 110.2, 95% CI = 10.67 - 2783.29) in NSCL/P. A stratified study in patients revealed that the SfaN1 site IVS5+104A > G substitution was strongly associated with an increased risk of NSCL/P in males (p < 0.001), but not in females. In conclusion, the polymorphism of the SfaN1 site in TGF-beta3 was significantly different between the NSCL/P patients and the control. This may be a good screening marker for NSCL/P patients among Koreans.     

The effect of pH and various cations on the GTP hydrolysis of rice heterotrimeric G-protein alpha subunit expressed in Escherichia coli

Previously, we reported the biochemical properties of RGA1 that is expressed in Escherichia coli (Seo et al., 1997). The activities of RGA1 that hydrolyzes and binds guanine nucleotide were dependent on the MgCl(2) concentration. The steady state rate constant (k(cat) ) for GTP hydrolysis of RGA1 at 2 mM MgCl(2) was 0.0075 +/- 0.0001 min(-1). Here, we examined the effects of pH and cations on the GTPase activity. The optimum pH at 2 mM MgCl(2) was approximately 6.0; whereas, the pH at 2 mM NH(4)Cl was approximately 4.0. The result from the cation dependence on the GTPase (guanosine 5'-triphosphatase) activity of RGA1 under the same condition showed that the GTP hydrolysis rate (k(cat)= 0.0353 min(-1)) under the condition of 2 mM NH(4)Cl at pH 4.0 was the highest. It corresponded to about 3.24-fold of the k(cat) value of 0.0109 min(-1) in the presence of 2 mM MgCl(2) at pH 6.0.     

Identification of Fyn-binding proteins in MC/9 mast cells using mass spectrometry

Fyn is a Src kinase known to have an essential role in mast cell degranulation induced following aggregation of the high affinity IgE-receptor. Although Fyn possesses SH2 and SH3 protein binding domains, the molecules that interact with Fyn have not been characterized in mast cells. We thus analyzed Fyn-binding proteins in MC/9 mast cells to explore the Fyn-mediated signaling pathway. On mass spectrometric analysis of proteins binding to the SH2 and SH3 domains of Fyn, we identified six proteins that bind to Fyn including vimentin, pyruvate kinase, p62 ras-GAP associated phosphoprotein, SLP-76, HS-1, and FYB. Among these proteins, vimentin and pyruvate kinase have not been shown to bind to Fyn. After IgE-receptor mediated stimulation, binding of vimentin to Fyn was increased; and this interaction was via binding to the SH2, but not the SH3, domain of Fyn. Mast cells from vimentin-deficient mice showed enhanced mediator release and tyrosine phosphorylation of intracellular proteins including NTAL and LAT. The observation that vimentin and pyruvate kinase bind to Fyn provides additional insight into Fyn-mediated signaling pathways, and suggests a critical role for Fyn in mast cell degranulation in interacting with both cytosolic and structural proteins.     

Co-expression of a Modified Maize Ribosome-inactivating Protein and a Rice Basic Chitinase Gene in Transgenic Rice Plants Confers Enhanced Resistance to Sheath Blight

Chitinases, -1,3-glucanases, and ribosome-inactivating proteins are reported to have antifungal activity in plants. With the aim of producing fungus-resistant transgenic plants, we co-expressed a modified maize ribosome-inactivating protein gene, MOD1, and a rice basic chitinase gene, RCH10, in transgenic rice plants. A construct containing MOD1 and RCH10 under the control of the rice rbcS and Act1 promoters, respectively, was co-transformed with a plasmid containing the herbicide-resistance gene bar as a selection marker into rice by particle bombardment. Several transformants analyzed by genomic Southern-blot hybridization demonstrated integration of multiple copies of the foreign gene into rice chromosomes. Immunoblot experiments showed that MOD1 formed approximately 0.5% of the total soluble protein in transgenic leaves. RCH10 expression was examined using the native polyacrylamide-overlay gel method, and high RCH10 activity was observed in leaf tissues where endogenous RCH10 is not expressed. R₁ plants were analyzed in a similar way, and the Southern-blot patterns and levels of transgene expression remained the same as in the parental line. Analysis of the response of R₂ plants to three fungal pathogens of rice, Rhizoctonia solani, Bipolaris oryzae, and Magnaporthe grisea, indicated statistically significant symptom reduction only in the case of R. solani (sheath blight). The increased resistance co-segregated with herbicide tolerance, reflecting a correlation between the resistance phenotype and transgene expression.     

Neurology, technology, and the diagnostic imperative

Advancements in diagnostic technologies have revolutionized the field of neurology. The use of these tools in the course of neurological evaluations is driven by a strong version of the diagnostic imperative, with the goal of precisely identifying the locus and extent of disease processes. Because of the discrepancy between the sophistication of these technologies and the availability of therapeutic interventions, there is active debate regarding the appropriate use of these tools when the diagnosis is clear, or when no change is made to the therapeutic management. A narrow view of management that is bounded by the availability of pharmacological or surgical interventions results in a more rigid dichotomy between the needs of doctors and patients. A broader view that relaxes the constraint between diagnostic procedures and interventions is more in keeping with the observation that many acts are performed for the benefit of doctors and patients alike. An historical and ethical analysis of the diagnostic imperative, with attention to the rise of innovative medical technologies and current concepts of therapeutic intervention, can help clarify the principles of medical paternalism and beneficence that guide current models of decision making in the neurological sciences.     

Matrix attachment region from the chicken lysozyme locus reduces variability in transgene expression and confers copy number-dependence in transgenic rice plants

Matrix-attachment regions (MARs) may function as domain boundaries and partition chromosomes into independently regulated units. In this study, BP-MAR, a 1.3-kb upstream fragment of the 5MAR flanking the chicken lysozyme locus, was tested for its effects on integration and expression of transgenes in transgenic rice plants. Using the Agrobacterium-mediated method, we transformed rice with nine different constructs containing seven and six different promoters and coding sequences, respectively. Genomic Southern blot analyses of 357 independent transgenic lines revealed that in the presence of BP-MAR, 57% of the lines contained a single copy of the transgene, whereas in its absence, only 20% of the lines contained a single copy of the transgene. RNA gel-blot and immunoblot experiments demonstrated that in the presence of BP-MAR, transgene expression levels were similar among different lines. These data were in direct contrast to those derived from transgenes expressed in the absence of BP-MAR, which varied markedly with the chromosomal integration site . Thus, it can be concluded that BP-MAR significantly reduces the variability in transgene expression between independent transformants. Moreover, the presence of BP-MAR appears to confer a copy number-dependent increase in transgene expression, although it does not increase expression levels of individual transgenes. These data contrast with results previously obtained with various MARs that increased expression levels of transgene significantly. Therefore, we conclude that the incorporation of BP-MAR sequences into the design of transformation vectors can minimize position effects and regulate transgene expression in a copy number-dependent way.S.-J. Oh, J.S. Jeong, E.-H. Kim, N.R. Yi and S.-I. Yi contributed equally to the paper