Group I mGluR5 metabotropic glutamate receptors regulate proliferation of neuronal progenitors in specific forebrain developmental domains

Major classical neurotransmitters including GABA and glutamate play novel morphogenic roles during development of the mammalian CNS. During forebrain neurogenesis, glutamate regulates neuroblast proliferation in different germinal domains using receptor subtype-specific mechanisms. For example, ionotropic N -methyl-D-aspartate (NMDA) or alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) glutamate receptors mediate distinct proliferative effects in ventral or dorsal forebrain germinal domains, and regulate the correct number of neurons that populate the striatum or cerebral cortex. Recent work suggests metabotropic receptors may also mediate glutamate's proliferative effects. Group I mGluR5 receptor subtypes are highly expressed in forebrain germinal zones. Using in vitro and in vivo methods, we demonstrate mGluR5 receptor activation plays an important role in neuroblast proliferation in the ventral telencephalon, and helps determine the complement of striatum projection neurons. mGluR5 receptor-mediated effects on striatal neuronal progenitors are restricted mainly to early cycling populations in the ventricular zone, with little effect on secondary proliferative populations in the subventricular zone. In contrast to proliferative effects in the ventral telencephalon, mGluR5 receptors do not modulate proliferation of dorsal telencephalon-derived cortical neuroblasts. Heterogeneous domain-specific proliferative effects of glutamate-mediated by specific receptor subtypes provide an important developmental mechanism allowing generation of the correct complement of neuronal subtypes that populate the mammalian forebrain.     

Nutrient resorption patterns of plant functional groups in a tropical savanna: variation and functional significance

Green and senesced leaf nitrogen (N) and phosphorus (P) concentrations of different plant functional groups in savanna communities of Kruger National Park, South Africa were analyzed to determine if nutrient resorption was regulated by plant nutritional status and foliar N:P ratios. The N and P concentrations in green leaves and the N concentrations in senesced leaves differed significantly between the dominant plant functional groups in these savannas: fine-leaved trees, broad-leaved trees and grasses. However, all three functional groups reduced P to comparable and very low levels in senesced leaves, suggesting that P was tightly conserved in this tropical semi-arid savanna ecosystem. Across all functional groups, there was evidence for nutritional control of resorption in this system, with both N and P resorption efficiencies decreasing as green leaf nutrient concentrations increased. However, specific patterns of resorption and the functional relationships between nutrient concentrations in green and senesced leaves varied by nutrient and plant functional group. Functional relationships between N concentrations in green and senesced leaves were indistinguishable between the dominant groups, suggesting that variation in N resorption efficiency was largely the result of inter-life form differences in green leaf N concentrations. In contrast, observed differences in P resorption efficiencies between life forms appear to be the result of both differences in green leaf P concentrations as well as inherent differences between life forms in the fraction of green leaf P resorbed from senescing leaves. Our results indicate that foliar N:P ratios are poor predictors of resorption efficiency in this ecosystem, in contrast to N and P resorption proficiencies, which are more responsive to foliar N:P ratios.     

Synthesis of spacer-equipped di-, tri-, and the tetrasaccharide fragments of the deacetylated O-PS1 of Citrobacter gillenii O9a,9b, and a related pentasaccharide

The title rhamnooligosaccharides [alpha-D-Rhap4NAc-(1-->3)-alpha-D-Rhap4NAc-1-O-(CH(2))(5)COOMe, alpha-D-Rhap4NAc-(1-->3)-alpha-D-Rhap4NAc-(1-->3)-alpha-D-Rhap4NAc-1-O-(CH(2))(5)COOMe, alpha-D-Rhap4NAc-(1-->2)-alpha-D-Rhap4NAc-(1-->3)-alpha-D-Rhap4NAc-(1-->3)-alpha-D-Rhap4NAc-1-O-(CH(2))(5)COOMe, and alpha-D-Rhap4NAc-(1-->3)-alpha-D-Rhap4NAc-(1-->2)-alpha-D-Rhap4NAc-(1-->3)-alpha-D-Rhap4NAc-(1-->3)-alpha-D-Rhap4NAc-1-O-(CH(2))(5)COOMe] were synthesized in a stepwise fashion from 5-methoxycarbonylpentyl 4-azido-4,6-dideoxy-2-O-benzyl-alpha-D-mannopyranoside and orthogonally protected 1-thioglycoside glycosyl donors. The amorphous, final products were fully characterized as corresponding per-O-acetyl derivatives.     

Eye formation in the absence of retina

Eye development is a complex process that involves the formation of the retina and the lens, collectively called the eyeball, as well as the formation of auxiliary eye structures such as the eyelid, lacrimal gland, cornea and conjunctiva. The developmental requirements for the formation of each individual structure are only partially understood. We have shown previously that the homeobox-containing gene Rx is a key component in eye formation, as retinal structures do not develop and retina-specific gene expression is not observed in Rx-deficient mice. In addition, Rx−/− embryos do not develop any lens structure, despite the fact that Rx is not expressed in the lens. This demonstrates that during normal mammalian development, retina-specific gene expression is necessary for lens formation. In this paper we show that lens formation can be restored in Rx-deficient embryos experimentally, by the elimination of β-catenin expression in the head surface ectoderm. This suggests that β-catenin is involved in lens specification either through Wnt signaling or through its function in cell adhesion. In contrast to lens formation, we demonstrate that the development of auxiliary eye structures does not depend on retina-specific gene expression or retinal morphogenesis. These results point to the existence of two separate developmental processes involved in the formation of the eye and its associated structures. One involved in the formation of the eyeball and the second involved in the formation of the auxiliary eye structures.     

Preparation of glycoconjugates by dialkyl squarate chemistry revisited

The methyl 6-hydroxyhexanoyl glycoside of lactose was treated with each of 1,2-diaminoethane or hydrazine hydrate, and the corresponding amino amide 4 and acyl hydrazide 13, were treated with each of squaric acid dimethyl, diethyl, dibutyl, and didecyl esters. The monoesters were conjugated to bovine serum albumin (BSA) at different concentrations of hapten using 0.05 and 0.5M pH 9 borate buffer. Maximum loading was achieved faster, and the conjugation efficiency was higher, when the conjugation was conducted at higher concentrations of both hapten and buffer. Conjugations involving haptens 14-17 prepared from hydrazide 13 were generally slower and less efficient than those with compounds 5-8, which were made from amino amide 4. Maintaining pH 9 during conjugation was found to be the most important factor in ensuring that the conjugation was a fast, highly efficient, and reproducible process. When the pH of the conjugation mixture fell during the reaction, resulting in decreased reaction rate or even termination of the conjugation process, the normal course of the conjugation process could be restored by addition of buffer salts. Hydrolysis studies with monoesters formed from amino amide 4 under conjugation conditions showed that decyl ester 8 was the most stable and that the methyl compound 5 was the one most readily hydrolyzed. The stability of monoesters prepared from hydrazide 13 was similar and comparable to the decyl ester prepared from 4. No definite advantage was found for the use of any of the four dialkyl squarate reagents (methyl-, ethyl-, butyl-, and decyl-) for conversion of carbohydrate derivatives to species amenable for conjugation. Nevertheless, dimethyl squarate seemed to be the most convenient reagent because it is a crystalline, easy to handle, and commercially available material with very good reactivity.     

Effect of plant growth regulators on regeneration of plantlets from bud cultures ofCymbopogon nardus L. and the detection of essential oils from thein vitro plantlets

Cymbopogon nardus L. could be propagated via tissue culture using axillary buds as explants. The aseptic bud explants obtained using double sterilization methods produced stunted abnormal multiple shoots when they were cultured on Murashige and Skoog medium (MS) supplemented with 1.0 mg L^-1 or 2.0 mg L^-1 benzyladenine (BA). Stunted shoots that cultured on MS + 1.0 mg L^-1 BA + 1.0 mg L^-1 N⁶-isopentenyl-adenine (2iP) could induce elongation of shoots from about 60% of the stunted shoots. Normal multiple shoots could be induced at the highest (19.7 shoots per bud) from the bud explants within six weeks when cultured on proliferation medium consisted of MS supplemented with 0.3 mg L^-1 BA and 0.1 mg L^-1 indole-3-butyric acid (IBA). The separated individual shoot produced roots when transferred to basic MS solid medium. The essential oils that were contained in the mature plants namely citronellal, geraniol and citronellol were also found in thein vitro C. nardus plantlets. Citronellal was the main essential oil component in the matured plants while geraniol was the main component in thein vitro plantlets.     

Transactivation of ErbB2 and ErbB3 by tumor necrosis factor-alpha and anisomycin leads to impaired insulin signaling through serine/threonine phosphorylation of IRS proteins.

The cellular pathways involved in the impairment of insulin signaling by cellular stress, triggered by the inflammatory cytokine tumor necrosis factor-alpha (TNF) or by translational inhibitors like cycloheximide and anisomycin were studied. Similar to TNF, cycloheximide and anisomycin stimulated serine phosphorylation of IRS-1 and IRS-2, reduced their ability to interact with the insulin receptor, inhibited the insulin-induced tyrosine phosphorylation of IRS proteins, and diminished their association with phosphatidylinositol 3-kinase (PI3K). These defects were partially reversed by wortmannin and LY294002, indicating that a PI3K-regulated step is critical for the impairment of insulin signaling by cellular stress. Induction of cellular stress resulted in complex formation between PI3K and ErbB2/ErbB3 and enhanced PI3K activity, implicating ErbB proteins as downstream effectors of stress-induced insulin resistance. Indeed, stimulation of ErbB2/ErbB3 by NDFbeta1, the ErbB3 ligand, inhibited IRS protein tyrosine phosphorylation and recruitment of downstream effectors. Specific inhibitors of the ErbB2 tyrosine kinase abrogated the activation of ErbB2/ErbB3 and in parallel prevented the reduction in IRS protein functions. Taken together, our results suggest a novel mechanism by which cellular stress induces cross-talk between two different signaling pathways. Stress-dependent transactivation of ErbB2/ErbB3 receptors triggers a PI3K cascade that induces serine phosphorylation of IRS proteins culminating in insulin resistance.     

Feeding ecology and specialist diet of critically endangered Ridgway's Hawks

Ridgway's Hawks (Buteo ridgwayi) are critically endangered forest raptors endemic to the Caribbean island of Hispaniola, with ～100 pairs remaining in the world. The species is ecologically little known yet such studies are important for understanding critical habitat needs and population dynamics. We studied the provisioning behavior of adults at 22 nests on the northeast coast of the Dominican Republic from 2005 to 2008. Mean brood size was 1.80 ± 0.45, and the mean number of fledglings per nest was 1.10 ± 0.97. We found that 80% of the prey items delivered to nestlings were reptiles, with lizards accounting for 65% of the prey and those in the genus Celestus accounting for nearly 35% of prey. Other prey items included snakes (14%), rats (9%), and smaller proportions of birds, frogs, and centipedes. The number of prey items and amount of biomass delivered to nestlings did not vary with brood size, but adults delivered more prey to 3‐ to 5‐week‐old nestlings and more biomass to 5‐week‐old nestlings. Food delivery rates did not differ between successful or failed nests, suggesting that food availability did not influence nest outcome. Given that most prey items delivered to nestlings in our study were reptiles, conservation strategies developed for Ridgway's Hawks (e.g., translocations and habitat conservation) should take into consideration their specialist reptile diet.