Hox genes: the instructors working at motor pools

Motor neurons are assigned unique subidentities preceding their axon navigation. This ensures proper innervation of muscle targets and is accompanied by a stereotypical clustering of motor neuron cell bodies into "motor pools" within the spinal cord. However, the mechanisms that drive motor neuron diversification have been poorly understood. A new study by Dasen et al. (2005) in this issue of Cell shows that a network of Hox genes is responsible for instructing motor pool development.     

Modifications in P62 occur due to proteasome inhibition in alcoholic liver disease

P62 is capable of binding the polyubiquitin chain that targets proteins for degradation by the proteasome through its ubiquitin associated domain (UBA). Immunostaining of hepatocytes from human liver with alcoholic hepatitis showed colocalization of ubiquitin and P62 in Mallory bodies. Rats fed ethanol chronically and their controls showed that P62 is colocalized with the proteasome in hepatocytes as shown by confocal microscopy. P62 cosedimented with 26S proteasomes isolated from livers of control and alcohol fed rats. P62 was increased in the 26S proteasome fraction when the proteasome chymotrypsin-like (ChT-L) activity decreased in rats fed ethanol. PS-341, a potent proteasome inhibitor was used to compare the inhibition of the proteasome with the inhibition which occurs with ethanol feeding. P62 protein levels were also increased in the purified proteasome fraction of rats given PS-341. This data indicates that modifications in P62 occur due to proteasome inhibition in experimental alcoholic liver disease.     

Electro-acupuncture potentiates the disulphide-reducing activities of thioredoxin system by increasing thioredoxin expression in ischemia-reperfused rat brains

Reactive oxygen species can directly affect the conformation and activity of sulfhydryl-containing proteins by oxidation of their thiol moiety. During the process of ischemia-reperfusion, the thioredoxin (Trx) system (consisting of thioredoxin reductase (TR), Trx and NADPH) prevents susceptible proteins from this oxidative modification. Oxidative damage is one of the most damaging stress in ischemia. If oxidative stress could be minimized, the damage occurred will be minimized accordingly. We therefore investigated whether electroacupuncture (EA) treatment at Fengchi (GB20) or Zusanli (ST36) acupoints in post-ischemic rats could increase TR-related activities and Trx expression which would translate into maintaining the intact thiol moiety of susceptible proteins in the surrounding. Our results indicated that EA treatment at either acupoint increased the Trx expression in ischemic-reperfused brain tissues. Induced Trx expressed levels gradually increased from post-ischemia day 1 to day 4. Statistical analysis revealed that there was no observable difference in the effect of EA treatment at GB20 and ST36. Sham EA treatment did not induce any Trx expression. EA at either acupoint did not alter TR activities in both non-ischemic and ischemic-reperfused rat brains. Taken overall, our finding suggests that EA treatment at GB20 or ST36 could increase Trx expression which could minimize oxidative modifications of thiol groups of surrounding proteins.     

Ultraviolet radiation: effects on risks of prostate cancer and other internal cancers

Governmental and research agencies worldwide have strongly advocated sun avoidance strategies in an attempt to counter marked increases in skin cancer incidence. Concurrently, there are reports describing widespread Vitamin D3 deficiency. Because 1,25-dihydroxyvitamin D3, through interaction with the Vitamin D receptor, exerts pleiotrophic effects, such deficiency might be expected to have clinical consequences. Indeed, various reports indicate that exposure to ultraviolet radiation (UVR) exerts a protective effect on development of some common diseases including internal cancers and multiple sclerosis. We describe studies indicating that modest exposure reduces risk of prostate cancer. The effect of UVR is mediated by skin type; at lower levels of exposure a relative inability to effect skin pigmentation is protective presumably because it allows more efficient Vitamin D3 synthesis. Polymorphic variants in genes associated with pigmentation including melanocyte stimulating hormone receptor and tyrosinase are also associated with prostate cancer risk. Overall, though preliminary and requiring cautious interpretation, these data indicate that moderate UVR exposure together with characteristics linked with less effective tanning confer reduced prostate cancer risk. Clearly, it is important to define safe levels of UVR that do not result in increased risk of skin cancers such as malignant melanoma.     

Effect of peripherally administered ghrelin on gastric emptying and acid secretion in the rat

Ghrelin is a gut peptide that is secreted from the stomach and stimulates food intake. There are ghrelin receptors throughout the gut and intracerebroventricular ghrelin has been shown to increase gastric acid secretion. The aim of the present study was to examine the effects of peripherally administered ghrelin on gastric emptying of a non-nutrient and nutrient liquid, as well as, basal and pentagastrin-stimulated gastric acid secretion in awake rats. In addition, gastric contractility was studied in vitro. Rats equipped with a gastric fistula were subjected to an intravenous infusion of ghrelin (10-500 pmol kg(-1) min(-1)) during saline or pentagastrin (90 pmol kg(-1) min(-1)) infusion. After administration of polyethylene glycol (PEG) 4000 with 51Cr as radioactive marker, or a liquid nutrient with (51)Cr, gastric retention was measured after a 20-min infusion of ghrelin (500 pmol kg(-1) min(-1)). In vitro isometric contractions of segments of rat gastric fundus were studied (10(-9) to 10(-6) M). Ghrelin had no effect on basal acid secretion, but at 500 pmol kg(-1) min(-1) ghrelin significantly decreased pentagastrin-stimulated acid secretion. Ghrelin had no effect on gastric emptying of the nutrient liquid, but significantly increased gastric emptying of the non-nutrient liquid. Ghrelin contracted fundus muscle strips dose-dependently (pD2 of 6.93+/-0.7). Ghrelin IV decreased plasma orexin A concentrations and increased plasma somatostatin concentrations. Plasma gastrin concentrations were unchanged during ghrelin infusion. Thus, ghrelin seems to not only effect food intake but also gastric motor and secretory function indicating a multifunctional role for ghrelin in energy homeostasis.     

Stimulatory effect of endogenous orexin A on gastric emptying and acid secretion independent of gastrin

Orexin A (OXA) increases food intake and inhibits fasting small bowel motility in rats. The aim of this study was to examine the effect of exogenous OXA and endogenous OXA on gastric emptying, acid secretion, glucose metabolism and distribution of orexin immunoreactivity in the stomach. Rats equipped with a gastric fistula were subjected to intravenous (IV) infusion of OXA or the selective orexin-1 receptor (OX1R) antagonist SB-334867-A during saline or pentagastrin infusion. Gastric emptying was studied with a liquid non-nutrient or nutrient, using 51Cr as radioactive marker. Gastric retention was measured after a 20-min infusion of OXA or SB-334867-A. Plasma concentrations of OXA, insulin, glucagon, glucose and gastrin were studied. Immunohistochemistry against OXA, OX1R and gastrin in gastric tissue was performed. OXA alone had no effect on either acid secretion or gastric emptying. SB-334867-A inhibited both basal and pentagastrin-induced gastric acid secretion and increased gastric retention of the liquid nutrient, but not PEG 4000. Plasma gastrin levels were unchanged by IV OXA or SB-334867-A. Plasma OXA levels decreased after intake of the nutrient meal and infusion of the OX1R antagonist. Only weak effects were seen on plasma glucose and insulin by OXA. Immunoreactivity to OXA and OX1R were found in the mucosa, myenteric cells bodies and varicose nerve fibers in ganglia and circular muscle of the stomach. In conclusion, endogenous OXA influences gastric emptying of a nutrient liquid and gastric acid secretion independent of gastrin. This indicates a role for endogenous OXA, not only in metabolic homeostasis, but also in the pre-absorptive processing of nutrients in the gut.     

The <Emphasis Type="Italic">Chlamydomonas reinhardtii gtr </Emphasis>Gene Encoding the Tetrapyrrole Biosynthetic Enzyme Glutamyl-tRNA Reductase: Structure of the Gene and Properties of the Expressed Enzyme

Plants, algae, cyanobacteria and many other bacteria synthesize the tetrapyrrole precursor, δ-aminolevulinic acid (ALA), from glutamate by means of a tRNA^Glu-mediated pathway. The enzyme glutamyl-tRNA reductase (GTR) catalyzes the first committed step in this pathway, which is the reduction of tRNA-bound glutamate to produce glutamate 1-semialdehyde. Chlamydomonas reinhardtii mRNA encoding gtr was sequenced from a cDNA and genomic libraries. The 3179-bp gtr cDNA contains a 1566-bp open reading frame that encodes a 522-amino acid polypeptide. After removal of the predicted transit peptide, the mature 480-residue GTR has a calculated molecular weight of 52,502. The deduced C. reinhardtii mature GTR amino acid sequence has more than 55% identity to a GTR sequence of Arabidopsis thaliana, and significant similarity to GTR proteins of other plants and prokaryotes. Southern blot analysis of C. reinhardtii genomic DNA indicates that C. reinhardtii has only one gtr gene. Genomic DNA sequencing revealed the presence of a small intron near the putative transit peptide cleavage site. Expression constructs for the full-length initial gtr translation product, the mature protein after transit peptide removal, and the coding sequence of the second exon were cloned into expression vector that also introduced a C-terminal His₆ tag. All of these constructs were expressed in E. coli, and both the mature protein and the exon 2 translation product complemented a hemA mutation. The expressed proteins were purified by Ni-affinity column chromatography to yield active GTR. Purified mature GTR was not inhibited by heme, but heme inhibition was restored upon addition of C. reinhardtii soluble proteins.     

Profiling the Expression of Genes Controlling Rice Grain Quality

Rice provides a staple source of energy, protein and other nutrients to half of the world population. Over 90 of the rice seeds consists of starch and protein by dry weight. The quantity and property of starch and protein thus play a dominant role in the yield and quality of rice. The amylase content of starch is a determining factor in the eating and cooking quality while the amount and essential amino acids balance of storage proteins affect the nutritional quality of rice. In China, the super-hybrid rice currently under the last phase of development has a 35 yield advantage over the best inbred rice varieties. However, its grain quality needs further improvement. This study reported the expression patterns of 44 genes participating in starch, storage protein, and lysine synthesis in the developing rice grain. Field grown rice cultivar 9311, the paternal line of an elite super-hybrid rice LYP9with its draft genomic sequence released, was used as plant material. Results revealed diverse yet coordinated expression profiles of the genes involved in the three pathways which lead to the final composition and property of starch, protein and lysine that determine the quality of rice, providing useful information for rice quality improvement.     

Enhanced oligonucleotide binding to self-assembled nanofibers

A peptide nucleic acid/peptide amphiphile conjugate (PNA-PA) that self-assembles into fiber-shaped nanostructures was designed to bind oligonucleotides with high affinity and specificity. Oligonucleotide binding to PNA-PA nanofibers was studied using fluorescence polarization, and thermal stability was examined by UV-vis measurement of duplex melting temperatures. The self-assembled PNA-PA DNA system was observed to bind more strongly than the corresponding DNA-DNA duplex. We also observed single base specificity with a 16 degrees C in thermal stability. As expected from the previous PNA studies, PNA-PA RNA binding is also stronger than the corresponding RNA-RNA duplex.