The transforming growth factor beta type II receptor can replace the activin type II receptor in inducing mesoderm.

The type II receptors for the polypeptide growth factors transforming growth factor beta (TGF-beta) and activin belong to a new family of predicted serine/threonine protein kinases. In Xenopus embryos, the biological effects of activin and TGF-beta 1 are strikingly different; activin induces a full range of mesodermal cell types in the animal cap assay, while TGF-beta 1 has no effects, presumably because of the lack of functional TGF-beta receptors. In order to assess the biological activities of exogenously added TGF-beta 1, RNA encoding the TGF-beta type II receptor was introduced into Xenopus embryos. In animal caps from these embryos, TGF-beta 1 and activin show similar potencies for induction of mesoderm-specific mRNAs, and both elicit the same types of mesodermal tissues. In addition, the response of animal caps to TGF-beta 1, as well as to activin, is blocked by a dominant inhibitory ras mutant, p21(Asn-17)Ha-ras. These results indicate that the activin and TGF-beta type II receptors can couple to similar signalling pathways and that the biological specificities of these growth factors lie in their different ligand-binding domains and in different competences of the responding cells.     

Correlation of phospholipid structure with functional effects on the nicotinic acetylcholine receptor. A modulatory role for phosphatidic acid.

Fourier transform infrared spectroscopy is used to characterize specific interactions between negatively charged lipids, such as phosphatidic acid, and the purified nicotinic acetylcholine receptor from Torpedo californica. The specific interaction of phosphatidic acid with acetylcholine receptor is demonstrated by the receptor-induced perturbation of the lipid ionization state, which is monitored using Fourier transform infrared bands arising from the phosphate head group. The acetylcholine receptor shifts the pKa of phosphatidic acid molecules adjacent to the receptor to a lower value by almost 2 pH units from 8.5 to 6.6. Decreased pH also leads to changes in ion channel function and to changes in the secondary structure of the acetylcholine receptor in membranes containing ionizable phospholipids. Phospholipase D restores functional activity of acetylcholine receptor reconstituted in an unfavorable environment containing phosphatidylcholine by generating phosphatidic acid. Lipids such as phosphatidic acid may serve as allosteric effectors for membrane protein function and the lipid-protein interface could be a site for activity-dependent changes that lead to modulation of synaptic efficacy.     

Isolation, Purification and Partial Characterisation of Urease from Seeds of Water Melon (Citrullus vulgaris)

Urease from seeds of water melon was purified to apparent homogeniety upto a sp act of 3750 units/mg protein with 31% recovery. Enzyme showed single protein band on native PAGE by urease specific staining. The mol wt of the enzyme was 4,70,000 and the preparation was free from bound nucleotides (A₂₈₀/A₂₆₀=1.14). The enzyme exhibited maximum activity in 50 mM Tris-acetate buffer (pH 8.5). The Km for urease was 8 mM. The enzyme was not inhibited by 25 mM of EDTA in 50 mM Tris-acetate buffer (pH 8.0 and 8.5).     

Brassinolide, a growth-promoting steroidal lactone

Brassinolide (BR), a naturally-occurring-steroidal lactone from rape ( Brassica napus L.) pollen, was compared with auxin for activity in a number of bioassay systems. Responses similar to IAA were elicited by BR in bioassays based upon bean hypocotyl hook opening, elongation of maize mesocotyl, pea epicotyl and azuki bean epicotyl sections, and fresh weight increase in Jerusalem artichoke (2,4-D used) and pea epicotyl sections. The azuki bean and dwarf pea epicotyl bioassays were much more responsive to BR than IAA (at 10 μ M ). Responses approximately two-fold greater in magnitude were elicited by IAA in the maize mesocotyl, bean hypocotyl hook and Jerusalem artichoke bioassays. Little or no response was elicited by BR (0.01 to μ M ) in the cress root or decapitated pea-lateral bud bioassays. A powerful synergism between BR and IAA was observed in the azuki bean, pea epicotyl and bean hypocotyl hook bioassays. Although, as previously reported, other steroidal substances are active in some of the bioassay systems tested, none compared with BR in magnitude and diversity of elicited responses.     

Synthesis and biological activity of brassinolide and its 22β,23β-isomer: Novel plant growth-promoting steroids

Brassinolide (2α,3α,22α, 23α-tetrahydroxy-24α-methyl-B-homo-7-oxa-5α-cholestan-6-one), a novel plant growth-promoting steroid isolated from rape pollen, and its hitherto unknown 22β, 23β-isomer were synthesized from a C-24 epimeric 60:40 mixture of 22-dehydrocampesterol (24α-methyl) and brassicasterol (24β-methyl) from oysters. The method of synthesis favored the formation of the 22β, 23β-isomer by better than 4:1. Comparative plant growth-promoting capabilities of brassinolide, both natural and synthetic, and its three side chain $\text{cis}$-glycolic isomers in the bean second internode bioassay showed that the natural and synthetic brassinolides were equally active and caused splitting of the internode at the 0.1 μg level. The least active was the 22β,23β-isomer of brassinolide. The isomers with the 22α, 23α and 24β, and the 22β, 23β and 24β configurations were highly active and were required at about 10 times the concentration of brassinolide to cause the same physiological response. In the bean first internode bioassay, an auxin-induced growth test system which employs isolated bean plant segments, the isomer with 22β, 23β and 24β configuration caused a greater response than brassinolide. Two of the four tetrahydroxy ketones obtained in the synthesis of the isomers were also active in both assays.     

Methylmercury: Effects on electrical properties of squid axon membranes

At low concentrations (25–100 μM) methylmercury chloride caused a steady increase in the threshold for excitation and on eventual block of action potentials without changing the resting membrane potential in squid giant axons. In the axons exposed to 25 μM methylmercury chloride, peak transient and steady-state conductances were decreased by 58.8 ± 5.1% and 35.9 ± 4.3% (mean ± SEM, 4 axons), respectively and leakage conductance increased to about five times of the control value. Higher concentrations of methylmercury chloride decreased the resting membrane potential. A concentration of 0.5 mM depolarizing the nerve membrane by 16 ± 2 mV (mean ± SEM, 3 axons) in 40 minutes. These changes in ionic conductances and membrane potential were irreversible on washing the axon with drug-free sea water.     

Rapid resolution of phenylthiohydantoin amino acids by thin-layer chromatography on silica gel plates impregnated with transition metal ions

The resolution of a 15-component mixture of phenylthiohydantoin (PTH) amino acids using metal ion impregnated silica gel plates is reported. The spots are located by exposing the chromatograms to an iodine chamber. The method provides a rapid, simple, and less expensive chromatographic system, provides resolution for certain difficult combinations, and leaves the PTH amino acids unaltered chemically.     

Diversity and polymorphism in AHL-lactonase gene (aiiA) of Bacillus

To explore bacterial diversity for elucidating genetic variability in acylhomoserine lactone (AHL) lactonase structure, we screened 800 bacterial strains. It revealed the presence of a quorum quenching (QQ) AHL-lactonase gene (aiiA) in 42 strains. These 42 strains were identified using rrs (16S rDNA) sequencing as Bacillus strains, predominantly B. cereus. An in silico restriction endonuclease (RE) digestion of 22 AHL lactonase gene (aiiA) sequences (from NCBI database) belonging to 9 different genera, along with 42 aiiA gene sequences from different Bacillus spp. (isolated here) with 14 type II REs, revealed distinct patterns of fragments (nucleotide length and order) with four REs; AluI, DpnII, RsaI, and Tru9I. Our study reflects on the biodiversity of aiiA among Bacillus species. Bacillus sp. strain MBG11 with polymorphism (115Alanine > Valine) may confer increased stability to AHL lactonase, and can be a potential candidate for heterologous expression and mass production. Microbes with ability to produce AHL-lactonases degrade quorum sensing signals such as AHL by opening of the lactone ring. The naturally occurring diversity of QQ molecules provides opportunities to use them for preventing bacterial infections, spoilage of food, and bioremediation.     

Population genomics of wild and laboratory zebrafish (Danio rerio)

Understanding a wider range of genotype–phenotype associations can be achieved through ecological and evolutionary studies of traditional laboratory models. Here, we conducted the first large‐scale geographic analysis of genetic variation within and among wild zebrafish (Danio rerio) populations occurring in Nepal, India, and Bangladesh, and we genetically compared wild populations to several commonly used lab strains. We examined genetic variation at 1832 polymorphic EST‐based single nucleotide polymorphisms (SNPs) and the cytb mitochondrial gene in 13 wild populations and three lab strains. Natural populations were subdivided into three major mitochondrial DNA clades with an average among‐clade sequence divergence of 5.8%. SNPs revealed five major evolutionarily and genetically distinct groups with an overall F_ST of 0.170 (95% CI 0.105–0.254). These genetic groups corresponded to discrete geographic regions and appear to reflect isolation in refugia during past climate cycles. We detected 71 significantly divergent outlier loci (3.4%) and nine loci (0.5%) with significantly low F_ST values. Valleys of reduced heterozygosity, consistent with selective sweeps, surrounded six of the 71 outliers (8.5%). The lab strains formed two additional groups that were genetically distinct from all wild populations. An additional subset of outlier loci was consistent with domestication selection within lab strains. Substantial genetic variation that exists in zebrafish as a whole is missing from lab strains that we analysed. A combination of laboratory and field studies that incorporates genetic variation from divergent wild populations along with the wealth of molecular information available for this model organism provides an opportunity to advance our understanding of genetic influences on phenotypic variation for a vertebrate species.