Chlorophyll-deficient gene and morphological variations in Korean populations of maize (Zea mays)

We studied cultivated and naturalized Korean maize populations to determine the extent to which the chlorophylldeficient mutation and the phenotypic variations of two morphological characters (i.e., red coleoptiles and epicotyls, and the number of the first root hairs) are maintained. The frequency of the chlorophyll-deficient mutant gene (2.73% on average) was highly variable. Frequencies of red coleoptiles and epicotyls also were higher than expected from a mutation-selection balance. The average number of hairy phenotypes within populations was 1.8, ranging from 0.0 to 4.0. Naturalized populations were closely related to with cultivated communities. Most striking, however, was the more significant difference among populations than within populations with regard to both the frequency of chlorophyll-deficient mutant genes and the phenotypic variations of our two morphological characters. On a per-gene basis, the majority of the phenotypic variation (mean of 73.3%) resided among populations.     

The structure of S100A11 fragment explains a local structural change induced by phosphorylation

S100A11 protein is a member of the S100 family containing two EF‐hand motifs. It undergoes phophorylation on residue T10 after cell stimulation such as an increase in Ca²⁺ concentration. Phosphorylated S100A11 can be recognized by its target protein, nucleolin. Although S100A11 is initially expressed in the cytoplasm, it is transported to the nucleus by the action of nucleolin. In the nucleus, S100A11 suppresses the growth of keratinocytes through p21^CIP1/WAF1 activation and induces cell differentiation. Interestingly, the N‐terminal fragment of S100A11 has the same activity as the full‐length protein; i.e. it is phosphorylated in vivo and binds to nucleolin. In addition, this fragment leads to the arrest of cultured keratinocyte growth. We examined the solution structure of this fragment peptide and explored its structural properties before and after phosphorylation. In a trifluoroethanol solution, the peptide adopts the α‐helical structure just as the corresponding region of the full‐length S100A11. Phosphorylation induces a disruption of the N‐capping conformation of the α‐helix, and has a tendency to perturb its surrounding structure. Therefore, the phosphorylated threonine lies in the N‐terminal edge of the α‐helix. This local structural change can reasonably explain why the phosphorylation of a residue that is initially buried in the interior of protein allows it to be recognized by the binding partner. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd.     

Rectal water absorption in seawater-adapted Japanese eel Anguilla japonica

Marine teleosts drink large amounts of seawater to compensate for continuous osmotic water loss. We investigated a possible significant role of the rectum in water absorption in seawater-adapted eel. In rectal sacs filled with balanced salt solution (BSS) and incubated in isotonic BSS, water absorption was greater in seawater-adapted eel than in freshwater eel. Since rectal fluid osmolality was slightly lower than plasma osmolality in seawater-adapted eel, effects of rectal fluid osmolality on water absorption were examined in rectal sacs filled with artificial rectal fluid with different osmolality. Rectal water absorption was greater at lower rectal fluid osmolality, suggesting that an osmotic gradient between the blood and rectal fluid drives the water movement. Ouabain, a specific inhibitor of Na⁺/K⁺-ATPase, inhibited water absorption in rectal sacs, indicating that an osmotic gradient favorable to rectal water absorption was created by ion uptake driven by Na⁺/K⁺-ATPase. Expression levels of aquaporin 1 (AQP1), a water-selective channel, were significantly higher in the rectum than in the anterior and posterior intestines. Immunoreaction for Na⁺/K⁺-ATPase was detected in the mucosal epithelial cells in the rectum with more intense staining in the basal half than in the apical half, whereas AQP1 was located in the apical membrane of Na⁺/K⁺-ATPase-immunoreactive epithelial cells. The rectum is spatially separated from the posterior intestine by a valve structure and from the anus by a sphincter. Such structures allow the rectum to swell as intestinal fluid flows into it, and a concomitant increase in hydrostatic pressure may provide an additional force for rectal water absorption. Our findings indicate that the rectum contributes greatly to high efficiency of intestinal water absorption by simultaneous absorption of ions and water.     

Lysophosphatidic acid-induced c-fos up-regulation involves cyclic AMP response element-binding protein activated by mitogen- and stress-activated protein kinase-1

Lysophosphatidic acid (LPA) is a lipid growth factor that exerts diverse biological effects through its cognate receptor-mediated signaling cascades. Recently, we reported that LPA stimulates cAMP response element-binding protein (CREB) through mitogen- and stress-activated protein kinase-1 (MSK1). Previously, LPA has been shown to stimulate c-fos mRNA expression in Rat-2 fibroblast cells via a serum response element binding protein (SRF). However, involvement of CREB in LPA-stimulated c-fos gene expression is not elucidated yet. To investigate the CREB-mediated c-fos activation by LPA, various c-fos promoter-reporter constructs containing wild-type and mutated SRE and CRE were tested for their inducibility by LPA in transient transfection assays. LPA-stimulated c-fos promoter activation was markedly decreased when SRE and CRE were mutated. A dominant negative CREB significantly down-regulated the LPA-stimulated c-fos promoter activation. Chromatin immunoprecipitation assay revealed that LPA induced an increased binding of phosphorylated CREB and CREB-binding protein (CBP) to the CRE region of the endogenous c-fos promoter. Immunoblot analyses with various pharmacological inhibitors further showed that LPA induces up-regulation of c-fos mRNA level by activation of ERK, p38 MAPK, and MSK1. Taken together, our results suggest that CREB plays an important role in up-regulation of c-fos mRNA level in LPA-stimulated Rat-2 fibroblast cells.     

Ion exclusion mechanism in aquaporin at an atomistic level

Although the mechanism of proton exclusion in aquaporin is investigated by many researchers, the detailed molecular mechanism for ion exclusion in aquaporin is still not completely understood. In the present work, a detailed mechanism for ion exclusion in aquaporin-1 (AQP1) at an atomistic level is investigated by calculating the free energy for transport of ions in AQP1 using an atomistic molecular dynamics simulation. For this purpose, sodium and chloride ions are chosen as representatives for nonprotonic ions. The simulation shows that the free energy barrier showing its maximum is located at the NPA region for sodium ion while it is located at both the front and the rear for chloride ion and that the barrier height is 18 and 9 kcal/mol, respectively, indicating that the ions are not able to pass through aquaporin. Analysis of the pair interaction energy between the permeating ion and its environment reveals that sodium ion is excluded by the positive charge generated by two alpha-helical macro-dipoles, while chloride ion is expelled by carbonyl oxygen atoms protruding from pore-making residues before it reaches the NPA motif. It is also found that the number of water molecules hydrating the ions is reduced as the ions enter the pore, implying that the energetic cost for detaching water molecules from a permeating ion also contributes to the free energy barriers of ion transport in AQP1.