Ultrastructure of auxiliary and gonimoblast cells during carposporophyte development in the red alga Cryptopleura ruprechtiana (Delesseriaceae, Ceramiales, Rhodophyta)

The ultrastructure sequence for the complete post-fertilization development is described in Cryptopleura ruprechtiana (C. Agardh) Kylin, a member of the Delesseriaceae. Following fertilization the diploid nucleus is transferred to the auxiliary cell. This contains typical red algal proplastids, cytoplasmic concentric membranes, numerous small vacuoles and lipid bodies. Crystalline inclusions and virus-like particles are also present. In addition darkly staining spherical masses possibly represent dehydrated haploid chromatin. The multinucleate auxiliary cell produces initially one large gonimoblast initial and subsequently many smaller gonimoblast initials. The first formed generative gonimoblast cell is similar in cellular structure to the auxiliary cell. Gonimoblast initials are uninucleate but through caryokinesis they become multinucleate. They undergo repeated cleavage to form more gonimoblast cells. Subsequent, centripetal cytokinesis results in the formation of clusters of gonimoblast cells. A new type structural cap or association is observed in the septal plugs that interconnect gonimoblast initials. Terminal or generative gonimoblast cells cleave to form additional gonimoblast cells. Only terminal gonimoblast cells are differentiated to carpospores.     

Behavioral, plasma, and calorimetric changes related to food texture modification in men

We hypothesized that food texture modifications might alter anticipatory reflexes, feeding behavior, and the postabsorptive consequences of ingestion. Two sets of complete meals with different textures but the same macronutrient composition were prepared. The first set was either a soup containing chunks of food (mixture) or the same soup blended until smooth (purée). The second set was either a rusk (R), a sandwich loaf (SL), or a liquid rusk meal (LR). We measured hunger and fullness feelings after ingestion of each food in a calibrated lunch, the ingestion rate, the duration between lunch and a spontaneous dinner request, the energy value, and the macronutrient composition of the ad libitum dinner. We also studied plasma modifications and respiratory gas exchanges from lunch to dinner. Feelings of hunger and fullness were not affected by texture modifications. The purée soup was consumed faster than the mixture (P < 0.05), and insulin, triacylglycerol, and energy expenditure were greater with the purée (P < 0.05). LR was less palatable than the other rusk lunch versions (P < 0.001), and R was ingested more slowly (P < 0.05). The lowest increase in plasma glucose occurred with SL, and the highest energy expenditure was seen with LR (P < 0.05). In humans, food texture modification affects not only eating patterns and palatability of ingestants but also metabolic management.     

Highly polymorphic repeat marker within the β-amyloid precursor protein gene

We have identified a polymorphic compound dinucleotide repeat sequence in intron 1 of the -amyloid precursor protein (APP) gene on chromosome 21. Using polymerase chain reaction (PCR) amplification of the locus, designated APPivsl, we detected 13 alleles in the CEPH family members (heterozygosity = 0.69). Lod score analysis showed complete linkage of the marker to the loci D21S210 and D21221.     

Thiocyanate catalyzes myeloperoxidase-initiated lipid oxidation in LDL

There is evidence that LDL oxidation may render the lipoprotein atherogenic. The myeloperoxidase-hydrogen peroxide (MPO/H2O2) system of activated phagocytes may be involved in this process. Chloride is supposed to be the major substrate for MPO, generating reactive hypochlorous acid (HOCl), modifying LDL. The pseudo-halide thiocyanate (SCN-) has been shown to be a suitable substrate for MPO, forming reactive HOSCN/SCN*. As relatively abundant levels of SCN- are found in plasma of smokers--a well-known risk group for cardiovascular disease--the ability of SCN- to act as a catalyst of LDL atherogenic modification by MPO/H2O2 was tested. Measurement of conjugated diene and lipid hydroperoxide formation in LDL preparations exposed to MPO/H2O2 revealed that SCN- catalyzed lipid oxidation in LDL. Chloride did not diminish the effect of SCN- on lipid oxidation. Surprisingly, SCN inhibited the HOCl-mediated apoprotein modification in LDL. Nitrite--recently found to be a substrate for MPO--showed some competing properties. MPO-mediated lipid oxidation was inhibited by heme poisons (azide, cyanide) and catalase. Ascorbic acid was the most effective compound in inhibiting the SCN- -catalyzed reaction. Bilirubin showed some action, whereas tocopherol was ineffective. When LDL oxidation was performed with activated human neutrophils, which employ the MPO pathway, SCN- catalyzed the cell-mediated LDL oxidation. The MPO/H2O2/SCN- system may have the potential to play a significant role in the oxidative modification of LDL--an observation further pointing to the link between the long-recognized risk factors of atherosclerosis: elevated levels of LDL and smoking.     

Ultrastructure of the differentiating zygotospores of Porphyra leucosticta (Rhodophyta)

The ultrastructure of zygotosporogenesis is described for the red alga Porphyra leucosticta Thuret. Packets of eight zygotosporangia, each packet derived from a single carpogonium are interspersed among vegetative cells. Zygotospore differentiation in Porphyra can be separated into three developmental stages. (i) Young zygotospores exhibit a nucleus and a large centrally located, lobed plastid with pyrenoid. Mucilage is produced within concentric membrane structures during their dilation, thus resulting in the formation of mucilage sacs. Subsequently, these sacs release their contents, initiating the zygotospore wall formation. Straight‐profiled dictyosomes produce vesicles that also provide wall material. During the later stages of young zygotospores, starch polymerization commences, (ii) Medium‐aged zygotospores are characterized by the presence of fibrous vacuoles. These are formed from the ‘fibrous vacuole associated organelles’. The fibrous vacuoles finally discharge their contents. (iii) Mature zygotospores are recognized by the presence of numerous cored vesicles produced by dictyosomes. Cored vesicles either discharge their contents or are incorporated into the fibrous vacuoles. There is a gradual reduction of starch granules during zygotospore differentiation. Mature zygotospores are surrounded by a fibrous wall, have a large chloroplast with pyrenoid and well‐depicted phycobilisomes but are devoid of starch granules.     

Aluminum ions stimulate the oxidizability of low density lipoprotein by Fe2+: implication in hemodialysis mediated atherogenic LDL modification

Objective: Al³⁺ stimulates Fe²⁺ induced lipid oxidation in liposomal and cellular systems. Low-density lipoprotein (LDL) oxidation may render the particle atherogenic. As elevated levels of Al³⁺ and increased lipid oxidation of LDL are found in sera of hemodialysis patients, we investigated the influence of Al³⁺ on LDL oxidation.

Materials and methods: Using different LDL modifying systems (Fe²⁺, Cu²⁺, free radical generating compounds, human endothelial cells, hemin/H₂O₂ and HOCl), the influence of Al³⁺ on LDL lipid and apoprotein alteration was investigated by altered electrophoretic mobility, lipid hydroperoxide-, conjugated diene- and TBARS formation.

Results: Al³⁺ could stimulate the oxidizability of LDL by Fe²⁺, but not in the other systems tested. Al³⁺ and Fe²⁺ were found to bind to LDL and Al³⁺could compete with Fe²⁺ binding to the lipoprotein. Fluorescence polarization data indicated that Al³⁺ does not affect the phospholipid compartment of LDL.

Conclusions:The results indicate that increased LDL oxidation by Fe²⁺ in presence of Al³⁺ might be due to blockage of Fe²⁺ binding sites on LDL making more free Fe²⁺ available for lipid oxidation.     

Conserved non-genic sequences - an unexpected feature of mammalian genomes

Mammalian genomes contain highly conserved sequences that are not functionally transcribed. These sequences are single copy and comprise approximately 1-2% of the human genome. Evolutionary analysis strongly supports their functional conservation, although their potentially diverse, functional attributes remain unknown. It is likely that genomic variation in conserved non-genic sequences is associated with phenotypic variability and human disorders. So how might their function and contribution to human disorders be examined?     

Alanine reverses the inhibitory effect of phenylalanine on acetylcholinesterase activity

The aim of this work was to evaluate, in vitro, the effect of L-alanine (Ala) on suckling rat brain acetylcholinesterase (AChE) and on eel Electrophorus electricus pure AChE inhibited by L-phenylalanine (Phe) as well as to investigate whether Phe or Ala is a competitive inhibitor or an effector of the enzyme. AChE activity was determined in brain homogenates and in the pure enzyme after 1 h preincubation with 1.2 mM of Phe or Ala as well as with Phe plus Ala. The activity of the pure AChE was also determined using as a substrate different amounts of acetylthiocholine. Ala reversed completely the inhibited AChE by Phe (18-20% in 500-600 microM substrate, p<0.01). Lineweaver-Burk plots showed that Vmax remained unchanged. However, Km was found increased with Phe (150%, p<0.001), decreased with Ala alone (50%, p<0.001) and unaltered with Phe plus Ala. It is suggested that: a) Phe presents a competitive inhibitory action with the substrate whereas Ala a competitive activation; b) Ala competition with Phe might unbind the latter from AChE molecule inducing the enzyme stimulation; c) Ala might reverse the inhibitory effect of Phe on brain AChE in phenylketonuric patients, if these results are extended into the in vivo reality.     

Isolation and Initial Characterization of a Novel Zinc Finger Gene, DNMT3L, on 21q22.3, Related to the Cytosine-5- Methyltransferase 3 Gene Family

We have isolated the DNMT3L gene that is related to the cytosine-5-methyltransferase 3 (DNMT3) family. The gene is located on chromosome 21q22.3 between the AIRE and the KIAA0653 genes and spans approximately 16 kb of genomic sequence. The encoded protein of 387 amino acids has a cysteine-rich region containing a novel-type zinc finger domain that is conserved in DNMT3A and DNMT3B but also in ATRX, a member of the SNF2 protein family. The novel domain, called an ADD (ATRX, DNMT3, DNMT3L)-type zinc finger, contains two subparts: a C2C2 and an imperfect PHD zinc finger. Expression of the DNMT3L mRNA was not detectable by Northern blotting; however, RT-PCR amplification revealed that it is expressed at low levels in several tissues including testis, ovary, and thymus.