In vitro toxicology of fumonisins and the mechanistic implications

The effects of fumonisins B₁FB₁, B₂(FB{2}), and the backbone of fumonisin B₁ remaining after hydrolysis of the tricarballylic groups with base (HFB₁) on sphingolipid biosynthesis were studied in both primary rat hepatocytes and pig kidney epithelial cells (LLC-PK₁). Fumonisins were potent inhibitors of sphingolipid biosynthesis in hepatocytes (IC₅₀ of FB₁=0.1 M), but overt toxicity was not observed. In renal cells, fumonisins also inhibited sphingosine biosynthesis (IC₅₀ for FB₁=35 M), and caused decreased cell proliferation as well. Higher doses (70 M) killed renal cells after exposure for 3 days. The inhibition of de novo sphingolipid biosynthesis was specific, and appeared to be at the site of ceramide synthase, which catalyzes the formation of dihydroceramide or ceramide by the addition of the amide-linked fatty acid to sphinganine or sphingosine. These results may account for the ability of fumonisins to cause equine leucoencephalomalacia and to promote tumor formation.     

Differentially regulated malate synthase genes participate in carbon and nitrogen metabolism of S. cerevisiae.

We have isolated a second gene (MLS1), which in addition to DAL7, encodes malate synthase from S. cerevisiae. Expression of the two genes is specific for their physiological roles in carbon and nitrogen metabolism. Expression of MLS1, which participates in the utilization of non-fermentable carbon sources, is sensitive to carbon catabolite repression, but nearly insensitive to nitrogen catabolite repression. DAL7, which participates in catabolism of the nitrogenous compound allantoin, is insensitive to carbon catabolite repression, but highly sensitive to nitrogen catabolite repression. Results obtained with null mutations in these genes suggest that S. cerevisiae contains at least one and perhaps two additional malate synthase genes.     

Genotype of Yupik Eskimos with congenital adrenal hyperplasia due to 21-hydroxylase deficiency

Summary An A-to-G transition in the second intron was the sole mutation detected in four Yupik Eskimo patients with salt-wasting congenital adrenal hyperplasia due to steroid 21-hydroxylase deficiency. Allele-specific hybridization should be an efficient means of performing prenatal diagnosis of the disease in this highly inbred population.     

Regional assignment of the human uroporphyrinogen III synthase (UROS) gene to chromosome 10q25.2→q26.3

Summary Uroporphyrinogen III synthase [UROS; hydroxymethylbilane hydro-lyase (cyclizing), EC 4.2.1.75] is the fourth enzyme in the human heme biosynthetic pathway. The recent isolation of the cDNA encoding human UROS facilitated its chromosomal localization. Human UROS sequences were specifically amplified by the polymerase chain reaction (PCR) from genomic DNA of two independent panels of human-rodent somatic cell hybrids. There was 100% concordance for the presence of the human UROS PCR product and human chromosome 10. For each of the other chromosomes, there was 19%–53% discordance with human UROS. The chromosomal assignment was confirmed by Southern hybridization analysis of DNA from somatic cell hybrids with the full-length UROS cDNA. Using human-rodent hybrids containing different portions of human chromosome 10, we assigned the UROS gene to the region 10q25.2 q26.3.     

Targeted Selection Experiments and Enzyme Polymorphism: Negative Evidence for Octanoate Selection at the G6PD Locus in DROSOPHILA MELANOGASTER

Published studies have reported significant selection with respect to the G6pd locus for Drosophila melanogaster reared on Na-octanoate food. We have reexamined the selective effects of Na-octanoate on egg to adult viability with respect to the G6pd polymorphism using specially constructed X chromosomes. Four experiments were carried out using different 6Pgd backgrounds in two recombinant sets of chromosomes segregating for the G6pd locus but constructed so as to minimize variation over most of the X chromosome. In addition, two measures of viability were used, and the size of the experiments and their associated degrees of freedom are approximately double those reported in the former studies. Our results find no evidence for differential selection on G6pd genotypes (males and females) by Na-octanoate and, therefore, do not corroborate the positive results of selection reported by other investigators. The reasons for our different results are discussed.     

On the Theory of Speciation Induced by Transposable Elements

A simple methematical model describes the invasion of panmictic, sexually reproducing populations by a newly introduced transposon. The model places important constraints on the properties that transposons must have to successfully invade a population and describes the kinetics with which such an invasion will occur. Invasibility conditions serve as a basis for new, detailed scenarios whereby transposon-mediated depression in fitness produces reproductive isolation of populations. These scenarios, in turn, lead to several speculations concerning the role of transposons in evolution.     

Digestion by the larva of the pruinose scarab, Sericesthis geminata

An in vitro study of digestion by the subterranean larva of S. geminata revealed the presence of enzymes able to digest starch, trehalose, salicin, cellobiose, melibiose, maltose, sucrose, casein, and several forms of cellulose. The midgut is the major source of all enzymes except invertase and CMC-cellulase, for which hindgut preparations are more active. The pH values of the gut contents are: foregut 6.9, midgut 9.0 and hindgut 7.5. The midgut fluid is pumped forward into the foregut, and the carbohydrases in it are generally more active at the pH of the foregut than at the pH of the midgut. It is possible, therefore, that the foregut, which is itself insignificant as a source of enzymes, is the site of considerable carbohydrate digestion. The proteinase is inhibited 28% by trypsin inhibitors.

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Zusammenfassung Eine in vitro-Untersuchung über die Verdauungsvorgänge in den unterirdisch lebenden Larven von S. geminata wies Enzyme nach, die Stärke, Trehalose, Salicin, Cellobiose, Melibiose, Maltose, Rohrzucker, Kasein und mehrere Celluloseformen abbauen können. Versuche mit Vorder-, Mittel- und Enddarmextrakten zeigten, daß der Abbau von Rohrzucker und CMC-Cellulose in Ansätzen mit Enddarmpräparaten prozentual am höchsten war. Maximale Verdauung aller anderen geprüften Substrate erfolgte dagegen mit Mitteldarmpräparaten.Die pH-Werte betrugen im Vorderdarm 6,9, im Mitteldarm 9,0 und im Enddarm 7,5. Im Mittel- und Enddarm lagen die jewciligen optimalen pH-Werte für Maltose bei 6,5–7,0 und 7,5, für Melibiose bei 6,0–7,0 und 7,0–7,5, für Cellobiose bei 6,0–7,0 und 4,5, für Rohrzucker bei 7,0 und 6,0, für CMC bei 5,2 und 5,6.Die Verdauung unlöslicher Celluloseformen war durchweg gering, die der CMC dagegen beträchtlich.Die Mitteldarmflüssigkeit wird nach vorn in den Vorderdarm gepumpt. Die darin enthaltenen Carbohydrasen sind beim pH-Wert des Vorderdarmes meistens wirksamer als in dem des Mitteldarmes. Es ist deshalb möglich, daß im Vorderdarm, welcher selbst wahrscheinlich keine Enzyme produziert, doch eine beträchtliche Kohlenhydratverdauung stattfindet.Die Wirksamkeit der Proteinase wird durch bekannte Tryptin-Hemmstoffe um 28% reduziert.