Pluripotent differentiation in vitro of murine Es-D3 embryonic stem cells

Although the ES-D3 murine embryonic stem cell line was one of the first derived, little information exists on the in vitro differentiation potential of these cells. We have used immunocytochemical and flow cytometric methods to monitor ES-D3 embryoid body differentiation in vitro during a 21-d period. Spontaneous differentiation of embryoid body cells was induced by leukemia inhibitory factor withdrawal in the absence of feeder cells. The pluripotent stem cell markers Oct-3/4, SSEA-1, and EMA-1 were found to persist for at least 7 d, whereas the primitive endoderm marker cytokeratin endo-A was expressed at increasing levels from day 6. The localization of these antigens within the embryoid bodies suggested that embryonic ectoderm- and primitive endoderm-derived tissues were segregated. Localized expression of class III beta-tubulin and sarcomeric myosin also was detected, indicating that representatives of all three embryonic germ layers were present after induction of differentiation in vitro.     

alpha-Adrenergic response and myofilament activity in mouse hearts lacking PKC phosphorylation sites on cardiac TnI

Protein kinase C (PKC)-mediated phosphorylation of cardiac myofilament (MF) proteins has been shown to depress the actomyosin interaction and may be important during heart failure. Biochemical studies indicate that phosphorylation of Ser(43) and Ser(45) of cardiac troponin I (cTnI) plays a substantial role in the PKC-mediated depression. We studied intact and detergent-extracted papillary muscles from nontransgenic (NTG) and transgenic (TG) mouse hearts that express a mutant cTnI (Ser43Ala, Ser45Ala) that lacks specific PKC-dependent phosphorylation sites. Treatment of NTG papillary muscles with phenylephrine (PE) resulted in a transient increase and a subsequent 62% reduction in peak twitch force. TG muscles showed no transient increase and only a 45% reduction in force. There was a similar difference in maximum tension between NTG and TG fiber bundles that had been treated with a phorbol ester and had received subsequent detergent extraction. Although levels of cTnI phosphorylation correlated with these differences, the TG fibers also demonstrated a decrease in phosphorylation of cardiac troponin T. The PKC-specific inhibitor chelerythrine inhibited these responses. Our data provide evidence that specific PKC-mediated phosphorylation of Ser(43) and Ser(45) of cTnI plays an important role in regulating force development in the intact myocardium.     

Type A and type B botulism in the North: first reported cases due to toxin other than type E in Alaskan Inuit.

Botulism outbreaks shown to be due to type A and type B toxin occurred in Alaska, a region previously known for only type E botulism. The outbreak due to type A toxin involved three people, two of whom died. The outbreak due to type B toxin involved nine people, none of whom died. Both outbreaks were in Inuit villages, and native foods were incriminated. The occurrence of these outbreaks strongly suggests that Clostridium botulinum, types A and B are indigenous to Alaska. The outbreaks underscore the need for initial treatment of patients with antitoxin that is trivalent (ABE), even in Arctic regions.     

Predators of citrus blackfly [Hom.: Aleyrodidae]

A 2-year survey of known whitefly predators was conducted from winter 1976 to winter 1978 in Broward County, Florida. Also, the impact of predators on citrus blackfly populations was measured under field conditions using lifetable data and predator exclusion data. In addition, feeding experiments were conducted to determine specific predators on different citrus blackfly stages. In the survey, the total number of predators caught in 1977 was significantly greater than 1978 and reasons for this difference are discussed. Spiders and the coccinellid,Delphastes pusillus Lec. were the most abundant predators being ca. 90% of all predators caught. Results from the lifetable and predator exclusion technique were similar showing that predators caused a 52 to 66% reduction in citrus blackfly populations. Feeding tests showed that predator responses to feeding on citrus blackfly were variable depending on species of predator, stage of predator, and stage of citrus blackfly.

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Résumé Une étude pendant 2 ans des prédateurs de l'aleurode des citrus a été réalisée de l'hiver 1976 à l'hiver 1978 dans le Comté de Broward en Floride. L'influence des prédateurs sur les populations d'aleurodes a été mesurée dans les conditions naturelles par l'élaboration d'une table de vie et par des essais d'exclusion des prédateurs. En outre des expériences ont été effectuées afin de déterminer les prédateurs spécifiques pour chacun des stades de l'aleurode. Le nombre total de prédateurs capturés en 1977 fut significativement plus élevé qu'en 1978; les causes de cette différence sont discutées. Des araignées et la coccinelleDelphastes pusillus Lec. ont été les plus abondants, représentant et iron 90% du total. Les résultats de la table de vie et de l'exclusion des prédateurs ont été analogues et montrent que ceux-ci provoquent une réduction de 52 à 66% des populations d'aleurodes. Les essais sur l'alimentation indiquent que les réponses ont été variables selon l'espèce de prédateur, le stade du prédateur et de l'aleurode.

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Florida Agricultural Experiment Station Journal Series No. 1791. Partly supported by funds from Cooperative Agreement # 12-14-7001-1148 between U.S.D.A., and University of Florida.     

Evaluation of several lightweight stochastic context-free grammars for RNA secondary structure prediction

Background

RNA secondary structure prediction methods based on probabilistic modeling can be developed using stochastic context-free grammars (SCFGs). Such methods can readily combine different sources of information that can be expressed probabilistically, such as an evolutionary model of comparative RNA sequence analysis and a biophysical model of structure plausibility. However, the number of free parameters in an integrated model for consensus RNA structure prediction can become untenable if the underlying SCFG design is too complex. Thus a key question is, what small, simple SCFG designs perform best for RNA secondary structure prediction?

Results

Nine different small SCFGs were implemented to explore the tradeoffs between model complexity and prediction accuracy. Each model was tested for single sequence structure prediction accuracy on a benchmark set of RNA secondary structures.

Conclusions

Four SCFG designs had prediction accuracies near the performance of current energy minimization programs. One of these designs, introduced by Knudsen and Hein in their PFOLD algorithm, has only 21 free parameters and is significantly simpler than the others.

     

Host Cell Participation in Small Virus Replication I. Replication of M-13 in a Strain of Escherichia coli with a Temperature-sensitive Lesion in Deoxyribonucleic Acid Synthesis

The replication of M-13 in a strain of Escherichia coli with a thermosensitive lesion in deoxyribonucleic acid synthesis was studied. M-13 failed to replicate at the restrictive temperature, even when the parental replicative form was allowed to form at the permissive temperature. When cells which were actively producing phage at the permissive temperature were shifted to the restrictive temperature, phage production continued. The incorporation of radioactive label into phage particles at 42 C indicated that continued single-strand synthesis was unaffected by the lesion in the host cell.