CCS with Hennessy's merge has no finite-equational axiomatization

Abstract This paper confirms a conjecture of Bergstra and Klop¿s from 1984 by establishing that the process algebra obtained by adding an auxiliary operator proposed by Hennessy in 1981 to the recursion free fragment of Milner¿s Calculus of Communicationg Systems is not finitely based modulo bisimulation equivalence. Thus Hennessy¿s merge cannot replace the left merge and communication merge operators proposed by Bergstra and Klop, at least if a finite axiomatization of parallel composition is desired. 2000 MATHEMATICS SUBJECT CLASSIFICATION: 08A70, 03B45, 03C05, 68Q10, 68Q45, 68Q55, 68Q70. CR SUBJECT CLASSIFICATION (1991): D.3.1, F.1.1, F.1.2, F.3.2, F.3.4, F.4.1. KEYWORDS AND PHRASES: Concurrency, process algebra, CCS, bisimulation, Hennessy¿s merge, left merge, communication merge, parallel composition, equational logic, complete axiomatizations, non-finitely based algebras

The Independent, No. 18, Febrary 19, 1976

The Independent was a student run newspaper created in 1960 at Newark State College, now Kean University. The proceeding title was The Reflector. The editor of this issue was Buz Whelan.https://digitalcommons.kean.edu/independent_1975-1979/1011/thumbnail.jp

Dysfunctional prefrontal cortical network activity and interactions following cannabinoid receptor activation

Coordinated activity spanning anatomically distributed neuronal networks underpins cognition and mediates limbic-cortical interactions during learning, memory, and decision-making. We used CP55940, a potent agonist of brain cannabinoid receptors known to disrupt coordinated activity in hippocampus, to investigate the roles of network oscillations during hippocampal and medial prefrontal cortical (mPFC) interactions in rats. During quiet wakefulness and rest, CP55940 dose-dependently reduced 0.1-30 Hz local field potential power in CA1 of the hippocampus while concurrently decreasing 30-100 Hz power in mPFC; these contrasting population-level effects were paralleled by differential effects on underlying single-unit activity in the two structures. During decision-making phases of a spatial working memory task, CP5540-induced deficits in hippocampal theta and prefrontal gamma oscillations were observed alongside disrupted theta-frequency coherence between the two structures. These changes in coordinated limbic-cortical network activities correlated with (1) reduced accuracy of task performance, (2) impaired phase-locking of prefrontal single-unit spiking to the local gamma and hippocampal theta rhythms, and (3) impaired task-dependent activity in a subset of mPFC units. In addition to highlighting the importance of CA1-mPFC network oscillations for cognition, these results implicate disrupted theta-frequency coordination of CA1-mPFC activity in the cognitive deficits caused by exogenous activation of brain cannabinoid receptors

From CoA ester supply to a yeast communication toolkit in Saccharomyces cerevisiae

Saccharomyces cerevisiae is the most widely used eukaryotic chassis in synthetic biology, as hu-manity and yeast share a long and fruitful history. For synthetic biology applications, S. cerevisiae was extensively used for metabolic engineering as well as for the construction of artificial net-works. To contribute to the metabolic engineering achievements conducted in S. cerevisiae, we extended its metabolic capacities by providing non-native short-chain acyl-coenzyme A esters as metabolic precursors. In order to advance the construction of artificial networks to multicel-lular systems we provided a comprehensive yeast communication toolkit (YCTK), and demon-strated its usability for the rapid assembly of synthetic cell-cell communication systems. Engineered production of short-chain acyl-coenzyme A esters in Saccharomyces cerevisiae Globally, S. cerevisiae is one of the most commonly used chassis organisms in modern biotech-nology and constitutes a high economic value to the growing bioecomomy. With the objective to produce novel natural products in S. cerevisiae a bottleneck of the chassis was uncovered. Short-chain acyl-coenzyme A esters serve as intermediate compounds in fatty acid biosynthesis, and are building blocks for the production of polyketides, biopolymers, and other value-added chemicals. However, S. cerevisiae’s limited repertoire of short-chain acyl-CoAs effectively pre-vents its application as a production host for a plethora of natural products. To address and re-solve this limitation, we introduced metabolic pathways to five different acyl-CoA esters into S. cerevisiae. We engineered plasmid-based yeast strains that provide propionyl-CoA, methylmalonyl-CoA, n-butyryl-CoA, isovaleryl-CoA, and n-hexanoyl-CoA. For the production of propionyl-CoA and methylmalonyl-CoA, we reestablished a published feeding-dependent pro-duction route using the PrpE and Pcc enzymes to serve as benchmark for our feeding-independent production pathways that provided in our study comparable product concentra-tions. To ensure efficient extraction of the produced metabolites we established a yeast-specific metabolite extraction protocol to determine the intracellular acyl-CoA concentrations in the engineered strains. For the production of isovaleryl-CoA, we tested two different pathways but only obtained product formation from the alternative isovaleryl-CoA biosynthetic (AIB) pathway originating from Myxococcus xanthus and obtained 5.5±1.2 µM isovaleryl-CoA. To our knowledge, this is the first reported functional heterologous expression of this pathway in S. cerevisiae. For the production of n-butyryl-CoA and n-hexanoyl-CoA, we adapted the butanol production pathway for our purposes and measured approximately 6 µM intracellular concen-tration of butyryl-CoA and hexanoyl-CoA. For the feeding-dependent pathway towards propio-nyl-CoA we obtained intracellular concentrations of 5.3 ± 2.4 µM while the feeding independ-ent 3-hydroxypropionate (3HP) pathway produced 8.5 ± 3.7 µM. The extension of both propio-nyl-CoA pathways to produce methylmalonyl-CoA resulted only into production of 0.5 ± 0.1 µM and 0.3 ± 0.3 µM methylmalonyl-CoA. Not only but particularly for the production of methylmalonyl-CoA further optimization is required. To allow rapid pathway prototyping, op-timization and testing of alternative enzymes, we established a short-chain acyl-CoA Golden Gate collection. This collection enables together with the well-known Dueber yeast toolkit YTK collection the examination of different enzymes variants and to investigate optimized expres-sion of the corresponding genes. We conclude that the acyl-CoAs produced here, that are common building blocks of secondary metabolites, prepared the ground for prospective engineered production of a variety of natural products in S. cerevisiae. These acyl-CoA producing strains together with the short-chain acyl-CoA collection lay the foundation to further explore S. cerevisiae as a heterologous production host for high-value secondary metabolite production. Yeast communication toolkit The construction of multicellular networks was a proposed aim already early on in synthetic biology. Today, they still hold many promises like the division of labor or the performance of more complex tasks. Most of the systems so far were implemented in bacterial chassis and only a few examples exist for the eukaryotic chassis S. cerevisiae. Especially for gram-negative bacterial chassis, the quorum sensing system provides a large diversity of ready to use communication systems. Also, yeast species evolved a communication system using peptide-based pheromones to interact with the opposite mating type. Here, we employed the natural diversity of the pep-tide α-factor pheromones, the corresponding GPCR receptors, as well as of barrier proteases, that function similarly to quorum quenching enzymes. With the establishment of the Golden Gate yeast communication toolkit (YCTK) we provide a standardized collection of parts that al-low the rapid construction of multicellular networks in the model organism S. cerevisiae. The feasible designs are limitless as well as the number of envisioned applications. The YCTK collec-tion consists of responder (pheromone-responsive promoters), sender (mfα1 genes – α-factors), receiver (Ste2 receptors) and barrier (Bar1 proteases) parts. We characterized the dynamics of the pheromone-inducible promoters in the different mating-type strain backgrounds and de-termined the dose-response to the α-factor as well as their temporal response. The different promoters exhibited a range of different dynamics and properties that enable the implementa-tion of different prospective network design motives. The characterization results of the Ste2 receptors indicated that our collection is comprised of receptors with high α-factor promiscuity and of receptors with high substrate specificity for their cognate α-factor. Further we found that different Ste2 receptors exhibit different sensitivities towards the cognate as well as to non-cognate α-factors. The promiscuity of the Ste2 receptors did not correlate with the α-factor se-quences. Our likelihood analysis of the Ste2 receptors indicated that the ones closer related to S. cerevisiae tend to be stimulated by the α-factors of related species. Our likelihood analysis of the Ste2 receptors coincided with the phylogenetic relationships of the species. Interesting is also the finding that α-factors of species for which the receptor exhibited high α-factor promis-cuity stimulated only a few receptors. Even though only five of the selected barrier proteases were functionally expressed the characterization of the protease promiscuity was to our knowledge the most comprehensive study of its kind so far. Similar to the receptors we identi-fied promiscuous and substrate specific barrier proteases. The proposed model of a coevolution between the receptor and barrier proteases to recognize similar sequence motives of the α-factor was partly validated, however, the model is not universally applicable according to our results. The extended knowledge of the pheromone-inducible promoters, the crosstalk be-tween α-factors, receptors and barrier proteases, and an initial tunability test enabled proof of principle construction of multicellular systems using the YTCK collection. We engineered mul-ticellular logic gate-like population networks that allow the receiver cells to conditionally re-spond to the population composition. While the α-factor signaling motif is functional and was used to successfully establish OR and AND gate-like systems, signal disruption by a barrier pro-tease of a self-stimulating or a signaling motif requires further optimization. Overall, the reali-zation of multicellular networks using the YCTK was proven to be successful. To summarize, with the YCTK we provide a set of comprehensively characterized sender, re-ceiver, and barrier parts to facilitate the implementation of cell-cell and thus multicellular communication networks in S. cerevisiae