Towards Synthetic Life: Establishing a Minimal Segrosome for the Rational Design of Biomimetic Systems

DNA segregation is a fundamental life process, crucial for renewal, reproduction and propagation of all forms of life. Hence, a dedicated segregation machinery, a segrosome, must function reliably also in the context of a minimal cell. Conceptionally, the development of such a minimal cell follows a minimalistic approach, aiming at engineering a synthetic entity only consisting of the essential key elements necessary for a cell to survive. In this thesis, various prokaryotic segregation systems were explored as possible candidates for a minimal segrosome. Such a minimal segrosome could be applied for the rational design of biomimetic systems including, but not limited to, a minimal cell. DNA segregation systems of type I (ParABS) and type II (ParMRC) were compared for ensuring genetic stabilities in vivo using vectors derived from the natural secondary chromosome of Vibrio cholerae. The type II segregation system R1-ParMRC was chosen as the most promising candidate for a minimal segrosome, and it was characterized and reconstituted in vitro. This segregation system was encapsulated into biomimetic micro-compartments and its lifetime prolonged by coupling to ATP-regenerating as well as oxygen-scavenging systems. The segregation process was coupled to in vitro DNA replication using DNA nanoparticles as a mimic of the condensed state of chromosomes. Furthermore, another type II segregation system originating from the pLS20 plasmid from Bacillus subtilis (Alp7ARC) was reconstituted in vitro as a secondary orthogonal segrosome. Finally, a chimeric RNA segregation system was engineered that could be applied for an RNA-based protocell. Overall, this work demonstrates successful bottom-up assemblies of functional molecular machines that could find applications in biomimetic systems and lead to a deeper understanding of living systems

Perceptual bistability in auditory streaming: how much do stimulus features matter?

The auditory two-tone streaming paradigm has been used extensively to study the mechanisms that underlie the decomposition of the auditory input into coherent sound sequences. Using longer tone sequences than usual in the literature, we show that listeners hold their first percept of the sound se¬quence for a relatively long period, after which perception switches between two or more alternative sound organizations, each held on average for a much shorter duration. The first percept also differs from subsequent ones in that stimulus parameters influence its quality and duration to a far greater degree than the subsequent ones. We propose an account of auditory streaming in terms of rivalry be¬tween competing temporal associations based on two sets of processes. The formation of associations (discovery of alternative interpretations) mainly affects the first percept by determining which sound group is discovered first and how long it takes for alternative groups to be established. In contrast, sub¬sequent percepts arise from stochastic switching between the alternatives, the dynamics of which are determined by competitive interactions between the set of coexisting interpretations

Dynamical segregation of galaxies in groups and clusters

We have performed a systematic analysis of the dynamics of different galaxy populations in galaxy groups from the 2dFGRS. For this purpose we have combined all the groups into a single system, where velocities v and radius r are expressed adimensionally. We have used several methods to compare the distributions of relative velocities of galaxies with respect to the group centre for samples selected according to their spectral type (as defined by Madgwick et al., 2002), bj band luminosity and B-R colour index. We have found strong segregation effects: spectral type I objects show a statistically narrower velocity distribution than that of galaxies with a substantial star formation activity (type II-IV). Similarly, the same behavior is observed for galaxies with colour index B-R>1 compared to galaxies with B-R<1. Bright (Mb-19) galaxies show the same segregation. It is not important once the sample is restricted to a given spectral type. These effects are particularly important in the central region (Rp<Rvirial/2) and do not have a strong dependence on the mass of the parent group. These trends show a strong correlation between the dynamics of galaxies in groups and star formation rate reflected both by spectral type and by colour index.Comment: 7 pages, 8 figures. Accepted for publication in MNRA

Modulation-frequency acts as a primary cue for auditory stream segregation

In our surrounding acoustic world sounds are produced by different sources and interfere with each other before arriving to the ears. A key function of the auditory system is to provide consistent and robust descriptions of the coherent sound groupings and sequences (auditory objects), which likely correspond to the various sound sources in the environment. This function has been termed auditory stream segregation. In the current study we tested the effects of separation in the frequency of amplitude modulation on the segregation of concurrent sound sequences in the auditory stream-segregation paradigm (van Noorden 1975). The aim of the study was to assess 1) whether differential amplitude modulation would help in separating concurrent sound sequences and 2) whether this cue would interact with previously studied static cues (carrier frequency and location difference) in segregating concurrent streams of sound. We found that amplitude modulation difference is utilized as a primary cue for the stream segregation and it interacts with other primary cues such as frequency and location difference

Dynamics of Multidimensional Secession

We explore a generalized Seceder Model with variable size selection groups and higher dimensional genotypes, uncovering its well-defined mean-field limiting behavior. Mapping to a discrete, deterministic version, we pin down the upper critical size of the multiplet selection group, characterize all relevant dynamically stable fixed points, and provide a complete analytical description of its self-similar hierarchy of multiple branch solutions.Comment: 4 pages, 4 figures, PR

Chromosome segregation in plant meiosis

Faithful chromosome segregation in meiosis is essential for ploidy stability over sexual life cycles. In plants, defective chromosome segregation caused by gene mutations or other factors leads to the formation of unbalanced or unreduced gametes creating aneuploid or polyploid progeny, respectively. Accurate segregation requires the coordinated execution of conserved processes occurring throughout the two meiotic cell divisions. Synapsis and recombination ensure the establishment of chiasmata that hold homologous chromosomes together allowing their correct segregation in the first meiotic division, which is also tightly regulated by cell-cycle dependent release of cohesin and monopolar attachment of sister kinetochores to microtubules. In meiosis II, bi-orientation of sister kinetochores and proper spindle orientation correctly segregate chromosomes in four haploid cells. Checkpoint mechanisms acting at kinetochores control the accuracy of kinetochore-microtubule attachment, thus ensuring the completion of segregation. Here we review the current knowledge on the processes taking place during chromosome segregation in plant meiosis, focusing on the characterization of the molecular factors involved