University of Fribourg

About: University of Fribourg is a education organization based out in Fribourg, Freiburg, Switzerland. It is known for research contribution in the topics: Population & Context (language use). The organization has 6040 authors who have published 14975 publications receiving 542500 citations. The organization is also known as: UNIFR & Universität Freiburg.

Elastic Domains Regulate Growth and Organogenesis in the Plant Shoot Apical Meristem

Abstract: Although genetic control of morphogenesis is well established, elaboration of complex shapes requires changes in the mechanical properties of cells In plants, the first visible sign of leaf formation is a bulge on the flank of the shoot apical meristem Bulging results from local relaxation of cell walls, which causes them to yield to internal hydrostatic pressure By manipulation of tissue tension in combination with quantitative live imaging and finite-element modeling, we found that the slow-growing area at the shoot tip is substantially strain-stiffened compared with surrounding fast-growing tissue We propose that strain stiffening limits growth, restricts organ bulging, and contributes to the meristem's functional zonation Thus, mechanical signals are not just passive readouts of gene action but feed back on morphogenesis

Synapsis and chiasma formation in Caenorhabditis elegans require HIM-3, a meiotic chromosome core component that functions in chromosome segregation.

Abstract: Meiotic chromosomes are organized about a proteinaceous core that forms between replicated sister chromatids. We have isolated a Caenorhabditis elegans gene, him-3, which encodes a meiosis-specific component of chromosome cores with some similarity to the yeast lateral element protein Hop1p. Antibodies raised against HIM-3 localize the protein to condensing chromosomes in early prophase I and to the cores of both synapsed and desynapsed chromosomes. In RNA interference experiments, chromosomes appear to condense normally in the absence of detectable protein but fail to synapse and form chiasmata, indicating that HIM-3 is essential for these processes. Hypomorphs of him-3, although being synapsis proficient, show severe reductions in the frequency of crossing-over, demonstrating that HIM-3 has a role in establishing normal levels of interhomolog exchange. Him-3 mutants also show defects in meiotic chromosome segregation and the persistence of the protein at the chromosome core until the metaphase I‐anaphase I transition suggests that HIM-3 may play a role in sister chromatid cohesion. The analysis of him-3 provides the first functional description of a chromosome core component in a multicellular organism and suggests that a mechanistic link exists between the early meiotic events of synapsis and recombination, and later events such as segregation.

Neuronal activity in monkey striatum related to the expectation of predictable environmental events.

Abstract: 1. This study investigated neuronal activity in the striatum preceding predictable environmental events and behavioral reactions. Monkeys performed in a delayed go-nogo task that included separate time periods during which animals expected signals of behavioral significance, prepared for execution or inhibition of arm reaching movements, and expected the delivery of reward. In the task, animals were instructed by a green light cue to perform an arm reaching movement when a trigger stimulus came on approximately 3 s later (go situation). Movement was withheld after the same trigger light when the instruction cue had been red (nogo situation). Liquid reward was delivered on correct performance in both situations. 2. A total of 1,173 neurons were studied in the striatum (caudate nucleus and putamen) of 3 animals, of which 615 (52%) showed some change in activity during task performance. This report describes how the activity of 193 task-related neurons increased in advance of at least 1 component of the task, namely the instruction cue, the trigger stimulus, or the delivery of liquid reward. These neurons were found in dorsal and anterior parts of caudate and putamen and were slightly more frequent in the proximity of the internal capsule. 3. The activity of 16 neurons increased in both go and nogo trials before the onset of the instruction and subsided shortly after this signal. These activations may be related to the expectation of the instruction as the first signal in each trial. 4. The activity of 15 neurons increased between the instruction and the trigger stimulus in both go and nogo trials. These activations may be related to the expectation of the trigger stimulus independent of an arm movement. Further 56 neurons showed sustained activations only when the instruction requested a movement reaction. Activations were absent in trials in which the movement was withheld. Twenty-one of these neurons were tested with 2 different movement targets, 5 of which showed activity related to the direction of movement. These activations may be related to the preparation of movement or expectation of the specific movement triggering signal. The activity of an additional 20 neurons was unmodulated before the trigger stimulus in movement trials but increased in the interval between the no-movement instruction and the trigger stimulus for withholding the movement. These activations may be related to the preparation of movement inhibition as specific nogo reaction.(ABSTRACT TRUNCATED AT 400 WORDS)

Effective interactions in active Brownian suspensions.

Abstract: Active colloids exhibit persistent motion, which can lead to motility-induced phase separation (MIPS). However, there currently exists no microscopic theory to account for this phenomenon. We report a first-principles theory, free of fit parameters, for active spherical colloids, which shows explicitly how an effective many-body interaction potential is generated by activity and how this can rationalize MIPS. For a passively repulsive system the theory predicts phase separation and pair correlations in quantitative agreement with simulation. For an attractive system the theory shows that phase separation becomes suppressed by moderate activity, consistent with recent experiments and simulations, and suggests a mechanism for reentrant cluster formation at high activity.