The mitotic spindle is a microtubule (MT) based structure that sets the position of cell division. Its positioning is crucial for proper cell division and is highly regulated by hundreds of MT associated proteins and molecular motors. One of them is dynein, minus end directed motor protein that can be recruited at the membrane and pull on astral microtubules to position the spindle. In vivo, it is often difficult to assess the specific function of microtubules or its associated proteins in spindle formation and positioning.
Here, we reconstitute in vitro the interaction of two asters inside 3D water in oil emulsion droplets. We study the positioning of two centrosomes from which microtubules are nucleated, that exert pushing and/or dynein mediated pulling forces when reaching the cortex.
We show that very simple systems, involving only microtubule dynamics, confinement, pushing and pulling forces can lead to self-organized patterns that are biologically relevant. In particular, we reproduce a 'mitotic spindle' like organization with just these components.

At the LHC, New Physics could be better parametrised with form factors than with contact interactions, if the New Physics scale is similar to the LHC energy. As a toy example, I consider the process pp -> l+l- , fit the high-energy tail to a function, and show that the resulting limits can be analytically translated to a wide variety of models (no event simulation required).

The study of plants from a biophysical point of view offers new highlights about plant growth, development and sensing. I will describe a range of experiments, where mechanical measurements combined with modelling help us to unravel interesting plant properties such as cytoskeleton rearrangement under an external force or modification of the seed properties along developmental stages. Among all mechanical parameters, I will focus on the hydrostatic pressure inside plant cells and present a new method to measure it using atomic force microscopy.

In the coming years the LHC will continue the exploration of the TeV scale by measuring the detailed properties of the discovered Higgs boson and by looking for signatures of new physics beyond the Standard Model. I will discuss why a full exploitation of the LHC physics reach requires precise theoretical predictions and simulation tools. I will then explain the basic concepts and approximations upon which these computations are based and review the theoretical developments that in the last decade allowed to improve substantially their accuracy, by including higher-order corrections. Examples of future LHC searches where the above improvements can be relevant to explore (directly or indirectly) BSM signatures will be discussed.

Although the DNA structure in double-helix is robust enough to enable
the preservation of the genetic code, it is sufficiently loose to allow
the formation of denaturation bubbles, i.e. the cooperative opening of a
sequence of consecutive base-pairs, even at physiological temperature.
DNA opening is central in biological mechanisms such as replication,
transcription, repair, or protein binding.

The issue of the nucleation and slow closure mechanisms of non
superhelical stress-induced denaturation bubbles in DNA is tackled using
coarse-grained MetaDynamics and Brownian simulations. A minimal
mesoscopic model is used where the double helix is made of two
interacting bead-spring rotating strands with a prescribed torsional
modulus in the duplex state. We demonstrate that timescales for the
nucleation (resp. closure) of an approximately 10 base-pair bubble, in
agreement with experiments, are associated to the crossing of a
free-energy barrier of 22 k_B T (resp. 13 k_B T) at room temperature T.
MetaDynamics allows us to reconstruct accurately the free-energy
landscape, to show that the free-energy barriers come from the
difference in torsional energy between the bubble and the duplex states,
and thus to highlight the limiting step, a collective twisting, that
controls the nucleation/closure mechanism, and to access opening time
scales on the millisecond range. Contrary to small breathing bubbles,
these more than 4 base-pair bubbles are of biological relevance, for
example when a preexisting state of denaturation is required by specific
DNA-binding proteins.

Thèse de Fernando.