Controversy and debate: the nature of science

How Cancer Exploits Ribosomal RNA Biogenesis: A Journey beyond the Boundaries of rRNA Transcription

The generation of new ribosomes is a coordinated process essential to sustain cell growth. As such, it is tightly regulated according to cell needs. As cancer cells require intense protein translation to ensure their enhanced growth rate, they exploit various mechanisms to boost ribosome biogenesis. In this review, we will summarize how oncogenes and tumor suppressors modulate the biosynthesis of the RNA component of ribosomes, starting from the description of well-characterized pathways that converge on ribosomal RNA transcription while including novel insights that reveal unexpected regulatory networks hacked by cancer cells to unleash ribosome production.

Collective effects in ciliar arrays

Collective effects in one-dimensional ciliar arrays are studied analytically and numerically. A new phase oscillator description for ciliar motion is introduced which depends only on a single parameter. It allows the systematic study of hydrodynamic interactions between cilia exhibiting arbitrary beating patterns. It is shown that if the hydrodynamic interactions do not alter the beating pattern of the cilia no synchronization of ciliar motion occurs. This is in particular the case in arrays with low ciliar densities. But hydrodynamic interactions can lead to formation of a collective (metachronal) wave which is stable for periodic boundary conditions. In finite arrays free boundaries destroy this collective motion. The dispersion relation for metachronal waves is found to be non-universal, i.e., to depend crucially on the microscopic details of the ciliar beating pattern.

Membranes with rotating motors: microvortex assemblies

We study collections of rotatory motors confined to 2-dimensional manifolds. The rotational motion induces a repulsive hydrodynamic interaction between motors leading to a non-trivial collective behavior. For high rotation speed, motors should arrange on a triangular lattice exhibiting crystalline order. At low speed, they form a disordered phase where diffusion is enhanced by velocity fluctuations. In confining geometries and under suitable boundary conditions, motor-generated flow might enhance left-right symmetry-breaking transport. All these effects should be experimentally observable for motors driven by external fields and for dipolar biological motors embedded into lipid membranes in a viscoelastic solvent.